AREA CODE AND TIME ZONE LISTING

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_
|_ _|
_| _ _ _ _ |_
|_ ((___)) cDc communications ((___)) _|
_| [ x x ] presents... [ x x ] |_
|_ \ / \ / _|
_| (` ') AREA CODE AND TIME ZONE LISTING (` ') |_
|_ (U) (U) _|
_| |_
|_ by Bovine Priest and Cultee: _|
_| |_
|_ Reverend Dial Tone _|
_| |_
|_ dEM0n r0ACh uNDERGR0UNd (300/1200/2400) [806] 794-4362 _|
_| dRAG0NFIRe pRIVATe (1200 only) [609] 424-2606 |_
|_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _|
|_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_|


Ok this is nothing big, it's my third text file for 1988 from cDc
communications. Here goes.

Time Zones
----------

Atlantic
--------

Newfoundland Nova Scotia New Brunswick

Eastern
-------

Maine New Hampshire Vermont Massachussets New York Rhode Island
Connecticut Pennsylvania New Jersey Delaware Maryland Ohio Indiana
Michigan West Virginia Virginia Kentucky North Carolina Tennessee
South Carolina Georgia Florida Quebec Ontario

Central
-------

Manitoba North Dakota South Dakota Minnesota Wisconsin Michigan Iowa
Nebraska Illinois Kansas Missouri Kentucky Tennessee Arkansas Oklahoma
Texas Louisiana Alabama Mississippi Indiana

Mountain
--------

Alberta Saskatchewan Montana Idaho Wyoming South Dakota Nebraska
Utah Colorado Kansas Oklahoma Arizona New Mexico

Pacific
-------

British Columbia Washington Montana Oregon Nevada California Utah


Area Code Listing
-----------------

205 - Alabama 907 - Alaska 602 - Arizona
501 - Arkansas 714 - California (Orange) 818 - California
213 - California (LA) 916 - California 619 - California
415 - California (SF) 408 - California (San Jose) 303 - Colorado
203 - Connecticut 302 - Delaware 904 - Florida
305 - Florida (Miami) 404 - Georgia (Atlanta) 808 - Hawaii
208 - Idaho 312 - Illinois (Chicago) 317 - Indiana
219 - Indiana (Souend) 515 - Iowa (Des Moines) 316 - Kansas
502 - Kentucky 504 - Lousiana (N. Orleans) 207 - Maine
301 - Maryland 617 - Massachusetts 313 - Michigan
616 - Michigan 612 - Minnesota 601 - Mississippi
816 - Missouri (Kansas C) 314 - Kansas (St. Louis) 406 - Montana
402 - Nebraska 702 - Nevada 603 - New Hampshire
201 - New Jersey (Newark) 609 - New Jersey (I'm here) 505 - New Mexico
718 - NYC (Brooklyn, S.I.) 212 - NYC (Bronx, Mhattan) 518 - NY (Albany)
716 - NY (Buffalo) 516 - NY (Long Island) 315 - NY (Syracuse)
914 - NY (White Plains) 704 - North Carolina 919 - North Carolina
701 - North Dakota 513 - Ohio (Cincinnati) 216 - Ohio
614 - Ohio (Columbus) 419 - Ohio (Toledo) 405 - Oklahoma
918 - Oklahoma (Tulsa) 503 - Oregon 215 - Philadelphia PA
401 - Rhode Island (cough) 803 - South Carolina 605 - South Dakota
901 - Tennessee (Memphis) 615 - Tennessee (Nashville) 806 - Texas(Cow Hell)
214 - Texas (Dallas) 817 - Texas (Forth Worth) 713 - Texas (Houston)
512 - Texas (San Antonio) 801 - Utah 802 - Vermont
703 - Virginia (Arlington) 804 - Virginia (Richmond) 202 - Washington DC
206 - Washington (Seattle) 304 - West Virginia 608 - Wisconsin
307 - Wyoming 666 - Where do you think

Well that will make a nice printout for your wall, won't it. Now
you know where you're calling...


Thanks to : Franken Gibe (cause he made me happy haha) and Swamp Rat

===============================================================================
(c) 1987, 1988 cDc communications e.o.f. 10:01 EST Jersey 1/13/88-38

by Reverend Dial Tone [Joel]

BOVINE IS FINE | BEEF IS CHIEF | COW IS NOW

A Web Standards Checklist, How to make a proper websiteA Web Standards Checklist, How to make a proper website

A Web Standards Checklist, How to make a proper website

A web standards checklist

The term web standards can mean different things to different people. For some, it is 'table-free sites', for others it is 'using valid code'. However, web standards are much broader than that. A site built to web standards should adhere to standards (HTML, XHTML, XML, CSS, XSLT, DOM, MathML, SVG etc) and pursue best practices (valid code, accessible code, semantically correct code, user-friendly URLs etc).

In other words, a site built to web standards should ideally be lean, clean, CSS-based, accessible, usable and search engine friendly.

About the checklist

This is not an uber-checklist. There are probably many items that could be added. More importantly, it should not be seen as a list of items that must be addressed on every site that you develop. It is simply a guide that can be used:

* to show the breadth of web standards
* as a handy tool for developers during the production phase of websites
* as an aid for developers who are interested in moving towards web standards

The checklist

1.Quality of code
1. Does the site use a correct Doctype?
2. Does the site use a Character set?
3. Does the site use Valid (X)HTML?
4. Does the site use Valid CSS?
5. Does the site use any CSS hacks?
6. Does the site use unnecessary classes or ids?
7. Is the code well structured?
8. Does the site have any broken links?
9. How does the site perform in terms of speed/page size?
10. Does the site have JavaScript errors?

2. Degree of separation between content and presentation
1. Does the site use CSS for all presentation aspects (fonts, colour, padding, borders etc)?
2. Are all decorative images in the CSS, or do they appear in the (X)HTML?

3. Accessibility for users
1. Are "alt" attributes used for all descriptive images?
2. Does the site use relative units rather than absolute units for text size?
3. Do any aspects of the layout break if font size is increased?
4. Does the site use visible skip menus?
5. Does the site use accessible forms?
6. Does the site use accessible tables?
7. Is there sufficient colour brightness/contrasts?
8. Is colour alone used for critical information?
9. Is there delayed responsiveness for dropdown menus (for users with reduced motor skills)?
10. Are all links descriptive (for blind users)?

4. Accessibility for devices
1. Does the site work acceptably across modern and older browsers?
2. Is the content accessible with CSS switched off or not supported?
3. Is the content accessible with images switched off or not supported?
4. Does the site work in text browsers such as Lynx?
5. Does the site work well when printed?
6. Does the site work well in Hand Held devices?
7. Does the site include detailed metadata?
8. Does the site work well in a range of browser window sizes?

5. Basic Usability
1. Is there a clear visual hierarchy?
2. Are heading levels easy to distinguish?
3. Does the site have easy to understand navigation?
4. Does the site use consistent navigation?
5. Are links underlined?
6. Does the site use consistent and appropriate language?
7. Do you have a sitemap page and contact page? Are they easy to find?
8. For large sites, is there a search tool?
9. Is there a link to the home page on every page in the site?
10. Are visited links clearly defined with a unique colour?

6. Site management
1. Does the site have a meaningful and helpful 404 error page that works from any depth in the site?
2. Does the site use friendly URLs?
3. Do your URLs work without "www"?
4. Does the site have a favicon?

1. Quality of code

1.1 Does the site use a correct Doctype?
A doctype (short for 'document type declaration') informs the validator which version of (X)HTML you're using, and must appear at the very top of every web page. Doctypes are a key component of compliant web pages: your markup and CSS won't validate without them.
CODE
http://www.alistapart.com/articles/doctype/


More:
CODE
http://www.w3.org/QA/2002/04/valid-dtd-list.html

CODE
http://css.maxdesign.com.au/listamatic/about-boxmodel.htm

CODE
http://gutfeldt.ch/matthias/articles/doctypeswitch.html


1.2 Does the site use a Character set?
If a user agent (eg. a browser) is unable to detect the character encoding used in a Web document, the user may be presented with unreadable text. This information is particularly important for those maintaining and extending a multilingual site, but declaring the character encoding of the document is important for anyone producing XHTML/HTML or CSS.
CODE
http://www.w3.org/International/tutorials/tutorial-char-enc/


More:
CODE
http://www.w3.org/International/O-charset.html


1.3 Does the site use Valid (X)HTML?
Valid code will render faster than code with errors. Valid code will render better than invalid code. Browsers are becoming more standards compliant, and it is becoming increasingly necessary to write valid and standards compliant HTML.
CODE
http://www.maxdesign.com.au/presentation/sit2003/06.htm


More:
CODE
http://validator.w3.org/


1.4 Does the site use Valid CSS?
You need to make sure that there aren't any errors in either your HTML or your CSS, since mistakes in either place can result in botched document appearance.
CODE
http://www.meyerweb.com/eric/articles/webrev/199904.html


More:
CODE
http://jigsaw.w3.org/css-validator/


1.5 Does the site use any CSS hacks?
Basically, hacks come down to personal choice, the amount of knowledge you have of workarounds, the specific design you are trying to achieve.
CODE
http://www.mail-archive.com/wsg@webstandardsgroup.org/msg05823.html


More:
CODE
http://css-discuss.incutio.com/?page=CssHack

CODE
http://css-discuss.incutio.com/?page=ToHackOrNotToHack

CODE
http://centricle.com/ref/css/filters/


1.6 Does the site use unnecessary classes or ids?
I've noticed that developers learning new skills often end up with good CSS but poor XHTML. Specifically, the HTML code tends to be full of unnecessary divs and ids. This results in fairly meaningless HTML and bloated style sheets.
CODE
http://www.clagnut.com/blog/228/


1.7 Is the code well structured?
Semantically correct markup uses html elements for their given purpose. Well structured HTML has semantic meaning for a wide range of user agents (browsers without style sheets, text browsers, PDAs, search engines etc.)
CODE
http://www.maxdesign.com.au/presentation/benefits/index04.htm


More:
CODE
http://www.w3.org/2003/12/semantic-extractor.html


1.8 Does the site have any broken links?
Broken links can frustrate users and potentially drive customers away. Broken links can also keep search engines from properly indexing your site.

More:
CODE
http://validator.w3.org/checklink


1.9 How does the site perform in terms of speed/page size?
Don't make me wait... That's the message users give us in survey after survey. Even broadband users can suffer the slow-loading blues.
CODE
http://www.websiteoptimization.com/speed/


1.10 Does the site have JavaScript errors?
Internet Explore for Windows allows you to turn on a debugger that will pop up a new window and let you know there are javascript errors on your site. This is available under 'Internet Options' on the Advanced tab. Uncheck 'Disable script debugging'.

2. Degree of separation between content and presentation

2.1 Does the site use CSS for all presentation aspects (fonts, colour, padding, borders etc)?
Use style sheets to control layout and presentation.
CODE
http://www.w3.org/TR/WCAG10/wai-pageauth.html#tech-style-sheets


2.2 Are all decorative images in the CSS, or do they appear in the (X)HTML?
The aim for web developers is to remove all presentation from the html code, leaving it clean and semantically correct.
CODE
http://www.maxdesign.com.au/presentation/benefits/index07.htm


3. Accessibility for users

3.1 Are "alt" attributes used for all descriptive images?
Provide a text equivalent for every non-text element
CODE
http://www.w3.org/TR/WCAG10/wai-pageauth.html#tech-text-equivalent


3.2 Does the site use relative units rather than absolute units for text size?
Use relative rather than absolute units in markup language attribute values and style sheet property values'.
CODE
http://www.w3.org/TR/WCAG10/wai-pageauth.html#tech-relative-units


More:
CODE
http://www.w3.org/TR/WCAG10/wai-pageauth.html#tech-relative-units

CODE
http://www.clagnut.com/blog/348/


3.3 Do any aspects of the layout break if font size is increased?
Try this simple test. Look at your website in a browser that supports easy incrementation of font size. Now increase your browser's font size. And again. And again... Look at your site. Does the page layout still hold together? It is dangerous for developers to assume that everyone browses using default font sizes.
3.4 Does the site use visible skip menus?

A method shall be provided that permits users to skip repetitive navigation links.
CODE
http://www.section508.gov/index.cfm?FuseAction=Content&ID=12


Group related links, identify the group (for user agents), and, until user agents do so, provide a way to bypass the group.
CODE
http://www.w3.org/TR/WCAG10-TECHS/#tech-group-links


...blind visitors are not the only ones inconvenienced by too many links in a navigation area. Recall that a mobility-impaired person with poor adaptive technology might be stuck tabbing through that morass.
CODE
http://joeclark.org/book/sashay/serialization/Chapter08.html#h4-2020


More:
CODE
http://www.niehs.nih.gov/websmith/508/o.htm


3.5 Does the site use accessible forms?
Forms aren't the easiest of things to use for people with disabilities. Navigating around a page with written content is one thing, hopping between form fields and inputting information is another.
CODE
http://www.htmldog.com/guides/htmladvanced/forms/


More:
CODE
http://www.webstandards.org/learn/tutorials/accessible-forms/01-accessible-forms.html

CODE
http://www.accessify.com/tools-and-wizards/accessible-form-builder.asp

CODE
http://accessify.com/tutorials/better-accessible-forms.asp


3.6 Does the site use accessible tables?
For data tables, identify row and column headers... For data tables that have two or more logical levels of row or column headers, use markup to associate data cells and header cells.
CODE
http://www.w3.org/TR/WCAG10/wai-pageauth.html#tech-table-headers


More:
CODE
http://www.bcc.ctc.edu/webpublishing/ada/resources/tables.asp

CODE
http://www.accessify.com/tools-and-wizards/accessible-table-builder_step1.asp

CODE
http://www.webaim.org/techniques/tables/


3.7 Is there sufficient colour brightness/contrasts?
Ensure that foreground and background colour combinations provide sufficient contrast when viewed by someone having colour deficits.
CODE
http://www.w3.org/TR/WCAG10/wai-pageauth.html#tech-colour-contrast


More:
CODE
http://www.juicystudio.com/services/colourcontrast.asp


3.8 Is colour alone used for critical information?
Ensure that all information conveyed with colour is also available without colour, for example from context or markup.
CODE
http://www.w3.org/TR/WCAG10/wai-pageauth.html#tech-colour-convey


There are basically three types of colour deficiency; Deuteranope (a form of red/green colour deficit), Protanope (another form of red/green colour deficit) and Tritanope (a blue/yellow deficit- very rare).

More:
CODE
http://colourfilter.wickline.org/

CODE
http://www.toledo-bend.com/colourblind/Ishihara.html

CODE
http://www.vischeck.com/vischeck/vischeckURL.php


3.9 Is there delayed responsiveness for dropdown menus?
Users with reduced motor skills may find dropdown menus hard to use if responsiveness is set too fast.

3.10 Are all links descriptive?
Link text should be meaningful enough to make sense when read out of context - either on its own or as part of a sequence of links. Link text should also be terse.
CODE
http://www.w3.org/TR/WCAG10/wai-pageauth.html#tech-meaningful-links


4. Accessibility for devices.

4.1 Does the site work acceptably across modern and older browsers?

Before starting to build a CSS-based layout, you should decide which browsers to support and to what level you intend to support them.
CODE
http://www.maxdesign.com.au/presentation/process/index_step01.cfm



4.2 Is the content accessible with CSS switched off or not supported?
Some people may visit your site with either a browser that does not support CSS or a browser with CSS switched off. In content is structured well, this will not be an issue.

4.3 Is the content accessible with images switched off or not supported?
Some people browse websites with images switched off - especially people on very slow connections. Content should still be accessible for these people.

4.4 Does the site work in text browsers such as Lynx?
This is like a combination of images and CSS switched off. A text-based browser will rely on well structured content to provide meaning.

More:
CODE
http://www.delorie.com/web/lynxview


4.5 Does the site work well when printed?
You can take any (X)HTML document and simply style it for print, without having to touch the markup.
CODE
http://www.alistapart.com/articles/goingtoprint/


More:
CODE
http://www.d.umn.edu/itss/support/Training/Online/webdesign/css.html#print


4.6 Does the site work well in Hand Held devices?
This is a hard one to deal with until hand held devices consistently support their correct media type. However, some layouts work better in current hand-held devices. The importance of supporting hand held devices will depend on target audiences.

4.7 Does the site include detailed metadata?
Metadata is machine understandable information for the web
CODE
http://www.w3.org/Metadata/


Metadata is structured information that is created specifically to describe another resource. In other words, metadata is 'data about data'.


4.8 Does the site work well in a range of browser window sizes?
It is a common assumption amongst developers that average screen sizes are increasing. Some developers assume that the average screen size is now 1024px wide. But what about users with smaller screens and users with hand held devices? Are they part of your target audience and are they being disadvantaged?

5. Basic Usability
5.1 Is there a clear visual hierarchy?
Organise and prioritise the contents of a page by using size, prominence and content relationships.
CODE
http://www.great-web-design-tips.com/web-site-design/165.html


5.2 Are heading levels easy to distinguish?
Use header elements to convey document structure and use them according to specification.
CODE
http://www.w3.org/TR/WCAG10/wai-pageauth.html#tech-logical-headings


5.3 Is the site's navigation easy to understand?
Your navigation system should give your visitor a clue as to what page of the site they are currently on and where they can go next.
CODE
http://www.1stsitefree.com/design_nav.htm


5.4 Is the site's navigation consistent?
If each page on your site has a consistent style of presentation, visitors will find it easier to navigate between pages and find information
CODE
http://www.juicystudio.com/tutorial/accessibility/navigation.asp


5.5 Does the site use consistent and appropriate language?
The use of clear and simple language promotes effective communication. Trying to come across as articulate can be as difficult to read as poorly written grammar, especially if the language used isn't the visitor's primary language.
CODE
http://www.juicystudio.com/tutorial/accessibility/clear.asp


5.6 Does the site have a sitemap page and contact page? Are they easy to find?
Most site maps fail to convey multiple levels of the site's information architecture. In usability tests, users often overlook site maps or can't find them. Complexity is also a problem: a map should be a map, not a navigational challenge of its own.
CODE
http://www.useit.com/alertbox/20020106.html


5.7 For large sites, is there a search tool?
While search tools are not needed on smaller sites, and some people will not ever use them, site-specific search tools allow users a choice of navigation options.

5.8 Is there a link to the home page on every page in the site?
Some users like to go back to a site's home page after navigating to content within a site. The home page becomes a base camp for these users, allowing them to regroup before exploring new content.

5.9 Are links underlined?
To maximise the perceived affordance of clickability, colour and underline the link text. Users shouldn't have to guess or scrub the page to find out where they can click.
CODE
http://www.useit.com/alertbox/20040510.html


5.10 Are visited links clearly defined?
Most important, knowing which pages they've already visited frees users from unintentionally revisiting the same pages over and over again.
CODE
http://www.useit.com/alertbox/20040503.html


6. Site management

6.1 Does the site have a meaningful and helpful 404 error page that works from any depth in the site?
You've requested a page - either by typing a URL directly into the address bar or clicking on an out-of-date link and you've found yourself in the middle of cyberspace nowhere. A user-friendly website will give you a helping hand while many others will simply do nothing, relying on the browser's built-in ability to explain what the problem is.
CODE
http://www.alistapart.com/articles/perfect404/


6.2 Does the site use friendly URLs?
Most search engines (with a few exceptions - namely Google) will not index any pages that have a question mark or other character (like an ampersand or equals sign) in the URL... what good is a site if no one can find it?
CODE
http://www.sitepoint.com/article/search-engine-friendly-urls


One of the worst elements of the web from a user interface standpoint is the URL. However, if they're short, logical, and self-correcting, URLs can be acceptably usable
CODE
http://www.merges.net/theory/20010305.html


More:
CODE
http://www.sitepoint.com/article/search-engine-friendly-urls

CODE
http://www.websitegoodies.com/article/32

CODE
http://www.merges.net/theory/20010305.html


6.3 Does the site's URL work without "www"?
While this is not critical, and in some cases is not even possible, it is always good to give people the choice of both options. If a user types your domain name without the www and gets no site, this could disadvantage both the user and you.
6.4 Does the site have a favicon?

A Favicon is a multi-resolution image included on nearly all professionally developed sites. The Favicon allows the webmaster to further promote their site, and to create a more customized appearance within a visitor's browser.
CODE
http://www.favicon.com/


Favicons are definitely not critical. However, if they are not present, they can cause 404 errors in your logs (site statistics). Browsers like IE will request them from the server when a site is bookmarked. If a favicon isn't available, a 404 error may be generated. Therefore, having a favicon could cut down on favicon specific 404 errors. The same is true of a 'robots.txt' file.

Introduction to denial service

===================================
=INTRODUCTION TO DENIAL OF SERVICE=
===================================

Hans Husman
t95hhu@student.tdb.uu.se
Last updated: Mon Oct 28 14:56:31 MET 1996

.0. FOREWORD

.A. INTRODUCTION
.A.1. WHAT IS A DENIAL OF SERVICE ATTACK?
.A.2. WHY WOULD SOMEONE CRASH A SYSTEM?
.A.2.1. INTRODUCTION
.A.2.2. SUB-CULTURAL STATUS
.A.2.3. TO GAIN ACCESS
.A.2.4. REVENGE
.A.2.5. POLITICAL REASONS
.A.2.6. ECONOMICAL REASONS
.A.2.7. NASTINESS
.A.3. ARE SOME OPERATING SYSTEMS MORE SECURE?

.B. SOME BASIC TARGETS FOR AN ATTACK
.B.1. SWAP SPACE
.B.2. BANDWIDTH
.B.3. KERNEL TABLES
.B.4. RAM
.B.5. DISKS
.B.6. CACHES
.B.7. INETD

.C. ATTACKING FROM THE OUTSIDE
.C.1. TAKING ADVANTAGE OF FINGER
.C.2. UDP AND SUNOS 4.1.3.
.C.3. FREEZING UP X-WINDOWS
.C.4. MALICIOUS USE OF UDP SERVICES
.C.5. ATTACKING WITH LYNX CLIENTS
.C.6. MALICIOUS USE OF telnet
.C.7. MALICIOUS USE OF telnet UNDER SOLARIS 2.4
.C.8. HOW TO DISABLE ACCOUNTS
.C.9. LINUX AND TCP TIME, DAYTIME
.C.10. HOW TO DISABLE SERVICES
.C.11. PARAGON OS BETA R1.4
.C.12. NOVELLS NETWARE FTP
.C.13. ICMP REDIRECT ATTACKS
.C.14. BROADCAST STORMS
.C.15. EMAIL BOMBING AND SPAMMING
.C.16. TIME AND KERBEROS
.C.17. THE DOT DOT BUG
.C.18. SUNOS KERNEL PANIC
.C.19. HOSTILE APPLETS
.C.20. VIRUS
.C.21. ANONYMOUS FTP ABUSE
.C.22. SYN FLOODING
.C.23. PING FLOODING
.C.24. CRASHING SYSTEMS WITH PING FROM WINDOWS 95 MACHINES
.C.25. MALICIOUS USE OF SUBNET MASK REPLY MESSAGE
.C.26. FLEXlm
.C.27. BOOTING WITH TRIVIAL FTP

.D. ATTACKING FROM THE INSIDE
.D.1. KERNEL PANIC UNDER SOLARIS 2.3
.D.2. CRASHING THE X-SERVER
.D.3. FILLING UP THE HARD DISK
.D.4. MALICIOUS USE OF eval
.D.5. MALICIOUS USE OF fork()
.D.6. CREATING FILES THAT IS HARD TO REMOVE
.D.7. DIRECTORY NAME LOOKUPCACHE
.D.8. CSH ATTACK
.D.9. CREATING FILES IN /tmp
.D.10. USING RESOLV_HOST_CONF
.D.11. SUN 4.X AND BACKGROUND JOBS
.D.12. CRASHING DG/UX WITH ULIMIT
.D.13. NETTUNE AND HP-UX
.D.14. SOLARIS 2.X AND NFS
.D.15. SYSTEM STABILITY COMPROMISE VIA MOUNT_UNION
.D.16. trap_mon CAUSES KERNEL PANIC UNDER SUNOS 4.1.X

.E. DUMPING CORE
.E.1. SHORT COMMENT
.E.2. MALICIOUS USE OF NETSCAPE
.E.3. CORE DUMPED UNDER WUFTPD
.E.4. ld UNDER SOLARIS/X86

.F. HOW DO I PROTECT A SYSTEM AGAINST DENIAL OF SERVICE ATTACKS?
.F.1. BASIC SECURITY PROTECTION
.F.1.1. INTRODUCTION
.F.1.2. PORT SCANNING
.F.1.3. CHECK THE OUTSIDE ATTACKS DESCRIBED IN THIS PAPER
.F.1.4. CHECK THE INSIDE ATTACKS DESCRIBED IN THIS PAPER
.F.1.5. EXTRA SECURITY SYSTEMS
.F.1.6. MONITORING SECURITY
.F.1.7. KEEPING UP TO DATE
.F.1.8. READ SOMETHING BETTER
.F.2. MONITORING PERFORMANCE
.F.2.1. INTRODUCTION
.F.2.2. COMMANDS AND SERVICES
.F.2.3. PROGRAMS
.F.2.4. ACCOUNTING

.G. SUGGESTED READING
.G.1. INFORMATION FOR DEEPER KNOWLEDGE
.G.2. KEEPING UP TO DATE INFORMATION
.G.3. BASIC INFORMATION

.H. COPYRIGHT

.I. DISCLAIMER

.0. FOREWORD
------------

In this paper I have tried to answer the following questions:

- What is a denial of service attack?
- Why would someone crash a system?
- How can someone crash a system.
- How do I protect a system against denial of service attacks?

I also have a section called SUGGESTED READING were you can find
information about good free information that can give you a deeper
understanding about something.

Note that I have a very limited experience with Macintosh, OS/2 and
Windows and most of the material are therefore for Unix use.

You can always find the latest version at the following address:
http://www.student.tdb.uu.se/~t95hhu/secure/denial/DENIAL.TXT

Feel free to send comments, tips and so on to address:
t95hhu@student.tdb.uu.se

.A. INTRODUCTION
~~~~~~~~~~~~~~~~

.A.1. WHAT IS A DENIAL OF SERVICE ATTACK?
-----------------------------------------

Denial of service is about without permission knocking off
services, for example through crashing the whole system. This
kind of attacks are easy to launch and it is hard to protect
a system against them. The basic problem is that Unix
assumes that users on the system or on other systems will be
well behaved.

.A.2. WHY WOULD SOMEONE CRASH A SYSTEM?
---------------------------------------

.A.2.1. INTRODUCTION
--------------------

Why would someone crash a system? I can think of several reasons
that I have presentated more precisely in a section for each reason,
but for short:

.1. Sub-cultural status.
.2. To gain access.
.3. Revenge.
.4. Political reasons.
.5. Economical reasons.
.6. Nastiness.

I think that number one and six are the more common today, but that
number four and five will be the more common ones in the future.

.A.2.2. SUB-CULTURAL STATUS
---------------------------

After all information about syn flooding a bunch of such attacks
were launched around Sweden. The very most of these attacks were
not a part of a IP-spoof attack, it was "only" a denial of service
attack. Why?

I think that hackers attack systems as a sub-cultural pseudo career
and I think that many denial of service attacks, and here in the
example syn flooding, were performed for these reasons. I also think
that many hackers begin their carrer with denial of service attacks.

.A.2.3. TO GAIN ACCESS
----------------------

Sometimes could a denial of service attack be a part of an attack to
gain access at a system. At the moment I can think of these reasons
and specific holes:

.1. Some older X-lock versions could be crashed with a
method from the denial of service family leaving the system
open. Physical access was needed to use the work space after.

.2. Syn flooding could be a part of a IP-spoof attack method.

.3. Some program systems could have holes under the startup,
that could be used to gain root, for example SSH (secure shell).

.4. Under an attack it could be usable to crash other machines
in the network or to deny certain persons the ability to access
the system.

.5. Also could a system being booted sometimes be subverted,
especially rarp-boots. If we know which port the machine listen
to (69 could be a good guess) under the boot we can send false
packets to it and almost totally control the boot.

.A.2.4. REVENGE
---------------

A denial of service attack could be a part of a revenge against a user
or an administrator.

.A.2.5. POLITICAL REASONS
-------------------------

Sooner or later will new or old organizations understand the potential
of destroying computer systems and find tools to do it.

For example imaginate the Bank A loaning company B money to build a
factory threating the environment. The organization C therefor crash A:s
computer system, maybe with help from an employee. The attack could cost
A a great deal of money if the timing is right.

.A.2.6. ECONOMICAL REASONS
--------------------------

Imaginate the small company A moving into a business totally dominated by
company B. A and B customers make the orders by computers and depends
heavily on that the order is done in a specific time (A and B could be
stock trading companies). If A and B can't perform the order the customers
lose money and change company.

As a part of a business strategy A pays a computer expert a sum of money to
get him to crash B:s computer systems a number of times. A year later A
is the dominating company.

.A.2.7. NASTINESS
-----------------

I know a person that found a workstation where the user had forgotten to
logout. He sat down and wrote a program that made a kill -9 -1 at a
random time at least 30 minutes after the login time and placed a call to
the program from the profile file. That is nastiness.

.A.3. ARE SOME OPERATING SYSTEMS MORE SECURE?
---------------------------------------------

This is a hard question to answer and I don't think that it will
give anything to compare different Unix platforms. You can't say that
one Unix is more secure against denial of service, it is all up to the
administrator.

A comparison between Windows 95 and NT on one side and Unix on the
other could however be interesting.

Unix systems are much more complex and have hundreds of built in programs,
services... This always open up many ways to crash the system from
the inside.

In the normal Windows NT and 95 network were is few ways to crash
the system. Although were is methods that always will work.

That gives us that no big different between Microsoft and Unix can
be seen regardning the inside attacks. But there is a couple of
points left:

- Unix have much more tools and programs to discover an
attack and monitoring the users. To watch what another user
is up to under windows is very hard.

- The average Unix administrator probably also have much more
experience than the average Microsoft administrator.

The two last points gives that Unix is more secure against inside
denial of service attacks.

A comparison between Microsoft and Unix regarding outside attacks
are much more difficult. However I would like to say that the average
Microsoft system on the Internet are more secure against outside
attacks, because they normally have much less services.

.B. SOME BASIC TARGETS FOR AN ATTACK
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.B.1. SWAP SPACE
----------------

Most systems have several hundred Mbytes of swap space to
service client requests. The swap space is typical used
for forked child processes which have a short life time.
The swap space will therefore almost never in a normal
cause be used heavily. A denial of service could be based
on a method that tries to fill up the swap space.

.B.2. BANDWIDTH
---------------

If the bandwidth is to high the network will be useless. Most
denial of service attack influence the bandwidth in some way.

.B.3. KERNEL TABLES
-------------------

It is trivial to overflow the kernel tables which will cause
serious problems on the system. Systems with write through
caches and small write buffers is especially sensitive.

Kernel memory allocation is also a target that is sensitive.
The kernel have a kernelmap limit, if the system reach this
limit it can not allocate more kernel memory and must be rebooted.
The kernel memory is not only used for RAM, CPU:s, screens and so
on, it it also used for ordinaries processes. Meaning that any system
can be crashed and with a mean (or in some sense good) algorithm pretty
fast.

For Solaris 2.X it is measured and reported with the sar command
how much kernel memory the system is using, but for SunOS 4.X there
is no such command. Meaning that under SunOS 4.X you don't even can
get a warning. If you do use Solaris you should write sar -k 1 to
get the information. netstat -k can also be used and shows how much
memory the kernel have allocated in the subpaging.

.B.4. RAM
---------

A denial of service attack that allocates a large amount of RAM
can make a great deal of problems. NFS and mail servers are
actually extremely sensitive because they do not need much
RAM and therefore often don't have much RAM. An attack at
a NFS server is trivial. The normal NFS client will do a
great deal of caching, but a NFS client can be anything
including the program you wrote yourself...

.B.5. DISKS
-----------

A classic attack is to fill up the hard disk, but an attack at
the disks can be so much more. For example can an overloaded disk
be misused in many ways.

.B.6. CACHES
-------------

A denial of service attack involving caches can be based on a method
to block the cache or to avoid the cache.

These caches are found on Solaris 2.X:

Directory name lookup cache: Associates the name of a file with a vnode.

Inode cache: Cache information read from disk in case it is needed
again.

Rnode cache: Holds information about the NFS filesystem.

Buffer cache: Cache inode indirect blocks and cylinders to realed disk
I/O.

.B.7. INETD
-----------

Well once inetd crashed all other services running through inetd no
longer will work.


.C. ATTACKING FROM THE OUTSIDE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


.C.1. TAKING ADVANTAGE OF FINGER
--------------------------------

Most fingerd installations support redirections to an other host.

Ex:

$finger @system.two.com@system.one.com

finger will in the example go through system.one.com and on to
system.two.com. As far as system.two.com knows it is system.one.com
who is fingering. So this method can be used for hiding, but also
for a very dirty denial of service attack. Lock at this:

$ finger @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@host.we.attack

All those @ signs will get finger to finger host.we.attack again and
again and again... The effect on host.we.attack is powerful and
the result is high bandwidth, short free memory and a hard disk with
less free space, due to all child processes (compare with .D.5.).

The solution is to install a fingerd which don't support redirections,
for example GNU finger. You could also turn the finger service off,
but I think that is just a bit to much.

.C.2. UDP AND SUNOS 4.1.3.
--------------------------

SunOS 4.1.3. is known to boot if a packet with incorrect information
in the header is sent to it. This is the cause if the ip_options
indicate a wrong size of the packet.

The solution is to install the proper patch.

.C.3. FREEZING UP X-WINDOWS
---------------------------

If a host accepts a telnet session to the X-Windows port (generally
somewhere between 6000 and 6025. In most cases 6000) could that
be used to freeze up the X-Windows system. This can be made with
multiple telnet connections to the port or with a program which
sends multiple XOpenDisplay() to the port.

The same thing can happen to Motif or Open Windows.

The solution is to deny connections to the X-Windows port.

.C.4. MALICIOUS USE OF UDP SERVICES
-----------------------------------

It is simple to get UDP services (echo, time, daytime, chargen) to
loop, due to trivial IP-spoofing. The effect can be high bandwidth
that causes the network to become useless. In the example the header
claim that the packet came from 127.0.0.1 (loopback) and the target
is the echo port at system.we.attack. As far as system.we.attack knows
is 127.0.0.1 system.we.attack and the loop has been establish.

Ex:

from-IP=127.0.0.1
to-IP=system.we.attack
Packet type:UDP
from UDP port 7
to UDP port 7

Note that the name system.we.attack looks like a DNS-name, but the
target should always be represented by the IP-number.

Quoted from proberts@clark.net (Paul D. Robertson) comment on
comp.security.firewalls on matter of "Introduction to denial of service"

" A great deal of systems don't put loopback on the wire, and simply
emulate it. Therefore, this attack will only effect that machine
in some cases. It's much better to use the address of a different
machine on the same network. Again, the default services should
be disabled in inetd.conf. Other than some hacks for mainframe IP
stacks that don't support ICMP, the echo service isn't used by many
legitimate programs, and TCP echo should be used instead of UDP
where it is necessary. "

.C.5. ATTACKING WITH LYNX CLIENTS
---------------------------------

A World Wide Web server will fork an httpd process as a respond
to a request from a client, typical Netscape or Mosaic. The process
lasts for less than one second and the load will therefore never
show up if someone uses ps. In most causes it is therefore very
safe to launch a denial of service attack that makes use of
multiple W3 clients, typical lynx clients. But note that the netstat
command could be used to detect the attack (thanks to Paul D. Robertson).

Some httpd:s (for example http-gw) will have problems besides the normal
high bandwidth, low memory... And the attack can in those causes get
the server to loop (compare with .C.6.)

.C.6. MALICIOUS USE OF telnet
-----------------------------

Study this little script:

Ex:

while : ; do
telnet system.we.attack &
done

An attack using this script might eat some bandwidth, but it is
nothing compared to the finger method or most other methods. Well
the point is that some pretty common firewalls and httpd:s thinks
that the attack is a loop and turn them self down, until the
administrator sends kill -HUP.

This is a simple high risk vulnerability that should be checked
and if present fixed.

.C.7. MALICIOUS USE OF telnet UNDER SOLARIS 2.4
-----------------------------------------------

If the attacker makes a telnet connections to the Solaris 2.4 host and
quits using:

Ex:

Control-}
quit

then will inetd keep going "forever". Well a couple of hundred...

The solution is to install the proper patch.

.C.8. HOW TO DISABLE ACCOUNTS
-----------------------------

Some systems disable an account after N number of bad logins, or waits
N seconds. You can use this feature to lock out specific users from
the system.

.C.9. LINUX AND TCP TIME, DAYTIME
----------------------------------

Inetd under Linux is known to crash if to many SYN packets sends to
daytime (port 13) and/or time (port 37).

The solution is to install the proper patch.

.C.10. HOW TO DISABLE SERVICES
------------------------------

Most Unix systems disable a service after N sessions have been
open in a given time. Well most systems have a reasonable default
(lets say 800 - 1000), but not some SunOS systems that have the
default set to 48...

The solutions is to set the number to something reasonable.

.C.11. PARAGON OS BETA R1.4
---------------------------

If someone redirects an ICMP (Internet Control Message Protocol) packet
to a paragon OS beta R1.4 will the machine freeze up and must be
rebooted. An ICMP redirect tells the system to override routing
tables. Routers use this to tell the host that it is sending
to the wrong router.

The solution is to install the proper patch.

.C.12. NOVELLS NETWARE FTP
--------------------------

Novells Netware FTP server is known to get short of memory if multiple
ftp sessions connects to it.

.C.13. ICMP REDIRECT ATTACKS
----------------------------

Gateways uses ICMP redirect to tell the system to override routing
tables, that is telling the system to take a better way. To be able
to misuse ICMP redirection we must know an existing connection
(well we could make one for ourself, but there is not much use for that).
If we have found a connection we can send a route that
loses it connectivity or we could send false messages to the host
if the connection we have found don't use cryptation.

Ex: (false messages to send)

DESTINATION UNREACHABLE
TIME TO LIVE EXCEEDED
PARAMETER PROBLEM
PACKET TOO BIG

The effect of such messages is a reset of the connection.

The solution could be to turn ICMP redirects off, not much proper use
of the service.

.C.14. BROADCAST STORMS
-----------------------

This is a very popular method in networks there all of the hosts are
acting as gateways.

There are many versions of the attack, but the basic method is to
send a lot of packets to all hosts in the network with a destination
that don't exist. Each host will try to forward each packet so
the packets will bounce around for a long time. And if new packets
keep coming the network will soon be in trouble.

Services that can be misused as tools in this kind of attack is for
example ping, finger and sendmail. But most services can be misused
in some way or another.

.C.15. EMAIL BOMBING AND SPAMMING
---------------------------------

In a email bombing attack the attacker will repeatedly send identical
email messages to an address. The effect on the target is high bandwidth,
a hard disk with less space and so on... Email spamming is about sending
mail to all (or rather many) of the users of a system. The point of
using spamming instead of bombing is that some users will try to
send a replay and if the address is false will the mail bounce back. In
that cause have one mail transformed to three mails. The effect on the
bandwidth is obvious.

There is no way to prevent email bombing or spamming. However have
a look at CERT:s paper "Email bombing and spamming".

.C.16. TIME AND KERBEROS
------------------------

If not the the source and target machine is closely aligned will the
ticket be rejected, that means that if not the protocol that set the
time is protected it will be possible to set a kerberos server of
function.

.C.17. THE DOT DOT BUG
----------------------

Windows NT file sharing system is vulnerable to the under Windows 95
famous dot dot bug (dot dot like ..). Meaning that anyone can crash
the system. If someone sends a "DIR ..\" to the workstation will a
STOP messages appear on the screen on the Windows NT computer. Note that
it applies to version 3.50 and 3.51 for both workstation and server
version.

The solution is to install the proper patch.

.C.18. SUNOS KERNEL PANIC
-------------------------

Some SunOS systems (running TIS?) will get a kernel panic if a
getsockopt() is done after that a connection has been reset.

The solution could be to install Sun patch 100804.

.C.19. HOSTILE APPLETS
----------------------

A hostile applet is any applet that attempts to use your system
in an inappropriate manner. The problems in the java language
could be sorted in two main groups:

1) Problems due to bugs.
2) Problems due to features in the language.

In group one we have for example the java bytecode verifier bug, which
makes is possible for an applet to execute any command that the user
can execute. Meaning that all the attack methods described in .D.X.
could be executed through an applet. The java bytecode verifier bug
was discovered in late March 1996 and no patch have yet been available
(correct me if I'am wrong!!!).

Note that two other bugs could be found in group one, but they
are both fixed in Netscape 2.01 and JDK 1.0.1.

Group two are more interesting and one large problem found is the
fact that java can connect to the ports. Meaning that all the methods
described in .C.X. can be performed by an applet. More information
and examples could be found at address:

http://www.math.gatech.edu/~mladue/HostileArticle.html

If you need a high level of security you should use some sort of
firewall for protection against java. As a user you could have
java disable.

.C.20. VIRUS
------------

Computer virus is written for the purpose of spreading and
destroying systems. Virus is still the most common and famous
denial of service attack method.

It is a misunderstanding that virus writing is hard. If you know
assembly language and have source code for a couple of virus it
is easy. Several automatic toolkits for virus construction could
also be found, for example:

* Genvir.
* VCS (Virus Construction Set).
* VCL (Virus Construction Laboratory).
* PS-MPC (Phalcon/Skism - Mass Produced Code Generator).
* IVP (Instant Virus Production Kit).
* G2 (G Squared).

PS-MPC and VCL is known to be the best and can help the novice programmer
to learn how to write virus.

An automatic tool called MtE could also be found. MtE will transform
virus to a polymorphic virus. The polymorphic engine of MtE is well
known and should easily be catch by any scanner.

.C.21. ANONYMOUS FTP ABUSE
--------------------------

If an anonymous FTP archive have a writable area it could be misused
for a denial of service attack similar with with .D.3. That is we can
fill up the hard disk.

Also can a host get temporarily unusable by massive numbers of
FTP requests.

For more information on how to protect an anonymous FTP site could
CERT:s "Anonymous FTP Abuses" be a good start.

.C.22. SYN FLOODING
-------------------

Both 2600 and Phrack have posted information about the syn flooding attack.
2600 have also posted exploit code for the attack.

As we know the syn packet is used in the 3-way handshake. The syn flooding
attack is based on an incomplete handshake. That is the attacker host
will send a flood of syn packet but will not respond with an ACK packet.
The TCP/IP stack will wait a certain amount of time before dropping
the connection, a syn flooding attack will therefore keep the syn_received
connection queue of the target machine filled.

The syn flooding attack is very hot and it is easy to find more information
about it, for example:

[.1.] http://www.eecs.nwu.edu/~jmyers/bugtraq/1354.html
Article by Christopher Klaus, including a "solution".

[.2.] http://jya.com/floodd.txt
2600, Summer, 1996, pp. 6-11. FLOOD WARNING by Jason Fairlane

[.3.] http://www.fc.net/phrack/files/p48/p48-14.html
IP-spoofing Demystified by daemon9 / route / infinity
for Phrack Magazine

.C.23. PING FLOODING
--------------------

I haven't tested how big the impact of a ping flooding attack is, but
it might be quite big.

Under Unix we could try something like: ping -s host
to send 64 bytes packets.

If you have Windows 95, click the start button, select RUN, then type
in: PING -T -L 256 xxx.xxx.xxx.xx. Start about 15 sessions.

.C.24. CRASHING SYSTEMS WITH PING FROM WINDOWS 95 MACHINES
----------------------------------------------------------

If someone can ping your machine from a Windows 95 machine he or she might
reboot or freeze your machine. The attacker simply writes:

ping -l 65510 address.to.the.machine

And the machine will freeze or reboot.

Works for kernel 2.0.7 up to version 2.0.20. and 2.1.1. for Linux (crash).
AIX4, OSF, HPUX 10.1, DUnix 4.0 (crash).
OSF/1, 3.2C, Solaris 2.4 x86 (reboot).

.C.25. MALICIOUS USE OF SUBNET MASK REPLY MESSAGE
--------------------------------------------------

The subnet mask reply message is used under the reboot, but some
hosts are known to accept the message any time without any check.
If so all communication to or from the host us turned off, it's dead.

The host should not accept the message any time but under the reboot.

.C.26. FLEXlm
-------------

Any host running FLEXlm can get the FLEXlm license manager daemon
on any network to shutdown using the FLEXlm lmdown command.

# lmdown -c /etc/licence.dat
lmdown - Copyright (C) 1989, 1991 Highland Software, Inc.

Shutting down FLEXlm on nodes: xxx
Are you sure? [y/n]: y
Shut down node xxx
#

.C.27. BOOTING WITH TRIVIAL FTP
-------------------------------

To boot diskless workstations one often use trivial ftp with rarp or
bootp. If not protected an attacker can use tftp to boot the host.


.D. ATTACKING FROM THE INSIDE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.D.1. KERNEL PANIC UNDER SOLARIS 2.3
------------------------------------

Solaris 2.3 will get a kernel panic if this
is executed:

EX:

$ndd /dev/udp udp_status

The solution is to install the proper patch.

.D.2. CRASHING THE X-SERVER
---------------------------

If stickybit is not set in /tmp then can the file /tmp/.x11-unix/x0
be removed and the x-server will crash.

Ex:

$ rm /tmp/.x11-unix/x0

.D.3. FILLING UP THE HARD DISK
-----------------------------

If your hard disk space is not limited by a quota or if you can use
/tmp then it`s possible for you to fill up the file system.

Ex:

while : ;
mkdir .xxx
cd .xxx
done

.D.4. MALICIOUS USE OF eval
---------------------------

Some older systems will crash if eval '\!\!' is executed in the
C-shell.

Ex:

% eval '\!\!'

.D.5. MALICIOUS USE OF fork()
-----------------------------

If someone executes this C++ program the result will result in a crash
on most systems.

Ex:

#include
#include
#include

main()
{
int x;
while(x=0;x<1000000;x++)
{
system("uptime");
fork();
}
}

You can use any command you want, but uptime is nice
because it shows the workload.

To get a bigger and very ugly attack you should however replace uptime
(or fork them both) with sync. This is very bad.

If you are real mean you could also fork a child process for
every child process and we will get an exponential increase of
workload.

There is no good way to stop this attack and
similar attacks. A solution could be to place a limit
on time of execution and size of processes.

.D.6. CREATING FILES THAT IS HARD TO REMOVE
-------------------------------------------

Well all files can be removed, but here is some ideas:

Ex.I.

$ cat > -xxx
^C
$ ls
-xxx
$ rm -xxx
rm: illegal option -- x
rm: illegal option -- x
rm: illegal option -- x
usage: rm [-fiRr] file ...
$

Ex.II.

$ touch xxx!
$ rm xxx!
rm: remove xxx! (yes/no)? y
$ touch xxxxxxxxx!
$ rm xxxxxxxxx!
bash: !": event not found
$

(You see the size do count!)

Other well know methods is files with odd characters or spaces
in the name.

These methods could be used in combination with ".D.3 FILLING UP THE
HARDDISK". If you do want to remove these files you must use some sort
of script or a graphical interface like OpenWindow:s File
Manager. You can also try to use: rm ./. It should work for
the first example if you have a shell.

.D.7. DIRECTORY NAME LOOKUPCACHE
--------------------------------

Directory name lookupcache (DNLC) is used whenever a file is opened.
DNLC associates the name of the file to a vnode. But DNLC can only
operate on files with names that has less than N characters (for SunOS 4.x
up to 14 character, for Solaris 2.x up 30 characters). This means
that it's dead easy to launch a pretty discreet denial of service attack.

Create lets say 20 directories (for a start) and put 10 empty files in
every directory. Let every name have over 30 characters and execute a
script that makes a lot of ls -al on the directories.

If the impact is not big enough you should create more files or launch
more processes.

.D.8. CSH ATTACK
----------------

Just start this under /bin/csh (after proper modification)
and the load level will get very high (that is 100% of the cpu time)
in a very short time.

Ex:

|I /bin/csh
nodename : **************b

.D.9. CREATING FILES IN /tmp
----------------------------

Many programs creates files in /tmp, but are unable to deal with the problem
if the file already exist. In some cases this could be used for a
denial of service attack.

.D.10. USING RESOLV_HOST_CONF
-----------------------------

Some systems have a little security hole in the way they use the
RESOLV_HOST_CONF variable. That is we can put things in it and
through ping access confidential data like /etc/shadow or
crash the system. Most systems will crash if /proc/kcore is
read in the variable and access through ping.

Ex:

$ export RESOLV_HOST_CONF="/proc/kcore" ; ping asdf

.D.11. SUN 4.X AND BACKGROUND JOBS
----------------------------------

Thanks to Mr David Honig for the following:

" Put the string "a&" in a file called "a" and perform "chmod +x a".
Running "a" will quickly disable a Sun 4.x machine, even disallowing
(counter to specs) root login as the kernel process table fills."

" The cute thing is the size of the
script, and how few keystrokes it takes to bring down a Sun
as a regular user."

.D.12. CRASHING DG/UX WITH ULIMIT
---------------------------------

ulimit is used to set a limit on the system resources available to the
shell. If ulimit 0 is called before /etc/passwd, under DG/UX, will the
passwd file be set to zero.

.D.13. NETTUNE AND HP-UX
------------------------

/usr/contrib/bin/nettune is SETUID root on HP-UX meaning
that any user can reset all ICMP, IP and TCP kernel
parameters, for example the following parameters:

- arp_killcomplete
- arp_killincomplete
- arp_unicast
- arp_rebroadcast
- icmp_mask_agent
- ip_defaultttl
- ip_forwarding
- ip_intrqmax
- pmtu_defaulttime
- tcp_localsubnets
- tcp_receive
- tcp_send
- tcp_defaultttl
- tcp_keepstart
- tcp_keepfreq
- tcp_keepstop
- tcp_maxretrans
- tcp_urgent_data_ptr
- udp_cksum
- udp_defaultttl
- udp_newbcastenable
- udp_pmtu
- tcp_pmtu
- tcp_random_seq

The solution could be to set the proper permission on
/sbin/mount_union:

#chmod u-s /sbin/mount_union

.D.14. SOLARIS 2.X AND NFS
--------------------------

If a process is writing over NFS and the user goes over the disk
quota will the process go into an infinite loop.

.D.15. SYSTEM STABILITY COMPROMISE VIA MOUNT_UNION
--------------------------------------------------

By executing a sequence of mount_union commands any user
can cause a system reload on all FreeBSD version 2.X before
1996-05-18.

$ mkdir a
$ mkdir b
$ mount_union ~/a ~/b
$ mount_union -b ~/a ~/b

The solution could be to set the proper permission on
/sbin/mount_union:

#chmod u-s /sbin/mount_union

.D.16. trap_mon CAUSES KERNEL PANIC UNDER SUNOS 4.1.X
----------------------------------------------------

Executing the trap_mon instruction from user mode can cause
a kernel panic or a window underflow watchdog reset under
SunOS 4.1.x, sun4c architecture.


.E. DUMPING CORE
~~~~~~~~~~~~~~~~

.E.1. SHORT COMMENT
-------------------

The core dumps things don't really belongs in this paper but I have
put them here anyway.

.E.2. MALICIOUS USE OF NETSCAPE
-------------------------------

Under Netscape 1.1N this link will result in a segmentation fault and a
core dump.

Ex:


.F.1.7. MONITORING SECURITY
---------------------------

Also monitor security regular, for example through examining system log
files, history files... Even in a system without any extra security systems
could several tools be found for monitoring, for example:

- uptime
- showmount
- ps
- netstat
- finger

(see the man text for more information).

.F.1.8. KEEPING UP TO DATE
--------------------------

It is very important to keep up to date with security problems. Also
understand that then, for example CERT, warns for something it has often
been dark-side public for sometime, so don't wait. The following resources
that helps you keeping up to date can for example be found on the Internet:

- CERT mailing list. Send an e-mail to cert@cert.org to be placed
on the list.

- Bugtraq mailing list. Send an e-mail to bugtraq-request@fc.net.

- WWW-security mailing list. Send an e-mail to
www-security@ns2.rutgers.edu.

.F.1.9. READ SOMETHING BIGGER AND BETTER
----------------------------------------

Let's start with papers on the Internet. I am sorry to say that it is not
very many good free papers that can be found, but here is a small collection
and I am sorry if have have over looked a paper.

(1) The Rainbow books is a long series of free books on computer security.
US citizens can get the books from:

INFOSEC AWARENESS OFFICE
National Computer Security Center
9800 Savage Road
Fort George G. Meader, MD 20755-600

We other just have to read the papers on the World Wide Web. Every
paper can not however be found on the Internet.

(2) "Improving the security of your Unix system" by Curry is also very
nice if you need the very basic things. If you don't now anything about
computer security you can't find a better start.

(3) "The WWW security FAQ" by Stein is although it deal with W3-security
the very best better on the Internet about computer security.

(4) CERT have aklso published several good papers, for example:

- Anonymous FTP Abuses.
- Email Bombing and Spamming.
- Spoofed/Forged Email.
- Protecting yourself from password file attacks.

I think however that the last paper have overlooked several things.

(5) For a long list on papers I can recommend:
"FAQ: Computer Security Frequently Asked Questions".

(6) Also see section ".G. SUGGESTED READING"

You should also get some big good commercial book, but I don't want
to recommend any.

.F.2. MONITORING PERFORMANCE
----------------------------

.F.2.1. INTRODUCTION
--------------------

There is several commands and services that can be used for
monitoring performance. And at least two good free programs can
be found on Internet.

.F.2.2. COMMANDS AND SERVICES
-----------------------------

For more information read the man text.

netstat Show network status.
nfsstat Show NFS statistics.
sar System activity reporter.
vmstat Report virtual memory statistics.
timex Time a command, report process data and system
activity.
time Time a simple command.
truss Trace system calls and signals.
uptime Show how long the system has been up.

Note that if a public netstat server can be found you might be able
to use netstat from the outside. netstat can also give information
like tcp sequence numbers and much more.

.F.2.3. PROGRAMS
----------------

Proctool: Proctool is a freely available tool for Solaris that monitors
and controls processes.
ftp://opcom.sun.ca/pub/binaries/

Top: Top might be a more simple program than Proctool, but is
good enough.

.F.2.4. ACCOUNTING
------------------

To monitor performance you have to collect information over a long
period of time. All Unix systems have some sort of accounting logs
to identify how much CPU time, memory each program uses. You should
check your manual to see how to set this up.

You could also invent your own account system by using crontab and
a script with the commands you want to run. Let crontab run the script
every day and compare the information once a week. You could for
example let the script run the following commands:

- netstat
- iostat -D
- vmstat


.G. SUGGESTED READING
~~~~~~~~~~~~~~~~~~~~~

.F.1. INFORMATION FOR DEEPER KNOWLEDGE
-------------------------------------

(1) Hedrick, C. Routing Information Protocol. RFC 1058, 1988.
(2) Mills, D.L. Exterior Gateway Protocol Formal Specification. RFC 904, 1984.
(3) Postel, J. Internet Control Message Protocol. RFC 792, 1981.
(4) Harrenstien, K. NAME/FINGER Protocol, RFC 742, 1977.
(5) Sollins, K.R. The TFTP Protocol, RFC 783, 1981.
(6) Croft, W.J. Bootstrap Protocol, RFC 951, 1985.

Many of the papers in this category was RFC-papers. A RFC-paper
is a paper that describes a protocol. The letters RCS stands for
Request For Comment. Hosts on the Internet are expected to understand
at least the common ones. If you want to learn more about a protocol
it is always good to read the proper RFC. You can find a nice sRFC
index search form at URL:

http://pubweb.nexor.co.uk/public/rfc/index/rfc.html

.F.2. KEEPING UP TO DATE INFORMATION
------------------------------------

(1) CERT mailing list. Send an e-mail to cert@cert.org to be placed
on the list.
(2) Bugtraq mailinglist. Send an e-mail to bugtraq-request@fc.net.
(3) WWW-security mailinglist. Send an e-mail to www-security@ns2.rutgers.edu.
(4) Sun Microsystems Security Bulletins.
(5) Various articles from: - comp.security.announce
- comp.security.unix
- comp.security.firewalls
(6) Varius 40Hex Issues.

.F.3. BASIC INFORMATION
-----------------------

(1) Husman, H. INTRODUKTION TILL DATASÄKERHET UNDER X-WINDOWS, 1995.
(2) Husman, H. INTRODUKTION TILL IP-SPOOFING, 1995.
(3) The following rainbow books: - Teal Green Book (Glossary of
Computer Security Terms).
- Bright Orange Book( A Guide
to Understanding Security Testing
and Test Documentation in Trusted
Systems).
- C1 Technical Report-001
(Computer Viruses: Preventation,
Detection, and Treatment).
(4) Ranum, Marcus. Firewalls, 1993.
(5) Sun Microsystems, OpenWindows V3.0.1. User Commands, 1992.
(6) Husman, H. ATT SPÅRA ODOKUMENTERADE SÄKERHETSLUCKOR, 1996.
(7) Dark OverLord, Unix Cracking Tips, 1989.
(8) Shooting Shark, Unix Nasties, 1988.
(9) LaDue, Mark.D. Hostile Applets on the Horizone, 1996.
(10) Curry, D.A. Improving the security of your unix system, 1990.
(11) Stein, L.D. The World Wide Web security FAQ, 1995.
(12) Bellovin, S.M. Security Problems in the TCP/IP Protocol, 1989.

.H. COPYRIHT
------------

This paper is Copyright (c) 1996 by Hans Husman.

Permission is hereby granted to give away free copies electronically. You
may distribute, transfer, or spread this paper electronically. You may not
pretend that you wrote it. This copyright notice must be maintained in any
copy made. If you wish to reprint the whole or any part of this paper in any
other medium excluding electronic medium, please ask the author for
permission.

.I. DISCLAIMER
--------------

The information within this paper may change without notice. Use of this
information constitutes acceptance for use in an AS IS condition. There are
NO warranties with regard to this information. In no event shall the author
be liable for any damages whatsoever arising out of or in connection with
the use or spread of this information. Any use of this information is at the
user's own risk.

All Imrc Commands

All mIRC Commands

/ Recalls the previous command entered in the current window.
/! Recalls the last command typed in any window.
/action {action text} Sends the specifed action to the active channel or query window.
/add [-apuce] {filename.ini} Loads aliases, popups, users, commands, and events.
/ame {action text} Sends the specifed action to all channels which you are currently on.
/amsg {text} Sends the specifed message to all channels which you are currently on.
/auser {level} {nick|address} Adds a user with the specified access level to the remote users
list.
/auto [on|off|nickname|address] Toggles auto-opping of a nick or address or sets it on or off
totally.
/away {away message} Sets you away leave a message explaining that you are not currently paying
attention to IRC.
/away Sets you being back.
/ban [#channel] {nickname} [type] Bans the specified nick from the curent or given channel.
/beep {number} {delay} Locally beeps 'number' times with 'delay' in between the beeps. /channel
Pops up the channel central window (only works in a channel).
/clear Clears the entire scrollback buffer of the current window.
/ctcp {nickname} {ping|finger|version|time|userinfo|clientinfo} Does the given ctcp request on
nickname.
/closemsg {nickname} Closes the query window you have open to the specified nick.
/creq [ask | auto | ignore] Sets your DCC 'On Chat request' settings in DCC/Options.
/dcc send {nickname} {file1} {file2} {file3} ... {fileN} Sends the specified files to nick.
/dcc chat {nickname} Opens a dcc window and sends a dcc chat request to nickname.
/describe {#channel} {action text} Sends the specifed action to the specified channel window.
/dde [-r] {service} {topic} {item} [data] Allows DDE control between mIRC and other
applications.
/ddeserver [on [service name] | off] To turn on the DDE server mode, eventually with a given
service name.
/disable {#groupname} De-activates a group of commands or events.
/disconnect Forces a hard and immediate disconnect from your IRC server. Use it with care.
/dlevel {level} Changes the default user level in the remote section.
/dns {nickname | IP address | IP name} Uses your providers DNS to resolve an IP address.
/echo [nickname|#channel|status] {text} Displays the given text only to YOU on the given place
in color N.
/enable {#groupname} Activates a group of commands or events.
/events [on|off] Shows the remote events status or sets it to listening or not.
/exit Forces mIRC to closedown and exit.
/finger Does a finger on a users address.
/flood [{numberoflines} {seconds} {pausetime}] Sets a crude flood control method.
/fsend [on|off] Shows fsends status and allows you to turn dcc fast send on or off.
/fserve {nickname} {maxgets} {homedirectory} [welcome text file] Opens a fileserver.
/guser {level} {nick} [type] Adds the user to the user list with the specified level and
address type.
/help {keyword} Brings up the Basic IRC Commands section in the mIRC help file.
/ignore [on|off|nickname|address] Toggles ignoring of a nick or address or sets it on or off
totally.
/invite {nickname} {#channel} Invites another user to a channel.
/join {#channel} Makes you join the specified channel.
/kick {#channel} {nickname} Kicks nickname off a given channel.
/list [#string] [-min #] [-max #] Lists all currently available channels, evt. filtering for
parameters.
/log [on|off] Shows the logging status or sets it on or off for the current window.
/me {action text} Sends the specifed action to the active channel or query window.
/mode {#channel|nickname} [[+|-]modechars [parameters]] Sets channel or user modes.
/msg {nickname} {message} Send a private message to this user without opening a query window.
/names {#channel} Shows the nicks of all people on the given channel.
/nick {new nickname} Changes your nickname to whatever you like.
/notice {nick} {message} Send the specified notice message to the nick.
/notify [on|off|nickname] Toggles notifying you of a nick on IRC or sets it on or off totally.
/onotice [#channel] {message} Send the specified notice message to all channel ops.
/omsg [#channel] {message} Send the specified message to all ops on a channel.
/part {#channel} Makes you leave the specified channel.
/partall Makes you leave all channels you are on.
/ping {server address} Pings the given server. NOT a nickname.
/play [-c] {filename} [delay] Allows you to send text files to a window.
/pop {delay} [#channel] {nickname} Performs a randomly delayed +o on a not already opped nick.
/protect [on|off|nickname|address] Toggles protection of a nick or address or sets it on or off
totally.
/query {nickname} {message} Open a query window to this user and send them the private message.
/quit [reason] Disconnect you from IRC with the optional byebye message.
/raw {raw command} Sends any raw command you supply directly to the server. Use it with care!!
/remote [on|off] Shows the remote commands status or sets it to listening or not.
/rlevel {access level} Removes all users from the remote users list with the specified access
level.
/run {c:\path\program.exe} [parameters] Runs the specified program, evt. with parameters.
/ruser {nick[!]|address} [type] Removes the user from the remote users list.
/save {filename.ini} Saves remote sections into a specified INI file.
/say {text} Says whatever you want to the active window.
/server [server address [port] [password]] Reconnects to the previous server or a newly
specified one.
/sound [nickname|#channel] {filename.wav} {action text} Sends an action and a fitting sound.
/speak {text} Uses the external text to speech program Monologue to speak up the text.
/sreq [ask | auto | ignore] Sets your DCC 'On Send request' settings in DCC/Options.
/time Tells you the time on the server you use.
/timer[N] {repetitions} {interval in seconds} {command} [| {more commands}] Activates a timer.
/topic {#channel} {newtopic} Changes the topic for the specified channel.
/ulist [{|}]{level} Lists all users in the remote list with the specified access levels.
/url [-d] Opens the URL windows that allows you to surf the www parallel to IRC.
/uwho [nick] Pops up the user central with information about the specified user.
/who {#channel} Shows the nicks of all people on the given channel.
/who {*address.string*} Shows all people on IRC with a matching address.
/whois {nickname} Shows information about someone in the status window.
/whowas {nickname} Shows information about someone who -just- left IRC.
/wavplay {c:\path\sound.wav} Locally plays the specified wave file.
/write [-cidl] {filename} [text] To write the specified text to a .txt file.

MoViEBoT #xdcc-help /server irc.atomic-irc.net

We strive to make IRC easier for you!

Setting Up Your Ftp[

Setting Up A Ftp:


Well, since many of us have always wondered this, here it is. Long and drawn out. Also, before attempting this, realize one thing; You will have to give up your time, effort, bandwidth, and security to have a quality ftp server.
That being said, here it goes. First of all, find out if your IP (Internet Protocol) is static (not changing) or dynamic (changes everytime you log on). To do this, first consider the fact if you have a dial up modem. If you do, chances are about 999 999 out of 1 000 000 that your IP is dynamic. To make it static, just go to a place like h*tp://www.myftp.org/ to register for a static ip address.

You'll then need to get your IP. This can be done by doing this:
Going to Start -> Run -> winipcfg or www.ask.com and asking 'What is my IP?'

After doing so, you'll need to download an FTP server client. Personally, I'd recommend G6 FTP Server, Serv-U FTPor Bullitproof v2.15 all three of which are extremely reliable, and the norm of the ftp world.
You can download them on this site: h*tp://www.liaokai.com/softw_en/d_index.htm

First, you'll have to set up your ftp. For this guide, I will use step-by-step instructions for G6. First, you'll have to go into 'Setup -> General'. From here, type in your port # (default is 21). I recommend something unique, or something a bit larger (ex: 3069). If you want to, check the number of max users (this sets the amount of simultaneous maximum users on your server at once performing actions - The more on at once, the slower the connection and vice versa).

The below options are then chooseable:
-Launch with windows
-Activate FTP Server on Start-up
-Put into tray on startup
-Allow multiple instances
-Show "Loading..." status at startup
-Scan drive(s) at startup
-Confirm exit

You can do what you want with these, as they are pretty self explanatory. The scan drive feature is nice, as is the 2nd and the last option. From here, click the 'options' text on the left column.

To protect your server, you should check 'login check' and 'password check', 'Show relative path (a must!)', and any other options you feel you'll need. After doing so, click the 'advanced' text in the left column. You should then leave the buffer size on the default (unless of course you know what you're doing ), and then allow the type of ftp you want.

Uploading and downloading is usually good, but it's up to you if you want to allow uploads and/or downloads. For the server priority, that will determine how much conventional memory will be used and how much 'effort' will go into making your server run smoothly.

Anti-hammering is also good, as it prevents people from slowing down your speed. From here, click 'Log Options' from the left column. If you would like to see and record every single command and clutter up your screen, leave the defaults.

But, if you would like to see what is going on with the lowest possible space taken, click 'Screen' in the top column. You should then check off 'Log successful logins', and all of the options in the client directry, except 'Log directory changes'. After doing so, click 'Ok' in the bottom left corner.

You will then have to go into 'Setup -> User Accounts' (or ctrl & u). From here, you should click on the right most column, and right click. Choose 'Add', and choose the username(s) you would like people to have access to.

After giving a name (ex: themoonlanding), you will have to give them a set password in the bottom column (ex: wasfaked). For the 'Home IP' directory, (if you registered with a static server, check 'All IP Homes'. If your IP is static by default, choose your IP from the list. You will then have to right click in the very center column, and choose 'Add'.

From here, you will have to set the directory you want the people to have access to. After choosing the directory, I suggest you choose the options 'Read', 'List', and 'Subdirs', unless of course you know what you're doing . After doing so, make an 'upload' folder in the directory, and choose to 'add' this folder seperately to the center column. Choose 'write', 'append', 'make', 'list', and 'subdirs'. This will allow them to upload only to specific folders (your upload folder).

Now click on 'Miscellaneous' from the left column. Choose 'enable account', your time-out (how long it takes for people to remain idle before you automatically kick them off), the maximum number of users for this name, the maximum number of connections allowed simultaneously for one ip address, show relative path (a must!), and any other things at the bottom you'd like to have. Now click 'Ok'.
**Requested**


From this main menu, click the little boxing glove icon in the top corner, and right click and unchoose the hit-o-meter for both uploads and downloads (with this you can monitor IP activity). Now click the lightning bolt, and your server is now up and running.

Post your ftp info, like this:

213.10.93.141 (or something else, such as: 'f*p://example.getmyip.com')

User: *** (The username of the client)

Pass: *** (The password)

Port: *** (The port number you chose)

So make a FTP and join the FTP section


Listing The Contents Of A Ftp:

Listing the content of a FTP is very simple.
You will need FTP Content Maker, which can be downloaded from here:
ht*p://www.etplanet.com/download/application/FTP%20Content%20Maker%201.02.zip

1. Put in the IP of the server. Do not put "ftp://" or a "/" because it will not work if you do so.
2. Put in the port. If the port is the default number, 21, you do not have to enter it.
3. Put in the username and password in the appropriate fields. If the login is anonymous, you do not have to enter it.
4. If you want to list a specific directory of the FTP, place it in the directory field. Otherwise, do not enter anything in the directory field.
5. Click "Take the List!"
6. After the list has been taken, click the UBB output tab, and copy and paste to wherever you want it.


If FTP Content Maker is not working, it is probably because the server does not utilize Serv-U Software.

If you get this error message:
StatusCode = 550
LastResponse was : 'Unable to open local file test-ftp'
Error = 550 (Unable to open local file test-ftp)
Error = Unable to open local file test-ftp = 550
Close and restart FTP Content Maker, then try again.




error messages:

110 Restart marker reply. In this case, the text is exact and not left to the particular implementation; it must read: MARK yyyy = mmmm Where yyyy is User-process data stream marker, and mmmm server's equivalent marker (note the spaces between markers and "=").
120 Service ready in nnn minutes.
125 Data connection already open; transfer starting.
150 File status okay; about to open data connection.
200 Command okay.
202 Command not implemented, superfluous at this site.
211 System status, or system help reply.
212 Directory status.
213 File status.
214 Help message. On how to use the server or the meaning of a particular non-standard command. This reply is useful only to the human user.
215 NAME system type. Where NAME is an official system name from the list in the Assigned Numbers document.
220 Service ready for new user.
221 Service closing control connection. Logged out if appropriate.
225 Data connection open; no transfer in progress.
226 Closing data connection. Requested file action successful (for example, file transfer or file abort).
227 Entering Passive Mode (h1,h2,h3,h4,p1,p2).
230 User logged in, proceed.
250 Requested file action okay, completed.
257 "PATHNAME" created.
331 User name okay, need password.
332 Need account for login.
350 Requested file action pending further information.
421 Too many users logged to the same account
425 Can't open data connection.
426 Connection closed; transfer aborted.
450 Requested file action not taken. File unavailable (e.g., file busy).
451 Requested action aborted: local error in processing.
452 Requested action not taken. Insufficient storage space in system.
500 Syntax error, command unrecognized. This may include errors such as command line too long.
501 Syntax error in parameters or arguments.
502 Command not implemented.
503 Bad sequence of commands.
504 Command not implemented for that parameter.
530 Not logged in.
532 Need account for storing files.
550 Requested action not taken. File unavailable (e.g., file not found, no access).
551 Requested action aborted: page type unknown.
552 Requested file action aborted. Exceeded storage allocation (for current directory or dataset).
553 Requested action not taken. File name not allowed.


Active FTP vs. Passive FTP, a Definitive Explanation

Introduction
One of the most commonly seen questions when dealing with firewalls and other Internet connectivity issues is the difference between active and passive FTP and how best to support either or both of them. Hopefully the following text will help to clear up some of the confusion over how to support FTP in a firewalled environment.

This may not be the definitive explanation, as the title claims, however, I've heard enough good feedback and seen this document linked in enough places to know that quite a few people have found it to be useful. I am always looking for ways to improve things though, and if you find something that is not quite clear or needs more explanation, please let me know! Recent additions to this document include the examples of both active and passive command line FTP sessions. These session examples should help make things a bit clearer. They also provide a nice picture into what goes on behind the scenes during an FTP session. Now, on to the information...



The Basics
FTP is a TCP based service exclusively. There is no UDP component to FTP. FTP is an unusual service in that it utilizes two ports, a 'data' port and a 'command' port (also known as the control port). Traditionally these are port 21 for the command port and port 20 for the data port. The confusion begins however, when we find that depending on the mode, the data port is not always on port 20.



Active FTP
In active mode FTP the client connects from a random unprivileged port (N > 1024) to the FTP server's command port, port 21. Then, the client starts listening to port N+1 and sends the FTP command PORT N+1 to the FTP server. The server will then connect back to the client's specified data port from its local data port, which is port 20.

From the server-side firewall's standpoint, to support active mode FTP the following communication channels need to be opened:

FTP server's port 21 from anywhere (Client initiates connection)
FTP server's port 21 to ports > 1024 (Server responds to client's control port)
FTP server's port 20 to ports > 1024 (Server initiates data connection to client's data port)
FTP server's port 20 from ports > 1024 (Client sends ACKs to server's data port)


In step 1, the client's command port contacts the server's command port and sends the command PORT 1027. The server then sends an ACK back to the client's command port in step 2. In step 3 the server initiates a connection on its local data port to the data port the client specified earlier. Finally, the client sends an ACK back as shown in step 4.

The main problem with active mode FTP actually falls on the client side. The FTP client doesn't make the actual connection to the data port of the server--it simply tells the server what port it is listening on and the server connects back to the specified port on the client. From the client side firewall this appears to be an outside system initiating a connection to an internal client--something that is usually blocked.



Active FTP Example
Below is an actual example of an active FTP session. The only things that have been changed are the server names, IP addresses, and user names. In this example an FTP session is initiated from testbox1.slacksite.com (192.168.150.80), a linux box running the standard FTP command line client, to testbox2.slacksite.com (192.168.150.90), a linux box running ProFTPd 1.2.2RC2. The debugging (-d) flag is used with the FTP client to show what is going on behind the scenes. Everything in red is the debugging output which shows the actual FTP commands being sent to the server and the responses generated from those commands. Normal server output is shown in black, and user input is in bold.

There are a few interesting things to consider about this dialog. Notice that when the PORT command is issued, it specifies a port on the client (192.168.150.80) system, rather than the server. We will see the opposite behavior when we use passive FTP. While we are on the subject, a quick note about the format of the PORT command. As you can see in the example below it is formatted as a series of six numbers separated by commas. The first four octets are the IP address while the second two octets comprise the port that will be used for the data connection. To find the actual port multiply the fifth octet by 256 and then add the sixth octet to the total. Thus in the example below the port number is ( (14*256) + 178), or 3762. A quick check with netstat should confirm this information.

testbox1: {/home/p-t/slacker/public_html} % ftp -d testbox2
Connected to testbox2.slacksite.com.
220 testbox2.slacksite.com FTP server ready.
Name (testbox2:slacker): slacker
---> USER slacker
331 Password required for slacker.
Password: TmpPass
---> PASS XXXX
230 User slacker logged in.
---> SYST
215 UNIX Type: L8
Remote system type is UNIX.
Using binary mode to transfer files.
ftp> ls
ftp: setsockopt (ignored): Permission denied
---> PORT 192,168,150,80,14,178
200 PORT command successful.
---> LIST
150 Opening ASCII mode data connection for file list.
drwx------ 3 slacker users 104 Jul 27 01:45 public_html
226 Transfer complete.
ftp> quit
---> QUIT
221 Goodbye.


Passive FTP
In order to resolve the issue of the server initiating the connection to the client a different method for FTP connections was developed. This was known as passive mode, or PASV, after the command used by the client to tell the server it is in passive mode.

In passive mode FTP the client initiates both connections to the server, solving the problem of firewalls filtering the incoming data port connection to the client from the server. When opening an FTP connection, the client opens two random unprivileged ports locally (N > 1024 and N+1). The first port contacts the server on port 21, but instead of then issuing a PORT command and allowing the server to connect back to its data port, the client will issue the PASV command. The result of this is that the server then opens a random unprivileged port (P > 1024) and sends the PORT P command back to the client. The client then initiates the connection from port N+1 to port P on the server to transfer data.

From the server-side firewall's standpoint, to support passive mode FTP the following communication channels need to be opened:

FTP server's port 21 from anywhere (Client initiates connection)
FTP server's port 21 to ports > 1024 (Server responds to client's control port)
FTP server's ports > 1024 from anywhere (Client initiates data connection to random port specified by server)
FTP server's ports > 1024 to remote ports > 1024 (Server sends ACKs (and data) to client's data port)



In step 1, the client contacts the server on the command port and issues the PASV command. The server then replies in step 2 with PORT 2024, telling the client which port it is listening to for the data connection. In step 3 the client then initiates the data connection from its data port to the specified server data port. Finally, the server sends back an ACK in step 4 to the client's data port.

While passive mode FTP solves many of the problems from the client side, it opens up a whole range of problems on the server side. The biggest issue is the need to allow any remote connection to high numbered ports on the server. Fortunately, many FTP daemons, including the popular WU-FTPD allow the administrator to specify a range of ports which the FTP server will use. See Appendix 1 for more information.

The second issue involves supporting and troubleshooting clients which do (or do not) support passive mode. As an example, the command line FTP utility provided with Solaris does not support passive mode, necessitating a third-party FTP client, such as ncftp.

With the massive popularity of the World Wide Web, many people prefer to use their web browser as an FTP client. Most browsers only support passive mode when accessing ftp:// URLs. This can either be good or bad depending on what the servers and firewalls are configured to support.



Passive FTP Example
Below is an actual example of a passive FTP session. The only things that have been changed are the server names, IP addresses, and user names. In this example an FTP session is initiated from testbox1.slacksite.com (192.168.150.80), a linux box running the standard FTP command line client, to testbox2.slacksite.com (192.168.150.90), a linux box running ProFTPd 1.2.2RC2. The debugging (-d) flag is used with the FTP client to show what is going on behind the scenes. Everything in red is the debugging output which shows the actual FTP commands being sent to the server and the responses generated from those commands. Normal server output is shown in black, and user input is in bold.

Notice the difference in the PORT command in this example as opposed to the active FTP example. Here, we see a port being opened on the server (192.168.150.90) system, rather than the client. See the discussion about the format of the PORT command above, in the Active FTP Example section.

testbox1: {/home/p-t/slacker/public_html} % ftp -d testbox2
Connected to testbox2.slacksite.com.
220 testbox2.slacksite.com FTP server ready.
Name (testbox2:slacker): slacker
---> USER slacker
331 Password required for slacker.
Password: TmpPass
---> PASS XXXX
230 User slacker logged in.
---> SYST
215 UNIX Type: L8
Remote system type is UNIX.
Using binary mode to transfer files.
ftp> passive
Passive mode on.
ftp> ls
ftp: setsockopt (ignored): Permission denied
---> PASV
227 Entering Passive Mode (192,168,150,90,195,149).
---> LIST
150 Opening ASCII mode data connection for file list
drwx------ 3 slacker users 104 Jul 27 01:45 public_html
226 Transfer complete.
ftp> quit
---> QUIT
221 Goodbye.


Summary
The following chart should help admins remember how each FTP mode works:

Active FTP :
command : client >1024 -> server 21
data : client >1024 <- server 20

Passive FTP :
command : client >1024 -> server 21
data : client >1024 -> server >1024

A quick summary of the pros and cons of active vs. passive FTP is also in order:

Active FTP is beneficial to the FTP server admin, but detrimental to the client side admin. The FTP server attempts to make connections to random high ports on the client, which would almost certainly be blocked by a firewall on the client side. Passive FTP is beneficial to the client, but detrimental to the FTP server admin. The client will make both connections to the server, but one of them will be to a random high port, which would almost certainly be blocked by a firewall on the server side.

Luckily, there is somewhat of a compromise. Since admins running FTP servers will need to make their servers accessible to the greatest number of clients, they will almost certainly need to support passive FTP. The exposure of high level ports on the server can be minimized by specifying a limited port range for the FTP server to use. Thus, everything except for this range of ports can be firewalled on the server side. While this doesn't eliminate all risk to the server, it decreases it tremendously.