Saturday, December 16, 2006

Hole Punching: To Do Or Not To Do

Hole punching technique is nothing new. It is as old as the firewalls through which it punches hole. But due to the huge popularity of Skype which does hole punching to make VoIP work even when behind firewalls and due to the apparent inability of network administrators to block them, there is a new wave of articles on this topic.

Slashdot covered one such article. After reading the comments there it became clear that many don't really understand how protocols like TCP and UDP work or why hole punching works.

Hole punching head-ache at office:
Hype is that network administrators will have a lot of headache managing the bandwidth consumed by all these p2p applications that punch holes and "illegally" transfer data. But that isn't the case in reality. Network administrators have a variety of options at their disposal. Like in case of Skype, they can always block the various Skype central site IP addresses. Also, an advanced stateful firewall like IPTables in Linux can be configured to block hole-punching. But, in some cases, hole punching applications can actually save bandwidth. If you and your colleague sitting on the other end of the office are talking to each other over skype and are on the same local network, then your traffic isn't even leaving your network! You two would be connected peer 2 peer directly. So there you go! Your network administrator should be happy!

Hole Punching at home?:
In this part of the world(India), majority ISPs like Airtel or BSNL provide public IPs for their broadband customers. So, when I'm connected to Internet at home, I've a public IP (non-static). So, there is no question of complex NAT firewalls getting in the way.(We all do have firewalls on our machines and on the router, but they are just filtering unwanted traffic and not actually doing any NAT). So, I can actually tell my firewall to allow Skype traffic bothways and no hole punching is required. Skype MAY become a super node and start using your bandwidth for routing other people's voice data. Now, if you aren't on a unlimited usage bill-plan this might hurt you. So, its best to turn off the application when you are not using it yourself.

We at pi are building an application that also does hole punching. It's more exciting than skype and has lot more functionality. Currently it is in free beta mode. Go grab it and try it for yourself.
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Tuesday, December 12, 2006

Free Google for Small Businesses!

Most people think Google is a search company! Well, yes they are a search company. But primarily they are a very good web technology company. What they do brings Internet and its way of life much closer and more easier to many people. Can you imagine that if you are a small business owner, you have quite a few things going for you because of Google. The product of theirs I'm referring to here is Google Apps for Domains.
Google Apps for Domain provides free e-mail (2GB) accounts at your domain address. This, along with the google talk messenger service at the same address, pages, and calendar make it a pretty nice offering, all for free. Also, throw in a restricted private groups at google groups beta, you have a pretty good online infra structure for your company! Very reliable, secure and free!

I just setup all this for a company called SSC Vanilla. And the handful of people at this company are already using it and seeing the benefits.

More to come later, may be.
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Friday, December 08, 2006

Google 403 Bot Error! on trying to set preferences from Firefox!

Today I searched for "form $PHP_SELF" on Google the search within Firefox. I got 10 results. I wanted more. So, I hit preferences and changed the number to 100. When I save the preferences and it gets back to the page, this is what it says!


Google
Error

We're sorry...

... but your query looks similar to automated requests from a computer virus or spyware application. To protect our users, we can't process your request right now.

We'll restore your access as quickly as possible, so try again soon. In the meantime, if you suspect that your computer or network has been infected, you might want to run a virus checker or spyware remover to make sure that your systems are free of viruses and other spurious software.

We apologize for the inconvenience, and hope we'll see you again on Google.



Then I opened google home page, went straight to preferences and changed results to 100 and then did my search. viola! everything was fine! So there was nothing inherently wrong with the query. its some bug in the way they handle redirection from preferences page after changing the results count, i guess!
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Monday, December 04, 2006

Microsoft Office 2007 First Impressions!

I just got my hands on Microsoft Office 2007. My first impression about it is very positive. Its very slick and nice. The UI is very refreshing and easy to use. And its faster and intelligent. I've tried just the Word, Excel and Powerpoint till now. Saving Powerpoint to pdf is very nice. It needs a plugin to be installed. Its not obvious why they didn't include it by default.

Although the installation took a lot of time, it was very easy and asked few questions. It detected and upgraded my Office 2003 installation.

Outlook 2007 still sucks. Nothing much different. Too slow and still hangs with IMAP over SSL.

Probably I post a more detailed review later.

Once again, Microsoft has made sure that its stronghold office presence isn't threatened by any other Free or commerical offerings.
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Thursday, November 23, 2006

Access Apache WebDAV from Windows XP

This is a work-in-progress. This is not complete, may be never will be. It is purely for my own reference. Use at your own risk.

Here I try to remember how to configure Apache and Windows XP so that WebDAV on Apache
is accessible from Windows XP clients.



Links:
http://www.thrrrust.com/~pclark/blog/2005/03/fun-with-windows-xp-and-webdav.html
http://www.hss.caltech.edu/help/unix/admin/web/apache-webdav-xp
http://support.microsoft.com/?kbid=909423
http://www.greenbytes.de/tech/webdav/webdav-redirector-list.html

Registry changes required to support large files and many files:
http://support.microsoft.com/default.aspx/kb/900900/
http://support.microsoft.com/?kbid=912152

Automatic Protocol Driver Selection for MSDAIPP
http://msdn2.microsoft.com/en-us/library/ms691698.aspx
http://msdn2.microsoft.com/en-us/library/ms691696.aspx
http://msdn2.microsoft.com/en-us/library/ms691722.aspx

DHTML Behaviors for making webfolder open automatically.
http://dean.edwards.name/moz-behaviors/
http://msdn.microsoft.com/workshop/author/behaviors/reference/behaviors/anchor.asp
http://codebetter.com/blogs/darrell.norton/archive/2004/12/10/36022.aspx
http://msdn.microsoft.com/workshop/author/behaviors/overview.asp
http://www.w3.org/TR/becss

http://www.hss.caltech.edu/help/web/webdav/accessing/windowsxp
http://ulihansen.kicks-ass.net/aero/webdav/

General ASP auth gyaan
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnaspp/html/madam.asp

Interesting page about different dlls and functionalities related security
http://msdn2.microsoft.com/en-us/library/ms838345.aspx#windows_xpe_security_internet_connection_security_support
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Friday, November 17, 2006

Sitemaps.org - Google - Yahoo - Microsoft!

Seems like the search engine #1 #2 and #3 have come together to cook up something to make their jobs easier. Meet sitemaps.org Basically you tell them the links your site using a xml file and let them know what you think is relatively important. There was already a "Sitemaps" as part of Google Webmaster's Tools which had similar features. Its good that they standardized the protocol across three major search engines and have made the specification licensed under Attribution-ShareAlike Creative Commons license. And there are many online sitemaps generators. But there seems to be no way to add one to blogspot.
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Thursday, September 28, 2006

Apache Notes

My Apache configuration:
./configure --enable-pie --with-mpm=worker --enable-exception-hook --enable-auth-digest --enable-deflate --enable-expires --enable-suexec --enable-rewrite --enable-so
make
make install


This installs everything in /usr/local/Apache2/

cgid daemon runs as the user configured in apache configuration and shuts down fine.

Work Items:
Optimizations. For Speed and Size.
Security: Suexec modifications.
Directory Layout changes. --with-layout.
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Saturday, September 09, 2006

Code Commentary: dvd-audio tools

Recently I've got interested in dvd-audio free software. I'm getting a universal player. So then want to be able author my own content in high definition multi-track audio DVD. Currently there is only one DVD Audio authoring free software hosted at http://dvd-audio.sourceforge.net/

This project hasn't been worked on since its last alpha release on 20050703. And there are some nice TODO items on its status page. Some of them are really good to have. So I'm thinking of working on them.

To start off, I would comment on the code and log it here for my understanding and reference. (might help others too!).

Source I'm using for this purpose is taken from here.

Let's look at the source code organization.
amg.c /amg.h - has code for Audio Manager (AMG) - this is stored in the AUDIO_TS.* files and consists of the AUDIO_TS.IFO file, an optional moving video menu in the AUDIO_TS.VOB file and the backup file AUDIO_TS.BUP.

samg.c /samg.h - has code for Simple Audio Manager (SAMG) - this is stored in the AUDIO_PP.IFO file and is the equivalent of the table of contents on a Red Book audio CD.

ats.c / ats.h - has code for Audio Title Set creation and writing of actual audio data in to AOB files.
atsi.c / atsi.h - has code for audio titleset information creation. writes the file ATS_XX_0.IFO

audio.c / audio.h -

dvda-author.c
version.h - contains #define VERSION "0.1-cvs"
libFLAC/ - contains the libFLAC library sources.


[To be continued]

Suggestions / Corrections / Comments are welcome.
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Wednesday, August 23, 2006

Writing Apache 2.x Filters

I'm writing a Apache 2.x output filter to append arbitrary query parameter variables to all the urls in the response body. Some of the references online that helped me get started on the output filter are listed below. For the actual work of finding the url tags, extracting the url and appending the required query param, I'm using a Lex scanner. (no parser required).

Flex Resources:

Apache Reference Online:

http://wendtstud1.hpi.uni-potsdam.de

This is the website. Most of the pages are in German; but you can make out.
The specific presentation I was talking about are here:
http://wendtstud1.hpi.uni-potsdam.de/sysmod-seminar/SS2003/presentations/

Then, there is http://f-m-c.org/projects/apache/index.php . This was the output of a project by the same university.

For Apache Filters,
http://www.projectcomputing.com/resources/apacheFilterFAQ/index.html
http://httpd.apache.org/docs/2.2/filter.html

Specifically about output filters:
http://www.onlamp.com/pub/a/apache/2001/09/13/apache_2.html

About bucket brigades:
http://www.apachetutor.org/dev/brigades

Many other articles by Ryan Bloom (the APR guy)
http://www.onlamp.com/pub/ct/38
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