Skip to main content

Verizon DSL and MTU


From Brett Charbeneau of the Tidewater UNIX Users Group:

Verizon was adjusting the Maximum Transmission Unit of all
packets on the fly on their routers - and they stopped doing that recently.

Some sites, Microsoft Update in specific, demand that the MTU be between 1400 and 1536 or they simply won't interact with a browser. Any browser. At all.

Packets that have a frame size larger or smaller than that are ignored or otherwise mangled beyond recognition by any browser I know of.

So, if you are like me and have several locations sharing Verizon DSL
circuits between lots of Windows users via an iptables-based firewall/router, Microsoft Update, mail.yahoo.com, and a bunch of other sites suddenly became inaccessible on February 9, 2009 for no apparent reason.

The fix is to set a "clamp" on packet size via a variety of iptables
commands, I like to do it in the FORWARD chain like so (all one line):

# iptables -I FORWARD -p tcp -m tcp --tcp-flags SYN,RST SYN -m tcpmss --mss 1400:1536 -j TCPMSS --clamp-mss-to-pmtu

but here are other ways to do it.

Comments

Popular posts from this blog

DOS4GW.EXE Version 2.01a and Alternative DOS Extenders

DOS4GW.EXE The Tenberry DOS extender DOS4GW.EXE was used by many early DOS games. I still enjoy playing many of these games and DOS4GW.EXE is usable with DOSBox , so they can be played on Linux. However, the version of DOS4GW.EXE that was included with the game was whatever was current at the time. The most recent version that includes many bugfixes that possibly affected the games when used with DOSBox have been fixed in the latest version, 2.01a. It's not free at US$49, but you can downloaded it here . Simply substitute it for whatever version of DOS4GW.EXE your game provided and enjoy the bug-fixed goodness. Tenberry also makes a "high-performance" "pro" version of DOS4GW.EXE, but it costs $300. I think that they could sell quite a few of these to hobby users (since, you know, DOS is dead) for US$5. Open Souce to the Rescue There are better performing, free and Open Source alternatives available and worth a look. DPMI Explained Let's unders

Return to Castle Wolfenstein for Modern Linux

Return to Castle Wolfenstein is a first-person shooter originally released on November 19, 2001. The game, like many other classic games, is available at GOG.com and costs only US$5.99. iortcw for Linux Don't bother with old and crusty Linux binaries offered by idsoft; they are problematic and it's painful to use them on a modern Linux. Fortunately for us, there are more modern GPL-licensed Linux binaries available for 32- and 64-bit systems as well as high resolution textures packages. The project at GitHub provides source code that can also be compiled for MS Windows using MinGW. iortcw for Windows and Mac You can download pre-compiled binaries for 32- and 64-bit Linux, MS Windows and Mac from here . Let's put our files in /usr/local/games/rtcw . As root, extract the downloaded .ZIP file for your architecture to  /usr/local/games/rtcw . All we are missing are the game data files. I purchased them from GOG.com. The game installer downloaded from GOG.com can be

Unreal Tournament GOTY/UT99 for Modern Linux

Released on November 16, 1999, Unreal Tournament (also known as UT99) is an arena first-person shooter for Multiplayer on-line competition or you can play against bots off-line. It features several game types, with more details provided at Wikipedia . The game was re-released on February 25, 2000 as Unreal Tournament Game of the Year Edition (GOTY) which included the three bonus packs released previously and additional mods, or game modifiers that had become popular. It is the GOTY version that is available from STEAM or  GOG.com . The GOG version for Windows installs in Linux and plays well using WINE , PlayOnLinux or Codeweaver's Crossover . There is a Linux binary available in two versions, one for the original game and one for the GOTY edition . Also provided at that site is the Official Bonus Pack with a Linux installer. All these Linux installers are created with makeself . There are some issues using such a crusty old Linux binary. Let's see why getting a Lin