[3740] in linux-net channel archive
Network MTU/Fragmentation problem
daemon@ATHENA.MIT.EDU (Garry Adkins)
Wed Jul 17 21:12:24 1996
From: Garry Adkins <gpa@piranha.ianet.net>
To: linux-net@vger.rutgers.edu
Date: Tue, 16 Jul 1996 23:56:06 -0400 (EDT)
Hi!
I have a fragmentation problem that seems to have surfaced
around 1.3.66. It seems to persist even through 2.0.3.
When using an mtu on a network smaller than the default 1500,
the packets get corrupted. Two internet sites that are unreachable
because of this are www.mu.edu, and www.webcrawler.com.
Notice in the dump (appended to the end) how the IP number actually
changes. (presumably from the truncation) It looks as though the
packet is fragmented, but the size of the packet isn't properly
updated in the header.
After conferring with a few others with the same problem, we've
determined that it's probably in the networking code in
the kernel (not ppp). This determination was made in two ways:
1) the system works with ppp 2.2.0f with early kernels
and fails with later kernels
2) One guy was not using ppp at all and was seeing identical
problems.
Please don't think I'm a slacker, because I have searched
dejanews, and all the web search engines, and all the related
linux newsgroups prior to bringing this here.
My setup is:
Sprintlink 256k to the internet
Cisco router to Thinnet
linux box on the thinnet
modem connected to linux box
******Dump from connecting with www.mu.edu ***************
18:24:03.142021 www.mu.edu.80 > kenova1.ianet.net.nterm: tcp 0
18:24:09.152021 truncated-ip - 864 bytes missing!134.48.140.77 > kenova1.ianet.net: (frag 43672:1044@1568)
18:24:09.152021 truncated-ip - 876 bytes missing!134.48.152.17 > kenova1.ianet.net: (frag 43672:1044@1472)
18:24:21.132021 truncated-ip - 864 bytes missing!134.48.104.75 > kenova1.ianet.net: (frag 43736:1044@1568)
18:24:21.132021 truncated-ip - 864 bytes missing!134.48.232.227 > kenova1.ianet.net: (frag 43736:1044@1568)
******Dump from connecting with www.webcrawler.com ***************
18:24:40.372021 kenova1.ianet.net.1028 > wc-s2.web.aol.com.80: tcp 170 (DF)
18:24:40.502021 truncated-ip - 1300 bytes missing!i5-16.fep.aol.com > kenova1.ianet.net: (frag 59350:1480@1568)
18:24:40.502021 truncated-ip - 1300 bytes missing!152.163.206.192 > kenova1.ianet.net: (frag 59350:1480@1568)
18:24:40.502021 truncated-ip - 1404 bytes missing!152.163.99.32 > kenova1.ianet.net: (frag 59350:1480@736)
18:24:40.542021 truncated-ip - 1300 bytes missing!152.163.63.196 > kenova1.ianet.net: (frag 59351:1480@1568)
Thanks for any help!
Garry
P.S. The others I have been conferring with are:
bb@world.std.com
pwhite@randomhouse.com
dietmar@highway.bertelsmann.de
