[2213] in linux-net channel archive
Re[2]: IP forwarding bug in 1.3.73
daemon@ATHENA.MIT.EDU (Paul McCallum)
Fri Mar 22 13:47:21 1996
Date: Fri, 22 Mar 1996 12:19:50 -0600
From: Paul_McCallum@crow.bmc.com (Paul McCallum)
To: linux-net@vger.rutgers.edu
I am just learning about TCP/IP so I dont understand all its re-send
implications at this time but these are my recollections for TU sizes on
phones lines:
1) small sizes reduce the time to detect and re-transmit bad frames on
low-quality lines. modern facilities have reduced this need to a large
extent.
2) small sizes make for better line sharing. PPP by definition cannot
share a line.
3) small sizes are required by some hardware due to cost. again time has
cured this not to mention the fact that both devices are programmed and
memory is controllable.
The bottom line is I agree, MTU should be reasonably large, less management
overhead is better.
______________________________ Reply Separator _________________________________
Subject: Re: IP forwarding bug in 1.3.73
Author: Todd Graham Lewis <tlewis@mindspring.com> at UNIXLINK
Date: 3/20/96 10:13 PM
On Thu, 14 Mar 1996, Zoltan Hidvegi wrote:
> We have a ppp dial-in server running linux-1.3.73. Normally it uses 296
> MRU/MTU on the ppp interfaces and 1500 MTU on the ethernet card.
> Unfortunately it cannot forward UDP packages larger that 296 bytes correctly.
>
> When I raise the MTU on the ppp line to 1500 everything works fine.
Why does everyone insist on running such a small mtu on their ppp
connections? Larger mtu's are tougher to tweak, but everyone should be
aiming at the largest mtu they can handle, and rarely do you really have
to bump it below 1000. Smaller mtu's will cause excessive fragmentation,
with end-to-end mtu discovery, they place a much larger load on the
intervening routers, which almost always includes the backbone routers,
which are _way_ overburdened as it is, and it decreases performance.
I simply do not understand why people insist on doing this. If there is
a reason, could someone please clue me in to the big secret?
Todd
____________________________________________________________________________
| |
|Todd Graham Lewis Core Engineering Mindspring Enterprises, Inc.|
|tlewis@mindspring.com (800) 719 4664|
|__________________________________________________________________________|
