Re: A router bug?[Useful report this time :) (hopefully)]
Scott Laird (laird@sigkill.org)
Mon, 01 Feb 1999 09:42:04 -0800
In message <m107KWx-00038sC@ocean.lucon.org>, H.J. Lu writes:
>>
>> In article <m10781J-000392C@ocean.lucon.org> you write:
>> >
>> >Thanks for everyone. Now my slip connection works fine now after
>> >changing MTU on both ends to 1500. Since 1500 is used by ethernet,
>> >shouldn't it be the default for SLIP/PPP under Linux also?
>>
>> You don't really want to use a MTU of 1500 on a normal low-speed
>> PPP/SLIP link, because it makes it hard to do interactive work while
>> the line is busy. With a 576-byte MTU, ssh is still usable over a
>> 28.8k link while downloading large files. With a 1500-byte MTU, ssh
>> would be pretty painful.
>>
>
>That is useful. But what is the alternative to setting MTU to
>1500? There are so many sites with the MTU problem. We have to fix
>the MTU problem on the Linux site.
Set the MTU/MSS on outgoing packets via your default route. It works
fine for me -- without it, I see pMTU problems on the site you posted,
with it, I don't see the problems. It doesn't hurt performance on
your local network, because it only affects packets bound for remote
networks.
I'm using ANK's iproute instead of ifconfig and route, but you should
be able to use either. Here's my default route line from
/etc/init.d/network:
ip route add default via 206.253.199.129 window 6000 mtu 576
I also dropped the window size to 6k, because large windows over slow
links can cause problems, particularly when dealing with Ascend's
flaky terminal servers.
Scott
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