slip, vpnd, and mtu

slip, vpnd, and mtu

Post by Yan Seine » Tue, 11 Apr 2000 04:00:00

I am running vpnd 1.1.0 and I am experiencing failure of the sl0
interface under very heavy load.

I saw an article somewhere for the 1.x kernels about slip not handling
large (1500) mtu sizes.  I looked at the slip.c code and it dates back
to 1993.

The default size in the slip code is 296.  vpnd sets it to 1500.  Has
anyone experienced problems with this?

System: rh 6.0, 2.2.13 kernel, dial up connections.



Think different
        ride a recumbent
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1. How to modify MTU value under DIP slip mode ?

I have tried to add the command "get $mtu 1500" in my diphost
configuration file. Then, use "dip /etc/diphosts" to connect my Internet
Service Provider. After connection, I used "ifconfig" to check the MTU of
my slip/ppp line. The value is still 296 (default one). The MTU of my LAN
segent (el0) is 1500. Afterwards, I used "dip -m 1500 /etc/diphosts" to
call my Internet Service Provider for testing again. But I still got the
same MTU value. It is still 296.

My provider had set the MTU value to 1500 at the ppp port of the ppp server.
So my linux cannot receive any ip packets which size is bigger than 296.
When I want to download one file via ftp (which file size is bigger 296), my
linux will freeze and get nothing.

Anyone can tell me how to change the default value of MTU to 1500 except
the above two method. Or tell me what's the problem for the above problem.

Thanks a lot for your kind attention !

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