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Subjectmtu problem with masquerading+pppoe(adsl) setup

Hello, (i am sorry if this is the wrong place to ask)

despite the frequent discussions concerning this topic on usenet, i failed
to solve my problem:

- i have a debian potatoe box that acts as a masquerading server for a
heterogenous win2k/winnt/mac LAN. pppoe works fine, and so does
masquerading ... almost

- the kernel i installed is the latest 2.2 kernel (2.2.19)

the problem:

i can't access some sites from the masq clients, while i can access them
from the masq server. (like

The problem seems to be widely known, and seems to be an MTU+no-fragment
packets issue. and indeed:
- the MTU on my LAN is 1500 bytes
- the MTU on my ppp connection is 1492 bytes.

on the archives, i found the following solutions:
- raising the ppp MTU to 1500 bytes. it won't work. even if i specify 1500,
the mtu is still 1492.
- lowering the mtu of the LAN to 1492 bytes. thats not an option according
to my boss.
- upgrade to something newer than 2.2.14. i run 2.2.19 and i still have the

So my questions are:

- are there other options ? i read some vague german things about msschamp
or something like that, but i don't know if they are even related.

- will an upgrade to linux 2.4 or the kernelspace pppoe driver fix my
problem ? (i would like to keep my current setup, i don't know how
difficult it is to upgrade a potatoe box to such a recent version ..)

Some other observations:

- win2k as masquerading server does not have the problem, but switching to
win2k is not really an option since win2k seems to have severe problems
with ftp connections.

- the problem also occurs for some mail servers.

Thanks in advance,

Frank Dekervel

Frank Dekervel
Mechelsestraat 88
3000 Leuven
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