> This has been a problem since the 2.0 days, with anyone using IP Masq.
> There seems to be an interaction problem when the masq box has a smaller
> MTU than the firewalled system, and Path MTU Discovery breaks down. At
> some point, the ICMP messages necessary to support it are not being
> passed along correctly. Unfortunately, no one seems to have a clear
> handle no the nature of the problem. Setting the PPP MTU to be the same
> as the ethernet MTU (1500) cures the problem in all cases, but many
> people dislike the performance ramifications this has.
I concur. This ailed me since 2.0, on both intel and Alpha. A buddy of
mine ran into it recently when he started using masq on 2.0 and I told him
to try changing the MTU on his ppp to 1500, which solved the problem (as I
figured it would).
David Miller asked me for some tcpdumps when I first reported it on
linux-kernel over a year ago, which I sent, but he was unable to find the
source of the problem. Toggling ip_no_pmtu_disc has no effect. Sort of
embarrassing that Linux networking has held this bug for so long.
cheers,
-bp
-- B. James Phillippe . bryan@terran.org Software Engineer, WGT Inc. . http://www.terran.org/~bryan
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