Re: ppp mru/mtu and ip masquerading
Alan Cox (alan@lxorguk.ukuu.org.uk)
Sun, 28 Feb 1999 20:31:39 +0000 (GMT)
> > (If you think about it masquerading doesnt kick in on a download problem
> > error case. The errored tcp frame bounces off the start of the low MTU
> > PPP link before it is masqueraded)
>
> There is a known bug with masquerading and path mtu discovery in 2.2. Icmp
> forgets to unmasquerade an already masqueraded packet, so the ICMP payload
> header contains the wrong address and the other end drops it.
>
> For NAT it is handled in icmp.c, but not for Masquerading
> currently. Fix is a bit more complex though because unlike NAT the
> masquerading rule is not easily accessable from the skb.
Not for the case described.
--1500 MTU---PPP gate-------------512---------MASQhost------1500---MASQ
So the MTU problem is coming off the PPP gateway host which is the ISP itself.
I can believe the masq code has a bug in 2.2.x - but note that it doesnt
get triggered inthe described scenario (just some others)
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