Andreas Steinmetz wrote:
> Patrick McHardy wrote:
>
>>Andreas Steinmetz wrote:
>>
>>>[...]
>>>The tcpdump on the client shows that the mss of the incoming syn reply
>>>packet is *NOT* clamped to the ppp interface mtu.
>>
>>
>>You forgot to mention *how* you're clamping the MSS. Using
>>TCPMSS? Do you have a rule for incoming packets?
>>
>
>
> The relevant iptables commands I do use for masquerading and clamping are:
>
> iptables -t nat -A POSTROUTING -o ppp0 -j MASQUERADE
> iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS \
> --clamp-mss-to-pmtu
Two things here:
- tcpdumps on ppp0 will show unclamped packets since they haven't
been forwarded yet
- assuming you have ethernet internally, the PMTU from your router
to the internal hosts is 1500, so it won't do any clamping.
Does that explain it?
A useful thing for TCPMSS for routers would be to clamp to the
minimum of the PMTU of both directions. But thats not supported
so far.
-
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