lkml.org 
[lkml]   [2007]   [Jun]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: mss to pmtu clamping partially broken?
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.

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-06-29 14:05    [W:0.033 / U:0.196 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site