From: Jason Opperisano <opie@817west.com>
To: netfilter@lists.netfilter.org
Subject: Re: broken SNAT with fixed external MTU
Date: Thu, 14 Oct 2004 14:17:47 -0400 [thread overview]
Message-ID: <20041014181747.GA3929@bender.817west.com> (raw)
In-Reply-To: <416EA61A.9030600@lucomp.net>
On Thu, Oct 14, 2004 at 06:15:22PM +0200, Mailing List Reader wrote:
> Hello everybody,
>
> My DSL router (very bad firmwares) wants me to force the MTU
> (buggy MTU auto-setting). The firewall has a public IP and mtu 1500:
>
> ---snip
> #route to the router net
> ip route add 192.168.1.0/24 dev eth1 mtu 1440
> # default to the router (mtu not needed here)
> ip route add default via 192.168.1.1 mtu 1440
> --snip
>
> the firewall itself NATs one client back-to-back connected
> (cable checked!):
>
> ---snip
> #mss clamping 1)
> iptables -A FORWARD -d $net1 -p tcp --tcp-flags SYN,RST SYN -j TCPMSS
> --set-mss 1440
> iptables -A FORWARD -s $net1 -p tcp --tcp-flags SYN,RST SYN -j TCPMSS
> --set-mss 1440
try not to confuse MTU with MSS, as they are not the same. if you're
going for an MTU of 1440--you should be setting MSS to 1400 (MSS = MTU -
40).
-j
--
Jason Opperisano <opie@817west.com>
next prev parent reply other threads:[~2004-10-14 18:17 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-10-14 16:15 broken SNAT with fixed external MTU Mailing List Reader
2004-10-14 18:17 ` Jason Opperisano [this message]
2004-10-14 19:52 ` Luigi Corsello
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