[Openswan Users] Unusual packet loss

Paul Wouters paul at xelerance.com
Mon Jan 24 13:35:37 CET 2005

On Mon, 24 Jan 2005, Philip Burrow wrote:

> I have since altered the MTU in gradual steps on -both- machines 
> simultaneously (steps of 50 from 1500 to 1000), yet it still drops pings when 
> I restart ipsec, and data streams seem to stop after the first bunch of data 
> as described in the original post.

Can you try clamping it?

iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS  --clamp-mss-to-pmtu

Otherwise, try pinging with different size packets until it fails, and then use
the last successful packet size (eg 1440) to:

iptables -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --set-mss 1440

Also, perhaps that DSL router is blocking ICMP's neccessary for proper PMTU to
begin with?


"At best it is a theory, at worst a fantasy" -- Michael Crichton

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