[Openswan Users] Tunnel up, some hosts work, others don't.

Richard Whittaker richard at avits.ca
Thu Feb 26 13:38:40 EST 2015

On 2015-02-26 09:31, Simon Deziel wrote:
> On 02/26/2015 12:22 PM, Richard Whittaker wrote:
>> I can also reproduce this with MySQL. I can establish an initial
>> connection and login to db2 from either 0.2 or 0.9, but as soon as I try
>> "connect mysql" from the client command line, everything just freezes in
>> the client.
> This looks like PMTU issue. I'd give "iptables --clamp-mss-to-pmtu" a try.

Would I set this on my end points, or on the servers I have acting as 

I did

iptables -A FORWARD -p tcp -s -d 
--tcp-flags SYN,RST SYN -j TCPMSS  --clamp-mss-to-pmtu
on the gateway
iptables -A FORWARD -p tcp -s -d 
--tcp-flags SYN,RST SYN -j TCPMSS  --clamp-mss-to-pmtu
on the gateway

...but they had no effect.

>> This got me to thinking the issue might be fragmentation,
>> but large pings work just fine.
> I haven't seen/looked at your config but if your have some compression
> going on, this could explain why large ICMP go through but not large TCP
> payloads.

I checked. I don't have compression enabled on either end of the tunnel. 
I think the PMTU thing might be the right direction, and could explain 
why a 2.6 kernel based machine works, but a 3.2 based one doesn't.

Is there a setting on the 3.2 machine I might be missing?


Alberni Valley IT Services

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