[Openswan Users] Unusual packet loss

Philip Burrow philburrow at blueyonder.co.uk
Mon Jan 24 12:09:03 CET 2005

Paul Wouters wrote:
> On Mon, 24 Jan 2005, Philip Burrow wrote:
>> To my point, I'm having an unusual problem with apparent packet loss 
>> across a tunnel. Let me describe the set up. I have two machines 
>> running Fedora 2, with 2.6.10 kernel and Openswan 2.3.0. Both are on 
>> ADSL connections with 256k upstream operated by the same ISP.
> Do you have the xfrm4_tunnel kernel module? If so, did you load it?

This module is loaded on both ends.

>> Any suggestions as to what may be causing this? From what I read in 
>> the documentation it looks like MTU may be involved but I don't see 
>> why it would be, and don't know what I can do to play with it. 
>> Guidance would be appreciated!
> I assume you're usig NETKEY, so try changing the mtu to something lower on
> both ends on the physical interface, eg ethX/pppX

Yes, I'm using NETKEY.

One of the machines (the "hub") has tunnels to other Openswan machines 
and they work with no issues like this. So I presume it's safe to assume 
there's no actual problem with this one. I'll try knocking the MTU down 
on the remote machine. One question though - if MTU were the problem, 
why is it only a problem when I bring the tunnels up?

Is it possible that a DSL modem/router could be causing this? I wasn't 
overwhelmed with confidence with the one my ISP supplied and apparently 
it does some 'content filtering' and other stuff I don't want and I have 
attempted to disable.

Thanks for the quick reply Paul, appreciated.



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