[Openswan Users] MTU problems

[Cameron Davidson]

Peter Farrow wrote:
> I've implemented a VPN on Centos 4.3 (64 bit platform) using openswan 
> between a pair of sites, and I seem to have encountered an MTU problem.
>
> Its seems the max MTU is 1492, and I have had to set this on all 
> windows and Linux boxes to make the link useable,
>
> ...snip...
> Pete
>
I have encountered different MTU behaviour with openswan and NETKEY in 
the Centos kernel,  compared to the latest kernels (2.6.16.18), but this 
is when interacting with older freeswan links.

However, setting mtu=1492 on the lan PCs will not fix a problem like 
that, because the mtu through the tunnel is lower than that. They will 
see an mtu about 1420, but it seems to depend on the encryption.

Does the MTU of 1492 apply to the WAN  interface on an openswan gateway 
box, or is it somewhere else in the chain?

Cameron.