[Bridge] new gretap, bridging and mtu

[Bridge] new gretap, bridging and mtu

[Jonathan Thibault]

Greetings all,

I've setup a new gretap device as per Herbert Xu's new patches and it 
works as expected for smaller MTU.  I'm wondering if gretap tunnels 
handle fragmentation at all or if this might be a bridge related issue.

The same setup works quite well if I use vtun with a tap device however, 
so while this isn't entirely bridge-related, Maybe someone here might 
have experienced the same problem or might have insight as to what's 
causing the problem.  I imagine this might be more of an inherent 
limitation in gretap than a bug but as I am not to good with coding, I 
figured I'd ask smarter people ;)

                     network1        box1       network2       
box2        network1
801.2q (1504 bytes max) <-> (eth1-br0-gretap eth0) <-> (eth0 
gretap-br0-eth1) <-> 801.2q (1504 bytes max)

Jonathan

Re: [Bridge] new gretap, bridging and mtu

[Herbert Xu]

On Tue, Jan 06, 2009 at 06:07:09PM -0500, Jonathan Thibault wrote:
>
>                     network1        box1       network2       box2        
> network1
> 801.2q (1504 bytes max) <-> (eth1-br0-gretap eth0) <-> (eth0  
> gretap-br0-eth1) <-> 801.2q (1504 bytes max)

gretap should handle fragmentation in the same way as IP over GRE.
The default for both is to disable fragmentation.  You need to
configure your tunnel to enable fragmentation by disabling PMTU
if you want to use a larger MTU.

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
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