On Maw, 2005-01-04 at 14:20, James Melin wrote:
> I'm in an interesting situation..... Our network, hence my linux guests,
> use an MTU size of 1500. As it turns out, our z/os systems use an MTU size
> of 1492. We just started using a z/os HTTP server outside the firewall to
> do reverse proxy inside to our linux guests. When I do not go through the
> z/OS httpd server, things go swimmingly. I suspect I'm getting retransmit
> delays with an 8 byte difference in MTU. I'm not sure under SLES8 where to
> change the MTU size for ETH0 to see if making those match will change the
> behaviour we are seeing.
>
> Anyone know where to tweak this particular thing after the fact?
Properly configured internet systems just work. The 1500 MTU packet will
be fragmented when it hits a point on the network it does not fit. Hosts
can chose to get an error instead and reduce the sizes themselves ("path
mtu discovery").
If you are getting hangs when talking through your firewall for large
but not small pages it normally means its ICMP filtering for ICMP must
fragment unreachable frames is not correct. Bad performance but no hangs
would point elsewhere.
Alan
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