[CentOS] Centos 7 as gateway - UDP performance is busted/awful?

Thu Aug 14 19:48:19 UTC 2014
Tom Horsley <horsley1953 at gmail.com>

On Thu, 14 Aug 2014 14:09:44 -0500
Les Mikesell wrote:

> Seems like a horrible thing to do, but does it fix it if you mount with
> rsize=1500, wsize=1500 - or maybe 1484?

I already tried that - no change :-).

> Are you just bridging to the NIC interface?   I don't see why that
> would need to change the packets at all.   What happens if you ping
> with a large -s value through the bridge (host or external box to
> guest)?

There are two NICs. The one with the bridge is also running a subnet
with the virtual machines and one real machine on the NIC. The other
NIC is connected to the wider world of our local LAN where the NFS
servers reside, so the host has to operate as a gateway for the traffic
from the LAN to the virtual machine subnet.

I did just try the ping experiment, and on the outer NFS server, if I
try to ping the virtual machine with a big size, I get the error about
the packet fragmentation:

dino> ping -c 1 -s 1500 ubu14d04x
PING ubu14d04x.ccur.kvm ( from : 1500(1528) bytes of data.
From godzilla ( icmp_seq=1 Frag needed and DF set (mtu = 1500)

But weirdly, I don't get that from every machine I try out here on the
LAN, some can ping it just fine, others get the error.

Whatever I discover just makes me more confused :-).