[Openstack] VM can receive traffic, but not send it

Sterdnot Shaken sterdnotshaken at gmail.com
Mon Mar 20 21:50:45 UTC 2017

Our info:

Openstack version: Mitaka (using OVS 2.5)
Firewall driver: Openvswitch

Anyone know why VM's that are directly on a Flat Provider Network (so the
VM would have a public IP directly assigned to it) can download data just
fine, but when we try and upload anything (iperf where the VM is the client
or something even like speedtest.net (upload portion)) the VM simply can't
get data out to the intended destination? Again, download works great,
upload doesn't.

If I take that VM and change it's interface to be a tenant network one that
has a Openstack HA virtual router, everything (upload and download) works
perfectly. The problem only seems to be apparent when the VM is directly on
the external network.

It seems like an MTU issue, but I don't see how... Here are the MTU's of
the part's at play:

VM: 1500
br-int (specific interface connecting to VM) - 9216
br-ex - (can't tell what that MTU is set to)

Any help would be GREATLY appreciated.

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