Bug 1405443

Description of problem:
Error - dropped over-mtu packet: 1500 > 1450 when accessing VIP created by LBaaS.

The network interfaces in qlbaas namespaces uses 1500 as their default MTU setting. This causes trouble when communicating with instances that have different MTU set (the default vlaue for MTU in vxlan tenant network is 1450)
There should be a setting in LBaas config files that allow to change the default MTU size to something else like 1540 or 8950 (in case of jumbo frames) Also if the value is not set it should be referencing the value set up in other part of Neutron instead of defaulting to 1500.


Version-Release number of selected component (if applicable):
Encountered on RH OSP 9 - LbaaS v1. However I believe this affects all version of OSP and LBaaS V1 and V2

How reproducible:
Every time when accessing content that exceeds 1400 bytes via LBaaS VIP.
Tested with curl 


Steps to Reproduce:
1. Configure RH OSP with LBaaS
2. Define a Pool of webservers that share content over 1400 bytes and assign VIP to it
3. curl the content of the vip to local machine

Actual results:
curl never finishes downloading the content.
/var/log/messages receive error - dropped over-mtu packet: 1500 > 1450

Expected results:
curl finishes with the content of the page

Additional info:
We were able to work this around by manually changing the mtu setting to lbaas port:
for i in `ip netns | grep lbaas`; do echo $i; ip netns exec $i ip a; done
ip netns exec qlbaas-82c190b6-538d-4e02-a217-5d7277c8cbbc ip link set tapfd14b090-36 mtu 1450

There are some abandoned bugs out there describing the same behavior:
https://bugs.launchpad.net/neutron/+bug/1376446
https://review.openstack.org/#/c/268321/