U/S bug: https://bugs.launchpad.net/neutron/+bug/2109388

We currently have an external provider network A (VLAN) MTU 1500 with about 100 routers using that external network A.

• case 1: I set ovn_emit_need_to_frag=False, then I perform an action to add 1 router interface with network type geneve MTU 6000 with completion time ~6 seconds

• case 2: I set ovn_emit_need_to_frag=true, then I perform an action to add 1 router interface with network type geneve MTU 6000 with completion time ~50 seconds

After I found out that neutron has proceeded to update the MTU for all LRPs belonging to the router using external network A, not just the router that I performed the action on, which resulted in a very long time to add the router interface.