Description of problem: Setup: RHOSP 16.2 z1 - OVN (DVR) client needed to extend floating ip network. They added a secondary subnet (IPv4) to the existing one, let's say subnet.a and subnet.b. - When neutron routers are created, their external interface is assigned an address randomly or by choosing manually from one of the external subnets. - This works fine for most communication. General external access via the subnet.a or subnet.b FiPs works without issues. - However, TCP/UDP FiP <-> FiP communication is broken. ROUTER: external gw on FiP subnet.a VM1: FiP on subnet.a VM2: FiP on subnet.b both vms are in the same internal network connected to the same router VM1 can reach via FiP VM2 without any issue VM2 can't reach correctly VM2, for example running a simple curl it receive a RST packet after a while. [root@test-vm-2 ~]# time curl "vm1.fip" curl: (56) Recv failure: Connection reset by peer real 0m53.694s user 0m0.052s sys 0m0.047s from tcpdump i can see: - request sent from vm2 to vm1 - reply sent from vm1 to vm2 - vm2 did not receive reply. ###ICMP Works without issues### I'll provide more details in comments. Version-Release number of selected component (if applicable): OSP 16.2 z1 - OVN (DVR) OSP 16.2 z3 - OVN (DVR) (my lab) How reproducible: 100% Steps to Reproduce: 1. create external network with 2 subnets 2. create a router connected to the external network (lets say with A.external.sub as gw) 3. create 2 vm in the same tenant subnet 4. add each vm 1 fip from every external subnet (vm1: A.external.sub.fip - vm2: B.external.sub.fip) 5. traffic from vm1 (A sub fip) to vm2 (B sub fip) will work without issues 6. TCP/UDP traffic from vm2 (B sub fip) to vm1 (A sub fip) seems not working properly (icmp works) Actual results: tcp/udp traffic between 2 fips from different subnets (same network) connected to the same router not working properly. Expected results: Traffic between 2 fips from different subnets (same network) connected to the same router working properly. Additional info: seems similar to 1929901 and clones, but as this should be fixed, i opened a new BZ