Reproduction steps：
1. Create an external network and create two subnet base on the network, this subnet cidrs as below:
ext-subnet01: 172.24.4.0/24
ext-subnet02: 10.20.30.0/24
2. Create a router and set external gateway on the external network for the router. Now, in the router's namespace the routes as below:
# ip netns exec qrouter-d91e7918-b511-4dd8-9f8f-4db0dacbfb4d ip r
default via 172.24.4.1 dev qg-38d2f0b6-96 proto static
10.20.30.0/24 dev qg-38d2f0b6-96 proto static scope link
172.24.4.0/24 dev qg-38d2f0b6-96 proto kernel scope link src 172.24.4.32
3. Create a tenant network, and create a subnet base on the tenant network, the ssubnet cidr as below:
tenant-subnet: 10.20.30.0/24 (It's same with the ext-subnet02's cidr)
4. Add the tenant-subnet to the router which created at step 2. Then, in the router's namespace the routes as below:
# ip netns exec qrouter-d91e7918-b511-4dd8-9f8f-4db0dacbfb4d ip r
default via 172.24.4.1 dev qg-38d2f0b6-96 proto static
10.20.30.0/24 dev qg-38d2f0b6-96 proto static scope link
10.20.30.0/24 dev qr-7b3f8319-45 proto kernel scope link src 10.20.30.1
172.24.4.0/24 dev qg-38d2f0b6-96 proto kernel scope link src 172.24.4.32
The duplicate routes (10.20.30.0/24) will disturb the North-South packets' forward, result the traffic breaking.
Fix proposed to branch: master
Review: https:/