neutron router static routes ecmp doesn't work

[Steve Ruan]

Create 1 router and set gateway network, then create 2 static routes with same prefix.
~/devstack$ neutron router-show R2
+-------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Field | Value |
+-------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| admin_state_up | True |
| availability_zone_hints | |
| availability_zones | nova |
| distributed | False |
| external_gateway_info | {"network_id": "d5d571b9-c7c2-443f-8591-7da9d40435a7", "enable_snat": true, "external_fixed_ips": [{"subnet_id": "4d033b6c-9a05-4aee-8462-ac909f86aa86", "ip_address": "172.16.3.3"}]} |
| ha | False |
| id | 1b2467b2-3b83-45bb-90e1-4d78c781d275 |
| name | R2 |
| routes | {"destination": "1.1.1.0/24", "nexthop": "172.16.3.100"} |
| | {"destination": "1.1.1.0/24", "nexthop": "172.16.3.101"} |
| status | ACTIVE |
| tenant_id | d1694a63f75a422b9c83e0693effa482 |
+-------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

~/devstack$ sudo ip netns exec qrouter-1b2467b2-3b83-45bb-90e1-4d78c781d275 ip neighbor show
172.16.3.101 dev qg-4515a36e-77 lladdr 00:00:01:00:00:02 PERMANENT
172.16.3.100 dev qg-4515a36e-77 lladdr 00:00:01:00:00:01 PERMANENT
fe80::f816:3eff:fe8e:a49f dev qg-4515a36e-77 lladdr fa:16:3e:8e:a4:9f STALE
fe80::5863:baff:fefe:c15e dev qg-4515a36e-77 lladdr 5a:63:ba:fe:c1:5e STALE
~/devstack$ sudo ip netns exec qrouter-1b2467b2-3b83-45bb-90e1-4d78c781d275 ip route
default via 172.16.3.1 dev qg-4515a36e-77
1.1.1.0/24 via 172.16.3.101 dev qg-4515a36e-77 ###ONLY 2nd route is installed.
172.16.3.0/24 dev qg-4515a36e-77 proto kernel scope link src 172.16.3.3

[Hong Hui Xiao (xiaohhui)]

I think the problem is not "it doesn't work", but is "it doesn't support". In the back end, every extra route is added to router namespace by "ip route replace" command. So, you can only see the 2nd route for a duplicated destination cidr.

Change to the route update policy can resolve the problem, but HA router and DVR may need more attention. I will look into it.

[Steve Ruan (ruansx)]

Yes. It's root cause.
But more attention, why it's "ip route replace", not "ip route add" when this code is submitted?

[Hong Hui Xiao (xiaohhui)]

I think that both "ip route add" and "ip route replace" can't add the duplicated routes that ECMP wants. I was thinking of using "ip route append" for the purpose.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/288533

[OpenStack Infra (hudson-openstack)]

Change abandoned by Hong Hui Xiao (<email address hidden>) on branch: master
Review: https://review.openstack.org/288533
Reason: Seems not too much attention to this feature.

[abdul nizamuddin (abdul-nizamuddin)]

hi all.. to overcome this problem we have to use "ip route append <dest_ip> via <nexthop>.. am i correct?

[Rodolfo Alonso (rodolfo-alonso-hernandez)]

Bug closed due to lack of activity, please feel free to reopen if needed.