Hello Bird users,
Have you ever use RFC 5004 and “older prefer” knob. I am trying to use it but
it seems not to work:
1.Router learns the same route from different ebgp peers, it prefers route from
r01a and this route is exported to BGP peers
172.232.160.0/19 unicast [192.168.196.129__r01a.tor106 2023-06-14] * (100)
[AS4250627481?]
via 192.168.196.129 on vlan.201
unicast [192.168.196.131__r01b.tor106 2023-06-14] (100)
[AS4250627481?]
via 192.168.196.131 on vlan.202
unicast [192.168.196.133__r02a.tor106 2023-06-14] (100)
[AS4250627482?]
via 192.168.196.133 on vlan.203
2.Once we lose links to r01a and r01b route from r02a is preferred and
exported to BGP peers. It is expected
172.232.160.0/19 unicast [192.168.196.133__r02a.tor106 2023-06-14] * (100)
[AS4250627482?]
via 192.168.196.133 on vlan.203
3.When links to r01a and r01b. are again online route, route from r01a is
pricked as primary and exported to BGP. It causes route oscillation
172.232.160.0/19 unicast [192.168.196.129__r01a.tor106 09:14:19.982] *
(100) [AS4250627481?]
via 192.168.196.129 on vlan.201
unicast [192.168.196.131__r01b.tor106
09:14:19.896] (100) [AS4250627481?]
via 192.168.196.131 on vlan.202
unicast [192.168.196.133__r02a.tor106 2023-06-14] (100)
[AS4250627482?]
via 192.168.196.133 on vlan.203
4.I believe it is default behavior not to prefer older path. According to
documentation RFC 5004 and "prefer older on" should fix my problem, but it does
not work.
Bird doc says:
prefer older switch
Standard route selection algorithm breaks ties by comparing router IDs. This
changes the behavior to prefer older routes (when both are external and from
different peer). For details, see RFC 5004. Default: off.
5. According to documentation RFC 5004 and "prefer older on" should fix my
problem, but it does not work.
a) added "prefer older on", bgp flapped and routes were re-learnt
172.232.160.0/19 unicast [192.168.196.129__r01a.tor106 09:22:12.949] *
(100) [AS4250627481?]
via 192.168.196.129 on vlan.201
unicast [192.168.196.131__r01b.tor106
09:22:13.527] (100) [AS4250627481?]
via 192.168.196.131 on vlan.202
unicast [192.168.196.133__r02a.tor106 09:22:12.683] (100)
[AS4250627482?]
via 192.168.196.133 on vlan.203
b) shut links to r01a and r01b
172.232.160.0/19 unicast [192.168.196.133__r02a.tor106 09:22:12.683] *
(100) [AS4250627482?]
via 192.168.196.133 on vlan.203
c) unshut links to r01a and r01b, route from r01a is again preferred, so looks
like "older" knob does not work
172.232.160.0/19 unicast [192.168.196.129__r01a.tor106 09:27:55.841] *
(100) [AS4250627481?]
via 192.168.196.129 on vlan.201
unicast [192.168.196.131__r01b.tor106 09:27:54.448] (100)
[AS4250627481?]
via 192.168.196.131 on vlan.202
unicast [192.168.196.133__r02a.tor106 09:22:12.683] (100)
[AS4250627482?]. ---> this route is older
via 192.168.196.133 on vlan.203
Thanks,
Dariusz
