Hello!
I suspect that the routes either aren't all external, or are otherwise
compared different before it comes to breaking ties. Could you please
share the `show route all` output to see all the relevant BGP attributes?
Maria
On 6/30/23 11:43, Mazur, Dariusz via Bird-users wrote:
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
--
Maria Matejka (she/her) | BIRD Team Leader | CZ.NIC, z.s.p.o.
