Hello Aleksander, Prepends does not work for me because I would prepending on every leaf so as-path still will be the same from perespective r01.leaf108 Looks like AIGP is not for me too because we don’t have IGP inside network. Every iBGP session is established over directly connected p2p links. I was thinking to increase BGP preference (not bgp local pref) on leafs to prefer routes from tor and not to compare them with the same routes from spine (I don’t like this workaround) Thanks, Dariusz On 9/13/23, 2:17 PM, "Alexander Zubkov" <green@qrator.net <mailto:green@qrator.net>> wrote: Hi Dariusz, Will ASPATH prepends work for you? Or this feature might help you: https://urldefense.com/v3/__https://bird.network.cz/?get_doc&v=20&f=bird-6.h... <https://urldefense.com/v3/__https://bird.network.cz/?get_doc&v=20&f=bird-6.html>*bgp-aigp__;Iw!!GjvTz_vk!Xxvtj4yzVIakFfyFYALg5qiCWoJ-VfKsSyJy2aYMXvIoY5myyvsy41XQPC862yoN5iLL7GvrlmJ2$ Regards, Alexander Zubkov Qrator Labs On Wed, Sep 13, 2023 at 11:43 AM Mazur, Dariusz via Bird-users <bird-users@network.cz <mailto:bird-users@network.cz>> wrote:
Hello Bird Users,
Have a question about bgp best path algorithm in Route Refletector environment and possible fix:
Topology ( we use only iBGP with multiply RR):
r01a.tor ----- r01.leaf.105---r01.spine----r01.leaf108-----r09a.tor
I announce the same block 172.232.0.0/19 from both tors
r01.leaf108 receives 172.232.0.0/19 from r01.spine and r09a.tor, and treat them as equal path (multipath).
All BGP attributes are equal except of BGP originator id and cluster-list
r01.leaf108.ord02.fab> show route for 172.232.0.0/19 all
172.232.0.0/19
unicast [192.168.226.56__r01.spine101 2023-09-06] * (100) [AS4250527481?]
via 192.168.226.56 on vlan.101
Type: BGP univ
BGP.origin: Incomplete
BGP.as_path: 4250527481
BGP.next_hop: 192.168.226.56
BGP.med: 0
BGP.local_pref: 400
BGP.atomic_aggr:
BGP.aggregator: 23.192.121.225 AS4250527481
BGP.community: (63949,1000) (63949,1002) (63949,1004) (63949,1005) (65110,31107) (65310,31107) (65518,31107)
BGP.originator_id: 23.205.212.134
BGP.cluster_list: 23.205.212.8 23.205.212.112
unicast [192.168.198.35__r09b.tor108 2023-09-06] (100) [AS4250827489?]
via 192.168.198.35 on vlan.218
Type: BGP univ
BGP.origin: Incomplete
BGP.as_path: 4250827489
BGP.next_hop: 192.168.198.35
BGP.med: 0
BGP.local_pref: 400
BGP.atomic_aggr:
BGP.aggregator: 23.213.15.233 AS4250827489
BGP.community: (63949,1000) (63949,1002) (63949,1004) (63949,1005) (65110,31107) (65310,31107) (65518,31107)
Looks like Bird does not check cluster_list length to determine better route, is it intentional? Can you suggest any possible fix to prefer route from r09a.tor using cluster-list or anything what is local for router (local pref is not option because all routers are in the same asn and use iBGP)
Thanks,
Dariusz