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<p class="MsoNormal">Hello Bird Users,<o:p></o:p></p>
<p class="MsoNormal">Have a question about bgp best path algorithm in Route Refletector environment and possible fix:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Topology ( we use only iBGP with multiply RR):<o:p></o:p></p>
<p class="MsoNormal">r01a.tor ----- r01.leaf.105---r01.spine----r01.leaf108-----r09a.tor<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I announce the same block 172.232.0.0/19 from both tors<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">r01.leaf108 receives 172.232.0.0/19 from r01.spine and r09a.tor, and treat them as equal path (multipath).
<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">All BGP attributes are equal except of BGP originator id and cluster-list<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="font-size:9.0pt">r01.leaf108.ord02.fab> show route for 172.232.0.0/19 all<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt">172.232.0.0/19 <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt"> unicast [192.168.226.56__r01.spine101 2023-09-06] * (100) [AS4250527481?]<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt"> via 192.168.226.56 on vlan.101<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt"> Type: BGP univ<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt"> BGP.origin: Incomplete<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt"> BGP.as_path: 4250527481<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt"> BGP.next_hop: 192.168.226.56<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt"> BGP.med: 0<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt"> BGP.local_pref: 400<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt"> BGP.atomic_aggr:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt"> BGP.aggregator: 23.192.121.225 AS4250527481<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt"> BGP.community: (63949,1000) (63949,1002) (63949,1004) (63949,1005) (65110,31107) (65310,31107) (65518,31107)<o:p></o:p></span></p>
<p class="MsoNormal"><b><span style="font-size:9.0pt"> BGP.originator_id: 23.205.212.134<o:p></o:p></span></b></p>
<p class="MsoNormal"><b><span style="font-size:9.0pt"> BGP.cluster_list: 23.205.212.8 23.205.212.112<o:p></o:p></span></b></p>
<p class="MsoNormal"><span style="font-size:9.0pt"> <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt"> unicast [192.168.198.35__r09b.tor108 2023-09-06] (100) [AS4250827489?]<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt"> </span><span lang="NL" style="font-size:9.0pt">via 192.168.198.35 on vlan.218<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="NL" style="font-size:9.0pt"> Type: BGP univ<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="NL" style="font-size:9.0pt"> </span>
<span style="font-size:9.0pt">BGP.origin: Incomplete<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt"> BGP.as_path: 4250827489<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt"> BGP.next_hop: 192.168.198.35<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt"> BGP.med: 0<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt"> BGP.local_pref: 400<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt"> BGP.atomic_aggr:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt"> BGP.aggregator: 23.213.15.233 AS4250827489<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt"> BGP.community: (63949,1000) (63949,1002) (63949,1004) (63949,1005) (65110,31107) (65310,31107) (65518,31107)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal">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)<br>
<br>
Thanks,<o:p></o:p></p>
<p class="MsoNormal">Dariusz<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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