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<p><font face="Gentium">Hello!</font></p>
<p><font face="Gentium">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?</font></p>
<p><font face="Gentium">Maria</font><br>
</p>
<div class="moz-cite-prefix">On 6/30/23 11:43, Mazur, Dariusz via
Bird-users wrote:<br>
</div>
<blockquote type="cite"
cite="mid:B5F97AD9-864F-4F56-9E0C-B6932E2F863E@akamai.com">
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<p class="MsoNormal">Hello Bird users,<o:p></o:p></p>
<p class="MsoNormal">Have you ever use RFC 5004 and “older
prefer” knob. I am trying to use it but it seems not to work:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><b>1.Router learns the same route from
different ebgp peers, it prefers route from r01a and this
route is exported to BGP peers<o:p></o:p></b></p>
<p class="MsoNormal">172.232.160.0/19 unicast
[192.168.196.129__r01a.tor106 2023-06-14] * (100)
[AS4250627481?]<o:p></o:p></p>
<p class="MsoNormal"> via 192.168.196.129 on
vlan.201<o:p></o:p></p>
<p class="MsoNormal"> unicast
[192.168.196.131__r01b.tor106 2023-06-14] (100)
[AS4250627481?]<o:p></o:p></p>
<p class="MsoNormal"> via 192.168.196.131 on
vlan.202<o:p></o:p></p>
<p class="MsoNormal"> unicast
[192.168.196.133__r02a.tor106 2023-06-14] (100)
[AS4250627482?]<o:p></o:p></p>
<p class="MsoNormal"> via 192.168.196.133 on
vlan.203<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><b>2.Once we lose links to r01a and r01b
route from r02a is preferred and exported to BGP peers. It
is expected<o:p></o:p></b></p>
<p class="MsoNormal">172.232.160.0/19 unicast
[192.168.196.133__r02a.tor106 2023-06-14] * (100)
[AS4250627482?]<o:p></o:p></p>
<p class="MsoNormal"> via 192.168.196.133 on
vlan.203<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><b>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<o:p></o:p></b></p>
<p class="MsoNormal">172.232.160.0/19 unicast
[192.168.196.129__r01a.tor106 09:14:19.982] * (100)
[AS4250627481?]
<o:p></o:p></p>
<p class="MsoNormal"> via 192.168.196.129 on
vlan.201<o:p></o:p></p>
<p class="MsoNormal"> unicast
[192.168.196.131__r01b.tor106 09:14:19.896] (100)
[AS4250627481?]<o:p></o:p></p>
<p class="MsoNormal"> via 192.168.196.131 on
vlan.202<o:p></o:p></p>
<p class="MsoNormal"> unicast
[192.168.196.133__r02a.tor106 2023-06-14] (100)
[AS4250627482?]<o:p></o:p></p>
<p class="MsoNormal"> via 192.168.196.133 on
vlan.203<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><b>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.<o:p></o:p></b></p>
<p class="MsoNormal">Bird doc says:<o:p></o:p></p>
<p class="MsoNormal"><i>prefer older switch<o:p></o:p></i></p>
<p class="MsoNormal"><i>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.<o:p></o:p></i></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><b>5. According to documentation RFC 5004
and "prefer older on" should fix my problem, but it does not
work.</b><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><b>a) added "prefer older on", bgp flapped
and routes were re-learnt<o:p></o:p></b></p>
<p class="MsoNormal">172.232.160.0/19 unicast
[192.168.196.129__r01a.tor106 09:22:12.949] * (100)
[AS4250627481?]<o:p></o:p></p>
<p class="MsoNormal"> via 192.168.196.129 on
vlan.201<o:p></o:p></p>
<p class="MsoNormal"> unicast
[192.168.196.131__r01b.tor106 09:22:13.527] (100)
[AS4250627481?]<o:p></o:p></p>
<p class="MsoNormal"> via 192.168.196.131 on
vlan.202<o:p></o:p></p>
<p class="MsoNormal"> unicast
[192.168.196.133__r02a.tor106 09:22:12.683] (100)
[AS4250627482?]<o:p></o:p></p>
<p class="MsoNormal"> via 192.168.196.133 on
vlan.203<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><b>b) shut links to r01a and r01b<o:p></o:p></b></p>
<p class="MsoNormal"><b>172.232.160.0/19 unicast
[192.168.196.133__r02a.tor106 09:22:12.683] * (100)
[AS4250627482?]<o:p></o:p></b></p>
<p class="MsoNormal"><b> via 192.168.196.133 on
vlan.203<o:p></o:p></b></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><b>c) unshut links to r01a and r01b, route
from r01a is again preferred, so looks like "older" knob
does not work<o:p></o:p></b></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">172.232.160.0/19 unicast
[192.168.196.129__r01a.tor106 09:27:55.841] * (100)
[AS4250627481?]<o:p></o:p></p>
<p class="MsoNormal"> via 192.168.196.129 on
vlan.201<o:p></o:p></p>
<p class="MsoNormal"> unicast
[192.168.196.131__r01b.tor106 09:27:54.448] (100)
[AS4250627481?]<o:p></o:p></p>
<p class="MsoNormal"> via 192.168.196.131 on
vlan.202<o:p></o:p></p>
<p class="MsoNormal"> unicast
[192.168.196.133__r02a.tor106 09:22:12.683] (100)
[AS4250627482?].
<b>---> this route is older</b><o:p></o:p></p>
<p class="MsoNormal"> via 192.168.196.133 on
vlan.203<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks,<o:p></o:p></p>
<p class="MsoNormal">Dariusz<o:p></o:p></p>
</div>
</blockquote>
<pre class="moz-signature" cols="72">--
Maria Matejka (she/her) | BIRD Team Leader | CZ.NIC, z.s.p.o.</pre>
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