Bird v3 BGP route selection

[Nigel Kukard]

On 2/25/25 01:02, Ondrej Zajicek wrote:
> On Tue, Feb 25, 2025 at 12:39:29AM +0000, Nigel Kukard via Bird-users wrote:
>> Hi there,
>>
>> I'm wondering if someone can point out how the best path is being selected
>> below in Bird 3.0.1?
>>
>> In Bird v2 the route via 100.201.0.2 was selected. With the exact same
>> configuration in Bird v3, the route via 100.201.0.4 is being selected.
> Hi
>
> I do not think this is really a change. If two routes have the same
> preference and are originated by the same protocol 'class' (e.g. BGP),
> they are compared using protocol-specific strategy (e.g. comparing
> bgp_local_pref, bgp_path length, ... in case of BGP). But in your case
> these two routes are from different protocols 'classes' (bgp_originate4
> -> BGP a static4 -> Static), in that case there is only fixed arbitrary
> ordering, and that may changed between Bird v2 and v3.
>
> I would suggest that different protocol 'classes' should always use
> different preference.
Hi there Ondrej,

Awesome, that explains it perfectly. Thanks!

So just to confirm in this specific case the bgp_local_pref isn't taken 
into account (ignored) in this specific case, right?

-N


>
>
>
>> In this case R1 is connected to R2. Both with the same ASN. The below table
>> is the table I have facing R2.
>>
>> In terms of my routing tables...
>> - originate4 =exports to=> bgp4
>> - static4 =exports to=> master4
>> - master4 <=exports/imports=> bgp4
>> - bgp4 <=exports/imports=> t_bgp4_AS65000_r2_peer (below)
>>
>>
>> 1007-Table t_bgp4_AS65000_r2_peer:
>>   0.0.0.0/0            unicast [bgp_originate4 2025-02-24 23:21:13] * (200)
>>         via 100.201.0.4 on eth2
>>   1012- preference: 200
>>         source: static
>>         bgp_local_pref: 930
>>         bgp_large_community: (65000, 3, 1)
>>   1008- Internal route handling values: 0L 24G 0S id 1
>>   1007-                     unicast [static4 2025-02-24 23:21:13] (200)
>>         via 100.201.0.2 on eth2
>>   1012- preference: 200
>>         source: static
>>         bgp_local_pref: 940
>>         bgp_large_community: (65000, 3, 1) (65000, 5000, 1)
>> 1008- Internal route handling values: 0L 22G 0S id 6
>>
>>
>> Kind Regards
>> Nigel
>>
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