Exporting a larger prefix if a smaller prefix is being exported

[Maria Matejka]

Sorry, sent this off-list by mistake.

Maria

On 13 January 2024 18:11:07 CET, Maria Matejka <maria.matejka at nic.cz> wrote:
>Hello!
>
>This will be possible in version 3, maybe not fully automatic in the first stable versions. There is some code (indirectly) enabling this, waiting for some finishing touches amd merging. You may expect to have an opportunity to test it with the next alpha version of BIRD 3.
>
>With BIRD 2, to some extent it may be also possible directly with the upcoming prefix aggregation feature. Not yet available now.
>
>Maria 
>
>On 13 January 2024 01:56:50 CET, Lukas Haase via Bird-users <bird-users at network.cz> wrote:
>>Hi,
>>
>>Is is somehow possible to export a larger prefix if one or more sub-prefixes (subnets) are exported ... but also remove that prefix if no smaller subnet exist any more?
>>
>>Example: As soon as 192.0.2.44/32 or 192.0.2.208/28 (or any other prefix inside 192.0.2.0/24) is exported via eBGP, also export prefix 192.0.2.0/24. If no sub-prefixes are left, also remove 192.0.2.0/24 from export.
>>
>>Background for my question is BGP. As is well known, the smallest prefix I can announce over eBGP is /24. I use bird as a border gateway and I announce various smaller prefixes via iBGP. The smaller prefixes will take precedence in my peering neighboring AS but the /24 is required to announce my network farther out.
>>
>>But why would I want that? Because there are actually two border gateways. If all internal links to one of these gateways breaks, the full subnet should not be announced any more (otherwise the traffic would be dropped). If at least one subnet is announced, I assume that the internal mesh is strong enough to find its way.
>>
>>
>>Thanks,
>>Luke
>>
>>
>
>-- 
>Maria Matejka (she/her) | BIRD Team Leader | CZ.NIC, z.s.p.o.
-- 
Maria Matejka (she/her) | BIRD Team Leader | CZ.NIC, z.s.p.o.
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