Re: [PATCH proxmox-ve-rs v2 1/7] sdn: fabric: add BGP protocol support

[Hannes Laimer <h.laimer@proxmox.com>]

On 2026-04-16 11:16, Gabriel Goller wrote:
> On 15.04.2026 13:11, Hannes Laimer wrote:
>> From: Stefan Hanreich <s.hanreich@proxmox.com>
>>
>> Add BGP as a fabric protocol for eBGP unnumbered underlays. Each node
>> has a mandatory, globally unique ASN for interface-based eBGP peering.
>>
>> Unlike OSPF and OpenFabric, BGP does not have its own FRR daemon -
> 
> This is a bit wrong, BGP has its own frr daemon, maybe rewrite this as "the bgp
> router is not exclusive to the bgp fabric"?

yeah, will improve in v3, thanks!

> 
>> the fabric config needs to coexist with EVPN in a single 'router bgp'
>> block. To handle this, the fabric merges into an existing router
>> rather than replacing it, using local-as to present the per-node ASN
>> to underlay peers when the router already runs under the EVPN ASN.
>>
>> For IPv6-only nodes, the BGP router-id is derived from the IPv6
>> address using FNV-1a, since router-id must be a 32-bit value.
> 
> Hmm this is a bit weird since the generated address is not really reachable
> right?

I mean, the route-id shares a format with ipv4 addresses, but it's not
supposed to be ip reachable. In perl we use part of the mac, for the
router-id if we don't have an ipv4 address. We can't really in rust, and
this seemed like a good(maybe better? cause macs may change) approach.

> 
> How do we handle this (frr bgp docs)?:
> 
>  To derive system-IP and anycast-IP, the default BGP instance’s router-id is
>  used as system-IP and the VxLAN interface’s local tunnel IP as the anycast-IP.
> 
> 
> Would it be stupid to select a ipv4 address, set it on the lo interface and then
> just use update-source and set the ipv6 address?
> 

hmm, good point actually, we need v4 reachability(at least for now),
just putting the derived router-id as an ipv4 address on the lo should
work. just not super sure if this is more on the actually common or
actually weird side of things... but I like the idea
But I don't think we should do this generally when creating a bgp
fabric, needing the router-id to be reachable is more of an EVPN
specific requirement I think

the alternative would be to require a configured v4 prefix on fabrics if
used for EVPN

either way it's more of an EVPN, than fabric, concern I think

>> Co-authored-by: Hannes Laimer <h.laimer@proxmox.com>
>> Signed-off-by: Stefan Hanreich <s.hanreich@proxmox.com>
>> Signed-off-by: Hannes Laimer <h.laimer@proxmox.com>
> 
> Maybe a few more tests with other existing fabrics, e.g. ospf and openfabric?
> These are quite easy to add, so adding a few more won't hurt.