bgp link bandwidth extended community question

[Ondrej Zajicek]

On Tue, Apr 19, 2022 at 12:45:29AM -0700, gautham devalapalli wrote:
> Hello,
> 
> I am using BIRD 2.0.8 to establish a bgp session with a nexus switch. I am
> trying to set bgp ext community link bandwidth. Since this is not
> explicitly supported I am following the thread below to set it as unknown.
> 
> https://marc.info/?l=bird-users&m=142108436602254&w=2
> 
> I tried setting
> *bgp_ext_community.add((unknown 0x4004,65000,1000));*
> 
> *and *
> *bgp_ext_community.add((unknown 0x4004, 65000, 0x447a0000));*
> 
> https://datatracker.ietf.org/doc/html/draft-ietf-idr-link-bandwidth-07#section-2
> 
> *bird bgp config:*
> protocol bgp ebgp_node01 {
> local 10.0.10.3 as 65000;
> neighbor 10.0.10.1 as 100;

> On wireshark I see the bird does not send this ext community as part of the
> bgp UPDATE message.

The link bandwidth extended community is non-transitive. From the draft you linked:

   The extended community is optional non-transitive. The value of the
   high-order octet of the extended Type Field is 0x40.

That means it is not propagated through EBGP, only through IBGP.
Different ASNs -> EBGP (unless configured as AS confederation).

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
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"To err is human -- to blame it on a computer is even more so."