BGP on /32 (/128) interfaces

[Arzhel Younsi]

Thank you all for your replies,

> Thinking about it, it makes sense to have something like direct mode that
works with unnumbered interfaces (or ones with /32 address).

We also think that's would be very useful, either transparently to the user
(depending on next hop resolution, eBGP/iBGP, IP's subnet mask) or through
the addition of an explicit "direct" keyword.
What would be the process to turn this thread into a feature request ? And
would the Bird maintainers be interested in implementing it ?

Thanks again !


On Mon, Apr 15, 2024 at 4:25 PM Ondrej Zajicek <santiago at crfreenet.org>
wrote:

> On Mon, Apr 15, 2024 at 12:10:05PM +0200, Daniel Gröber wrote:
> > Hi Arzhel,
> >
> > On Fri, Apr 12, 2024 at 11:57:38AM +0200, Arzhel Younsi wrote:
> > > But for IPv6, it's cleaner to only require the router's link local
> address:
> > > testvm2006:~$ ip -6 addr
> > > inet6 2620:0:860:140:10:192:24:4/128 scope global
> > > testvm2006:~$ ip -6 route
> > > default via fe80::2022:22ff:fe22:2201 dev ens13 metric 1024 pref medium
> > >
> > > In Bird:
> > > neighbor fe80::2022:22ff:fe22:2201%ens13 external;
> > >
> > > But then the link local address doesn't work with multihop (for obvious
> > > reason).
> > > bird: /etc/bird/bird.conf:22:1 Multihop BGP cannot be used with
> link-local
> > > addresses
> >
> > I use lladdrs for BGP endpoints in my network and that works fine. I
> think
> > using `direct` instead of `multihop` in the v6-lladdr case would make it
> > work for you.
> >
> > One word of advice: don't use the %scope syntax, use the `interface`
> > directive instead. I don't recall exactly why but I had some subtle
> problem
> > with that.
> >
> > As for your v4/32 problem, give `multihop 1` a try. That enforces no
> > routers on the path to the peer like direct but allows off-subnet
> > endpoints. Do keep in mind the docs recommend setting the source address
> > explicitly when enabling multihop.
>
> Hi
>
> Note that using multihop fixes the issue with waiting for the address
> range to appear, but there is still an issue with next hop resolution.
> Multihop routes use recursive next hop resolution and in the case of /32
> address ranges, there is no route for resolving neighbor IP announced as
> next hop.
>
> One would need a static route like:
>
> route NBR-IP/32 via "IFACE";
>
> So the next hop will be resolved.
>
>
> Thinking about it, it makes sense to have something like direct mode that
> works with unnumbered interfaces (or ones with /32 address).
>
> --
> Elen sila lumenn' omentielvo
>
> Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
> "To err is human -- to blame it on a computer is even more so."
>


-- 
Arzhel
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