[Babel-users] CRXN/DN42: interconnecting overlay networks with Babel and BGP

[Marek Küthe]

On Mon, 20 Feb 2023 01:29:40 +0100
Daniel Gröber <dxld at darkboxed.org> wrote:

> Interesting,
> 
> Did you notice this passage:
> 
> > This problem could be solved by calculating the Babel metric based on the
> > AS path length, but I am unsure if this is technically possible, on the
> > other hand this may compromise the loop-free nature of Babel. This
> > problem, but with no potential solution, also occurs with the Default
> > Route.  
> 
> I think the answer should be that no matter how you mess with the metrics
> babel should still remain loop-free, right?

The metrics thing actually works. I use the following "formula" in bird:
```
babel_metric = 70 + (2 * bgp_path.len);
```

My understanding is that it should remain loop-free as long as each
Babel hop increments the metric by at least one.

> 
> On Sun, Feb 19, 2023 at 03:53:03PM +0100, Juliusz Chroboczek wrote:
> > Interestingly, the two networks use overlapping prefixes, which requires
> > enumerating hundreds of prefixes in their filters.  This is a case where
> > BIRD's support for Babel is likely to be useful: babeld's filtering
> > engine is simply not designed for large numbers of filtering rules.  
> 
> I guess it would also help if babel could send some kind of metadata along
> with the routes. Like BGP communities or some such. Has this been thought
> about already?

That's right. This would be very practical a kind of BGP communities
for Babel. The only reason I personally prefer babeld over bird is that
babeld can calculate latency on its own with the RTT extension.

> 
> For example while debugging rtt based routing metrics I would have loved to
> be able to send along the raw RTT value along with each route :)
> 
> --Daniel
> 
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-- 
Marek Küthe
m.k at mk16.de
er/ihm he/him
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