[Babel-users] Does babel support ECMP ?

[Juliusz Chroboczek]

> Sorry if I’m missing something obvious but does bable support ECMP ?

No, it doesn't.  Babel selects a single "best" next-hop for a given route,
and pushes all traffic through that next-hop.  (See below, however, about
how a route may be more specific than a single destination.)

Babel is designed to work with continuous metrics (due to link-quality
estimation and hysteresis), so paths seldom have "equal" cost.  Babel
would need a notion of "close" cost to perform nondeterministic multipath;
this used to be supported in Cisco's EIGRP, but I don't think it worked
very well.

The multipath technique that I try to promote is source-specific routing
(SADR), which is purely deterministic.  It puts more control (and more
responsibility) on the end-hosts, which might be an advantage or
a disadvantage, depending on your setup.

  https://arxiv.org/pdf/1403.0445.pdf

> I tried a simple configuration with two routers annoucing the same network
> (4000::/64) with the same metric to a thrid routeur but babel install only one
> route in the routing table. The other is classified as « feasible ».

"Feasible" means that the route is provably loop-free, and that Babel may
switch to it at any time.  Keeping the fallback route "feasible" is the
right behaviour in your case.

Regards,

-- Juliusz