OSPF & merge external on

[Ondrej Zajicek]

On Sat, Jun 25, 2022 at 10:00:14PM +0300, Mikhail Mayorov wrote:
> Hello!
> 
> I would like use ECMP for 0.0.0.0/0. This route announced on 10.10.97.33,
> 10.10.97.72, 10.10.97.73 as LSA5. Below I have given the output of the
> command on the router 10.10.97.67.
> I expected to see a default route through 2 interfaces C3 to D1, but next
> hops not merge.
> Maybe I misunderstand the work "merge external on". I expected that the bird
> would combine routes from different routers for the same destination
> although OSPF.metric1 or OSPF.metric2.

Hello

Option "merge external" causes BIRD to combine external routes from
different routers, but only those that have the same metric (ECMP =
equal cost multipath).

In your example 0.0.0.0/0 from 10.10.97.33 has metric1 300 / metric2 10000,
while 0.0.0.0/0 from 10.10.97.73 has metric1 310 / metric2 10000.

Therefore, the only the first is used, which has only one next hop
(like the route to 10.10.97.33/32).

-- 
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."