Duplicated routes received from Route Reflectors

[Chriztoffer Hansen]

Hi,

On Tue, 2 Feb 2021 at 09:37, Délsio Cabá wrote:
> We have a installed 2 BIRD RR (10.200.2.125 and 10.200.2.124)  just
> installed to use as reflectors on our network
>
> We noticed the client is adding 2 entries to the routing table.
>
> Is this normal?
>
> Taking into consideration we do full global BGP is will be too much
> memory wasted:
>
> RR-CLIENT#show ip bgp 0.0.0.0
> BGP routing table entry for 0.0.0.0/0, version 0
> Paths: (2 available, no best path)
>   Not advertised to any peer
>   Refresh Epoch 1
>   xxxx
>     10.200.0.252 (inaccessible) from 10.200.2.125 (10.200.2.125)
>       Origin IGP, metric 0, localpref 350, valid, internal
>       Community: 2470515592
>       Originator: 10.200.0.252, Cluster list: 10.200.2.125
>       rx pathid: 0, tx pathid: 0
>   Refresh Epoch 1
>   xxxx
>     10.200.0.252 (inaccessible) from 10.200.2.124 (10.200.2.124)
>       Origin IGP, metric 0, localpref 350, valid, internal
>       Community: 2470515592
>       Originator: 10.200.0.252, Cluster list: 10.200.2.124
>       rx pathid: 0, tx pathid: 0

Yes.
This is completely normal for IBGP RR clients. (Regardless if you are
using BIRD or not)
Your RR client receives one best-route from each RR (or RR cluster).
Your RR client will install both routes in it's RIB.
And the "best" route (decided locally by RR client configured logic)
is installed in the FIB.

You will want to have multiple routes for the same destination in your
local RR client RIB. Should one of the RR's go offline. Being taken
down for maint, etc. (= RR not available). Your RR client will then
"fall-back" to the next best route it stores in it's RIB and install
that in the FIB. Instead of the "now" gone best route. (In short,
quicker failover to another route to the destination, and has high
potential lessening the time traffic is potentially blackholed during
a route convergence)

-- 
Cheers, Chriztoffer