[j-nsp] "set routing-options protect core" breaks local-preference

[adamv0025 at netconsultings.com]

> -----Original Message-----
> From: juniper-nsp [mailto:juniper-nsp-bounces at puck.nether.net] On Behalf
> Of Karl Gerhard
> 
> Hello
> 
> I am experimenting with BGP PIC before deploying it to production and I
> have found an oddity:
> With "set routing-options protect core" local-preference stops working the
> way I would expect it to work.
> 
> If I configure "local-preference 120" on import from my IBGP neighbor the
> router will send traffic for some prefixes to my IBGP neighbor (where they
> will egress through EBGP) and for other prefixes directly to my EBGP
> neighbor. It seems like they're getting load-balanced per destination subnet.
> This is how it looks in the routing table:
> 
> root at router1# run show route 1.0.143.0/24 table inet.0
> inet.0: 705394 destinations, 2116034 routes (705393 active, 0 holddown, 2
> hidden) @ = Routing Use Only, # = Forwarding Use Only
> + = Active Route, - = Last Active, * = Both
> 
> 1.0.143.0/24       @[BGP/170] 00:08:21, localpref 120
>                       AS path: 174 38040 23969 ?, validation-state: unverified
>                     > to 123.123.123.1 via ae1.0
>                       to 55.55.55.2 via ae3.0
>                     [BGP/170] 00:07:37, localpref 100
>                       AS path: 174 38040 23969 ?, validation-state: unverified
>                     > to 55.55.55.2 via ae3.0
>                    #[Multipath/255] 00:07:37, metric2 0
>                       to 123.123.123.1 via ae1.0
>                     > to 55.55.55.2 via ae3.0
>                       to 55.55.55.2 via ae3.0
> 
> 123.123.123.1 is my IBGP neighbor where I would like traffic to go
> 55.55.55.2 is my EBGP neighbor
> 
> This is the part that is causing issues:
>                    #[Multipath/255] 00:07:37, metric2 0
>                       to 123.123.123.1 via ae1.0
>                     > to 55.55.55.2 via ae3.0
>                       to 55.55.55.2 via ae3.0
> 
> With "local-preference 120" configured on my IBGP session I would expect all
> packets to go to my IBGP neighbor (123.123.123.1) - at least that's how it
> used to work. But for this specific subnet (and many others) the traffic will go
> directly to my EBGP neighbor.
> 
> How do I make all traffic go to my IBGP neighbor?
> Is that "by design" or is it a bug in Junos 18.2R1?
> 

There seem to be two next hops for the entry with localpref120 and AS path: 174 38040 23969, if everything else is equal then eBGP path wins.

1.0.143.0/24       @[BGP/170] 00:08:21, localpref 120
                      AS path: 174 38040 23969 ?, validation-state: unverified
                    > to 123.123.123.1 via ae1.0
                      to 55.55.55.2 via ae3.0

adam

netconsultings.com
::carrier-class solutions for the telecommunications industry::