Routing

Hi.

On R1 I have an inet.3 route to R4 installed via segment routing.

jcluser@vMX-addr-0> show route 4.4.4.4 table inet.3 logical-system R1

inet.3: 4 destinations, 4 routes (4 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

4.4.4.4/32         *[L-OSPF/10/5] 00:04:06, metric 3
                    >  to 10.10.10.2 via lt-0/0/0.1, Push 800004

This L-OSPF route has two route protocol preference values - 10 and 5. What does the second route protocol preference value of 5 mean?

Thanks,

Deepak

.

hi,

i have been looking for the same info myself.

So what i am gonna explain below is just a Guess, as i have not been able to find an explanation either.

You know there is this option in Junos mpls to copy inet.3 routes to inet.0 if you want the IGP  to  use labels for core traffic:

# set protocols mpls traffic-engineering bgp-igp-both-ribs

When you use Segment Routing, routes in inet.3 show as L-OSPF (with Admin distance of 10) or L-ISIS (with Admin distance (AD) of 14).

If your IGP is OSPF and you copy inet.3 L-OSPF routes to inet.0, your inet.3 routes will have the same AD of 10 as core OSPF routes which were already in inet.0.

In this case, which route is the router going to choose, OSPF (plain IP) or L-OSPF (labels)?

You have 2 routes to the same remote PE loopback, one as OSPF and the other one as L-OSPF, both with an AD of 10.

I think this why they added a 2nd AD (not sure if we can call it that),  like below,  to prefer L-OSPF over OSPF (this why you moved the routes from inet.3 to inet.0 in the first place):

*[L-OSPF/10/5]   <---- Preferred

*[OSPF/10/10]

*If your IGP is ISIS you will not have this issue as L-ISIS AD of 14 is lower than any other ISIS AD (15, 18, 160, 165)

------------------------------
NATHAN OLIVER
------------------------------