[j-nsp] track-igp-metric in LDP

[Mark Tinka]

On 2/Aug/20 16:21, Chen Jiang wrote:
> Hi! Dave
>
> Thanks for clarifying. So you mean BGP path selection tie breaker for IGP
> metric is happening in inet.3(LDP) but not inet.0(IGP like OSPF/IOSIS), so
> we need "track-igp-metric" to introduce metric into LDP for
> track-igp-metric. is it correct?

If you are forwarding in MPLS, yes.

That means an FEC built by LDP will be assigned the correct metric that
was calculated by the IGP. This way, you don't have your IGP telling you
A-B-C is the shortest path, but LDP says A-B-D-C is the shortest path.

Here's an example of some output when both inet6.3 and inet6.0 agree due
to "track-igp-metric":

tinka at er-01-jnb.za-re0# run show route 2c0f:feb0:0:2::8

inet6.0: 92801 destinations, 182856 routes (92796 active, 4 holddown, 2
hidden)
+ = Active Route, - = Last Active, * = Both

2c0f:feb0:0:2::8/128
                   *[IS-IS/18] 2d 07:53:40, metric 24700
                      to fe80::1205:caff:fe86:4ac3 via et-0/0/2.0
                    > to fe80::5287:89ff:fef3:25c3 via et-0/0/2.0
                      to fe80::1205:caff:fe86:4b10 via et-4/0/2.0
                      to fe80::5287:89ff:fef3:2610 via et-4/0/2.0

inet6.3: 1508 destinations, 1508 routes (1508 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

2c0f:feb0:0:2::8/128
                   *[LDP/9] 2d 07:53:40, metric 24700
                      to fe80::1205:caff:fe86:4ac3 via et-0/0/2.0, Push
25215
                    > to fe80::5287:89ff:fef3:25c3 via et-0/0/2.0, Push
25214
                      to fe80::1205:caff:fe86:4b10 via et-4/0/2.0, Push
25215
                      to fe80::5287:89ff:fef3:2610 via et-4/0/2.0, Push
25214

{master}[edit]
tinka at er-01-jnb.za-re0#

Same applies to IPv4.

Mark.