Junos Routing Tables

inet.0 is the default IPv4 unicast table.
inet.6 is the default IPv6 unicast table.

mpls.0 is used to store the LFIB; local incoming labels and the pop/swap/push operation for outgoing packets.

inet.3 (and inet6.3) is used to look up labelled routes learnt via an MPLS protocol such as MP-BGP or LDP by a LER placing traffic into one end of an LSP. In the example below a customer is dual-homed to PE 1 and PE2, the physical SP topology is PE1 - P1 - PE2. PE1 advertises the route "172.21.18.0/30" inside MP-BGP to PE2 and on PE2 we can see the local route and the MP-BGP route from PE1. The route via PE 1 is preferred:

james@PE1> show route table 0037.inet.0 172.21.18.0/30

0037.inet.0: 273 destinations, 298 routes (273 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

172.21.18.0/30     *[Direct/0] 67w0d 03:37:57
                    > via ge-2/3/0.2006
                    [BGP/170] 21w1d 19:38:23, MED 0, localpref 20
                      AS path: 11223 ?
                    > to 172.21.18.2 via ge-2/3/0.2006
172.21.18.1/32     *[Local/0] 67w0d 03:37:57
                      Local via ge-2/3/0.2006



james@PE1> show configuration interfaces lo0
description Primary-Loopback;
unit 0 {
    family inet {
        address 172.31.96.1/32;
    }
}




james@PE2> show route table 0037.inet.0 172.21.18.0/30

0037.inet.0: 257 destinations, 534 routes (257 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

172.21.18.0/30     *[BGP/170] 3w0d 17:27:19, localpref 100, from 172.31.96.1
                      AS path: I, validation-state: unverified
                    > to 172.31.98.37 via xe-0/0/0.0, Push 16, Push 375344(top)
                    [BGP/170] 3w0d 17:27:18, localpref 100, from 172.31.96.2
                      AS path: I, validation-state: unverified
                    > to 172.31.98.37 via xe-0/0/0.0, Push 16, Push 375344(top)
                    [BGP/170] 8w2d 18:04:54, localpref 10
                      AS path: 11223 ?, validation-state: unverified
                    > to 172.21.18.26 via xe-0/0/1.2006


james@PE2> show route table 0037.inet.0 active-path 172.21.18.0/30

0037.inet.0: 257 destinations, 534 routes (257 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

172.21.18.0/30     *[BGP/170] 3w0d 17:40:11, localpref 100, from 172.31.96.1
                      AS path: I, validation-state: unverified
                    > to 172.31.98.37 via xe-0/0/0.0, Push 16, Push 375344(top)

One can see below that inet.3 on PE2 contains the next-hop info to reach PE1 using an LSP, in this case the /32 loopback address on PE1 learnt via LDP. It shows the label to push is "375344" and the egress interface is xe-0/0/0.0 which faces P1:

james@PE2> show route table inet.3 172.31.96.1 detail

inet.3: 17 destinations, 17 routes (17 active, 0 holddown, 0 hidden)
172.31.96.1/32 (1 entry, 1 announced)
        State: 
        *LDP    Preference: 9
                Next hop type: Router
                Address: 0x9a5bf00
                Next-hop reference count: 2
                Next hop: 172.31.98.37 via xe-0/0/0.0, selected
                Label operation: Push 375344
                Label TTL action: no-prop-ttl
                Session Id: 0x1d5
                State: 
                Local AS: 123456
                Age: 3w0d 17:35:56      Metric: 30
                Validation State: unverified
                Task: LDP
                Announcement bits (1): 1-Resolve tree 1
                AS path: I

 Below on P1, since it is the penultimate hop the incoming label is PoP'ed:

james@P1> show route table mpls.0 label 375344

mpls.0: 141 destinations, 141 routes (141 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

375344             *[LDP/9] 2w2d 01:59:57, metric 1
                    > to 172.31.98.1 via xe-0/0/0.0, Pop
375344(S=0)        *[LDP/9] 2w2d 01:59:57, metric 1
                    > to 172.31.98.1 via xe-0/0/0.0, Pop

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