Viewing Information About RSVP-Signaled LSPs in the Routing Tables

Problem

You want to check the routing tables to verify that an RSVP-signaled LSP has been established and is being used.

Solution

On the ingress router, look in the inet.3 routing table to view the RSVP routes:

aviva@R1> show route table inet.3 inet.3: 1 destinations, 1 routes (1 active, 0 holddown, 0 hidden) + = Active Route, - = Last Active, * = Both 10.0.0.6/32 *[RSVP/7] 00:17:28, metric 2 > via so-0/0/2.0, label-switched-path R1-to-R6

On the transit router, look in the mpls.0 table to see the routers label information:

aviva@R3> show route table mpls.0 mpls.0: 7 destinations, 7 routes (7 active, 0 holddown, 0 hidden) + = Active Route, - = Last Active, * = Both 0 *[MPLS/0] 06:28:10, metric 1 Receive 1 *[MPLS/0] 06:28:10, metric 1 Receive 2 *[MPLS/0] 06:28:10, metric 1 Receive 100048 *[RSVP/7] 05:55:24, metric 1 > via so-0/0/2.0, label-switched-path R6-to-R1 100048(S=0) *[RSVP/7] 05:55:24, metric 1 > via so-0/0/2.0, label-switched-path R6-to-R1 100064 *[RSVP/7] 00:18:59, metric 1 > via so-0/0/3.0, label-switched-path R1-to-R6 100064(S=0) *[RSVP/7] 00:18:59, metric 1 > via so-0/0/3.0, label-switched-path R1-to-R6

Discussion

MPLS and RSVP store their routing and forwarding information in two routing tables, inet.3 and mpls.0. The inet.3 table contains the routers learned from the signaling protocol, RSVP (and also LDP), which MPLS uses to make forwarding decisions. The show route table inet.3 command lists the routes to RSVP-signaled LSP. You can also use the show route protocol rsvp command to display the same information:

aviva@R1> show route protocol rsvp inet.0: 14 destinations, 18 routes (14 active, 0 holddown, 0 hidden) inet.3: 1 destinations, 1 routes (1 active, 0 holddown, 0 hidden) + = Active Route, - = Last Active, * = Both 10.0.0.6/32 *[RSVP/7] 00:32:04, metric 2 > via so-0/0/2.0, label-switched-path R1-to-R6

The inet.0 unicast routing table doesn contain any routes learned from RSVP, and the inet.3 table has one route, to 10.0.0.6, the LSPs egress router. The second line of the routing entry shows that the path to the egress router goes out the so-0/0/2 interface and travels along LSP R1-to-R6. The detail version of both show route commands gives more information about the route and LSP:

aviva@R1> show route table inet.3 detail inet.3: 1 destinations, 1 routes (1 active, 0 holddown, 0 hidden) 10.0.0.6/32 (1 entry, 1 announced) State: * RSVP Preference: 7 Next-hop reference count: 7 Next hop: via so-0/0/2.0 weight 0x1, selected Label-switched-path R1-to-R6 Label operation: Push 100064 State: <Active Int> Local AS: 65432 Age: 23:52 Metric: 2 Task: RSVP Announcement bits (2): 2-Resolve tree 1 3-Resolve tree 2 AS path: I

The first highlighted line shows the name of the LSP, while the Label operation line shows the label operation performed by this route, here a push operation, and the label value that is placed into the MPLS header.

The inet.3 routing table is only on the ingress router because this is the only router that can place traffic into the LSP. This is important to remember when troubleshooting RSVP-signaled LSPs, so you don become confused when looking for routes on different routers. Checking the transit router confirms that the inet.3 table is not present:

aviva@R3> show route table inet.3 aviva@R3>

The second routing table used by RSVP is mpls.0, which stores the label bindings for the LSPs:

aviva@R3> show route table mpls.0 mpls.0: 7 destinations, 7 routes (7 active, 0 holddown, 0 hidden) + = Active Route, - = Last Active, * = Both 0 *[MPLS/0] 06:50:42, metric 1 Receive 1 *[MPLS/0] 06:50:42, metric 1 Receive 2 *[MPLS/0] 06:50:42, metric 1 Receive 100048 *[RSVP/7] 06:17:56, metric 1 > via so-0/0/2.0, label-switched-path R6-to-R1 100048(S=0) *[RSVP/7] 06:17:56, metric 1 > via so-0/0/2.0, label-switched-path R6-to-R1 100064 *[RSVP/7] 00:41:31, metric 1 > via so-0/0/3.0, label-switched-path R1-to-R6 100064(S=0) *[RSVP/7] 00:41:31, metric 1 > via so-0/0/3.0, label-switched-path R1-to-R6

Recipe 14.3 explains how to interpret the entries in the mpls.0 table.

The JUNOS software maintains the mpls.0 table on all routers along the LSP, but only the table on the transit router contains information about the labels being used for LSP signaling. On the egress and egress routers, the mpls.0 table lists only the reserved labels:

aviva@R1> show route table mpls.0 mpls.0: 3 destinations, 3 routes (3 active, 0 holddown, 0 hidden) + = Active Route, - = Last Active, * = Both 0 *[MPLS/0] 07:01:51, metric 1 Receive 1 *[MPLS/0] 07:01:51, metric 1 Receive 2 *[MPLS/0] 07:01:51, metric 1 Receive

Again, this is important to remember when monitoring and troubleshooting LSPs.

Because BGP is also configured on the MPLS routers, when the BGP next hop is the same as the LSP egress address, the JUNOS default behavior uses the LSP for the BGP traffic. You see this in the routing-table entry:

aviva@R1> show route protocol bgp inet.0: 14 destinations, 18 routes (14 active, 0 holddown, 0 hidden) + = Active Route, - = Last Active, * = Both 100.100.6.0/24 *[BGP/170] 4w6d 02:45:37, localpref 100, from 10.0.0.6 AS path: I > via so-0/0/2.0, label-switched-path R1-to-R6

Here, the route to 100.100.6.0, learned by BGP, is the route over the R1-to-R6 LSP.

The JUNOS software installs the active routes from the inet.3 and mpls.0 table into the Routing Engines forwarding table. On the ingress router, the IPv4 forwarding table includes the following routes:

aviva@R1> show route forwarding-table family inet Routing table: inet Internet: Destination Type RtRef Next hop Type Index NhRef Netif 10.0.0.3/32 user 1 ucst 330 6 so-0/0/2.0 10.0.0.6/32 user 1 ucst 330 6 so-0/0/2.0 100.100.6.0/24 user 0 indr 262142 2 Push 100064 so-0/0/2.0

The destinations to the transit and egress routers, 10.0.0.3 and 10.0.0.6, show up simply as unicast routes. The destination 100.100.6.0, learned from BGP and by using the LSP, shows as type indr (indirect) and you see the label (100064) and label operation (Push).

On the transit router, the MPLS forwarding table lists the labels used to forward the MPLS packets:

aviva@R3> show route forwarding-table family mpls Routing table: mpls MPLS: Destination Type RtRef Next hop Type Index NhRef Netif default perm 0 dscd 28 1 0 user 0 recv 27 3 1 user 0 recv 27 3 2 user 0 recv 27 3 100048 user 0 Pop so-0/0/2.0 100048(S=0) user 0 Pop so-0/0/2.0 100064 user 0 Pop so-0/0/3.0 100064(S=0) user 0 Pop so-0/0/3.0

These labels match what you see in the show route mpls.0 output on the transit router. These labels are installed into the Packet Forwarding Engines forwarding table:

aviva@R3> show pfe route mpls MPLS Route Table 0, MPLS.0, 0x0: Destination Type ID NhRef ----------------------- -------- ----- ----- default Discard 28 1 0 Receive 27 3 1 Receive 27 3 2 Receive 27 3 100048 Unicast 336 1 so-0/0/2.0 100048(S=0) Unicast 337 1 so-0/0/2.0 100064 Unicast 334 1 so-0/0/3.0 100064(S=0) Unicast 335 1 so-0/0/3.0

On the ingress and egress routers, the output of the show route forwarding-table family mpls and show pfe route mpls commands on the ingress and egress route lists only the reserved labels.

See Also

Recipes 8.1 and 14.3