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Example: Excluding SRLG Links Completely for the Secondary LSP

Requirements

• M Series, MX Series, or T Series devices
• Junos OS Release 11.4 or later running on all the devices

Overview

For critical links where it is imperative to keep the secondary and primary paths completely disjoint from any common SRLG, you can optionally configure the exclude-srlg statement at the [edit protocols mpls] or [edit protocols mpls label-switched-path path-name] hierarchy levels. For logical systems, you configure the exclude-srlg statement at the edit logical-systems protocols mpls[edit logical-systems logical-system-name protocols mpls label-switched-path path-name] hierarchy level.

If exclude-srlg is configured, the Constrained Shortest Path First (CSPF) algorithm excludes any link belonging to the set of SRLGs in the primary path. If exclude-srlg is not configured, and if a link belongs to the set of SRLGs in the primary path, CSPF adds the SRLG cost to the metric, but still accepts the link for computing the path.

In this example, PE1 is the ingress router and PE2 is the egress router. P1, P2, and P3, P4, and P5 are transit routers. OSPF is configured on all the routers as the interior gateway protocol (IGP). SRLG is configured on all seven routers. The primary path includes SRLG srlg-a. For the standby secondary path, the link P2>PE2 belongs to SRLG srlg-a. Because exclude-srlg is configured, CSPF rejects link P2>PE2 as the link belongs to the SRLG srlg-a. Therefore, the computed standby secondary path is PE1>P3>P4>P5>PE2.

Configuration

CLI Quick Configuration

To quickly configure this section of the example, copy the following commands, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, and then copy and paste the commands into the CLI at the [edit] hierarchy level.

Step-by-Step Procedure

1. Configure the device interfaces.
   [edit interfaces]user@PE1# set ge-0/0/1 unit 0 family inet address 192.168.12.1/24user@PE1# set ge-0/0/1 unit 0 family mplsuser@PE1# set ge-0/0/2 unit 0 family inet address 192.168.13.1/24user@PE1# set ge-0/0/2 unit 0 family mplsuser@PE1# set ge-0/0/3 unit 0 family inet address 192.168.14.1/24user@PE1# set ge-0/0/3 unit 0 family mplsuser@PE1# set lo0 unit 0 family inet address 10.255.0.1/32
2. Configure OSPF on the interfaces.
   [edit protocols ospf]user@PE1# set traffic-engineeringuser@PE1# set area 0.0.0.0 interface ge-0/0/1.0user@PE1# set area 0.0.0.0 interface ge-0/0/2.0user@PE1# set area 0.0.0.0 interface ge-0/0/3.0user@PE1# set area 0.0.0.0 interface lo0.0
3. Configure the SRLG definitions.
   [edit routing-options]user@PE1# set routing-options srlg srlg-a srlg-value 101
4. Configure MPLS and the LSPs.
   [edit protocols mpls]user@PE1# set interface ge-0/0/1.0user@PE1# set interface ge-0/0/2.0user@PE1# set interface ge-0/0/3.0user@PE1# set optimize-timer 120user@PE1# set exclude-srlguser@PE1# set label-switched-path pe1-pe2 to 10.255.0.7user@PE1# set label-switched-path pe1-pe2 primary via-p1user@PE1# set label-switched-path pe1-pe2 secondary path2 standbyuser@PE1# set path via-p1 10.255.0.2 strictuser@PE1# set path path2
5. Configure the exclude-srlg statement to forcibly keep the links for the secondary path completely disjoint from the primary LSP path.
   user@PE1 set protocols mpls exclude-srlg
6. Enable RSVP on the interfaces.
   [edit protocols rsvp]user@PE1# set interface ge-0/0/1.0user@PE1# set interface ge-0/0/2.0user@PE1# set interface ge-0/0/3.0

Results

From configuration mode, confirm your configuration by entering the show interfaces, show protocols ospf, show routing-options, show protocols mpls, and show protocols rsvp commands. If the output does not display the intended configuration, repeat the instructions in this example to correct the configuration.

If you are done configuring the device, enter commit from configuration mode.

Note: Repeat this procedure for every Juniper Networks router in the IGP domain, after modifying the appropriate interface names, addresses, and any other parameters for each router.

Verification

Confirm that the configuration is working properly.

Verifying the Secondary Path Link for the LSP

Purpose

Verify that the link for the secondary path is completely disjoint from the primary path.

Action

Ingress LSP: 1 sessions

10.255.0.7
  From: 10.255.0.1, State: Up, ActiveRoute: 0, LSPname: pe1-pe2
  ActivePath: via-p1 (primary)
  LSPtype: Static Configured
  LoadBalance: Random
  Encoding type: Packet, Switching type: Packet, GPID: IPv4
 *Primary   via-p1           State: Up
    Priorities: 7 0
    OptimizeTimer: 120
    SmartOptimizeTimer: 180
    SRLG: srlg-a
    Reoptimization in 77 second(s).
    Computed ERO (S [L] denotes strict [loose] hops): (CSPF metric: 2)
 192.168.12.2 S 192.168.27.7 S
    Received RRO (ProtectionFlag 1=Available 2=InUse 4=B/W 8=Node 10=SoftPreempt 20=Node-ID):
          192.168.12.2 192.168.27.7
  Standby   path2            State: Up
    Priorities: 7 0
    OptimizeTimer: 120
    SmartOptimizeTimer: 180
    Reoptimization in 106 second(s).
    Computed ERO (S [L] denotes strict [loose] hops): (CSPF metric: 4)
 192.168.14.4 S 192.168.45.5 S 192.168.56.6 S 192.168.67.7 S
    Received RRO (ProtectionFlag 1=Available 2=InUse 4=B/W 8=Node 10=SoftPreempt 20=Node-ID):
          192.168.14.4 192.168.45.5 192.168.56.6 192.168.67.7
Total 1 displayed, Up 1, Down 0

Link P1->PE2: SRLG srlg-a
Link P2->PE2: SRLG srlg-a

Primary path:      PE1-P1-PE2       (CSPF metric: 2)
Standby secondary: PE1-P3-P4-P5-PE2 (CSPF metric: 4)

Meaning

Primary path includes SRLG srlg-a. For the standby secondary path, the link P2>PE2 belongs to SRLG srlg-a. CSPF rejects link P2>PE2 because the link belongs to the SRLG srlg-a.