Example: Configuring MPLS Inter-AS Link-Node Protection

Requirements

No special configuration beyond device initialization is required before configuring this example.

Overview

In Figure 1. autonomous system border routers (ASBRs) run external BGP (EBGP) to ASBRs in another autonomous system (AS) to exchange labels for /32 IPv4 routes. Inside the ASs, internal BGP (IBGP) propagates the routes to provider edge (PE) devices.

If the link from Device ASBR3 to Device ASBR1 goes down, until ASBR3 reinstalls the new next hop, all traffic going toward AS 64510 from AS 64511 through the ASBR3-ASBR1 link is dropped.

This example shows how to achieve fast traffic restoration by configuring Device ASBR3 to preprogram a backup path through Device ASBR2.

Note: This solution does not handle the Device P3 to Device ASBR3 failure. Nor does it handle a failure on Device ASBR3 for traffic going toward AS 645111 from AS 64510 through the ASBR3-ASBR1 link. This traffic is dropped.

Figure 1: MPLS Inter-AS Link-Node Protection Example Topology

CLI Quick Configuration shows the configuration for all of the devices in Figure 1.

The section Step-by-Step Procedure describes the steps on Device ASBR3.

Configuration

CLI Quick Configuration

To quickly configure this 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 router interfaces.
   [edit interfaces]user@ASBR3# set fe-1/2/0 unit 0 description to-ASBR1user@ASBR3# set fe-1/2/0 unit 0 family inet address 21.21.21.2/30user@ASBR3# set fe-1/2/0 unit 0 family mpls
   user@ASBR3# set fe-1/2/2 unit 0 description to-P3user@ASBR3# set fe-1/2/2 unit 0 family inet address 22.22.22.1/30user@ASBR3# set fe-1/2/2 unit 0 family mpls
   user@ASBR3# set fe-1/2/1 unit 0 description to-ASBR2user@ASBR3# set fe-1/2/1 unit 0 family inet address 26.26.26.2/30user@ASBR3# set fe-1/2/1 unit 0 family mpls
   user@ASBR3# set lo0 unit 0 family inet address 5.5.5.5/32
2. Configure an interior gateway protocol (IGP), such as OSPF or IS-IS.
   [edit protocols ospf]user@ASBR3# set traffic-engineering
   [edit protocols ospf area 0.0.0.0]user@ASBR3# set interface fe-1/2/2.0user@ASBR3# set interface lo0.0 passiveuser@ASBR3# set interface fe-1/2/1.0
3. Configure the autonomous system (AS) number.
   [edit routing-options]user@ASBR3# set autonomous-system 64511
4. Configure the routing policy.
   [edit policy-options policy-statement To-ASBR1]user@ASBR3# set term 1 from route-filter 7.7.7.7/32 exactuser@ASBR3# set term 1 then acceptuser@ASBR3# set term 2 then reject
   [edit policy-options policy-statement To-ASBR2]user@ASBR3# set term 1 from route-filter 7.7.7.7/32 exactuser@ASBR3# set term 1 then acceptuser@ASBR3# set term 2 then reject
   [edit policy-options policy-statement next-hop-self]user@ASBR3# set then next-hop self
5. Configure the EBGP sessions.
   [edit protocols bgp group To-ASBR1]user@ASBR3# set type externaluser@ASBR3# set family inet labeled-unicast protectionuser@ASBR3# set export To-ASBR1user@ASBR3# set neighbor 21.21.21.1 peer-as 64510
   [edit protocols bgp group To-ASBR2]user@ASBR3# set type externaluser@ASBR3# set family inet labeled-unicast protectionuser@ASBR3# set export To-ASBR2user@ASBR3# set neighbor 26.26.26.1 peer-as 64510
6. Configure the IBGP sessions.
   [edit protocols bgp group To-PE2]user@ASBR3# set type internaluser@ASBR3# set local-address 5.5.5.5user@ASBR3# set family inet unicastuser@ASBR3# set export next-hop-selfuser@ASBR3# set neighbor 7.7.7.7 family inet labeled-unicast
7. Configure MPLS.
   [edit protocols mpls]user@ASBR3# set traffic-engineering bgp-igp-both-ribsuser@ASBR3# set label-switched-path To_PE2 to 7.7.7.7user@ASBR3# set interface lo0.0user@ASBR3# set interface fe-1/2/0.0user@ASBR3# set interface fe-1/2/2.0user@ASBR3# set interface fe-1/2/1.0
8. Configure a signaling protocol.
   [edit protocols rsvp]user@ASBR3# set interface fe-1/2/2.0user@ASBR3# set interface lo0.0user@ASBR3# set interface fe-1/2/0.0user@ASBR3# set interface fe-1/2/1.0

Results

From configuration mode, confirm your configuration by entering the show interfaces, show protocols, show policy-options, and show routing-options, 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 devices, enter commit from configuration mode.

Verification

Confirm that the configuration is working properly.

• Checking the BGP Neighbor Sessions
• Checking the Routes

Checking the BGP Neighbor Sessions

Purpose

Verify that BGP protection is enabled.

Action

Peer: 21.21.21.1+58259 AS 64510 Local: 21.21.21.2+179 AS 64511
  Type: External    State: Established    Flags: <ImportEval Sync>
  Last State: OpenConfirm   Last Event: RecvKeepAlive
  Last Error: None
  Export: [ To-ASBR1 ] 
  Options: <Preference AddressFamily PeerAS Refresh>
  Options: <Protection>
  Address families configured: inet-labeled-unicast
  Holdtime: 90 Preference: 170
  NLRI configured with protection: inet-labeled-unicast
  Number of flaps: 0
  Peer ID: 4.4.4.4         Local ID: 5.5.5.5           Active Holdtime: 90
  Keepalive Interval: 30         Group index: 4    Peer index: 0   
  BFD: disabled, down
  Local Interface: fe-1/2/0.0                       
  NLRI for restart configured on peer: inet-labeled-unicast
  NLRI advertised by peer: inet-labeled-unicast
  NLRI for this session: inet-labeled-unicast
  Peer supports Refresh capability (2)
  Stale routes from peer are kept for: 300
  Peer does not support Restarter functionality
  NLRI that restart is negotiated for: inet-labeled-unicast
  NLRI of received end-of-rib markers: inet-labeled-unicast
  NLRI of all end-of-rib markers sent: inet-labeled-unicast
  Peer supports 4 byte AS extension (peer-as 64510)
  Peer does not support Addpath
  Table inet.0 Bit: 10001
    RIB State: BGP restart is complete
    Send state: in sync
    Active prefixes:              2
    Received prefixes:            1
    Accepted prefixes:            1
    Suppressed due to damping:    0
    Advertised prefixes:          1
  Last traffic (seconds): Received 7    Sent 20   Checked 32  
  Input messages:  Total 170    Updates 2       Refreshes 0     Octets 3326
  Output messages: Total 167    Updates 1       Refreshes 0     Octets 3288
  Output Queue[0]: 0

Peer: 26.26.26.1+61072 AS 64510 Local: 26.26.26.2+179 AS 64511
  Type: External    State: Established    Flags: <ImportEval Sync>
  Last State: OpenConfirm   Last Event: RecvKeepAlive
  Last Error: None
  Export: [ To-ASBR2 ] 
  Options: <Preference AddressFamily PeerAS Refresh>
  Options: <Protection>
  Address families configured: inet-labeled-unicast
  Holdtime: 90 Preference: 170
  NLRI configured with protection: inet-labeled-unicast
  Number of flaps: 0
  Peer ID: 9.9.9.9         Local ID: 5.5.5.5           Active Holdtime: 90
  Keepalive Interval: 30         Group index: 5    Peer index: 0   
  BFD: disabled, down
  Local Interface: fe-1/2/1.0                      
  NLRI for restart configured on peer: inet-labeled-unicast
  NLRI advertised by peer: inet-labeled-unicast
  NLRI for this session: inet-labeled-unicast
  Peer supports Refresh capability (2)
  Stale routes from peer are kept for: 300
  Peer does not support Restarter functionality
  NLRI that restart is negotiated for: inet-labeled-unicast
  NLRI of received end-of-rib markers: inet-labeled-unicast
  NLRI of all end-of-rib markers sent: inet-labeled-unicast
  Peer supports 4 byte AS extension (peer-as 64510)
  Peer does not support Addpath
  Table inet.0 Bit: 10002
    RIB State: BGP restart is complete
    Send state: in sync
    Active prefixes:              1
    Received prefixes:            1
    Accepted prefixes:            1
    Suppressed due to damping:    0
    Advertised prefixes:          1
  Last traffic (seconds): Received 21   Sent 9    Checked 42  
  Input messages:  Total 170    Updates 2       Refreshes 0     Octets 3326
  Output messages: Total 168    Updates 1       Refreshes 0     Octets 3307
  Output Queue[0]: 0

Meaning

The output shows that the Protection option is enabled for the EBGP peers, Device ASBR1 and Device ASBR2.

This is also shown with the NLRI configured with protection: inet-labeled-unicast screen output.

Checking the Routes

Purpose

Make sure that the backup path is installed in the routing table.

Action

inet.0: 12 destinations, 14 routes (12 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

2.2.2.2/32         *[BGP/170] 01:36:25, MED 2, localpref 100
                      AS path: 64510 I, validation-state: unverified
                    > to 21.21.21.1 via fe-1/2/0.0, Push 299824
                      to 26.26.26.1 via fe-1/2/1.0, Push 299808
                    [BGP/170] 01:36:25, MED 2, localpref 100
                      AS path: 64510 I, validation-state: unverified
                    > to 26.26.26.1 via fe-1/2/1.0, Push 299808

Meaning

The show route command displays active as well as backup paths to Device PE1.