Example: Configuring Ingress PE Redundancy

This example shows how to configure one PE as part of a backup PE group to enable ingress PE redundancy for multicast traffic streams.

• Requirements
• Overview
• Configuration
• Verification

Requirements

Before you begin:

• Configure the router interfaces. See the Network Interfaces Configuration Guide.
• Configure a full mesh of P2P LSPs between the PEs in the backup group. See the Junos MPLS Applications Configuration Guide.

Overview

This feature provides PE redundancy when P2MP LSPs are configured for multicast distribution. When P2MP LSPs are used for multicast traffic, the PE is a single point of failure. One way to provide redundancy is by broadcasting duplicate streams from multiple PEs, thus doubling the bandwidth requirements for each stream. This feature implements redundancy between two or more PEs by designating a primary and one or more backup PEs for each configured stream. The solution depends on the configuration of a full mesh of P2P LSPs between the primary and backup PEs. These LSPs are configured with Bidirectional Forwarding Detection (BFD) running on top of them. BFD is used on the backup PEs to detect failure on the primary and elect a new designated forwarder for the stream.

A full mesh is required so that each member of the group can make an independent decision about the health of the other PEs and determine the designated forwarder for the group. The key concept in a backup PE group is that of a designated PE. A designated PE is a PE which forwards data on the static route. All other PEs in the backup PE group do not forward any data on the static route. This allows you to have one designated forwarder. If the designated forwarder goes down, another PE takes over as the designated forwarder, thus allowing the traffic flow to continue uninterrupted.

Each PE in the backup PE group makes its own local decision regarding the designated forwarder. Thus there is no inter-PE communication regarding designated forwarder. A PE computes the designated forwarder based on the IP address of all PEs and the connectivity status of other PEs. Connectivity status is determined based on the state of BFD session on the P2P LSP to a PE.

A PE chosen is as the designated forwarder if it satisfies the following conditions:

• The PE is in the UP state. Either it is the local PE, or the BFD session on the P2P LSP to that PE is in the UP state.
• The PE has the lowest IP address among all PEs that are in the UP state.

Because all PEs have P2P LSPs to each other, each PE can determine the UP state of each other PE. Thus all PEs converge to the same designated forwarder.

If the designated forwarder PE goes down, then all other PEs lose connectivity with the designated forwarder, and their BFD session goes down. Consequently, other PEs then choose another designated forwarder. The new forwarder starts forwarding traffic. Thus, the traffic loss is limited to the failure detection time, which is the BFD session detection time.

When a PE that was the designated forwarder goes down and then comes back up, all other PEs recognize this fact, rerun the designated forwarder algorithm, and choose the PE as the designated forwarder. Consequently, the backup designated forwarder stops forwarding traffic. Thus, traffic switches back to the most eligible designated forwarder.

This example includes the following statements:

• associate-backup-pe-groups—Monitors the health of the routing device at the other end of the LSP. You can configure multiple backup PE groups that contain the same routing device’s address. Failure of this LSP indicates to all of these groups that the destination PE routing device is down. So the associate-backup-pe-groups statement is not tied to any specific group but applies to all groups that are monitoring the health of the LSP to the remote address.

  If there are multiple LSPs with the associate-backup-pe-groups statement to the same destination PE, then the local routing device picks the first LSP to that PE for detection purposes.

  We do not recommend configuring multiple LSPs to the same destination. If you do, make sure that the LSP parameters (for example, liveliness detection) are similar in order to avoid false failure notification even when the remote PE is up.

• backup-pe-group—Configures ingress PE redundancy for multicast traffic streams.
• bfd-liveness-detection—Enables BFD for each LSP.
• label-switched-path—Configures an LSP. You must configure a full mesh of P2P LSPs between the primary and backup PEs.

  Note: We recommend that you configure the P2P LSPs with fast reroute and node link protection so that link failures do not result in the LSP failure. For the purpose of PE redundancy, a failure in the P2P LSP is treated as a PE failure; redundancy in the inter-PE path is also encouraged.

• p2mp-lsp-next-hop—Enables you to associate a backup PE group with a static route.
• static—Applies the backup group to a static route on the PE. This makes sure that the static route is active (installed in the forwarding table) when the local PE is the designated forwarder for the configure backup PE group.

Configuration

CLI Quick Configuration

To quickly configure ingress PE redundancy, copy the following commands into a text file, remove any line breaks, and then paste the commands into the CLI.

Step-by-Step Procedure

The following example requires you to navigate various levels in the configuration hierarchy. For information about navigating the CLI, see Modification of the Junos OS Configuration in Junos OS CLI, Release 10.3.

To configure ingress PE redundancy:

1. Configure the multicast settings.

   [edit]user@host# edit routing-options multicast[edit routing-options multicast]user@host# set rpf-check-policy no-rpf[edit routing-options multicast]user@host# set interface fe-1/3/3.0 enable

2. Configure the RPF policy.

   [edit]user@host# edit policy-options policy-statement no-rpf[edit policy-options policy-statement no-rpf]user@host# set from route-filter 225.1.1.1/32 exact[edit policy-options policy-statement no-rpf]user@host# set then reject[edit policy-options policy-statement no-rpf]user@host# exit

3. Configure the backup PE group.

   [edit routing-options multicast]user@host# set backup-pe-group g1 backups 10.255.16.61[edit routing-options multicast]user@host# set backup-pe-group g1 local-address 10.255.16.59[edit routing-options multicast]user@host# exit

4. Configure the static routes for the P2MP LSPs backup PE group.

   [edit]user@host# edit routing-options static[edit routing-options static]user@host# set route 1.1.1.1/32 p2mp-lsp-next-hop p2mp-lsp[edit routing-options static]user@host# set route 1.1.1.1/32 backup-pe-group g1[edit routing-options static]user@host# set route 225.1.1.1/32 p2mp-lsp-next-hop p2mp-lsp[edit routing-options static]user@host# set route 225.1.1.1/32 backup-pe-group g1[edit routing-options static]user@host# exit

5. Configure the MPLS interfaces.

   [edit]user@host# edit protocols mpls[edit protocols mpls]user@host# set interface all [edit protocols mpls]user@host# set interface fxp0.0 disable

6. Configure the LSP to the redundant router.

   [edit protocols mpls]user@host# set label-switched-path backup_PE1 to 10.255.16.61[edit protocols mpls]user@host# set label-switched-path backup_PE1 oam bfd-liveness-detection minimum-interval 500[edit protocols mpls]user@host# set label-switched-path backup_PE1 oam bfd-liveness-detection multiplier 3[edit protocols mpls]user@host# set label-switched-path backup_PE1 associate-backup-pe-groups

7. Configure LSPs to two traffic destinations.

   [edit protocols mpls]user@host# set label-switched-path dest1 to 10.255.16.57[edit protocols mpls]user@host# set label-switched-path dest1 p2mp p2mp-lsp[edit protocols mpls]user@host# set label-switched-path dest2 to 10.255.16.55[edit protocols mpls]user@host# set label-switched-path dest2 p2mp p2mp-lsp[edit protocols mpls]user@host# exit

8. If you are done configuring the device, commit the configuration.

   [edit protocols mpls]user@host# commit

Results

Confirm your configuration by entering the show policy, show protocols, and show routing-options commands.

Verification

To verify the configuration, run the following commands: command.

• show mpls lsp
• show multicast backup-pe-groups
• show multicast rpf

Related Topics

• Example: Configuring RPF Policies