Configuring Policies for Layer 2 Circuits

You can configure Junos routing policies to control the flow of packets over Layer 2 circuits. This capability allows you to provide different level of service over a set of equal-cost Layer 2 circuits. For example, you can configure a circuit for high-priority traffic, a circuit for average-priority traffic, and a circuit for low-priority traffic. By configuring Layer 2 circuit policies, you can ensure that higher-value traffic has a greater likelihood of reaching its destination.

The following sections explain how to configure Layer 2 circuit policies:

Configuring the Layer 2 Circuit Community

To configure a community for Layer 2 circuits, include the community statement.

community community-name {members [ community-ids ]; }

You can include this statement at the following hierarchy levels:

[edit policy-options]
[edit logical-systems logical-system-name policy-options]

name identifies the community or communities.

community-ids identifies the type of community or extended community:

A normal community uses the following community ID format:
as-number:community-value
as-number is the autonomous system (AS) number of the community member.
community-value is the identifier of the community member. It can be a number from 0 through 65,535.
An extended community uses the following community ID format:
type:administrator:assigned-number
type is the type of target community. The target community identifies the route’s destination.
administrator is either an AS number or an IP version 4 (IPv4) address prefix, depending on the type of community.
assigned-number identifies the local provider.
You also need to configure the community for the Layer 2 circuit interface; see Configuring Interfaces for Layer 2 Circuits.

Configuring the Policy Statement for the Layer 2 Circuit Community

To configure a policy to send community traffic over a specific LSP, include the policy-statement statement:

policy-statement policy-name {term term-name {from community community-name;then {install-nexthop (except | lsp lsp-name | lsp-regex lsp-regular-expression);accept;}}}

You can include this statement at the following hierarchy levels:

[edit policy-options]
[edit logical-systems logical-system-name policy-options]

To prevent the installation of any matching next hops, include the install-nexthop statement with the except option:

install-nexthop except;

You can include this statement at the following hierarchy levels:

[edit policy-options policy-statement policy-name term term-name then]
[edit logical-systems logical-system-name policy-options policy-statement policy-name term term-name then]

To assign traffic from a community to a specific LSP, include the install-nexthop statement with the lsp lsp-name option and the accept statement:

install-nexthop lsp lsp-name;accept;

You can include these statements at the following hierarchy levels:

[edit policy-options policy-statement policy-name term term-name then]
[edit logical-systems logical-system-name policy-options policy-statement policy-name term term-name then]

You can also use a regular expression to select an LSP from a set of similarly named LSPs for the install-nexthop statement. To configure a regular expression, include the install-nexthop statement with the lsp-regex option and the accept statement:

install-nexthop lsp-regex lsp-regular-expression;accept;

You can include these statements at the following hierarchy levels:

[edit policy-options policy-statement policy-name term term-name then]
[edit logical-systems logical-system-name policy-options policy-statement policy-name term term-name then]

Example: Configuring a Policy for a Layer 2 Circuit Community

The following example illustrates how you might configure a regular expression in a Layer 2 circuit policy. You create three LSPs to handle gold-tier traffic from a Layer 2 circuit. The LSPs are named alpha-gold, beta-gold, and delta-gold. You then include the install-nexthop statement with the lsp-regex option with the LSP regular expression .*-gold at the [edit policy-options policy-statement policy-name term term-name then] hierarchy level:

[edit policy-options]policy-statement gold-traffic {term to-gold-LSPs {from community gold;then {install-nexthop lsp-regex .*-gold;accept;}}}

The community gold Layer 2 circuits can now use any of the -gold LSPs. Given equal utilization across the three -gold LSPs, LSP selection is made at random.

You need to apply the policy to the forwarding table. To apply a policy to the forwarding table, configure the export statement at the [edit routing-options forwarding-table] hierarchy level:

[edit routing-options forwarding-table] export policy-name;

Verifying the Layer 2 Circuit Policy Configuration

To verify that you have configured a policy for the Layer 2 circuit, issue the show route table mpls detail command. It should display the community for ingress routes that corresponds to the Layer 2 circuits, as shown by the following example:

user@host> show route table mpls detail

so-1/0/1.0 (1 entry, 1 announced)
*L2VPN  Preference: 7
Next hop: via so-1/0/0.0 weight 1, selected
Label-switched-path to-community-gold
Label operation: Push 100000 Offset: -4
Next hop: via so-1/0/0.0 weight 1
Label-switched-path to-community-silver
Label operation: Push 100000 Offset: -4
Protocol next hop: 10.255.245.45
Push 100000 Offset: -4
Indirect next hop: 85333f0 314
State: <Active Int>
Local AS:   100 
Age: 22 
Task: Common L2 VC
Announcement bits (2): 0-KRT 1-Common L2 VC 
AS path: I
Communities: 100:1

For more information about how to configure routing policies, see the Junos Policy Framework Configuration Guide.