Supported Platforms
Configuring a Label Allocation and Substitution Policy for VPNs
You can control label-advertisements on MPLS ingress and AS border routers (ASBRs). Labels can be assigned on a per–next-hop (by default) or on a per-table basis (by configuring the vrf-table-label statement). This choice affects all routes of a given routing instance. You can also configure a policy to generate labels on a per-route basis by specifying a label allocation policy.
To specify a label allocation policy for the routing instance, configure the label statement and specify a label allocation policy using the allocation option:
You can configure this statement at the following hierarchy levels:
- [edit routing-instances routing-instance-name routing-options]
- [edit logical-systems logical-system-name routing-instances routing-instance-name routing-options]
To configure the label allocation policy, include the label-allocation statement at the [edit policy-options policy-statement policy-statement-name term term-name then] hierarchy level. You can configure the label allocation mode as either per-nexthop or per-table.
For a VPN option B ASBR, labels for transit routes are substituted for a local virtual tunnel label or vrf-table-label label. When a VRF table is configured on the ASBR (this type of configuration is uncommon for the option B model), the ASBR does not generate MPLS swap or swap and push state for transit routes. Instead, the ASBR re-advertises a local virtual-tunnel or vrf-table-label label and forwards that transit traffic based on IP forwarding tables. The label substitution helps to conserve labels on Juniper Networks routers.
However, this type of label substitution effectively breaks the MPLS forwarding path, which becomes visible when using an MPLS OAM command such as LSP ping. You can configure the way in which labels are substituted on a per-route basis by specifying a label substitution policy.
To specify a label substitution policy for the routing instance, configure the label statement and specify a label substitution policy using the substitution option:
You can configure this statement at the following hierarchy levels:
- [edit routing-instances routing-instance-name routing-options]
- [edit logical-systems logical-system-name routing-instances routing-instance-name routing-options]
The label substitution policy is used to determine whether or not a label should be substituted on an ASBR router. The results of the policy operation are either accept (label substitution is performed) or reject (label substitution is not performed). The default behavior is accept. The following set command example illustrates how you can configure a reject label substitution policy: set policy-options policy-statement no-label-substitution term default then reject.
