Setting Ingress DSCP Bits for Multicast Traffic over Layer 3 VPNs

By default, the DSCP bits on outer IP headers arriving at an ingress PE router using generic routing encapsulation (GRE) are not set for multicast traffic sent over an Layer 3 virtual private network (VPN) provider network. However, you can configure a type-of-service (ToS) rewrite rule so the router sets the DSCP bits of GRE packets to be consistent with the service provider’s overall core network CoS policy. The bits are set at the core-facing interface of the ingress provider edge (PE) router. For more information about rewriting IP header bits, see Rewriting Packet Headers to Ensure Forwarding Behavior.

This section describes this configuration from a CoS perspective. The examples are not complete multicast or VPN configurations. For more information about multicast, see the Junos OS Multicast Protocols User Guide. For more information about Layer 3 VPNs, see the Junos OS VPNs Library for Routing Devices.

To configure the rewrite rules on the core-facing interface of the ingress PE, include the rewrite-rules statement at the [edit class-of-service] hierarchy level. You apply the rule to the proper ingress interface at the [edit class-of-service interfaces] hierarchy level to complete the configuration. This ingress DSCP rewrite is independent of classifiers placed on ingress traffic arriving on the customer-facing interface of the PE router.

The rewrite rules are applied to all unicast packets and multicast groups. You cannot configure different rewrite rules for different multicast groups. The use of DSCPv6 bits is not supported because IPv6 multicast is not supported. You can configure another rewrite rule for the EXP bits on MPLS CE-CE unicast traffic.

This example defines a rewrite rule called dscp-rule that establishes a value of 000000 for best-effort traffic. The rule is applied to the outgoing, core-facing PE interface ge-2/3/0.