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Setting Ingress DSCP Bits for Multicast Traffic over L3 VPNs

By default, the DSCP bits on outer IP headers 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 DCSP bits of GRE packets to be consistent with the service provider’s overall CoS policy. The bits are written at the ingress provider edge (PE) router. For more information about rewriting IP header bits, see Rewriting Packet Header Information.

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 Software Multicast Configuration Guide. For more information about Layer 3 VPNs, see the JUNOS Software VPN Configuration Guide.

To configure the rewrite rules on 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.

The rewrite rules are applied to all unicast packets 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 cannot perform EXP marking in this fashion.

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 PE interface ge-2/3/0.



[edit class-of-service]
rewrite-rules {


dscp dscp-rule {


forwarding-class best-effort {
loss-priority low code-point 000000;
}


}


}

[edit class-of-service interfaces]
ge-2/3/0 {


unit 0 {


rewrite-rules {
dscp dscp-rule;
}


}


}

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