Understanding Class of Service and PBB for MX Series Routers

Class-of-service (CoS) support for PBB enables information to be mapped and carried across a provider backbone bridge. Service information is mapped and carried across the network using three bits of priority code point (PCP) and one bit of drop eligibility indicator (DEI). The PCP and DEI bits are present in the service VLAN (S-VLAN) and the backbone service instance identifier (ISID).

To provide appropriate QoS treatment inside the MX Series router and transport QoS information across the network, it is important to provide capabilities to classify and rewrite (mark) the PCP+DEI from one tag to another.

Behavior aggregate (BA) classification is used to classify a packet into various forwarding classes (FCs) and packet loss priorities (PLPs) based on certain fields of the packet. A VLAN-tagged logical interface can be configured to classify packets based on the PCP and DEI bits using the existing IEEE 802.1p (only PCP) or IEEE 802.1ad (PCP and DEI) classifier.

To classify packets for a VLAN-tagged logical interface based only on the PCP bits, include the ieee-802.1 statement at the [edit class-of-service interfaces interface-name unit logical-unit-number classifiers] hierarchy level. To classify packets based on both PCP and DEI bits, include the ieee-802.1ad statement at the same hierarchy level.

A rewrite rule sets the appropriate CoS bits in the outgoing packet, thus allowing the next downstream device to classify the packet into the appropriate service group. A VLAN-tagged logical interface can be configured to rewrite the PCP and DEI classifier of outgoing packets based on the forwarding class and the loss priority using IEEE 802.1p (PCP) or IEEE 802.1ad (PCP and DEI) rewrite rules.

To rewrite packets for a VLAN-tagged logical interface using the existing IEEE 802.1p (PCP) rewrite rules, include the ieee-802.1 statement at the [edit class-of-service interfaces interface-name unit logical-unit-number rewrite-rules] hierarchy level. To classify packets based on the IEEE 802.1ad (PCP and DEI) rewrite rules, include the ieee-802.1ad statement at the same hierarchy level.

To further support CoS for PBB, new ISID and DEI terms are available when configuring firewall filters. Include terms at the [edit firewall family bridge filter filter-name term term-name] hierarchy level.