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Example of Packet Flow on MX Series Ethernet Services Routers

MX Series routers, especially the MX960 Ethernet Services Router, have several features that differ from the usual CoS features in the JUNOS Software.

The MX960 router allows fixed classification of traffic. All packets on a logical interface can be put into the same forwarding class:

[edit interfaces ge-1/0/0 unit 0]forwarding-class af;

As on other routers, the MX Series routers allow BA classification, the classifying of packets into different forwarding classes (up to eight) based on a value in the packet header. However, MX Series routers allow a mixture of BA classifiers (IEEE 802.1p and others) for logical interfaces on the same port, as shown in the following example:

[edit class-of-service interfaces ge-0/0/0 unit 0]classifiers {inet-precedence IPPRCE-BA-1;ieee-802.1 DOT1P-BA-1;}

In this case, the IEEE classifier is applied to Layer 2 traffic and the Internet precedence classifier is applied to Layer 3 (IP) traffic. The IEEE classifier can also perform BA classification based on the bits of either the inner or outer VLAN tag on a dual-tagged logical interface, as shown in the following example:

[edit class-of-service interfaces ge-0/0/0]unit 0 {classifiers {ieee-802.1 DOT1-BA-1 {vlan-tag inner;}}}unit 1 {classifiers {ieee-802.1 DOT1-BA-1 {vlan-tag outer;}}}

The default action is based on the outer VLAN tag’s IEEE precedence bits.

As on other routers, the BA classification can be overridden with a multifield classifier in the action part of a firewall filter. Rewrites are handled as on other routers, but MX Series routers support classifications and rewrites for aggregated Ethernet (ae-) logical interfaces.

On MX Series routers, the 64 classifier limit is a theoretical upper limit. In practice, you cannot configure 64 classifiers. Three values are used internally by the default IP precedence, IPv6, and EXP classifiers. Two other classifiers are used for forwarding class and queue operations. This leaves 59 classifiers for configuration purposes. If you configure Differentiated Services code point (DSCP) rewrites for MPLS, the maximum number of classifiers you can configure is less than 59.

On MX Series routers, IEEE 802.1 classifier bit rewrites are determined by forwarding class and packet priority, not by queue number and packet priority as on other routers.

Published: 2010-04-15

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