CoS Features and Limitations on MX Series Routers

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

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. In the following example, 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, outer, or transparent VLAN tag on a dual-tagged logical interface, as shown in the following example:

Note:

The example above does not apply to single-tagged packets. The following example shows how to configure the classifier on single-tagged interfaces:

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. MX Series routers also support the use of egress firewall filters for DSCP rewrites for IPv4 and IPv6 packets. For example:

On MX Series routers, the 64 classifier limit is a theoretical upper limit. In practice, you can configure 63 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 58 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 58.

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.

The following scaling and performance parameters apply to MX Series routers:

• 48* classifiers of each type, when subscriber management is enabled

• 32 rewrite tables of each type, when subscriber management is enabled

• Eight queues per port

• 64 WRED profiles

• 100-ms queue buffering for interfaces 1 Gbps and above; 500 ms for all others

• Line-rate CoS features

Note:

*Starting with Junos OS Release 16.1R5, Junos OS Release 17.1R3, Junos OS Release 17.2R2, and Junos OS Release 17.3R2, you can configure up to 48 classifiers per family at the [edit class-of-service classifiers] hierarchy level when subscriber management is enabled. In earlier releases, you could only configure up to 32 classifiers per family.

For more information about MX Series router CoS capabilities, including software configuration, see Configuring Hierarchical Schedulers for CoS and Enhanced Queuing DPC CoS Properties.

For Juniper Networks MX Series 5G Universal Routing Platforms, the following restrictions apply:

• You can only use multifield classifiers (but not BA classifiers) for IPv4 DSCP bits for virtual private LAN service (VPLS).

• You cannot use BA classifiers for IPv4 DSCP bits for Layer 2 VPNs.

• You cannot use BA classifiers for IPv6 DSCP bits for VPLS.

• You cannot use BA classifiers for IPv6 DSCP bits for Layer 2 VPNs.

On MX Series routers, you can apply classifiers or rewrite rules to an integrated bridging and routing (IRB) interface at the [edit class-of-service interfaces irb unit logical-unit-number] level of the hierarchy. All types of classifiers and rewrite rules are allowed. These classifiers and rewrite rules are independent of others configured on an MX Series router.

For IQ PICs, you can only configure one IEEE 802.1 rewrite rule on a physical port. All logical ports (units) on that physical port should apply the same IEEE 802.1 rewrite rule.

The IRB classifiers and rewrite rules are applied only to the “routed” packets. For logical interfaces that are part of a bridge domain, only IEEE classifiers and IEEE rewrite rules are allowed. Only the listed options are available for rewrite rules on an IRB.

For dual-tagged bridge domain logical interfaces, you can configure classification based on the inner or outer VLAN tag’s IEEE 802.1p bits using the vlan-tag statement with the inner or outer option:

Also, for dual-tagged bridge domain logical interfaces, you can configure rewrite rules to rewrite the outer or both outer and inner VLAN tag’s IEEE 802.1p bits using the vlan-tag statement with the outer or outer-and-inner option: