Example of Packet Flow on MX Series 5G Universal Routing Platforms
MX Series routers, especially the MX960 Universal Routing Platform, have several features that differ from the usual CoS features in the Junos OS.
The MX960 router allows fixed classification of traffic. All packets on a logical interface can be put into the same forwarding class. For example:
[edit class-of-service interfaces ge-1/0/0 unit 0] user@host#set 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. 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.
[edit class-of-service interfaces ge-0/0/0 unit 0] user@host#set classifiers ieee-802.1 DOT1P-BA-1 user@host#set classifiers inet-precedence IPPRCE-BA-1
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] user@host#set unit 0 classifiers ieee-802.1 DOT1-BA-1 vlan-tag inner user@host#set unit 1 classifiers ieee-802.1 DOT1-BA-1 vlan-tag outer
The example above does not apply to single-tagged packets. The following example shows how to configure the classifier on single-tagged interfaces:
[edit class-of-service interfaces ge-0/0/0] user@host#set unit 0 classifiers ieee-802.1 DOT1-BA-1
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:
[edit firewall family inet] user@host# set term 1 from destination-address 198.51.100.100/32 user@host# set term 1 then dscp af21 user@host# set term 2 then accept
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.