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Understanding Queuing and Marking of Host Outbound Traffic

This topic covers the following information:

Host Outbound Traffic Overview

Host outbound traffic, also called locally generated traffic, consists of traffic generated by the Routing Engine and traffic generated by the distributed protocol handler.

Routing Engine Sourced Traffic

Traffic sent from the Routing Engine includes control plane packets such as OSPF Hello packets, ICMP echo reply (ping) packets, and TCP-related packets such as BGP and LDP control packets.

Distributed Protocol Handler Traffic

Distributed protocol handler traffic refers to traffic from the router’s periodic packet management (PPM) process when it runs sessions distributed to the Packet Forwarding Engine (the default mode) in addition to the Routing Engine. The PPM process is responsible for periodic transmission of protocol Hello or other keepalive packets on behalf of its various client processes, such as Bidirectional Forwarding Detection (BFD) Protocol or Link Aggregation Control Protocol (LACP), and it also receives packets on behalf of client processes. In addition, PPM handles time-sensitive periodic processing and performs such tasks as sending process-specific packets and gathering statistics. By default, PPM sessions on the Routing Engine run distributed on the Packet Forwarding Engine, and this enables client processes to run on the Packet Forwarding Engine.

Note:

For interfaces on MX80 routers, LACP control traffic is sent through the Routing Engine rather than through the Packet Forwarding Engine.

Distributed protocol handler traffic includes both IP (Layer 3) traffic such as BFD keepalivemessages and non-IP (Layer 2) traffic such as LACP control traffic on aggregated Ethernet.

Default Queuing and Marking of Host Outbound Traffic

By default, the router assigns host outbound traffic to the best-effort forwarding class (which maps to queue 0) or to the network-control forwarding class (which maps to queue 3) based on protocol. For more information, see Default Routing Engine Protocol Queue Assignments.

By default, the router marks the type of service (ToS) field of Layer 3 packets in the host outbound traffic flow with DifffServ code point (DSCP) bits 000000 (which correlate with the best-effort forwarding class). The router does not remark Layer 2 traffic such as LACP control traffic on aggregated Ethernet. For more information, see Default DSCP and DSCP IPv6 Classifiers.

Configured Queuing and Marking of Host Outbound Traffic

You can configure a nondefault forwarding class and DSCP bits that the router uses to queue and remark host outbound traffic. These configuration settings apply to the following types of traffic:

  • Packets generated by the Routing Engine

  • Distributed protocol handler traffic for egress interfaces hosted on MX Series routers, M120 routers, and Enhanced III FPCs in M320 routers.

To change these default settings, include the forwarding-class class-name statement and the dscp-code-point value statement at the [edit class-of-service host-outbound-traffic] hierarchy level. This feature does not affect transit traffic or incoming traffic.

The configured forwarding class override applies to all packets relating to Layer 2 protocols, Layer 3 protocols, and all application-level traffic (such as FTP or ping operations). The configured DSCP bits override value does not apply to MPLS EXP bits or IEEE 802.1p bits, however.

Configured Queuing and Marking of Outbound Routing Engine Traffic Only

To configure a nondefault forwarding class and DSCP bits that the router uses to queue and remark traffic generated by the Routing Engine only, attach an IPv4 firewall filter to the output of the router’s loopback address. Use the forwarding-class and dscp filter actions to specify override values.

This feature overrides the host-outbound-traffic settings for the Routing Engine output traffic only.