Juniper MX Series

MX Trio CoS Defaults

Junos software comes with a set of default CoS settings that are designed to ensure that both transit and control plane traffic is properly classified and forwarded. This means all Juniper boxes are IP CoS enabled, albeit at a low level of functionality, right out of the box, so to speak. You will want to modify these defaults to tailor behavior, gain support for additional forwarding classes, and to ensure consistent classification and header rewrite operations throughout your network. A summary of default CoS characteristics includes the following:

Support for two forwarding classes (BE and NC) and implements for an IP precedence-style BA classifier that maps network control into queue 3 while all other traffic is placed into queue 0 as BE.

A scheduler is placed into effect on all interfaces that allocates 95% of the bandwidth to queue 0 and the remaining 5% to queue 3. Both of the queues are low-priority, which guarantees no starvation in any platform.

A default WRED profile with a single loss point is placed into effect. The 100% drop at 100% fill setting effectively disables WRED.

No IP packet rewrite is performed with a default CoS configuration. Packets are sent with the same markers as when they were received.

No MPLS EXP or IEEE802.1p rewrites. The former is a departure from CoS defaults on M/T series platforms, which have a default EXP rewrite rule in effect that sets EXP based on queue number (0 to 3) and PLP.

Per port scheduling is enabled, no shaping ...