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Enabling Eight Queues on ATM Interfaces


By default, IQ, MPC, and DPC interfaces on M120, T320, T640, T1600, TX Matrix, and TX Matrix Plus routers, and MIC or MPC interfaces on MX Series routers, are restricted to a maximum of four egress queues per interface. You can enable eight egress queues by including the max-queues-per-interface statement at the [edit chassis fpc slot-number pic pic-number] hierarchy level:

The numerical value can be 4 or 8.

If you include the max-queues-per-interface statement, all ports on the PIC use the configured maximum.

When you include the max-queues-per-interface statement and commit the configuration, all physical interfaces on the PIC are deleted and re-added. Also, the PIC is taken offline and then brought back online immediately. You do not need to manually take the PIC offline and online. You should change modes between four queues and eight queues only when there is no active traffic going to the PIC.


When you are considering enabling eight queues on an ATM2 IQ interface, you should note the following:

  • ATM2 IQ interfaces using Layer 2 circuit trunk transport mode support only four CoS queues.

  • ATM2 IQ interfaces with MLPPP encapsulation support only four CoS queues.

  • You can configure only four RED profiles for the eight queues. Thus, queue 0 and queue 4 share a single RED profile, as do queue 1 and queue 5, queue 2 and queue 6, and queue 3 and queue 7. There is no restriction on EPD threshold per queue.

  • The default chassis scheduler allocates resources for queue 0 through queue 3, with 25 percent of the bandwidth allocated to each queue. When you configure the chassis to use more than four queues, you must configure and apply a custom chassis scheduler to override the default. To apply a custom chassis scheduler, include the scheduler-map-chassis statement at the [edit class-of-service interfaces at-fpc/pic/*] hierarchy level. For more information about configuring and applying a custom chassis scheduler, see Applying Scheduler Maps to Chassis-Level Queues.

Example: Enabling Eight Queues on ATM2 IQ Interfaces

In Figure 1, Router A generates IP packets with different IP precedence settings. Router B is an M320 router or a T Series router with two ATM2 IQ interfaces. On Router B, interface at-6/1/0 receives traffic from Router A, while interface at-0/1/0 sends traffic to Router C. This example shows the CoS configuration for Router B.

Figure 1: Example Topology for Router with Eight Queues
Example Topology for Router with Eight

On Router B:

To see the results of this configuration, you can issue the following operational mode commands:

  • show interfaces at-0/1/0 extensive

  • show interfaces queue at-0/1/0

  • show class-of-service forwarding-class