Configuring Frame Relay Broadcast Queue

On very large hub-and-spoke Frame Relay networks where several hundreds of branch sites terminate their DLCIs in the central site, it is highly possible to run into performance degradation issues. There is a significant amount of broadcast traffic generated if routing protocol updates or IPX service advertising updates must be replicated on each DLCI at the hub router. The broadcast traffic can consume access-link bandwidth and cause significant latency variation in user traffic; the updates can also consume interface buffers and lead to higher packet loss for both user data and routing updates.

To avoid these problems, Cisco supports a Frame Relay broadcast queue at the interface level to create a special queue for a specified interface to hold broadcast traffic that has been replicated for transmission on multiple DLCIs. The Frame Relay broadcast queue is created independently of other queues with its own buffers and has a configurable size and service rate.

A broadcast queue is given a maximum transmission rate (throughput) limit measured in bytes per second and packets per second. The queue is serviced to ensure that only this maximum is provided. The broadcast queue has priority when transmitting at a rate below the configured maximum and therefore has a guaranteed minimum bandwidth allocation. The two transmission rate limits are intended to avoid flooding the interface with broadcasts. The actual limit in any second is the first rate limit that is reached.

To configure a broadcast queue for a Frame Relay interface, perform the following command, beginning in the interface configuration mode:
Router(config-if)#frame-relay broadcast-queue size byte-rate packet-rate

Example 5-22 shows a configuration example creating a Frame Relay broadcast queue.

Example 5-22. Creating a Frame Relay Broadcast Queue
Router#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#interface serial4/2
Router(config-if)#frame-relay broadcast-queue ?
<1-65535> Queue size for broadcasts, <cr> to set default values
<cr>
Router(config-if)#frame-relay broadcast-queue 20 ?
<1000-8000000> Byte rate per sec. for broadcasts transmission

Router(config-if)#frame-relay broadcast-queue 20 1000 ?
<1-80000> Max. packets/S broadcasts transmission

Router(config-if)#frame-relay broadcast-queue 20 1000 1000 ?
<cr>

Router(config-if)#frame-relay broadcast-queue 20 1000 1000

Popularity: 4% [?]