Monday, April 13, 2009

Frame Relay - Broadcast Queue

The Cisco IOS creates a broadcast queue for interfaces running frame-relay. This queue performs 2 functions: it ensures routing traffic is dealt with as a priority but it also limits the bandwidth that can be consumed by such traffic.

When an interface has many DLCIs the overhead of replicating routing traffic can be significant.

The interface has the following default settings

size: 64 packets
byte-rate: 256000 bytes per second
packet-rate: 36 packets per second

To change the settings the following interface command can be used

frame-relay broadcast-queue {x} {y} {z}

The following example specifies a broadcast queue to hold 80 packets, to have a maximum byte transmission rate of 240000 bytes per second, and to have a maximum packet transmission rate of 160 packets per second:

frame-relay broadcast-queue 80 240000 160

The actual limit in any second is the first rate limit that is reached I.e. byte or packet.

To examine how the broadcast queue is performing simply use the show interface command:-

Rack1R1#show int s2/0
Serial2/0 is up, line protocol is up
{… output omitted …..}
Broadcast queue 0/64, broadcasts sent/dropped 83/0, interface broadcasts 86

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