2950 Series Switches

2950 Series Switches
The 2950 switch transmits network traffic in the following fashion: Frames are classified by
assigning priority-indexed class of service (CoS) values to them and giving preference to higher
priority traffic such as telephone calls.
Each transmit port has a default normal-priority transmit queue and may be configured
with up to four additional high-priority transmit queues. Frames in the high-priority queue
are forwarded before frames in the normal-priority queue. Frames are forwarded to queues
dependent upon the defined priority-to-queue mapping. Queues can be emptied using strict
priority queuing or weighted round-robin queuing as desired.
If your 2950 switch is running the standard software image, there are some restrictions on
what you can configure. In fact, you are limited to configuring the CoS priorities and the WRR
settings. To do this, use the wrr-queue cos-map global command to establish the queues, and
the wrr-queue bandwidth statement to set the queue thresholds if needed:
Terry_2950#conf t
Terry_2950(config)#wrr-queue ?
bandwidth Configure WRR bandwidth
cos-map Configure cos-map for a queue
Terry_2950(config)#wrr-queue cos-map ?
<1-4> enter cos-map queue id (1-4)
Terry_2950(config)#wrr-queue cos-map 1 ?
<0-7> cos values separated by spaces (up to 8 values total)
Terry_2950(config)#wrr-queue cos-map 1 0 1
Terry_2950(config)#wrr-queue cos-map 2 2 3
Terry_2950(config)#wrr-queue cos-map 3 4 5
Terry_2950(config)#wrr-queue cos-map 4 6 7
Terry_2950(config)#wrr-queue bandwidth 10 20 30 40
Terry_2950(config)#
Terry_2950#
If your switch has the enhanced image, you will be able to carry out classification and marking
in addition to being able to perform DSCP mapping.
The following example will identify a particular traffic stream, identified by MAN address,
and associate a DiffServe value with it. First, we need to establish the way that we will identify
the traffic to be classified. Use the class-maps name global command to define the match
criteria when classifying traffic:
Terry_2950(config)# class-map terry1
Terry_2950(config-cmap)# match access-group 701
Terry_2950(config-cmap)# exit
There is a selection of match options inside a class map:
Terry_2950(config-cmap)#match ?
access-group access group
input-interface Select an input interface to match
mpls Multi Protocol Label Switching values
protocol Protocol
<cr>
In this example, we will use an access list in conjunction with the class-map to clearly identify
the traffic to be classified:
Terry_2950(config)#access-list 701 permit 0011.2345.6789 00aa.1234.5678
Finally, we need to determine what the classification will be. Use the global configuration
command policy-map name to determine the classification criteria to be set for incoming
traffic:
Terry_2950(config)#policy-map macpolicy1
Terry_2950(config-pmap)#class terry1
Terry_2950(config-pmap-c)#set ip dscp 56
Terry_2950(config-pmap-c)#exit
Terry_2950(config)#int fa0/1
Terry_2950(config-if)#service-policy input macpolicy1
For a full explanation of the differences between the standard and enhanced
images available on the 2950 switch range, see Chapter 21, “Catalyst Switch
Technologies.”