Cisco IOS Cookbook, 2nd Edition

Tagging DLSw Packets for QoS

Problem

You want to set the Type of Service (TOS) field in DLSw packets to ensure that they get preferential treatment in the network.

Solution

In many organizations, the SNA traffic that is encapsulated in DLSw is considered both mission critical and time sensitive. So these organizations don’t want lower priority traffic to interfere with it. The simplest way to accomplish this is to tag these high priority packets using the standard IP Precedence field:

Router-A#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router-A(config)#ip local policy route-map dlswroutemap
Router-A(config)#ip route-cache policy
Router-A(config)#access-list 101 permit tcp any any eq 2065
Router-A(config)#access-list 101 permit tcp any eq 2065 any
Router-A(config)#access-list 101 permit tcp any any eq 2067
Router-A(config)#access-list 101 permit tcp any eq 2067 any
Router-A(config)#route-map dlswroutemap permit 10
Router-A(config-route-map)#match ip address 101
Router-A(config-route-map)#set ip precedence flash-override
Router-A(config-route-map)#exit
Router-A(config)#end
Router-A#

Discussion

The most important concept here is the idea that you should set the priority of a packet at the point where it enters the network. In this case, the DLSw packet is actually created by the router, so this is the perfect place to tag it. Then every other router in the network can simply react appropriately to this priority tag without having to look deeply into the ...