The router can also play a part in determining which traffic is more or less important on the
Frame Relay network. The Discard Eligibility list (frame-relay de-list global command)
and Discard Eligibility group (frame-relay de-group interface command) give the router the
capability to set the Discard Eligibility bit on a frame.
Consider a company that notices an increased number of dropped frames on the Frame Relay
network. They determine that the primary cause is an increase in the amount of AppleTalk traffic
across the Frame Relay network. The additional traffic has impaired the performance of missioncritical
traffic.
To have the router turn on the DE bit for AppleTalk traffic, thereby dropping the noncritical
AppleTalk traffic before any other traffic, use the frame-relay de-list command. Here is an
example of how to configure a router to do this:
RouterA#config t
RouterA(config)#frame-relay de-list 1 protocol appletalk
RouterA(config)#interface serial0
RouterA(config-if)#frame-relay de-group 1 100
In this example, the frame-relay de-list command uses a list number of 1 and a protocol
of AppleTalk. The list number of 1 is then applied to the interface connected to the Frame Relay
network with the frame-relay de-group command for a specified DLCI, in this case 100.
You could also use an AppleTalk access list (600–699) to define which Apple-
Talk traffic is set with the DE bit.
The modified router configuration looks like this:
RouterA#show running-config
Building configuration...
Current configuration:
!
version 11.2
!
hostname RouterA
!
appletalk routing
frame-relay de-list 1 protocol appletalk
!
interface Serial0
ip address 192.168.1.1 255.255.255.0
encapsulation frame-relay
appletalk address 8.202
appletalk zone Sybex
frame-relay de-group 1 100
frame-relay map appletalk 8.201 100 broadcast
frame-relay map ip 192.168.1.2 100 broadcast
!
end
RouterA#
The Frame Relay DE list will match AppleTalk frames. The frame-relay de-group command
binds the DE list to the interface. In the event of congestion, these two packet types are
much more likely to be dropped than mission-critical traffic. The 100 at the end of the framerelay
de-group command specifies to use the list on DLCI 100.