Frame-relay Discard Eligibility Bit (DE)
What is the DE bit ?
The DE bit is used to indicate that the frame has a lower importance than other frames and should be dropped first if the network experienced congestion.
How to set the DE bit?
We can use a simple network to test our configuration. R1 is connected via frame-relay to R2
Method1: Frame-relay de-list command
R1 Configuration
R1(config)#access-list 1 permit 1.1.1.1 !-- packets sourced from 1.1.1.1 with size > 500 will have DE bit set R1(config)#frame-relay de-list 1 protocol ip list 1 R1(config)#frame-relay de-list 1 protocol ip gt 500 !-- assign the DE list to the DLCI R1(config-if)#int s1/0 R1(config-if)#frame-relay de-group 1 102
Verification and troubleshooting:
!-- Before sending any frames with DE bit set R1#show frame-relay pvc 102 PVC Statistics for interface Serial1/0 (Frame Relay DTE) DLCI = 102, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial1/0 input pkts 14 output pkts 13 in bytes 1282 out bytes 1226 dropped pkts 0 in pkts dropped 0 out pkts dropped 0 out bytes dropped 0 in FECN pkts 0 in BECN pkts 0 out FECN pkts 0 out BECN pkts 0 in DE pkts 0 out DE pkts 0 out bcast pkts 3 out bcast bytes 186 5 minute input rate 0 bits/sec, 0 packets/sec 5 minute output rate 0 bits/sec, 0 packets/sec pvc create time 00:02:05, last time pvc status changed 00:00:55 !-- ping source is 1.1.1.1 with size greater than 500 as configured in the de-list R1#ping 192.168.123.2 source lo 1 size 1000 Type escape sequence to abort. Sending 5, 1000-byte ICMP Echos to 192.168.123.2, timeout is 2 seconds: Packet sent with a source address of 1.1.1.1 !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 44/107/184 ms R1#show frame-relay pvc 102 PVC Statistics for interface Serial1/0 (Frame Relay DTE) DLCI = 102, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial1/0 input pkts 25 output pkts 24 in bytes 6758 out bytes 6702 dropped pkts 0 in pkts dropped 0 out pkts dropped 0 out bytes dropped 0 in FECN pkts 0 in BECN pkts 0 out FECN pkts 0 out BECN pkts 0 in DE pkts 0 out DE pkts 5 out bcast pkts 9 out bcast bytes 642 5 minute input rate 1000 bits/sec, 1 packets/sec 5 minute output rate 2000 bits/sec, 0 packets/sec pvc create time 00:05:05, last time pvc status changed 00:03:55 !-- R2 output is showing DE packets received from R1 R2#sh frame-relay pvc 201 PVC Statistics for interface Serial1/0 (Frame Relay DTE) DLCI = 201, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial1/0 input pkts 27 output pkts 27 in bytes 6930 out bytes 6952 dropped pkts 0 in pkts dropped 0 out pkts dropped 0 out bytes dropped 0 in FECN pkts 0 in BECN pkts 0 out FECN pkts 0 out BECN pkts 0 in DE pkts 5 out DE pkts 0 out bcast pkts 12 out bcast bytes 892 5 minute input rate 0 bits/sec, 0 packets/sec 5 minute output rate 0 bits/sec, 0 packets/sec pvc create time 00:06:13, last time pvc status changed 00:06:13
Method2: Using MQC
R1 Configuration
!-- match packets sourced from 1.1.1.1 with size > 500 R1(config)#class-map match-all FRDE R1(config-cmap)#match access-group 1 R1(config-cmap)#match packet length min 500 !-- Set DE bit for matched frames R1(config)#policy-map SETDE R1(config-pmap)#class FRDE R1(config-pmap-c)#set fr-de !-- Assign the Policy map to the interface R1(config)#int s1/0 R1(config-if)#service-policy output SETDE
Verification and troubleshooting:
!-- Before sending any DE frames R1#sh fram pvc 102 PVC Statistics for interface Serial1/0 (Frame Relay DTE) DLCI = 102, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial1/0 input pkts 4 output pkts 2 in bytes 222 out bytes 152 dropped pkts 0 in pkts dropped 0 out pkts dropped 0 out bytes dropped 0 in FECN pkts 0 in BECN pkts 0 out FECN pkts 0 out BECN pkts 0 in DE pkts 0 out DE pkts 0 out bcast pkts 2 out bcast bytes 152 5 minute input rate 0 bits/sec, 0 packets/sec 5 minute output rate 0 bits/sec, 0 packets/sec pvc create time 00:00:58, last time pvc status changed 00:00:58 !-- Generate frames with DE bit set R1#ping 192.168.123.2 source lo 1 size 1000 Type escape sequence to abort. Sending 5, 1000-byte ICMP Echos to 192.168.123.2, timeout is 2 seconds: Packet sent with a source address of 1.1.1.1 !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 28/148/244 ms R1#sh fram pvc 102 PVC Statistics for interface Serial1/0 (Frame Relay DTE) DLCI = 102, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial1/0 input pkts 17 output pkts 15 in bytes 5990 out bytes 5920 dropped pkts 0 in pkts dropped 0 out pkts dropped 0 out bytes dropped 0 in FECN pkts 0 in BECN pkts 0 out FECN pkts 0 out BECN pkts 0 in DE pkts 0 out DE pkts 5 out bcast pkts 5 out bcast bytes 380 5 minute input rate 1000 bits/sec, 1 packets/sec 5 minute output rate 1000 bits/sec, 1 packets/sec pvc create time 00:02:26, last time pvc status changed 00:02:26 R2#sh frame-relay pvc 201 PVC Statistics for interface Serial1/0 (Frame Relay DTE) DLCI = 201, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial1/0 input pkts 6 output pkts 6 in bytes 5096 out bytes 5096 dropped pkts 0 in pkts dropped 0 out pkts dropped 0 out bytes dropped 0 in FECN pkts 0 in BECN pkts 0 out FECN pkts 0 out BECN pkts 0 in DE pkts 5 out DE pkts 0 out bcast pkts 1 out bcast bytes 76 5 minute input rate 2000 bits/sec, 0 packets/sec 5 minute output rate 2000 bits/sec, 0 packets/sec pvc create time 00:18:39, last time pvc status changed 00:01:03
I hope I have been informative in this article, see you in other posts.
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