Network Setup for EIGRP Offset List
A positive offset value can be added to the metrics of incoming or outgoing EIGRP routes.
The offset-list {acl-num | acl-name} {in | out} {offset} [intf-type intf-num] EIGRP router subcommand configures an EIGRP offset list. Access list number 0 indicates all access lists. No action will be taken if the offset value is 0. An offset list with an interface type and number is considered extended and takes precedence over a non-extended offset list which is without an interface type and number. When a route entry passes the extended and normal offset lists, the offset of the extended offset list will be in effect and added to the metric for the route entry.
Below shows the route entry learnt from RT2 via EIGRP before implementing any offset list:
RT1#sh ip route 172.16.1.0 Routing entry for 172.16.1.0/24 Known via "eigrp 100", distance 90, metric 30720, type internal Redistributing via eigrp 100 Last update from 10.10.10.2 on FastEthernet0/0, 00:13:36 ago Routing Descriptor Blocks: * 10.10.10.2, from 10.10.10.2, 00:13:36 ago, via FastEthernet0/0 Route metric is 30720, traffic share count is 1 Total delay is 200 microseconds, minimum bandwidth is 100000 Kbit Reliability 255/255, minimum MTU 1500 bytes Loading 1/255, Hops 1 RT1#
The metric and delay has increased by 100 and 3 respectively after an offset list is implemented. It seems that EIGRP offset list alters the delay variable in order to change the EIGRP metric.
RT1#conf t Enter configuration commands, one per line. End with CNTL/Z. RT1(config)#router eigrp 100 RT1(config-router)#offset-list 0 in 100 RT1(config-router)# 00:14:29: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.10.10.2 (FastEthernet0/0) is down: route configuration changed 00:14:30: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.10.10.2 (FastEthernet0/0) is up: new adjacency RT1(config-router)#do sh ip route 172.16.1.0 Routing entry for 172.16.1.0/24 Known via "eigrp 100", distance 90, metric 30820, type internal Redistributing via eigrp 100 Last update from 10.10.10.2 on FastEthernet0/0, 00:00:03 ago Routing Descriptor Blocks: * 10.10.10.2, from 10.10.10.2, 00:00:03 ago, via FastEthernet0/0 Route metric is 30820, traffic share count is 1 Total delay is 203 microseconds, minimum bandwidth is 100000 Kbit Reliability 255/255, minimum MTU 1500 bytes Loading 1/255, Hops 1
Modifying the weights of EIGRP variables on RT1 and RT2 in order to remove the delay variable used for EIGRP metric computation and remove the offset list to restore the original state:
RT1(config-router)#do sh ip prot | in weight EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0 RT1(config-router)# RT1(config-router)#metric weights 0 1 0 0 0 0 RT1(config-router)#no offset-list 0 in 100 RT1(config-router)# RT1(config-router)#do sh ip prot | in weight EIGRP metric weight K1=1, K2=0, K3=0, K4=0, K5=0 RT1(config-router)# ======================================================================== RT2#conf t Enter configuration commands, one per line. End with CNTL/Z. RT2(config)#router eigrp 100 RT2(config-router)#metric weights 0 1 0 0 0 0 RT2(config-router)# RT2(config-router)#do sh ip prot | in weight EIGRP metric weight K1=1, K2=0, K3=0, K4=0, K5=0 RT2(config-router)# ======================================================================== RT1(config-router)#do sh ip route 172.16.1.0 Routing entry for 172.16.1.0/24 Known via "eigrp 100", distance 90, metric 25600, type internal Redistributing via eigrp 100 Last update from 10.10.10.2 on FastEthernet0/0, 00:00:36 ago Routing Descriptor Blocks: * 10.10.10.2, from 10.10.10.2, 00:00:36 ago, via FastEthernet0/0 Route metric is 25600, traffic share count is 1 Total delay is 200 microseconds, minimum bandwidth is 100000 Kbit Reliability 255/255, minimum MTU 1500 bytes Loading 1/255, Hops 1 RT1(config-router)#
The metric remains unchanged while the delay has increased by 3. This shows that setting the weight for the delay variable to 0 breaks the functionality and operation of EIGRP offset list.
RT1(config-router)#offset-list 0 in 100 RT1(config-router)# 00:17:19: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.10.10.2 (FastEthernet0/0) is down: route configuration changed 00:17:20: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.10.10.2 (FastEthernet0/0) is up: new adjacency RT1(config-router)#do sh ip route 172.16.1.0 Routing entry for 172.16.1.0/24 Known via "eigrp 100", distance 90, metric 25600, type internal Redistributing via eigrp 100 Last update from 10.10.10.2 on FastEthernet0/0, 00:00:00 ago Routing Descriptor Blocks: * 10.10.10.2, from 10.10.10.2, 00:00:00 ago, via FastEthernet0/0 Route metric is 25600, traffic share count is 1 Total delay is 203 microseconds, minimum bandwidth is 100000 Kbit Reliability 255/255, minimum MTU 1500 bytes Loading 1/255, Hops 1 RT1(config-router)#
Modifying the weight for the delay variable to 4 on RT1 and RT2 in order to observe how offset list handle a delay variable of more than 1 and remove the offset list to restore the original state:
RT1(config-router)#metric weights 0 1 0 4 0 0 RT1(config-router)#no offset-list 0 in 100 ======================================================================== RT2(config-router)#metric weights 0 1 0 4 0 0 ======================================================================== RT1(config-router)#do sh ip route 172.16.1.0 Routing entry for 172.16.1.0/24 Known via "eigrp 100", distance 90, metric 46080, type internal Redistributing via eigrp 100 Last update from 10.10.10.2 on FastEthernet0/0, 00:01:01 ago Routing Descriptor Blocks: * 10.10.10.2, from 10.10.10.2, 00:01:01 ago, via FastEthernet0/0 Route metric is 46080, traffic share count is 1 Total delay is 200 microseconds, minimum bandwidth is 100000 Kbit Reliability 255/255, minimum MTU 1500 bytes Loading 1/255, Hops 1 RT1(config-router)#
The metric has increased by 400 instead of the 100 as specified in the offset list due to the weight for the delay variable is set to 4 times the default.
RT1(config-router)#offset-list 0 in 100 RT1(config-router)# 00:21:46: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.10.10.2 (FastE thernet0/0) is down: route configuration changed 00:21:49: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.10.10.2 (FastE thernet0/0) is up: new adjacency RT1(config-router)#do sh ip route 172.16.1.0 Routing entry for 172.16.1.0/24 Known via "eigrp 100", distance 90, metric 46480, type internal Redistributing via eigrp 100 Last update from 10.10.10.2 on FastEthernet0/0, 00:00:01 ago Routing Descriptor Blocks: * 10.10.10.2, from 10.10.10.2, 00:00:01 ago, via FastEthernet0/0 Route metric is 46480, traffic share count is 1 Total delay is 203 microseconds, minimum bandwidth is 100000 Kbit Reliability 255/255, minimum MTU 1500 bytes Loading 1/255, Hops 1 RT1(config-router)#
Modifying the weight for the delay variable to 1 and make it the only variable used for EIGRP metric calculation on RT1 and RT2 and remove the offset list to restore the original state:
RT1(config-router)#metric weights 0 0 0 1 0 0 RT1(config-router)#no offset-list 0 in 100 ======================================================================== RT2(config-router)#metric weights 0 0 0 1 0 0 ======================================================================== RT1(config-router)#do sh ip route 172.16.1.0 Routing entry for 172.16.1.0/24 Known via "eigrp 100", distance 90, metric 5120, type internal Redistributing via eigrp 100 Last update from 10.10.10.2 on FastEthernet0/0, 00:00:02 ago Routing Descriptor Blocks: * 10.10.10.2, from 10.10.10.2, 00:00:02 ago, via FastEthernet0/0 Route metric is 5120, traffic share count is 1 Total delay is 200 microseconds, minimum bandwidth is 100000 Kbit Reliability 255/255, minimum MTU 1500 bytes Loading 1/255, Hops 1
The metric has increased by 100 as expected. Additionally, the weight for the bandwidth variable is not required for the functionality and operation of EIGRP offset list.
RT1(config-router)#offset-list 0 in 100 RT1(config-router)# 00:24:25: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.10.10.2 (FastE thernet0/0) is down: route configuration changed RT1(config-router)#offset-list 0 in 100 00:24:27: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.10.10.2 (FastE thernet0/0) is up: new adjacency RT1(config-router)#do sh ip route 172.16.1.0 Routing entry for 172.16.1.0/24 Known via "eigrp 100", distance 90, metric 5220, type internal Redistributing via eigrp 100 Last update from 10.10.10.2 on FastEthernet0/0, 00:00:01 ago Routing Descriptor Blocks: * 10.10.10.2, from 10.10.10.2, 00:00:01 ago, via FastEthernet0/0 Route metric is 5220, traffic share count is 1 Total delay is 203 microseconds, minimum bandwidth is 100000 Kbit Reliability 255/255, minimum MTU 1500 bytes Loading 1/255, Hops 1 RT1(config-router)#
Lastly, modify the weight for the delay variable to 4 and make it the only variable used for EIGRP metric calculation on RT1 and RT2 and remove the offset list to restore the original state:
RT1(config-router)#metric weights 0 0 0 4 0 0 RT1(config-router)#no offset-list 0 in 100 ======================================================================== RT2(config-router)#metric weights 0 0 0 4 0 0 ======================================================================== RT1(config-router)#do sh ip route 172.16.1.0 Routing entry for 172.16.1.0/24 Known via "eigrp 100", distance 90, metric 20480, type internal Redistributing via eigrp 100 Last update from 10.10.10.2 on FastEthernet0/0, 00:00:08 ago Routing Descriptor Blocks: * 10.10.10.2, from 10.10.10.2, 00:00:08 ago, via FastEthernet0/0 Route metric is 20480, traffic share count is 1 Total delay is 200 microseconds, minimum bandwidth is 100000 Kbit Reliability 255/255, minimum MTU 1500 bytes Loading 1/255, Hops 1 RT1(config-router)#
The metric has increased by 400 instead of the 100 as specified in the offset list due to the weight for the delay variable is set to 4 times the default.
RT1(config-router)#offset-list 0 in 100 00:27:13: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.10.10.2 (FastE thernet0/0) is down: route configuration changed 00:27:15: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.10.10.2 (FastE thernet0/0) is up: new adjacency RT1(config-router)#do sh ip route 172.16.1.0 Routing entry for 172.16.1.0/24 Known via "eigrp 100", distance 90, metric 20880, type internal Redistributing via eigrp 100 Last update from 10.10.10.2 on FastEthernet0/0, 00:00:05 ago Routing Descriptor Blocks: * 10.10.10.2, from 10.10.10.2, 00:00:05 ago, via FastEthernet0/0 Route metric is 20880, traffic share count is 1 Total delay is 203 microseconds, minimum bandwidth is 100000 Kbit Reliability 255/255, minimum MTU 1500 bytes Loading 1/255, Hops 1 RT1(config-router)#
Throughout the various combinations of EIGRP offset list configurations above, it is proven that the EIGRP offset list only alters the delay variable and is only accurate when the weight for the delay variable is set to 1 (default).
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