I did warn you that this was only interesting to a handful of geeks.
Here’s the network topology. Really basic:
r1————r2
r1 and r2 are connected by a single serial link (s0/0 on both devices). Both routers running EIGRP on all interfaces. There are 3 loopbacks being advertised on each device.
r1#sh ip ei int
IP-EIGRP interfaces for process 100
IP-EIGRP interfaces for process 100
Xmit Queue Mean Pacing Time Multicast Pending
Interface Peers Un/Reliable SRTT Un/Reliable Flow Timer Routes
Se0/0 1 0/0 27 0/15 91 0
Lo0 0 0/0 0 0/10 0 0
Lo1 0 0/0 0 0/10 0 0
Lo2 0 0/0 0 0/10 0 0
Interface Peers Un/Reliable SRTT Un/Reliable Flow Timer Routes
Se0/0 1 0/0 27 0/15 91 0
Lo0 0 0/0 0 0/10 0 0
Lo1 0 0/0 0 0/10 0 0
Lo2 0 0/0 0 0/10 0 0
r1#sh ip ei nei
IP-EIGRP neighbors for process 100
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
0 10.1.12.2 Se0/0 13 00:01:47 27 200 0 3
IP-EIGRP neighbors for process 100
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
0 10.1.12.2 Se0/0 13 00:01:47 27 200 0 3
r1#sh ip route ei
D 222.222.222.0/24 [90/2297856] via 10.1.12.2, 00:01:55, Serial0/0
2.0.0.0/24 is subnetted, 1 subnets
D 2.2.2.0 [90/2297856] via 10.1.12.2, 00:01:55, Serial0/0
22.0.0.0/24 is subnetted, 1 subnets
D 22.22.22.0 [90/2297856] via 10.1.12.2, 00:01:55, Serial0/0
D 222.222.222.0/24 [90/2297856] via 10.1.12.2, 00:01:55, Serial0/0
2.0.0.0/24 is subnetted, 1 subnets
D 2.2.2.0 [90/2297856] via 10.1.12.2, 00:01:55, Serial0/0
22.0.0.0/24 is subnetted, 1 subnets
D 22.22.22.0 [90/2297856] via 10.1.12.2, 00:01:55, Serial0/0
r2#sh ip ei int
IP-EIGRP interfaces for process 100
IP-EIGRP interfaces for process 100
Xmit Queue Mean Pacing Time Multicast Pending
Interface Peers Un/Reliable SRTT Un/Reliable Flow Timer Routes
Se0/0 1 0/0 34 0/15 147 0
Lo0 0 0/0 0 0/10 0 0
Lo1 0 0/0 0 0/10 0 0
Lo2 0 0/0 0 0/10 0 0
Interface Peers Un/Reliable SRTT Un/Reliable Flow Timer Routes
Se0/0 1 0/0 34 0/15 147 0
Lo0 0 0/0 0 0/10 0 0
Lo1 0 0/0 0 0/10 0 0
Lo2 0 0/0 0 0/10 0 0
r2#sh ip ei nei
IP-EIGRP neighbors for process 100
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
0 10.1.12.1 Se0/0 13 00:02:15 34 204 0 3
r2#sh ip route ei
1.0.0.0/24 is subnetted, 1 subnets
D 1.1.1.0 [90/2297856] via 10.1.12.1, 00:02:19, Serial0/0
111.0.0.0/24 is subnetted, 1 subnets
D 111.111.111.0 [90/2297856] via 10.1.12.1, 00:02:19, Serial0/0
11.0.0.0/24 is subnetted, 1 subnets
D 11.11.11.0 [90/2297856] via 10.1.12.1, 00:02:19, Serial0/0
Okay to start with let’s see the routing information for net 1.1.1.0/24 on r2:IP-EIGRP neighbors for process 100
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
0 10.1.12.1 Se0/0 13 00:02:15 34 204 0 3
r2#sh ip route ei
1.0.0.0/24 is subnetted, 1 subnets
D 1.1.1.0 [90/2297856] via 10.1.12.1, 00:02:19, Serial0/0
111.0.0.0/24 is subnetted, 1 subnets
D 111.111.111.0 [90/2297856] via 10.1.12.1, 00:02:19, Serial0/0
11.0.0.0/24 is subnetted, 1 subnets
D 11.11.11.0 [90/2297856] via 10.1.12.1, 00:02:19, Serial0/0
r2#sh ip route 1.1.1.0
Routing entry for 1.1.1.0/24
Known via “eigrp 100″, distance 90, metric 2297856, type internal
Redistributing via eigrp 100
Last update from 10.1.12.1 on Serial0/0, 00:03:17 ago
Routing Descriptor Blocks:
* 10.1.12.1, from 10.1.12.1, 00:03:17 ago, via Serial0/0
Route metric is 2297856, traffic share count is 1
Total delay is 25000 microseconds, minimum bandwidth is 1544 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 1
On r2 let’s add 100 to the EIGRP metrics of all EIGRP routes advertised in s0/0 from r1:Routing entry for 1.1.1.0/24
Known via “eigrp 100″, distance 90, metric 2297856, type internal
Redistributing via eigrp 100
Last update from 10.1.12.1 on Serial0/0, 00:03:17 ago
Routing Descriptor Blocks:
* 10.1.12.1, from 10.1.12.1, 00:03:17 ago, via Serial0/0
Route metric is 2297856, traffic share count is 1
Total delay is 25000 microseconds, minimum bandwidth is 1544 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 1
[NOTE: access-list 0 selects all networks]
r2(config)#router ei 100
r2(config-router)#offset-list 0 in 100 s0/0
*Mar 1 00:15:01.055: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.1.12.1 (Serial0/0) is resync: route configuration changedr2(config-router)#offset-list 0 in 100 s0/0
r2(config-router)#do sh ip route 1.1.1.0
Routing entry for 1.1.1.0/24
Known via “eigrp 100″, distance 90, metric 2297956, type internal
Redistributing via eigrp 100
Last update from 10.1.12.1 on Serial0/0, 00:00:08 ago
Routing Descriptor Blocks:
* 10.1.12.1, from 10.1.12.1, 00:00:08 ago, via Serial0/0
Route metric is 2297956, traffic share count is 1
Total delay is 25003 microseconds, minimum bandwidth is 1544 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 1
Interesting…we’ve added 100 to the EIGRP metric as expected. The ‘total delay’ has also increased by 3 microseconds (not expected). It seems that the EIGRP offset-list alters the EIGRP variable in order to change the overall EIGRP metric. EIGRP uses this easy to remember Routing entry for 1.1.1.0/24
Known via “eigrp 100″, distance 90, metric 2297956, type internal
Redistributing via eigrp 100
Last update from 10.1.12.1 on Serial0/0, 00:00:08 ago
Routing Descriptor Blocks:
* 10.1.12.1, from 10.1.12.1, 00:00:08 ago, via Serial0/0
Route metric is 2297956, traffic share count is 1
Total delay is 25003 microseconds, minimum bandwidth is 1544 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 1
equation to calculate its metric:If k5 equals 0, the composite EIGRP metric is computed according to the following formula:
metric = [k1 * bandwidth + (k2 * bandwidth)/(256 - load) + k3 * delay]
metric = [k1 * bandwidth + (k2 * bandwidth)/(256 - load) + k3 * delay]
If k5 does not equal zero, an additional operation is performed:
metric = metric * [k5/(reliability + k4)]
This led me to wonder what would happen if we took delay out of the EIGRP equation. We can do that by setting the EIGRP K-Value for delay to 0 and just leaving bandwidth K-Value (we’ll need to do this on both routers):metric = metric * [k5/(reliability + k4)]
r1(config)# router ei 100
r1(config-router)# metric weights 0 1 0 0 0 0
r1(config-router)# metric weights 0 1 0 0 0 0
r2(config)#router ei 100
r2(config-router)#metric weights 0 1 0 0 0 0
r2(config-router)#no offset-list 0 in 100 s0/0
r2(config-router)#metric weights 0 1 0 0 0 0
r2(config-router)#no offset-list 0 in 100 s0/0
r2(config-router)#do sh ip proto | i EIGRP metric weight
EIGRP metric weight K1=1, K2=0, K3=0, K4=0, K5=0
Let’s see our metric before applying the offset-list:EIGRP metric weight K1=1, K2=0, K3=0, K4=0, K5=0
r2(config-router)#do sh ip route 1.1.1.0
Routing entry for 1.1.1.0/24
Known via “eigrp 100″, distance 90, metric 1657856, type internal
Redistributing via eigrp 100
Last update from 10.1.12.1 on Serial0/0, 00:00:32 ago
Routing Descriptor Blocks:
* 10.1.12.1, from 10.1.12.1, 00:00:32 ago, via Serial0/0
Route metric is 1657856, traffic share count is 1
Total delay is 25000 microseconds, minimum bandwidth is 1544 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 1
Okay, let’s reapply the offset-list:Routing entry for 1.1.1.0/24
Known via “eigrp 100″, distance 90, metric 1657856, type internal
Redistributing via eigrp 100
Last update from 10.1.12.1 on Serial0/0, 00:00:32 ago
Routing Descriptor Blocks:
* 10.1.12.1, from 10.1.12.1, 00:00:32 ago, via Serial0/0
Route metric is 1657856, traffic share count is 1
Total delay is 25000 microseconds, minimum bandwidth is 1544 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 1
r2(config-router)#offset-list 0 in 100 s0/0
*Mar 1 03:04:44.711: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.1.12.1 (Serial0/0) is resync: route configuration changed
r2(config-router)#do sh ip route 1.1.1.0
Routing entry for 1.1.1.0/24
Known via “eigrp 100″, distance 90, metric 1657856, type internal
Redistributing via eigrp 100
Last update from 10.1.12.1 on Serial0/0, 00:00:10 ago
Routing Descriptor Blocks:
* 10.1.12.1, from 10.1.12.1, 00:00:10 ago, via Serial0/0
Route metric is 1657856, traffic share count is 1
Total delay is 25003 microseconds, minimum bandwidth is 1544 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 1
BOOYAH! The offset-list is supposed to increase the EIGRP metric by 100. We can see that the metric did NOT change (still 1657856), BUT the total delay increased by 3 microseconds. It looks like we’ve discovered the mechanism used by the EIGRP offset-list to change the EIGRP metric. We’ve also discovered that setting the delay K-Value to zero “breaks” the offset-list function.Routing entry for 1.1.1.0/24
Known via “eigrp 100″, distance 90, metric 1657856, type internal
Redistributing via eigrp 100
Last update from 10.1.12.1 on Serial0/0, 00:00:10 ago
Routing Descriptor Blocks:
* 10.1.12.1, from 10.1.12.1, 00:00:10 ago, via Serial0/0
Route metric is 1657856, traffic share count is 1
Total delay is 25003 microseconds, minimum bandwidth is 1544 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 1
One last experiment. Let’s see if the offset-list is intelligent enough to handle a delay K-Value of more than 1:
r1(config-router)#metric weights 0 1 0 4 0 0
r2(config-router)#metric weights 0 1 0 4 0 0
r2(config-router)#no offset-list 0 in 100 s0/0
r2(config-router)#no offset-list 0 in 100 s0/0
r2(config-router)#do sh ip proto | i EIGRP metric weight
EIGRP metric weight K1=1, K2=0, K3=4, K4=0, K5=0
EIGRP metric weight K1=1, K2=0, K3=4, K4=0, K5=0
r2(config-router)#do sh ip route 1.1.1.0
Routing entry for 1.1.1.0/24
Known via “eigrp 100″, distance 90, metric 4217856, type internal
Redistributing via eigrp 100
Last update from 10.1.12.1 on Serial0/0, 00:01:09 ago
Routing Descriptor Blocks:
* 10.1.12.1, from 10.1.12.1, 00:01:09 ago, via Serial0/0
Route metric is 4217856, traffic share count is 1
Total delay is 25000 microseconds, minimum bandwidth is 1544 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 1
Routing entry for 1.1.1.0/24
Known via “eigrp 100″, distance 90, metric 4217856, type internal
Redistributing via eigrp 100
Last update from 10.1.12.1 on Serial0/0, 00:01:09 ago
Routing Descriptor Blocks:
* 10.1.12.1, from 10.1.12.1, 00:01:09 ago, via Serial0/0
Route metric is 4217856, traffic share count is 1
Total delay is 25000 microseconds, minimum bandwidth is 1544 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 1
r2(config-router)#offset-list 0 in 100 s0/0
*Mar 1 03:11:56.439: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.1.12.1 (Serial0/0) is resync: route configuration changed
r2(config-router)#do sh ip route 1.1.1.0
Routing entry for 1.1.1.0/24
Known via “eigrp 100″, distance 90, metric 4218256, type internal
Redistributing via eigrp 100
Last update from 10.1.12.1 on Serial0/0, 00:00:07 ago
Routing Descriptor Blocks:
* 10.1.12.1, from 10.1.12.1, 00:00:07 ago, via Serial0/0
Route metric is 4218256, traffic share count is 1
Total delay is 25003 microseconds, minimum bandwidth is 1544 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 1
Routing entry for 1.1.1.0/24
Known via “eigrp 100″, distance 90, metric 4218256, type internal
Redistributing via eigrp 100
Last update from 10.1.12.1 on Serial0/0, 00:00:07 ago
Routing Descriptor Blocks:
* 10.1.12.1, from 10.1.12.1, 00:00:07 ago, via Serial0/0
Route metric is 4218256, traffic share count is 1
Total delay is 25003 microseconds, minimum bandwidth is 1544 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 1
Weird. I would have thought that this would have worked as we have our default K-Values but have just increased the weight of delay 4 times. We can see that the delay was once again increased by 3 microseconds, but the overall metric was unaffected. Weird.
Thank you to reader Rich for pointing out that 4217856 and 4218256 are NOT the same value.
The EIGRP metric increased by 400 instead of the 100 that we specified in the offset-list. That’s because the K-Value for delay is set to 4 times the default.Hmmm…one more experiment. Let’s set the delay K-Value back to 1 but make it the only variable used for the EIGRP metric:
r1(config-router)#metric weights 0 0 0 1 0 0
r2(config-router)#metric weights 0 0 0 1 0 0
r2(config-router)#no offset-list 0 in 100 s0/0
r2(config-router)#no offset-list 0 in 100 s0/0
r2(config-router)#do sh ip proto | i EIGRP metric weight
EIGRP metric weight K1=0, K2=0, K3=1, K4=0, K5=0
EIGRP metric weight K1=0, K2=0, K3=1, K4=0, K5=0
r2(config-router)#do sh ip route 1.1.1.0
Routing entry for 1.1.1.0/24
Known via “eigrp 100″, distance 90, metric 640000, type internal
Redistributing via eigrp 100
Last update from 10.1.12.1 on Serial0/0, 00:00:33 ago
Routing Descriptor Blocks:
* 10.1.12.1, from 10.1.12.1, 00:00:33 ago, via Serial0/0
Route metric is 640000, traffic share count is 1
Total delay is 25000 microseconds, minimum bandwidth is 1544 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 1
Let’s reapply the offset-list and see what happens:Routing entry for 1.1.1.0/24
Known via “eigrp 100″, distance 90, metric 640000, type internal
Redistributing via eigrp 100
Last update from 10.1.12.1 on Serial0/0, 00:00:33 ago
Routing Descriptor Blocks:
* 10.1.12.1, from 10.1.12.1, 00:00:33 ago, via Serial0/0
Route metric is 640000, traffic share count is 1
Total delay is 25000 microseconds, minimum bandwidth is 1544 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 1
r2(config-router)#offset-list 0 in 100 s0/0
*Mar 1 03:22:54.319: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.1.12.1 (Serial0/0) is resync: route configuration changed
r2(config-router)#do sh ip route 1.1.1.0
Routing entry for 1.1.1.0/24
Known via “eigrp 100″, distance 90, metric 640100, type internal
Redistributing via eigrp 100
Last update from 10.1.12.1 on Serial0/0, 00:00:06 ago
Routing Descriptor Blocks:
* 10.1.12.1, from 10.1.12.1, 00:00:06 ago, via Serial0/0
Route metric is 640100, traffic share count is 1
Total delay is 25003 microseconds, minimum bandwidth is 1544 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 1
It worked. So we don’t need to have the bandwidth K-Value “turned on” for the offset-list to work.Routing entry for 1.1.1.0/24
Known via “eigrp 100″, distance 90, metric 640100, type internal
Redistributing via eigrp 100
Last update from 10.1.12.1 on Serial0/0, 00:00:06 ago
Routing Descriptor Blocks:
* 10.1.12.1, from 10.1.12.1, 00:00:06 ago, via Serial0/0
Route metric is 640100, traffic share count is 1
Total delay is 25003 microseconds, minimum bandwidth is 1544 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 1
Last experiment…I promise. Let’s set the delay K-Value to 4 and set the other K-Values to 0:
r1(config-router)#metric weights 0 0 0 4 0 0
r2(config-router)#metric weights 0 0 0 4 0 0
r2(config-router)#no offset-list 0 in 100 s0/0
r2(config-router)#no offset-list 0 in 100 s0/0
r2(config-router)#do sh ip proto | i EIGRP metric weight
EIGRP metric weight K1=0, K2=0, K3=4, K4=0, K5=0
EIGRP metric weight K1=0, K2=0, K3=4, K4=0, K5=0
r2(config-router)#do sh ip route 1.1.1.0
Routing entry for 1.1.1.0/24
Known via “eigrp 100″, distance 90, metric 2560000, type internal
Redistributing via eigrp 100
Last update from 10.1.12.1 on Serial0/0, 00:00:14 ago
Routing Descriptor Blocks:
* 10.1.12.1, from 10.1.12.1, 00:00:14 ago, via Serial0/0
Route metric is 2560000, traffic share count is 1
Total delay is 25000 microseconds, minimum bandwidth is 1544 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 1
Reapply the offset-list:Routing entry for 1.1.1.0/24
Known via “eigrp 100″, distance 90, metric 2560000, type internal
Redistributing via eigrp 100
Last update from 10.1.12.1 on Serial0/0, 00:00:14 ago
Routing Descriptor Blocks:
* 10.1.12.1, from 10.1.12.1, 00:00:14 ago, via Serial0/0
Route metric is 2560000, traffic share count is 1
Total delay is 25000 microseconds, minimum bandwidth is 1544 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 1
r2(config-router)#offset-list 0 in 100 s0/0
*Mar 1 03:33:52.279: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.1.12.1 (Serial0/0) is resync: route configuration changed
r2(config-router)#do sh ip route 1.1.1.0
Routing entry for 1.1.1.0/24
Known via “eigrp 100″, distance 90, metric 2560400, type internal
Redistributing via eigrp 100
Last update from 10.1.12.1 on Serial0/0, 00:00:06 ago
Routing Descriptor Blocks:
* 10.1.12.1, from 10.1.12.1, 00:00:06 ago, via Serial0/0
Route metric is 2560400, traffic share count is 1
Total delay is 25003 microseconds, minimum bandwidth is 1544 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 1
Ah hah! The metric changed by 400 instead of 100 (as we had configured it to be offset). I think that this is pretty good evidence that the EIGRP offset-list only alters the EIGRP delay variable and is only accurate when that K-Value is set to 1.Routing entry for 1.1.1.0/24
Known via “eigrp 100″, distance 90, metric 2560400, type internal
Redistributing via eigrp 100
Last update from 10.1.12.1 on Serial0/0, 00:00:06 ago
Routing Descriptor Blocks:
* 10.1.12.1, from 10.1.12.1, 00:00:06 ago, via Serial0/0
Route metric is 2560400, traffic share count is 1
Total delay is 25003 microseconds, minimum bandwidth is 1544 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 1
I don’t think that this will affect you in real life (who’s changing K-Values and using offset-lists with EIGRP?) but it could possibly come up in a lab. I could forsee a task that has you change the K-Values and then another task that has you altering EIGRP metrics (probably for some evil unequal-cost load-balancing task). At least now you’ll know why your perfectly executed offset-list solution has failed.
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