CCNP ROUTE: 4. EIGRP Metric tuning: Configuring the Metric Weights (K-values)

Rule: EIGRP requires that two routers’ k-values match before those routers can become neighbors.

-The k-values are multipliers used in calculating the extended formula of EIGRP metric: Metric = [K1 * bandwidth + (K2 * bandwidth) / (256 - load) + K3 * delay] * [K5 / (reliability + K4)]
-If at the end of calculating the EIGRP metric for 2 routes the metrics tie, then the route with the largest MTU is chosen. (Default MTU = 1500 bytes)

The default k-values of EIGRP are:
R6#show ip protocols 
Routing Protocol is "eigrp 1"
...
  EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0

R6(config-router)#metric weights ?
  <0-8>  Type Of Service (Only TOS 0 supported)

R6(config-router)#metric weights 0 ?
  <0-255>  K1

R6(config-router)#metric weights 0 1 ?
  <0-255>  K2

R6(config-router)#metric weights 0 1 1 ?
  <0-255>  K3

R6(config-router)#metric weights 0 1 1 1 ?
  <0-255>  K4

R6(config-router)#metric weights 0 1 1 1 1 ?
  <0-255>  K5

R6(config-router)#metric weights 0 1 1 1 1 1 ?
  <cr>

If setting all k-values to 1, R6 will not be able to maintain the neighborship with R4 and R5, who both have the default k-values (1 0 1 0 0)

R6(config-router)#metric weights 0 1 1 1 1 1 
R6(config-router)#
*Mar  1 06:33:04.578: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.16.0.2 (Serial0/0) is down: metric changed
*Mar  1 06:33:04.598: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.16.0.6 (FastEthernet0/1) is down: metric changed
*Mar  1 06:33:04.618: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.16.0.10 (Serial0/1) is down: metric changed
*Mar  1 06:33:05.314: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.16.0.6 (FastEthernet0/1) is down: K-value mismatch
*Mar  1 06:33:06.690: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.16.0.2 (Serial0/0) is down: K-value mismatch
*Mar  1 06:33:07.118: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.16.0.10 (Serial0/1) is down: K-value mismatch
*Mar  1 06:33:09.718: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.16.0.6 (FastEthernet0/1) is down: Interface Goodbye received
*Mar  1 06:33:11.226: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.16.0.2 (Serial0/0) is down: Interface Goodbye received
*Mar  1 06:33:11.590: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.16.0.10 (Serial0/1) is down: Interface Goodbye received

After reconfiguring R6 with the default values the neighborships are restored:

R6(config-router)#metric weights 0 1 0 1 0 0
R6(config-router)#
*Mar  1 06:33:59.630: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.16.0.6 (FastEthernet0/1) is up: new adjacency
*Mar  1 06:34:00.354: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.16.0.10 (Serial0/1) is up: new adjacency
*Mar  1 06:34:01.406: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.16.0.2 (Serial0/0) is up: new adjacency

R6#show ip eigrp neighbors 
IP-EIGRP neighbors for process 1
H   Address                 Interface       Hold Uptime   SRTT   RTO  Q  Seq
                                            (sec)         (ms)       Cnt Num
2   172.16.0.2              Se0/0             12 00:02:43   50   300  0  37
1   172.16.0.10             Se0/1             14 00:02:44   57   342  0  15
0   172.16.0.6              Fa0/1             11 00:02:45   87   522  0  28

-Cisco recommends again using k-values k2, k4, and k5, because a nonzero value for these parameters causes the metric calculation to include interface load and reliability.
-The load and reliability change over time, which causes EIGRP to reflood topology data, and may cause routers to continually choose different routes (route flapping).