Twicking EIGRP metrics

September 2, 2008 at 5:35 pm | Posted in EIGRP, Routing | Leave a comment

What if I want to prefer one EIGRP path over the other? Changing metrics of course ;-)

R1 —- R3 —- R2

Both R1 and R2 advertized 100.0.0.0/8 toward R3, but R1 advertises a better metrics, hence a prefered path. I want to make R3 to chose path via R2 instead.

We can change bandwidth or delay on R3 interface. Note that EIGRP uses the minimum bandwidth of the path as one of the metrics (BW). So bumping up the BW for interface connecting to R3 might not actually doing me any good. If we check the show ip ei topo for the route, we might still see minimum bandwidth metric the unchanged for the path via Serial1/3. Instead

  • We can decrease bandwidth of Serial1/2 to let say 56K.
  • Alternatively, you can give Serial1/3 a very high delay.
  • Another option is to use offset-list

Here’s metric before the change

R3#sh ip ei topology 100.0.0.0/8
IP-EIGRP (AS 100): Topology entry for 100.0.0.0/8
  State is Passive, Query origin flag is 1, 1 Successor(s), FD is 2244096
  Routing Descriptor Blocks:
  13.0.0.1 (Serial1/2), from 13.0.0.1, Send flag is 0x0
      Composite metric is (2244096/1732096), Route is External
      Vector metric:
        Minimum bandwidth is 1500 Kbit
        Total delay is 21000 microseconds
        Reliability is 255/255
        Load is 1/255
        Minimum MTU is 1500
        Hop count is 1
      External data:
        Originating router is 13.0.0.1 
        AS number of route is 0
        External protocol is Static, external metric is 0
        Administrator tag is 0 (0x00000000)
  23.0.0.2 (Serial1/3), from 23.0.0.2, Send flag is 0x0
      Composite metric is (5537536/5025536), Route is External
      Vector metric:
        Minimum bandwidth is 512 Kbit
        Total delay is 21000 microseconds
        Reliability is 255/255
        Load is 1/255
        Minimum MTU is 1500
        Hop count is 1
      External data:
        Originating router is 23.0.0.2 
        AS number of route is 0
        External protocol is Static, external metric is 0
        Administrator tag is 0 (0x00000000)

R3#sh ip route ei
D EX 100.0.0.0/8 [170/2244096] via 13.0.0.1, 00:02:55, Serial1/2

Offset-list configuration

access-list 99 permit 100.0.0.0 0.255.255.255
router eigrp 100
 offset-list 99 in 5000000 Serial1/2
R3#sh ip eigrp topology 100.0.0.0/8
IP-EIGRP (AS 100): Topology entry for 100.0.0.0/8
  State is Passive, Query origin flag is 1, 1 Successor(s), FD is 5537536
  Routing Descriptor Blocks:
  23.0.0.2 (Serial1/3), from 23.0.0.2, Send flag is 0x0
      Composite metric is (5537536/5025536), Route is External
      Vector metric:
        Minimum bandwidth is 512 Kbit
        Total delay is 21000 microseconds
        Reliability is 255/255
        Load is 1/255
        Minimum MTU is 1500
        Hop count is 1
      External data:
        Originating router is 23.0.0.2 
        AS number of route is 0
        External protocol is Static, external metric is 0
        Administrator tag is 0 (0x00000000)
  13.0.0.1 (Serial1/2), from 13.0.0.1, Send flag is 0x0
      Composite metric is (7244096/6732096), Route is External
      Vector metric:
        Minimum bandwidth is 1500 Kbit
        Total delay is 216312 microseconds
        Reliability is 255/255
        Load is 1/255
        Minimum MTU is 1500
        Hop count is 1
      External data:
        Originating router is 13.0.0.1 
        AS number of route is 0
        External protocol is Static, external metric is 0
        Administrator tag is 0 (0x00000000)

R3#sh ip route ei
D EX 100.0.0.0/8 [170/5537536] via 23.0.0.2, 00:01:21, Serial1/3
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