EIGRP Metric Manipulation: Offset-Lists

An offset list is the mechanism for increasing incoming and outgoing metrics to routes learned via EIGRP or Routing Information Protocol (RIP). (Offset lists are only used for distance vector routing protocols.) Optionally, an offset list can be limited by specifying either an access list or an interface.

Below is the lab example:  R4 I'll use the two path to get the R1 11.0.0.8/29 route.

R4(config-router)# do sh ip eigr topo 11.0.0.8/29

EIGRP-IPv4 Topology Entry for AS(100)/ID(2.4.2.4) for 11.0.0.8/29
  State is Passive, Query origin flag is 1, 1 Successor(s), FD is 435200
  Descriptor Blocks:
  2.4.2.2 (Ethernet0/1), from 2.4.2.2, Send flag is 0x0
      Composite metric is (435200/409600), route is Internal
      Vector metric:
        Minimum bandwidth is 10000 Kbit
        Total delay is 7000 microseconds
        Reliability is 255/255
        Load is 1/255
        Minimum MTU is 1500
        Hop count is 2
        Originating router is 11.0.0.9
  1.4.1.1 (Serial3/1), from 1.4.1.1, Send flag is 0x0
      Composite metric is (20640000/128256), route is Internal
      Vector metric:
        Minimum bandwidth is 128 Kbit
        Total delay is 25000 microseconds
        Reliability is 255/255
        Load is 1/255
        Minimum MTU is 1500
        Hop count is 1
        Originating router is 11.0.0.9

[*] To discover the magic number -> 20640000 - 435200 = 20204800

R4(config)#access-list 1 permit 11.0.0.8 0.0.0.7
R4(config)#router eigrp 100
R4(config-router)#offset-list 1 in 20204800 etherNet 0/1
R4(config-router)#end

[-] Before offset-list

R4# sh ip route eigrp

...
      1.0.0.0/8 is variably subnetted, 3 subnets, 2 masks
D        1.2.1.0/24 [90/307200] via 2.4.2.2, 00:09:01, Ethernet0/1
      11.0.0.0/29 is subnetted, 2 subnets
D        11.0.0.0 [90/435200] via 2.4.2.2, 00:09:01, Ethernet0/1
D        11.0.0.8 [90/20640000] via 1.4.1.1, 00:02:52, Serial3/1

[+] After offSet-list applied

R4# sh ip route eigrp

...
      1.0.0.0/8 is variably subnetted, 3 subnets, 2 masks
D        1.2.1.0/24 [90/307200] via 2.4.2.2, 00:09:47, Ethernet0/1
C        1.4.1.0/24 is directly connected, Serial3/1
L        1.4.1.4/32 is directly connected, Serial3/1
      2.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C        2.4.2.0/24 is directly connected, Ethernet0/1
L        2.4.2.4/32 is directly connected, Ethernet0/1
      11.0.0.0/29 is subnetted, 2 subnets
D        11.0.0.0 [90/435200] via 2.4.2.2, 00:09:47, Ethernet0/1
D        11.0.0.8 [90/20640000] via 2.4.2.2, 00:00:07, Ethernet0/1
                       [90/20640000] via 1.4.1.1, 00:00:07, Serial3/1

R4# sh ip eigrp topology 11.0.0.8/29

EIGRP-IPv4 Topology Entry for AS(100)/ID(2.4.2.4) for 11.0.0.8/29
  State is Passive, Query origin flag is 1, 2 Successor(s), FD is 435200
  Descriptor Blocks:
  1.4.1.1 (Serial3/1), from 1.4.1.1, Send flag is 0x0
      Composite metric is (20640000/128256), route is Internal
      Vector metric:
        Minimum bandwidth is 128 Kbit
        Total delay is 25000 microseconds
        Reliability is 255/255
        Load is 1/255
        Minimum MTU is 1500
        Hop count is 1
        Originating router is 11.0.0.9
  2.4.2.2 (Ethernet0/1), from 2.4.2.2, Send flag is 0x0
      Composite metric is (20640000/20614400), route is Internal
      Vector metric:
        Minimum bandwidth is 10000 Kbit
        Total delay is 796250 microseconds
        Reliability is 255/255
        Load is 1/255
        Minimum MTU is 1500
        Hop count is 2
        Originating router is 11.0.0.9

[+] Verification on R4

R4# traceroute 11.0.0.9

Type escape sequence to abort.
  1 1.4.1.1 10 msec
    2.4.2.2 5 msec
    1.4.1.1 12 msec

R4# traceroute 11.0.0.9

Type escape sequence to abort.
  1 2.4.2.2 5 msec
    1.4.1.1 10 msec
    2.4.2.2 5 msec

.!!!!

.!.!.

biOos