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Tuesday, June 18, 2013

EIGRP Unequal Cost Traffic Sharing Problem - %FIB-4-UNEQUAL

We have configured a router to prioritize among its three paths to the 150.1.1.0/24 network.  We can see that the topology table reflects the proper metrics after the changes were made.  However, only two routes are selected.  Initially after configuring the traffic-share min across-interfaces command, we received the following warning message:

%FIB-4-UNEQUAL: Range of unequal path weightings too large for prefix 150.1.1.0/24. Some available paths may not be used.
 
R3#show run | section eigrp
router eigrp 200
variance 2
traffic-share min across-interfaces
offset-list 0 in 1000000 Serial1/1
network 10.0.0.4 0.0.0.3
network 10.0.0.8 0.0.0.3
network 10.0.0.12 0.0.0.3
network 150.3.3.0 0.0.0.255
no auto-summary
 
R3#show ip route 150.1.1.0
Routing entry for 150.1.1.0/24
  Known via "eigrp 200", distance 170, metric 2172416, type external
  Redistributing via eigrp 200
  Last update from 10.0.0.5 on Serial1/1, 00:00:08 ago
  Routing Descriptor Blocks:
  * 10.0.0.14, from 10.0.0.14, 00:00:08 ago, via Serial1/2
      Route metric is 2172416, traffic share count is 1
      Total delay is 20100 microseconds, minimum bandwidth is 1544 Kbit
      Reliability 255/255, minimum MTU 1500 bytes
      Loading 1/255, Hops 1
    10.0.0.5, from 10.0.0.5, 00:00:08 ago, via Serial1/1
      Route metric is 3172416, traffic share count is 0
      Total delay is 59162 microseconds, minimum bandwidth is 1544 Kbit
      Reliability 255/255, minimum MTU 1500 bytes
      Loading 1/255, Hops 1
 
R3#show ip eigrp topology 150.1.1.0 255.255.255.0
IP-EIGRP (AS 200): Topology entry for 150.1.1.0/24
  State is Passive, Query origin flag is 1, 1 Successor(s), FD is 2172416
  Routing Descriptor Blocks:
  10.0.0.14 (Serial1/2), from 10.0.0.14, Send flag is 0x0
      Composite metric is (2172416/28160), Route is External
      Vector metric:
        Minimum bandwidth is 1544 Kbit
        Total delay is 20100 microseconds
        Reliability is 255/255
        Load is 1/255
        Minimum MTU is 1500
        Hop count is 1
      External data:
        Originating router is 4.4.4.4
        AS number of route is 100
        External protocol is EIGRP, external metric is 0
        Administrator tag is 0 (0x00000000)
  10.0.0.5 (Serial1/1), from 10.0.0.5, Send flag is 0x0
      Composite metric is (3172416/1028160), Route is External
      Vector metric:
        Minimum bandwidth is 1544 Kbit
        Total delay is 59162 microseconds
        Reliability is 255/255
        Load is 1/255
        Minimum MTU is 1500
        Hop count is 1
      External data:
        Originating router is 1.1.1.1
        AS number of route is 100
        External protocol is EIGRP, external metric is 0
        Administrator tag is 0 (0x00000000)
  10.0.0.9 (Serial1/0), from 10.0.0.9, Send flag is 0x0
      Composite metric is (2684416/2172416), Route is External
      Vector metric:
        Minimum bandwidth is 1544 Kbit
        Total delay is 40100 microseconds
        Reliability is 255/255
        Load is 1/255
        Minimum MTU is 1500
        Hop count is 2
      External data:
        Originating router is 1.1.1.1
        AS number of route is 100
        External protocol is EIGRP, external metric is 0
        Administrator tag is 0 (0x00000000)

One of the requirements for variance to work in EIGRP is that the reported distance from a neighbor must be less than the Feasible Distance of the successor route. Looking at the output from show ip eigrp topology we see FD is 2172416. So this is the value to compare with the reported distance from the neighbors.
The first neighbor reports the lowest distance and its route is the successor route using Serial 1/2. The second neighbor reports 1028160 as the distance. This is less than the FD and so the route through Serial 1/1 is also used.The third neighbor reports 2172416. This is not less than FD and so this route is not used by variance.
 

You are on the right track. It is just that one of the routes does not qualify to be used under variance.


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