EIGRP VARIANCE and OFFSET

 R1 Variance Command:

Variance commands allows you to do unequal cost load balancing. Variance 1 is default which means equal cost load balancing. Variance 2 to 128 is unequal cost load balancing. This commands takes the FD from the best eigrp route in the topology table and multiplies this by X. X being the number specified in the variance command.  We are going to take route 4.4.4.0/24 and unequal cost load balance it.

Before: You can see that we have two paths to reach 4.4.4.0/24 but the router is picking the path with the lower FD.

R1#show ip route
Gateway of last resort is not set

     4.0.0.0/24 is subnetted, 1 subnets
D       4.4.4.0 [90/179200] via 192.168.2.2, 00:00:05, FastEthernet0/1
C    192.168.1.0/24 is directly connected, FastEthernet0/0
C    192.168.2.0/24 is directly connected, FastEthernet0/1

R1#show ip eigrp topology all-links
IP-EIGRP Topology Table for AS(10)/ID(192.168.1.1)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
       r - reply Status, s - sia Status

P 4.4.4.0/24, 1 successors, FD is 179200, serno 12
        via 192.168.2.2 (179200/128256), FastEthernet0/1
        via 192.168.1.2 (409600/128256), FastEthernet0/0
P 192.168.1.0/24, 1 successors, FD is 281600, serno 1
        via Connected, FastEthernet0/0
        via 192.168.2.2 (307200/281600), FastEthernet0/1
P 192.168.2.0/24, 1 successors, FD is 51200, serno 9
        via Connected, FastEthernet0/1
        via 192.168.1.2 (307200/281600), FastEthernet0/0
R1#

After: You can see the FD is diffrent but when you multiply 179200*3, 4097000 is well within this range.

R1#show ip route
Gateway of last resort is not set

     4.0.0.0/24 is subnetted, 1 subnets
D       4.4.4.0 [90/179200] via 192.168.2.2, 00:12:53, FastEthernet0/1
                      [90/409700] via 192.168.1.2, 00:12:53, FastEthernet0/0
     5.0.0.0/24 is subnetted, 1 subnets
D       5.5.5.0 [90/179200] via 192.168.2.2, 00:11:29, FastEthernet0/1
                [90/409600] via 192.168.1.2, 00:11:29, FastEthernet0/0
C    192.168.1.0/24 is directly connected, FastEthernet0/0
C    192.168.2.0/24 is directly connected, FastEthernet0/1
R1#


Confirming the variance setting before and after the change:

Routing Protocol is "eigrp 10"
  Outgoing update filter list for all interfaces is not set
  Incoming update filter list for all interfaces is not set
  Default networks flagged in outgoing updates
  Default networks accepted from incoming updates
  EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0
  EIGRP maximum hopcount 100
  EIGRP maximum metric variance 1
  Redistributing: eigrp 10
  EIGRP NSF-aware route hold timer is 240s
  Automatic network summarization is not in effect
  Maximum path: 4
  Routing for Networks:
    192.168.1.0
    192.168.2.0
  Routing Information Sources:
    Gateway         Distance      Last Update
    192.168.2.2           90      00:00:37
    192.168.1.2           90      00:00:37
  Distance: internal 90 external 170

router eigrp 10
variance 3
exit
!
R1#show ip protocols
Routing Protocol is "eigrp 10"
  Outgoing update filter list for all interfaces is not set
  Incoming update filter list for all interfaces is not set
  Default networks flagged in outgoing updates
  Default networks accepted from incoming updates
  EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0
  EIGRP maximum hopcount 100
  EIGRP maximum metric variance 3
  Redistributing: eigrp 10
  EIGRP NSF-aware route hold timer is 240s
  Automatic network summarization is not in effect
  Maximum path: 4
  Routing for Networks:
    192.168.1.0
    192.168.2.0
  Routing Information Sources:
    Gateway         Distance      Last Update
    192.168.2.2           90      00:00:03
    192.168.1.2           90      00:00:03
  Distance: internal 90 external 170

R1#

Offset list allows you to inflate the FD of a route. You can apply this inbound or outbound. Depending on your needs.

Offset-list on R2:

ip access-list standard eigrp
 permit 4.4.4.0
!
router eigrp 10
offset-list eigrp out 100

Before:
R1#show ip route
Gateway of last resort is not set

     4.0.0.0/24 is subnetted, 1 subnets
D       4.4.4.0 [90/179200] via 192.168.2.2, 00:00:58, FastEthernet0/1
                [90/409600] via 192.168.1.2, 00:00:58, FastEthernet0/0
C    192.168.1.0/24 is directly connected, FastEthernet0/0
C    192.168.2.0/24 is directly connected, FastEthernet0/1

After:
R1#show ip route
Gateway of last resort is not set

     4.0.0.0/24 is subnetted, 1 subnets
D       4.4.4.0 [90/179300] via 192.168.2.2, 00:00:05, FastEthernet0/1
                [90/409700] via 192.168.1.2, 00:00:05, FastEthernet0/0
C    192.168.1.0/24 is directly connected, FastEthernet0/0
C    192.168.2.0/24 is directly connected, FastEthernet0/1
R1#