variance [multiplier]
The variance command allows EIGRP to load-balance across multiple routes with unequal costs by specifying a multiplier that defines the range of feasible successor metrics relative to the best successor metric.
variance [multiplier]When to Use This Command
- Load-balancing traffic across two links where one link has a lower bandwidth (e.g., 1.5 Mbps T1) and the other has higher bandwidth (e.g., 10 Mbps Ethernet) but both paths are feasible.
- Utilizing a backup satellite link (higher delay) alongside a primary fiber link to increase total throughput in a WAN environment.
- Distributing traffic across multiple paths to different ISPs when one ISP link has a higher cost due to slower speed or higher delay.
- Balancing traffic in a hub-and-spoke topology where the spoke has two paths to the hub with different metrics.
Command Examples
Basic variance configuration to allow load balancing across unequal-cost paths
router eigrp 100
variance 2router eigrp 100 network 192.168.1.0 variance 2 !
The command 'variance 2' is entered in EIGRP router configuration mode. It sets the multiplier to 2, meaning any feasible successor route with a metric less than or equal to 2 times the best successor metric will be installed in the routing table. The output shows the configuration snippet as it would appear in 'show running-config'.
Verifying unequal-cost load balancing with show ip route
show ip route 192.168.2.0Routing entry for 192.168.2.0/24
Known via "eigrp 100", distance 90, metric 30720
Redistributing via eigrp 100
Last update from 10.0.0.2 on Serial0/0/0, 00:00:05 ago
Routing Descriptor Blocks:
* 10.0.0.2, from 10.0.0.2, 00:00:05 ago, via Serial0/0/0
Route metric is 30720, traffic share count is 1
10.0.0.6, from 10.0.0.6, 00:00:05 ago, via Serial0/0/1
Route metric is 56320, traffic share count is 1The output shows two paths to 192.168.2.0/24. The best path has metric 30720 via 10.0.0.2. The second path has metric 56320, which is less than 2*30720=61440, so it is installed. Both have traffic share count 1, meaning traffic is distributed equally (since variance is 2, but share counts are equal because the metric ratio is less than 2). The asterisk (*) indicates the active path used for the next packet.
Understanding the Output
When you configure 'variance [multiplier]', EIGRP will include any feasible successor route whose metric is less than or equal to the product of the multiplier and the best successor metric. The 'show ip route' command displays all installed routes. Each route entry shows the metric and traffic share count. The traffic share count is inversely proportional to the metric; for example, if one path has metric 30720 and another 56320, the share counts would be 56320/30720 ≈ 1.83, but since variance only allows routes within the multiplier, both get share count 1 if the ratio is less than 2. In practice, the share counts are calculated as (worst metric / best metric) rounded down. Good values: variance set to 1 (default) means only equal-cost load balancing; variance >1 allows unequal-cost. Watch for routes that are not feasible successors (i.e., not meeting the feasibility condition) – they will not be installed even if within variance. Also, variance does not affect which route is the successor; it only affects which feasible successors are installed.
CCNA Exam Tips
The variance command only works with feasible successors; a route must first satisfy the feasibility condition (reported distance < feasible distance) to be considered.
The default variance is 1, meaning only equal-cost load balancing occurs.
Traffic share count is calculated as the integer ratio of the worst metric to the best metric; for example, if metrics are 100 and 150, share counts are 1 and 1 (since 150/100=1.5, truncated to 1).
CCNA exam may test that variance does not change the successor; the best path remains the successor and is used for all traffic if no other feasible successors exist.
Common Mistakes
Setting variance too high (e.g., 10) can cause suboptimal paths to be used, potentially causing routing loops or poor performance.
Forgetting that variance only applies to feasible successors; if a route does not meet the feasibility condition, it will not be installed regardless of variance.
Assuming variance affects the metric calculation; it only affects which routes are installed, not how metrics are computed.
Related Commands
show ip eigrp topology
Displays the EIGRP topology table, showing all learned routes and their feasible successors, used to verify EIGRP convergence and path selection.
show ip route
Displays the current IP routing table on a Cisco router, used to verify routes, check next-hop addresses, and troubleshoot connectivity issues.
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