EIGRP Variance: The Second Path That Never Loads
A feasible successor sits idle in the topology table because variance was never set. Diagnose it and load-share the second path yourself, live, right below.
Symptom
A perfectly good backup path sits in the topology table and never reaches the routing table. Variance is the feature that admits it, and there is one condition it will never override.
Your mission
Prove the cause, then fix it
Format
Guided CLI investigation
Investigate before you configure.
Use the CLI evidence to isolate the fault, make the smallest safe correction, then verify the network state changed.
Observe the symptom and link state.
Diagnose by comparing the protocol evidence.
Verify the expected device state and confirm the original symptom is resolved.
Console access: R1 · R2
This workspace stacks for portrait phones. Rotate to landscape for the full split-screen console.
Need a hint?
Reveal the root cause when you're ready.
Try the investigation first, then use this as your escape hatch, not a dead end.
Lab debrief
Turn the session into a repeatable troubleshooting pattern.
Use this reference after your attempt: first explain the symptom, then verify the evidence, then confirm the repair.
The problem
R1 reaches the 192.168.50.0/24 branch over a primary path with a feasible distance of 3072. A second, slower path exists and is a valid feasible successor, but all traffic uses the primary. The operator wants both links carrying traffic in proportion to their cost.
What you'll practice
- Read successors and feasible successors from the EIGRP topology table
- Understand the feasibility condition and why it exists
- Configure variance to install unequal-cost paths
- Know why variance never overrides the feasibility condition
1. The topology table holds more than the routing table
EIGRP already knows about the backup path and has already proved it loop-free. You will learn to read the FD and RD values in the topology table and recognise a feasible successor on sight, before deciding whether to use it.
2. The feasibility condition, and why it is not negotiable
A path only qualifies as a feasible successor when its reported distance is lower than the current feasible distance, which guarantees the neighbour is not routing back through you. That guarantee is what makes EIGRP loop-free without holding down, and it is why no variance value can waive it.
3. Variance is a multiplier, not a switch
Variance 2 admits any feasible successor whose FD is less than twice the best FD. You will try variance 1, see nothing happen because that is the default, and then try a large value on a path that fails feasibility and see it still refused.
The topology
R1 reaches the 192.168.50.0/24 branch via a successor with FD 3072 and a feasible successor with FD 5120 and RD 2560.
Commands to run yourself
The real diagnostic commands for this lab, copy-paste ready. Run these in the same order to reproduce the investigation on your own session.
show ip route 192.168.50.0show ip eigrp topologyshow ip protocolsTopology diagram
Frequently asked
What makes a path a feasible successor?
Its reported distance, the cost the neighbour advertises to reach the destination, must be strictly lower than your current feasible distance. That proves the neighbour is not reaching the destination through you, so using it cannot create a loop. A path can be perfectly usable in reality and still fail this test, in which case EIGRP will not treat it as a backup.
Why does a large variance not install every path?
Because variance only widens the metric window for paths that are already feasible successors. It never waives the feasibility condition, which exists to guarantee loop freedom rather than to control cost. A path whose reported distance is not lower than your feasible distance stays out of the routing table at any variance, and this is the single most misunderstood point about the feature.
How is traffic shared between unequal paths?
In inverse proportion to their metrics, so the better path carries more. That is the point of unequal-cost load balancing: rather than leaving a slower link idle or splitting traffic evenly onto a link that cannot take it, EIGRP weights the share to match the capability of each path.
Ready to run this lab yourself?
No setup, no image sourcing. Book a session or ask for a live demo.