Troubleshooting ECMP Load Balancing Failure: Recursive Next-Hop Resolution
Exhibit
user@router> show route 10.1.1.0/24
inet.0: 5 destinations, 6 routes (5 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
10.1.1.0/24 *[Static/5] 00:12:34, metric 0
> to 192.168.1.1 via ge-0/0/0.0
to 192.168.2.1 via ge-0/0/1.0Refer to the exhibit. How many next hops are installed for the 10.1.1.0/24 route?
⚠ Common exam trap
The trap here is that candidates often count the number of interfaces or paths shown in the output (e.g., two interfaces with two IPs each) and mistakenly think each interface represents a separate next hop, when JUNOS counts only the unique next-hop IP addresses.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
2
The route 10.1.1.0/24 has two next hops installed because the routing table shows two distinct next-hop addresses (e.g., 192.168.1.1 and 192.168.2.1) under the same route entry. In JUNOS, when equal-cost paths exist, the route is installed with multiple next hops, and the count reflects the number of unique next-hop entries, not the number of interfaces or paths in a load-balancing set.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
4
Why it's wrong here
Choosing 4 assumes the exhibit lists four distinct forwarding options for the 10.1.1.0/24 route. In Junos, only routes that share identical preference and metric are installed as ECMP next hops. Since the exhibit clearly shows just two such paths, the count is two, not four. This answer likely misreads the output columns or includes unrelated routes.
- ✓
2
Why this is correct
Two next hops are installed for the 10.1.1.0/24 route because Junos OS leverages Equal-Cost Multipath (ECMP). When the routing table contains multiple paths to a destination with identical metrics, Junos selects all of them. These paths are then installed as distinct next hops in the forwarding table, enabling traffic to be load-balanced. This directly addresses the question regarding the number of *installed* next hops.
- ✗
3
Why it's wrong here
Three would be correct only if three equal-cost paths existed in the routing table for 10.1.1.0/24. Junos installs exactly the number of routes that have equal preference and metric; a third route might appear in the table but with a worse metric, so it would not become an active next hop. The exhibit confirms both valid next hops, so three is an overcount.
- ✗
1
Why it's wrong here
Answering 1 assumes a single best path was chosen, which would happen if route preference or metric differed between the two entries. However, Junos enables Equal-Cost Multipath (ECMP) by default for IPv4: when two routes to the same destination have identical preference and metric, both are installed as next hops. The exhibit shows two such equal-cost next hops, so one is too low.
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Senior Network & Security Engineer · founder of Courseiva
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