Floating Static Route: Preference-Based Backup
Your company operates a dual-homed network with two Juniper MX routers (R1 and R2) each connected to a different ISP. R1 uses BGP to receive a default route from ISP-A (preference 170), and R2 uses BGP to receive a default route from ISP-B (preference 170). Additionally, both routers have a static default route pointing to a local next-hop (192.0.2.1) with preference 5 for backup. R1 and R2 are connected via an internal link (10.0.0.0/30) and run OSPF to exchange internal routes. You notice that traffic from internal hosts is always exiting via R1's ISP-A link, even when R1's BGP session to ISP-A goes down. The OSPF routes are preferred. You want traffic to fail over to R2's ISP-B link when R1 loses its BGP default. Which configuration change should you make?
Quick Answer
The correct answer is to configure the static default route with a preference of 180. This works because the floating static route preference determines which route is installed in the routing table when multiple routes to the same destination exist; a lower preference value is more preferred. Here, the static default route’s preference of 5 made it win over the BGP default (preference 170), so traffic never used the BGP-learned route. By raising the static route’s preference to 180—higher than BGP’s 170—you create a true backup: the BGP default is chosen when available, and the static route only activates when BGP fails. On the JNCIA-Junos exam, this tests your understanding of route preference as a tie-breaking mechanism, often with a trap where candidates forget that a static route’s default preference (5) overrides dynamic protocols. A helpful memory tip: “Static is king by default—raise its preference to make it a backup.”
⚠ Common exam trap
Watch out — candidates often assume static routes with a lower preference are always better, but the question requires the static route to act as a backup, so it must have a higher preference than the BGP route to be less preferred when the BGP route is available.
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
✓
Configure the static default route with a preference of 180 so that the BGP default routes (pref 170) are preferred when available.
The static default route currently has a preference of 5, making it preferred over the BGP default (preference 170) even when the BGP route is available. By raising the static default's preference to 180 (higher than BGP's 170), the BGP default will be chosen when present, and the static default will only be used as a backup when BGP is unavailable. This ensures traffic fails over to R2's ISP-B link when R1 loses its BGP default, as OSPF will propagate the default from R2.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Increase the preference of the BGP default routes to 180 so that the static default is always preferred.
Why it's wrong here
This would make the static default always active, preventing failover between ISPs.
- ✗
Configure a routing policy on R2 to reject the default route from ISP-B, forcing all traffic through R1.
Why it's wrong here
This would eliminate redundancy.
- ✗
Remove the static default route and rely on OSPF to propagate a default route from the router with the active BGP session.
Why it's wrong here
Without any static default, if both BGP sessions fail, there is no default route.
- ✓
Configure the static default route with a preference of 180 so that the BGP default routes (pref 170) are preferred when available.
Why this is correct
This ensures BGP default is used when up, and OSPF routes to R2's default become active when R1's BGP is down.
Visual reference
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
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Same concept, more angles
1 more way this is tested on JN0-106
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. An engineer wants to configure a static route that will be used only if the primary route (learned via OSPF) becomes unavailable. Which feature should be used?
easy- ✓ A.Floating static route with a higher preference.
- B.Static route with a lower metric.
- C.Reverse path forwarding.
- D.Routing policy.
Why A: A floating static route is configured with a higher preference (administrative distance) than the OSPF-learned route. Since JUNOS prefers routes with lower preference values, the static route will only be installed in the routing table when the OSPF route is withdrawn, providing a backup path.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This JN0-106 practice question is part of Courseiva's free Juniper Networks certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the JN0-106 exam.