Hi, I'm trying to understand routing in Junos. In particular, hidden routes.
Correct me if I'm wrong, but I understand that a hidden route is a route that can never be selected as active due to some issue.
The issue could be something like an unresolvable next-hop, or a reject in a policy.
To have a look at this, I tried to create a hidden route using:
set routing-options static route 169.254.1.1/32 next-hop 10.10.10.10
10.10.10.10 is an IP that my switch can't reach. I do have a default route, but this is not a real IP on my network.
As I would expect, this route does not appear in the routing table.
However, it also does not appear when using:
show route hidden
Have I misunderstood something? Is this not considered a hidden route?
Hi Luke Robertson,
yes, hidden routes are due to unresolvable next-hop or a reject in a policy as you mentioned, however, if you don't have any IP configured on the switch within your subnet (10.10.10/24) , the route will not be even created in the routing table, so this won't even be hidden in first place.
if you do "show route 169.254.1.1/32" it won't show anything because the route is not even active in the RT or because your outgoing interface is not configured (as you mentioned before).
hope this helps!
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Yeah, this makes sense, thanks.
What would count as an unresolvable next-hop in this case? A case where ARP fails to map the next-hop IP to a MAC?
Hi Luke Robertson,
it depends of so many factor - ARP failure, route flapping, policies , directly connected next hop not being resolved (you need to use the resolve command after static route command so it perform recursive lookup), misconfiguration , NH not reachable , memory issues, router dropping the arp ... you name it 🙂
Excellent! Makes full sense now, thanks!