How to Interpret Output from Junos Show Route Detail Command - dummies

How to Interpret Output from Junos Show Route Detail Command

By Walter J. Goralski, Cathy Gadecki, Michael Bushong

If the ouput from the base show route command doesn’t satisfy your hunger for knowledge, you can get a bit more detailed in your examination. To see more routing information, use the detail modifier after the show route command.

user@router1> show route detail
inet.0: 22 destinations, 23 routes (21 active, 0 holddown, 1 hidden) (1 entry, 1 announced)
    *Static Preference: 5
        Next-hop reference count: 29
        Next hop: via fxp0.0, selected
        State: <Active NoReadvrt Int Ext>
        Local AS:  69
        Age: 1:31:43
        Task: RT
        Announcement bits (2): 0-KRT 3-Resolve tree 2
        AS path: I (2 entries, 1 announced)
    *Direct Preference: 0
        Next hop type: Interface
        Next-hop reference count: 2
        Next hop: via so-0/3/0.0, selected
        State: <Active Int>
        Local AS:  69
        Age: 1:30:17
        Task: IF
        Announcement bits (1): 3-Resolve tree 2
        AS path: I
     OSPF  Preference: 10
        Next-hop reference count: 1
        Next hop: via so-0/3/0.0, selected
        State: <Int>
        Inactive reason: Route Preference
        Local AS:  69
        Age: 1:30:17  Metric: 1
        Task: OSPF
        AS path: I
(output snipped)

The detailed listing for your routes lists a little more information for each route. Most of that information is a bit esoteric, but some of it can be downright helpful. Here are a couple of output fields that you may enjoy knowing more about:

  • Age: This field tells you how long the route has been in the routing table. Imagine that traffic destined for a particular address experiences some problems.

    You may want to check the age to see whether there was a problem where the route was dropped from your routing table. So you look at the detailed routing information, and if the age is less than anticipated, you know that the route was newly added (or added again) to the routing table — a certain clue that something is amiss and you need to delve deeper.

  • Inactive reason: You may have an inactive route that is being supplanted by some other route to the same host. For example, if you’ve set up label-switched paths (LSPs) in your network with multiprotocol label switching (MPLS), you may be expecting traffic to flow a certain way. The inactive reason gives you an idea as to why a particular route has been preempted by another route.

    From the output, you can see that you have multiple routes to the destination In this case, the OSPF route is inactive because the route preference for an OSPF route is of lower priority than that of a direct route (nothing beats a direct route, which has a priority of 0 and means the router is directly connected to the destination sub-net).

Most of the other fields in the show route detail output are used very rarely.