Isolating the Causes of a Network Problem
Problem
Description
A particular symptom can be the result of one or more causes. Narrow down the focus of your search to find each individual cause of the unwanted behavior.
Solution
To isolate the cause of a particular problem, enter one or all of the following Junos OS CLI operational mode command:
user@host> show < configuration | bgp | interfaces | isis | ospf | route >
Your particular problem may require the use of more than just the commands listed above. See the appropriate command reference for a more exhaustive list of commonly used operational mode commands.
Sample Output
user@R6> show interfaces terse
Interface Admin Link Proto Local Remote
so-0/0/0 up up
so-0/0/0.0 up up inet 10.1.56.2/30
iso
so-0/0/2 up up
so-0/0/2.0 up up inet 10.1.26.2/30
iso
so-0/0/3 up up
so-0/0/3.0 up up inet 10.1.36.2/30
iso
[...Output truncated...]
The following sample output is from R2:
user@R2> show route 10.0.0.5
inet.0: 22 destinations, 25 routes (22 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
10.0.0.5/32 *[Static/5] 00:16:21
> to 10.1.26.2 via so-0/0/2.0
[BGP/170] 3d 20:23:35, MED 5, localpref 100
AS path: 65001 I
> to 10.1.12.1 via so-0/0/0.0
Meaning
The sample output shows that all interfaces on R6 are up. The output from R2 shows that a static route
[Static/5] configured on R2 points to R6 (10.1.26.2) and is the preferred route to R5 because of its low preference value. However, the route is looping
from R2 to R6, as indicated by the missing reference
to R5 (10.1.15.2).