JNCIE-SP: Using help from the Junos CLI

One of the tools at your disposal during the JNCIE-SP exam is the JUNOS CLI itself and there is an awful lot of documentation stored in it.

Help Apropos

The first tool you will need to learn how to use to take advantage of this is “help apropos XXX”.

Here are a couple of example outputs:

 lab@R1> help apropos anycast                       
 help topic pim examples anycast 
     Overview of anycast RP example
 help reference pim local-address 
     Local address for anycast rendezvous point
 help reference pim address-anycast 
     Anycast rendezvous point addresses in RP set
 help reference pim anycast-pim 
     Anycast rendezvous point using PIM
 help reference pim rp-set 
     Set of up to 15 rendezvous point addresses for anycast RP

 lab@R1> help apropos interpro 
 help topic layer3-vpns examples-cofc 
     Sample interprovider and carrier-of-carriers VPNs
 help topic layer3-vpns examples-cofc interprovider-ebgp 
     Overview of interprovider with multihop MP-EBGP
 help topic layer3-vpns examples-cofc interprovider-isp 
     Overview of interprovider with MP-EBGP between ISP peers
 help topic layer3-vpns examples-cofc terms 
     Terms in carrier-of-carriers and interprovider examples
 help topic layer3-vpns interprovider 
     Overview of interprovider VPNs

As you can see above, “help apropos…” acts as a sort of keyword search for the help system.

Beyond that, “help apropos…” can provide a context-sensitive search CLI commands.


 lab@R1> help apropos pfe      
 clear pfe 
     Clear Packet Forwarding Engine information
 show pfe 
     Show Packet Forwarding Engine information
 show pfe version 
     Show pfe version

lab@R1> help apropos uptime      
show system uptime
    Show time since system and processes started
show chassis pic
    Show Physical Interface Card state, type, and uptime


 [edit protocols bgp]
 lab@R1# help apropos override 
 set group  as-override 
     Replace neighbor AS number with our AS number
 set group  neighbor <address> as-override 
     Replace neighbor AS number with our AS number

 [edit policy-options]
 lab@R1# help apropos route-type 
 set policy-statement  term  from route-type 
     Route type
 set policy-statement  from route-type 
     Route type

Help Reference and Help Topic

Your mileage will vary with these help outputs. The output seems to be nearly verbatim copy from the JUNOS documentation. Where you would normally have images, you instead find a URL for a GIF. That may not turn out to be too helpful for someone who is completely blanking on how to configure something but if you forget a detail or two, it can probably save you a lot of time.

For instance, I forgot about which MPLS TTL mechanism supported LDP. So I ran a search and pulled up the reference for no-propagate-ttl

 lab@R1&gt; help apropos no-prop                  
 help topic mpls no-propagate-ttl 
     TTL value is decremented by 1 only
 help reference mpls no-propagate-ttl 
     TTL value is set to 255

 lab@R1&gt; help reference mpls no-propagate-ttl 


    Disable normal TTL decrementing. You configure this statement once per
    router, and it affects all RSVP-signaled or LDP-signaled LSPs. When this
    router acts as an ingress router for an LSP, it pushes an MPLS header with
    a TTL value of 255, regardless of the IP packet TTL. When the router acts
    as the penultimate router, it pops the MPLS header without writing the
    MPLS TTL into the IP packet.

By chance, this happened to be the correct one to configure to support LDP.

There is some seriously detail information available if you need it. For an example, see “help topic pim auto-rp”. It tells you just about every step you need to configure.

Good luck!