I’m constantly receiving interesting OSPF-related queries. Obviously the many hidden details of the OSPF specs result in slightly unexpected behavior and constant amazement of engineers studying OSPF. During this week, I’ll focus on a few interesting OSPF intricacies.

Let’s start with an easy one: you can use the show ip ospf interface brief command if you want to display the OSPF interface status (including the interface area, OSPF cost, link type and router status on broadcast links). Unfortunately, this command does not allow you to specify the OSPF process ID and displays interfaces belonging to all OSPF processes (if you run multiple OSPF processes on the router).

To display bandwidths of all interfaces configured on the router use show interface | include protocol|BW command.

To display IP addresses assigned to router’s interfaces (excluding interfaces with no IP address) use show ip interface brief | exclude unassigned command.

Displaying the BGP routes originated in the local AS is simple: you just filter the BGP table with a regular expression matching an empty AS path. Displaying routes originated by the local router is tougher. You could use the fact that the local routes have the weight set to 32768:

PE-A#show ip bgp quote-regexp "^$" | inc Network|32768
   Network          Next Hop            Metric LocPrf Weight Path
*> 10.0.1.1/32      0.0.0.0                  0         32768 i

This would work if you don’t play with BGP weights in network statements. If you’ve changed the weights, you should filter the routes based on the BGP next-hop: locally originated routes have the next-hop 0.0.0.0 and all other routes should have a non-zero BGP next-hop. To filter BGP routes based on the next-hop you have to:

• Define an access-list that matches desired next-hop (0.0.0.0)
• Define a route-map that uses the access-list to match IP next hop.
• Display BGP routes matched by a route-map.

A sample configuration and show command printout is included below:

ip access-list standard AllZeros
 permit 0.0.0.0
!
route-map NextHopSelf permit 10
 match ip next-hop AllZeros

PE-A#show ip bgp route-map NextHopSelf | begin Network
   Network          Next Hop            Metric LocPrf Weight Path
*> 10.0.1.1/32      0.0.0.0                  0         32768 i

To make this command simpler to use, define an alias: alias exec mybgp show ip bgp route-map NextHopSelf | begin Network.

The easiest way to display BGP routes originating in the local autonomous system is to use the regular expression ^$ (empty AS-path) in the show ip bgp regexp command, for example:

PE-A#show ip bgp regexp ^$
BGP table version is 10, local router ID is 10.0.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
              r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete

   Network          Next Hop            Metric LocPrf Weight Path
*> 10.0.1.1/32      0.0.0.0                  0         32768 i
r>i10.0.1.2/32      10.0.1.2                 0    100      0 i

If you want to apply a show filter to the printout of this command, you have to use the quote-regexp variant; otherwise the rest of the line is interpreted as regular expression. To skip the header explaining the BGP status code (we know them by heart by now, don’t we?), use …

PE-A#show ip bgp quote-regexp "^$" | begin Network
   Network          Next Hop            Metric LocPrf Weight Path
*> 10.0.1.1/32      0.0.0.0                  0         32768 i
r>i10.0.1.2/32      10.0.1.2                 0    100      0 i

… and end with the eye candy – define this command as an alias: alias exec localbgp show ip bgp quote-regexp "^$" | begin Network.