OSPF Commands

[Juraj Papic]

Greetings,

When you go to the new customer and you have to support/Troubleshoot  the network (in this case is OSPF) how will you proceed or what commands will you use in the network to know how ospf is working?

thanks. 

[pman]

Hi,

in case of Troubleshoot,

the following link should provide all the information you need according to the relevant scenario

please note the "show" commands in bold inside the rhombus

https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/12151-trouble-main.html

[MHM Cisco World]

What commend you looking for

there are commend for config

and commend for troubleshooting?

[Juraj Papic]

Hi all,

Im not looking for a specific command , I'm want to understand how other Ing approach to understand a new network cliente. I know you my request a HLD or LLD, but we know that in most of the cases that is not updated .

In my case I normally try to understand how the traffic flows, check if the traffic is symmetric or asymmetric .

Thanks.

[MHM Cisco World]

Traceroute 

this can help you in symmetric asymmetric issue.

if the traceroute show you two different hop in outbound direction 

check if ospf have equal cost then it ok and traffic is symmetric 

if the traceroute show  you two different hop in inbound direction 

then traffic go and return from different router and this asymmetric 

[David Ruess]

Hello,

My main commands for looking at and troubleshooting OSPF are as follows:

sh ip ospf interface brief <- this shows you what interfaces are operating with ospf. This does not include passive interfaces I believe. If it does not show up here it will NOT form a neighbor adjacency

sh ip ospf neighbors <- this shows you which interfaces have established neighbor adjacencies along with DR/BDR information on that link if applicable

show ip protocols <- this will show stuff like passive interface, reference bandwidth, networks advertising for and other metrics

sh ip ospf databse <- this is the OSPF database and everything it knows about the current structure of the network. This probably has the most information but is the most cumbersome to understand, especially in a new network.

There are many commands, these are just my go-to commands for tshooting and understanding.

Hope that helps

-David

[Deepak Kumar]

I think, no one have a direct answer for this and if I would say check OSPF database for whole network seating on a single router/switch, can you do it? 

So, don't try to fly a flight without going on the runway. Try to figure about what is issue? If you are not sure how to identify than i would recommend to go with a flow chart from top to down or down to top. Think about it, Which flow chart is good for your position. 

https://petri.com/ccnp-tshoot-cisco-troubleshooting-techniques/

however this guide will help you:

https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/12151-trouble-main.html

https://www.learncisco.net/courses/icnd-2/implementing-a-multiarea-ospf-solution/troubleshooting-multiarea-ospf.html

[Jon Marshall]

First thing is to look at the IP routing table and work out what subnets are where ie. forget about the specific routing protocol in use until you understand the L3 layout. 

Then you can start to look at the OSPF specifics with the commands and advice provided here. 

Jon

[Joseph W. Doherty]

Well, when troubleshooting a network issue, I would first like to gather as much information about the "issue" as possible.  This before I would investigate whatever routing is configured/used, whether implicit, static or using an IGP (like OSFP),

[Jon Marshall]

So you would wait for the first problem before you try and work out how the network works ?

You like a challenge then. 

Jon

[Joseph W. Doherty]

I do like challenges, but laugh, I think I focused too much on OP's "troubleshooting".  I.e. before I troubleshoot, I do like to know what the "trouble" is. 

Troubleshooting aside, though, OP also mentioned supporting a new customer network.  Also, again, I ran by that (supporting) to troubleshooting.

For supporting a new network, generally I like to start with a diagram of the network, check its accuracy and "learn" the network, including things like what IGP is being used, and for something like OSPF, including, yes, ". . . how ospf is working?", in the sense of OSPF topology, OSPF areas, kinds of areas, ABR summarizations, etc.  "Learning" the network, though, often includes much. much more than what is the IGP and how it's set up. 

Unfortunately, there are times, especially when working with a "new" (to you) network, where this is some "problem" and you need to immediately start troubleshooting.  In such cases, I start with "what's been changed last?" (often the source of a new problem) and proceed to further investigate/learn network functions that might cause the kind of trouble being reported.  Again, I like to learn as much about the "trouble", as the nature of the "trouble" often helps in directing your troubleshooting.