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Some CCNP Router Config Questions

hitmen

1) what is the difference between
router ospf 1
" area 20 range 172.16.2.0 255.255.255.0" and " network 172.16.2.0 0.0.0.255 area 20" ??

These two commands look the same to me.

2) What happens if you set your router id as your loopback address but you dont advertise your loopback address in the ospf network? In that case, how will other routers know what is your rid??

3) How do you check an interface authenication?

4) How do you check the config of "router ospf 1" without using the show run command?? In the CCIE exam, I heard that the show run command cannot be used. I am not sure about ccnp.

5) Where can I find ccnp ANSWERS and EXPLANATIONS??

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Comments

iamme4eva

Hi hitmen,

1) area range is used to perform summarisation, where as the network statement is used to state which interfaces OSPF runs on and which subnets are advertised into OSPF.

2) The RID doesn't have to be routable. Although it looks like an IP address, it is just a 32 bit number that identifies the router. If it's routable you can ping it, etc, but it doesn't have to be. It's advertised within the OSPF packets as the RID.

3) To verify OSPF authentication, use show ip ospf interface <interface-id>. Towards the end of the output to that command it will say something like "simple text authentication enabled" or "message digest authentication enabled".

4) show ip protocols is a good tool for displaying information about running routing protocols.

5) That would be cheating.

Nick.

networker050184

1. One is a summurization and the other is just a simple network command.

2. The router-id doesn't need tobe routed. It is just an 'indetifier' of that router in the domain. It is not used for any forwarding purposes.

3. 'show ip ospf interface'

4. Depends on the IOS version. Use the section ro begin keywords to parse the config.

5. Your study guide.

Edit: You beat me to it!

iamme4eva

Hey networker!

Nice to see similar answers though...after having my head in switch books for 2 months, it confirms I still remember something.

Nick.

hitmen

Hey I need to clarify the summarization part.

Why do you want to summarise an area when you already summarise the network interface?
Isnt that double work????

networker050184

No, it's not the same thing. The network command does not summarize an interface. There is a lot to understand in the way of LSA propagation to get a solid grasp on OSPF summarization.

hitmen

Can you elaborate on not summarising an interface? I thought it summarise a link between two interfaces?

networker050184

The network command simply makes an interface participate in the OSPF process. Absolutley nothing to do with summarization.

NetworkVeteran

hitmen wrote:

5) Where can I find ccnp ANSWERS and EXPLANATIONS??

This would all be explained in a decent CCNP Route study guide, e.g., the Cisco Press Foundation Learning Guide.

iamme4eva

hitmen - Think of a network statement as being like a match statement. If any of the interfaces match the scope of the network statement then include the interface in the OSPF process. Subject to other configuration, at a basic level that means that should an interface match a network statement, then the OSPF process will advertise a route of the interfaces network/mask - NOT the mask of the network statement, and also look for neighbours on that interface.

i.e.
network 10.0.0.0 0.0.255.255 area 0
would match any interface with an ip 10.0.0.0 - 10.0.255.255.

However, if the interface was:

fastethernet0/0
ip address 10.0.0.1 255.255.255.0

Then OSPF would be enabled on the interface, and 10.0.0.0/24 would be advertised as a route. Notice that the network statement was 10.0.0.0/16, and this has no effect on the routing table.

Your best bet is to lab it. Connect two routers together, and try it.