Neighbor config in OSPF

[omal]

Hi

This is a little confusing to me. In a non-broadcast environment that is obvious that you have to configure neighbors manually, by usiing the command:

Router(config-router)#neighbor x.x.x.x

My question is, do you have to give the addtional commands priority or cost after this or just assigning neighbors like above is enough?

That is:

a) Router(config-router)#neighbor x.x.x.x

b) Router(config-router)#neighbor x.x.x.x priority x

c) Router(config-router)#neighbor x.x.x.x cost x

In the above a,b,c which one is actually correct?

I tried with option (a) with a back-toback scenario and it worked. That is why I am confused, as to whether you really need either the option (b) or (c) or both, i.e. (b) & (c)

Thanks in advance!

Omal.

[smif101 · Accepted solution]

Configuring the neighbor command is just fine the priority and cost commands are optional. The priority command is used to deal with DR and BDR and the cost command deals with metrics.

Jason Smith

www.smif101.com

[samsam_wang]

For the hub-router

use

ip ospf prio 254

for the spoke router

use

ip ospf prio 0

[omal]

Hi Samsam

Thank you very much for the time that you have taken to give me an answer.

Could you please explain the spoke router a little bit if you don't mind? Hub router is I guess the router that you have hub ports for ethernet I guess. Please correct me if I'm wrong.

And can you also please tell me why do you say specifically 0 & 254 priorities?

Thanks again!

Omal.

[thisisshanky · Accepted solution]

Omal,

All 3 commands are correct. Priority and cost commands are optional parameters you can specify.

[omal]

Hi Thanks Shanky for your answer as well. Samsam has given a little diffrent answer to both of you. It sounds interesting. I'm just waiting to get it clarify from him.

Thanks again!

Omal.

[thisisshanky]

Omal,

Sam's answer is with respect to fixing who the DR in the cloud is..Its advisable to fix the hub router as the DR. So you can force the priority on the hub site to a higher value say 254. Force the priority on the spoke side to a value of 0, which would make them not participate in a DR/BDR election.

Alternative way to do this is, on the hub site use the command,

neighbor priority 0

On the spoke site, use command, neighbor priority 254.

The default value for neighbor priority is 0, so I think you dont have to specify the priority value as 0 at the Hub. Hope that helps!

[omal]

Hi Shanky

But what I don't understand in his answer is that what is this (well if I take it from your answer now):

1) hub router

2) spoke side

May be I haven't done that part in Cisco. Please clarify that to me, if you have some time to spare. I really appreciate it.

Thanks a lot, again.

Omal.

[jamey]

The hub router is the router with connections to all the spokes.

Like this:

Hub_Router---SpokeB

|

|

Spoke A

Check out this doc:

http://www.cisco.com/en/US/tech/tk713/tk237/technologies_tech_note09186a008014f8a7.shtml

There is a section called Hub and Spoke. In that section there is a diagram with 3 routers:

Spicey

Prasit

Aton

Spicey is the "hub" and Prasit and Aton are the "spokes"

-HTH

[omal]

Hi Jamey

Thanks a lot for your answer. I just have one question before we close this forum.

When we configure neighbors, (let's say in NBMA network), is it neighbors Router ID that we give for command or the same subnetwork interface ip address?

That is:

Let's say we are configuring neighbors to Router A.

Router B's Router ID is 2.2.2.2

In this NBMA network, Router A's interface ip address is, 10.10.10.1/24

And Router B's interface ip address is 10.10.10.2/24

Then when we give the neighbor command:

1) RouterA(config-router)#neighbor 2.2.2.2

2) RouterA(config-router)#neighbor 10.10.10.2

Is the option 1 or 2 correct?

Thanks in advance!

Omal.

[jtantsura]

Omal,

priority 0 means that this interface on this router will never become a DR or BDR.

[omal]

Hi Jeff

Thanks a lot. Yes you are right. I understand that part about priority 0, is it possible for you to give me an answer for that neighbor ip address post that I've posted a little while. The one which is just on top of your post?

Thanks in advance!

Omal.

[jamey]

You use the interface IP to define neighbors so option #2 would be correct in your example.

Here's more info on the neighbor command:

http://www.cisco.com/en/US/products/sw/iosswrel/ps1826/products_feature_guide09186a0080087d4e.html#33327

-HTH

[omal]

Hi

Thank you so much for the URL.

By the way do you know of any links for me to download about IS-IS. I mean if I need to study that from the beginning. I searched it on cisco.com today but couldn't find the kinda link that I am looking for. I mean a documentation which explains from the beginning of IS-IS. Let's say to someone who knows OSPF but who wants to learn IS-IS from the beginning.

Thanks in advance!

Omal.

[jamey · Accepted solution]

These may be of use:

http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/osi_rout.htm

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fipr_c/ipcprt2/1cfisis.htm

http://www.ciscopress.com/articles/article.asp?p=26850&seqNum=1

-HTH