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can a ospf router have more router id in more areas?

i've saw an example from <TCP/IP routing vo.1> it seems a router could have 2 router id in different areas.is it possible?

7 REPLIES
Purple

Re: can a ospf router have more router id in more areas?

Hi,

That is not correct. An OSPF router can only have a single OSPF router ID. It cannot have different IDs for different areas.

Hope that helps .. pls rate posts that help.

Paresh.

VIP Purple

Re: can a ospf router have more router id in more areas?

Hello,

on a side note, and in addition to Paresh´s post, you might be confusing this with running two OSPF processes on the same router, in which case you actually can assign two different router id´s:

Router

!

router ospf 1

router-id 1.1.1.1

!

router ospf 2

router-id 2.2.2.2

In that context, it might be worth mentioning that the router ID is the tie-breaker for OSPF path selection. The path selection process uses a variety of metrics to select a route. If all other metrics (accessibility, administrative weight, local preference, etc.) are equal, OSPF uses the router ID for path selection.

Regards,

GP

Re: can a ospf router have more router id in more areas?

Hi GP,

now I believe you mixed OSPF and BGP ;-)

First, I totally agree to the config examples you gave and that with each OSPF process you will have another OSPF router ID.

But OSPF will not use the router ID as a tie breaker, but install routes with equal metric (solely cost) in the IP routing table for load sharing purposes.

BGP does use the BGP router ID as a tie breaker under certain conditions and uses loc pref and other values for path selection.

Hope this helps! Please rate the posts

Martin

VIP Purple

Re: can a ospf router have more router id in more areas?

Martin,

I think I need a vacation ! Will go skiing for a week...;)

Regards,

GP

Re: can a ospf router have more router id in more areas?

Hello GP, have fun!

Martin

P.S.: better stay in one skiing area ... not to trigger bad memories ;-)

Cisco Employee

Re: can a ospf router have more router id in more areas?

Just as a precision, IOS would not install two routes from two different processes for load-balancing purposes.

It will rather pick the route based on which process installs it first in the RIB. Metrics or route types (intra-area, inter-area, external) are not compared between processes. Only the AD would be consider and they are equal by default. For this reason timing would be the only factor unless you change the AD for one of the processes.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México 
Paseo de la Reforma 222 Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

Re: can a ospf router have more router id in more areas?

Thank you Harold,

in the post I was indeed thinking about one OSPF process and the route selection within, but this didn´t come out clearly.

Cheers

Martin

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