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New Member

ospf rid

Can anyone tell me what this is used for, is this is what I would see in my other routers. where the route says via, will it have the RID of the other router in the table ?

14 REPLIES
Purple

Re: ospf rid

Carl,

The OSPF router ID is used to uniquely identify all the routers in the OSPF domain. As a result, it needs to be unique to each router.

When you do a 'sh ip route', it will show you the next-hop address of the router where it displays 'via'. That will not be the router ID. In fact, the router ID does not have much to do with routes. It is there simply so that routers can uniqely identify which router they are receiving information from.

Hope that helps.

Pls do take a moment to rate the posts of people who take the time to respond to your questions.

Paresh

New Member

Re: ospf rid

hi there, im still unsure what the rid is doing, Is this what the DR uses to send updates to ?

New Member

Re: ospf rid

Hi

I am completely agree with pkhatri.One thing i would like to tell that bydefault the highest ip of aphysical interface becomes the routerid.However u can configue a loopback interface(bcoz loopback never goes down and hence becomes router id).

or u can configure a router id by using follwing command

R1

R1(config)#router-id 200.200.200.200

Purple

Re: ospf rid

Carl,

It is not what the DR uses to send packets to. As I indicated in the first post, it's just an identifier. One way to think of this is to consider the following example: say you hvae 4 routers in a network. Now, each router has to have some way of identifying the others. The solution OSPF takes here is to give each router a "name" - which happens to be the OSPF Router ID. Now, every router can tell by looking at an LSA the "name" of the router it received it from.

ON a LAN segment, each router will come to find out the router ID of the DR/BDR as well as the other routers.....

Pls do remember to rate posts.

Paresh

Re: ospf rid

I will add a couple of things to what's said above. Router ID does provide some functions in addition to being a unique identifier.

In a DR/BDR election if the OSPF priorities are the same, the router with the highest router ID becomes the DR. Virtual links between the routers are created using the RID and not the interface addresses.

Pls. rate all helpful posts.

HTH,

Sundar

New Member

Re: ospf rid

Hi there, thanks for the reply, Firsty so If I did a debug on the ospf would it show packet recieved from xxxx x being the RID of the other router ? also what is the main aim of the DR and BDR, do these just send out all LSA's to the other routers rather than the other routers flooding the networks with advertisements ?

thanks

New Member

Re: ospf rid

where will I see the RID on the router, is there a command called sh ip ospf database ?

thanks

Purple

Re: ospf rid

If you just do a 'sh ip ospf' on the router, it will tell you what RID it is using...

Pls do remember to rate posts....

Paresh

New Member

Re: ospf rid

will I be able to see this from any other routers or just the router you are on ?

Purple

Re: ospf rid

That will only display the RID for the router you ran it on. To get the RIDs for all routers in the area, use the 'sh ip ospf database' command. The first part of the output will show 'Router Link States' - all of the IDs under the Link ID section of this output are the Router IDs of all the routers in that area.

Pls take a moment to rate replies to your queries as this will encourage people to continue responding to your queries...

Paresh.

New Member

Re: ospf rid

so when I do a debug on ospf, will the RID of the neighbour come up when it says I am recieving updates, or will the ip of the interface of the adjacent router be on there ?

Purple

Re: ospf rid

You will see both.

E.g If you do a 'debug ip ospf events', the output will be as follows:

Router1#debug ip ospf events

OSPF events debugging is on

Router1#

*Mar 1 04:04:11.926: OSPF: Rcv hello from 172.16.10.1 area 0 from

Ethernet0 10.10.10.2

In the above output, the RID is 172.160.10.1 whereas the interface IP is 10.10.10.2

Pls do remember to rate posts.

Paresh

New Member

Re: ospf rid

thanks for that, so just to Clarify, if we dont configure a RID it just uses the highest ip of an interface or if a loopback is configured it uses that, So its useful for debugging to see where the updates etc are coming from, just to add, am I correct in saying that on an ethernet network, All changes are propagted to the DR and then this sends them to the DRothers ?

Purple

Re: ospf rid

The rule for RID is as follows:

- highest address on a loopback interface

- if no loopback interface exists, it's the highest address on any interface that is up

The DR does indeed have the responsibility of sending all LSAs to the DROthers. If the DROthers have any LSAs to send, they send it to the DRs, and the DR then reflects them to the DROthers...

Pls remember to rate posts.

Paresh

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