This is the follow up discussion for the post titled, “Have you seen my Router ID?”

The underlying issue here was trying to get OSPF to bypass the usual selection process for Router ID. The normal selection order is:

Manual router ID configured under ospf process
Highest IP address of a loopback in the up state in the respective routing table
Highest IP address of an interface of an up state in the respective routing table

If there are no up interfaces and you have not manually configured a router ID, you will get an error when you try to configure an OSPF process.

In general, most solutions focused around either using the OSPF selection process to one’s advantage, or trying to “hide” the loopback from OSPF, so that it would select something else.

Some solutions were flat out wrong, because they broke the section requirements (mostly either configuring a router-id, or shutting down a loopback interface. Be sure to read the lab requirements carefully.

Solutions that didn’t work (at least on the versions that I tested)

Backup interface
The idea being that the interface is down, and will not be assigned out as a router ID. This worked fine initially, but the router grabbed the (wrong) address after a reload, violating the requirement of functionality after the reload.

Interface Dampening with a restart penalty
The idea here was presumably that the interface would start off dampened, and not be selected as the router ID. After a reload, the interface did indeed show as dampened, but the interface was still up, and was chosen as the router ID.

Solutions that worked:

Easiest / most common answer:

Two OSPF routing processes

If there are two processes configured on the router, the highest loopback will be assigned to the first one CONFIGURED, and the second highest loopback will be assigned to the second process. The first process doesn’t have to have any networks assigned, nor does it need to have a process number numerically smaller than the second process.

More complex:

One or more VRFs, possibly with secondary addresses.

Instructor Favorite (of the proposed solutions):

Kron scheduling to kick off a EEM applet when the router reloads to “no shut” the loopback interface. Since the loopback starts off shutdown, the OSPF process doesn’t use it, and grabs the other one. The EEM applet runs, enabling the loopback, allowing the networks to be advertised properly to the neighbor. Although this configuration did include the loopback being shutdown, it was only shutdown for a brief period of time while the device was loading.

(Note: Scott Morris laughed out loud when informed of this one.)

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10 Responses to “Router-ID Found! It was here the whole time.”

  1. Robert Roark says:

    Holy crap… I was way off… I know EEM is a powerful tool, but I am not that familiar with it yet. Dual router processes is brilliant. Thanks for info!

  2. Oh, you don’t need KRON scheduling. You can schedule an EEM applet to run 10 seconds after the restart ;) But I agree … it’s a hillarious use of EEM :D

  3. Murali Suriar says:

    I tried the ‘two OSPF process’ approach, but I thought it wouldn’t qualify due to the ‘must persist across reload’ requirement? The OSPF processes don’t appear to start in a deterministic order – over two reloads, OSPF process 1 was assigned first Lo111 as its RID, then Lo11.

  4. Andrius Adamavicius says:

    Yesterday you said:
    Currently we have 5 or so different working solutions, and a number of “non-working” proposed solutions.

    How does the other 2 solutions look like?

  5. Jeff says:

    Scott, glad I could provide you with some cheap entertainment! :)

  6. John Spaulding says:

    I think I say this on my lab ;)

  7. There are a variety of solutions using VRFs. In one of the earlier comments, Cristian Matei had a post listing three VRF options (comment 19), Matt Hubbard had one listed (comment 18) thinking “outside the box”. There are a couple others out there, but it gets into a bit of nitpicking as far as differentiating between similar VRF examples.

  8. Malick Ndiaye says:

    Good entertainment. Please keep coming with some more. Just to give the chance to pass their lab, I had a similar task on my CCIE lab when I was doing my OSPF section. ;-)

  9. Mohamed says:

    would you please clarify the 2nd trick briefly?

    “One or more VRFs, possibly with secondary addresses”

    Thanks in advance

  10. Prakash says:

    Would you please say on which do u have to configure multiple instance of OSPF process

    on R2 I tried while configurind second process it said RID (router id ) canoot be picked up manually configure the RID


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