CCIE Pursuit Blog

March 27, 2009

Core Knowledge Question of the Day: 27 March 2009

What is the multicast address that an OSPF device uses to communicate with the designated router?

Highlight for answer: 224.0.0.6

TIP: If you are allowed access to a command prompt during the open-ended questions and you want to verify your answer (or you know that the answer is 224.0.0.x but you forget what the last octet is)then you can always do an ‘nslookup 224.0.0.x’ and plug in values for the last octet.

Highlight below for some examples (from Linux but Windows will return the same/similar results):

1.0.0.224.in-addr.arpa    name = ALL-SYSTEMS.MCAST.NET.
2.0.0.224.in-addr.arpa    name = ALL-ROUTERS.MCAST.NET.

5.0.0.224.in-addr.arpa    name = OSPF-ALL.MCAST.NET.
6.0.0.224.in-addr.arpa    name = OSPF-DSIG.MCAST.NET.
9.0.0.224.in-addr.arpa    name = RIP2-ROUTERS.MCAST.NET.
10.0.0.224.in-addr.arpa    name = IGRP-ROUTERS.MCAST.NET.

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3 Comments »

  1. 224.0.0.5 is for all OSPF routers (should be correct answer)

    224.0.0.6 is for DR’s (only DR & BDR can communicate with this multicast)

    Comment by Vern — March 27, 2009 @ 8:36 am | Reply

  2. This is cool; however, it will only work if you have internet connection to resolve DNS. I doubt it if you have the cmd line or DNS in the lab.

    Comment by acg — March 27, 2009 @ 8:57 pm | Reply

  3. cool tip, thanks.

    Comment by ryan — April 2, 2009 @ 7:03 pm | Reply


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