From: Howard C. Berkowitz (hcb@gettcomm.com)
Date: Tue Feb 03 2004 - 17:45:15 GMT-3
At 10:14 PM +0200 2/3/04, K. Tahsin Hersan wrote:
>Howard,
>
>I agree your arguments.I do same thing as you do.
>For example, I know OSPF next-hop behaviour in various network types.
>
>But i am trying to understand a different behaviour.
>Since 0.0.0.0 as router-id is possible (according to RFC2328), we should be
>able to use it.
My recollection, from OSPF Working Group meetings, is that no one who
worked on the standard thinks that 0.0.0.0 should ever be used as a
router ID. Whether or not 2328 makes this clear is another matter.
It certainly was discussed on the mailing list and at IETF meetings I
attended.
What I quoted shows a number of specialized uses of the 0.0.0.0
value. It would seem very easy to get into trouble with a router
with a deliberately set ID of 0.0.0.0, which then gets involved in DR
election. I just don't see any good reason to use 0.0.0.0 even if
it's explicitly forbidden.
To me, the IOS behavior of changing 0.0.0.0 to something else is very
reasonable in terms of preventing errors. Just because something is
possible doesn't mean it's a good idea to do it.
>
>I tried to set router-id to 0.0.0.0 but router acts strange when i do it.
>It does not restrict you to enter the command but when you do show ip ospf,
>you dont see 0.0.0.0 as router-id. Depending on IOS version/platform,
>either 0.0.0.1 is set instead of 0.0.0.0 or nothing changes.
>
>Cheers,
>
>Tahsin
>
>-----Original Message-----
>From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
>Howard C. Berkowitz
>Sent: Tuesday, February 03, 2004 7:38 PM
>To: ccielab@groupstudy.com
>Subject: Re: OSPF Router-ID
>
>
>At 4:29 PM +0200 2/3/04, Tahsin Hersan wrote:
>>Hi,
>>
>>I am trying to be creative :) and I was wondering how we can set router-id
>>to 0.0.0.0 if we want to? We can do it on other vendors boxes like nortel /
>>lucent but on cisco i couldnt do it.
>>
>>"router-id 0.0.0.0" command accepted by router but it sets router id to
>>0.0.0.1.
>>
>>Any comments / advises?
>>
>>Best Regards,
>>Tahsin
>>
>
>What problem are you trying to solve with this creativity?
>Seriously, whenever I run into a restriction like that, I tend to
>want to look at the protocol specification (in this case, RFC 2328)
>to see if there is a reason for the restriction. In particular, my
>experience tells me that all zeroes and all ones values are
>frequently reserved for some protocol-specific question.
>
>Again trying to be helpful, the understanding needed at the CCIE
>level isn't likely to come simply from exploring the ranges of
>parameters than can be set.
>
>For example, on page 65:
>
>The Designated Router selected for the attached network. The
>Designated Router is selected on all broadcast and NBMA networks
>by the Hello Protocol. Two pieces of identification are kept
>for the Designated Router: its Router ID and its IP interface
>address on the network. The Designated Router advertises link
>state for the network; this network-LSA is labelled with the
>Designated Router's IP address. The Designated Router is initialized
>to 0.0.0.0, which indicates the lack of a Designated Router.
>
>... The Backup Designated Router is initialized to 0.0.0.0
>indicating the lack of a Backup Designated Router.
>
>Or on page 77,
>
>The Hello packet also contains the IP address mask of the attached
>network (Network Mask). On unnumbered point-to-point networks and
>on virtual links this field should be set to 0.0.0.0.
>
>These are not the only special cases of 0.0.0.0; other applications
>include default destinations of router IDs.
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