From: swm@emanon.com
Date: Sat Jan 31 2009 - 03:22:54 ARST
Actually, it not only doesn't need to be pingable, but it doesn't even need to
be a valid IPv4 address. It's simply a 32-bit number.
If you're bored, make your router-id's 240.1.1.1, 240.1.1.2, 240.1.1.3, etc.
Definitely can't put that on an IP interface... Definitely can't ping it.
But it works just fine.
Jared's got a point about name lookups, but on the other hand, if you properly
populate your DNS lookups you'll be good on that one!
Real life, most people use a loopback, whatever your main management interface
happens to be. Just keeps things simple. But it's just a 32-bit number, so
the fact that it relates to an actual IP address is for OUR benefit, not the
routers'!
Scott
---- Message from "Jared Scrivener" <jscrivener@ipexpert.com> at 2009-01-30
21:25:18 ------
>Whilst it is true that an OSPF Router ID doesn't have to be pingable, it
>generally makes life easier to use a reachable IP (normally Loopback 0).
>
>Let's say that you are asked to also turn on "ip ospf domain-lookup" which
>will translate your neighbor's Router-ID into a DNS name (which will either
>be defined by a hosts file or received via DNS).
>
>If you do it via hosts entries and your are ALSO a DNS server then your DNS
>clients would receive an unreachable IP address when they ping via DNS name.
>
>I know that's a rare case, but given the nature of question interdependency
>on the lab (and the evil nature of workbook vendors) I personally use L0 as
>my OSPF Router-ID (and set it manually using the "router-id" command) every
>time unless otherwise directed.
>
>Cheers,
>
>Jared Scrivener CCIE3 #16983 (R&S, Security, SP), CISSP
>Technical Instructor - IPexpert, Inc.
>Telephone: +1.810.326.1444
>Fax: +1.810.454.0130
>Mailto: jscrivener@ipexpert.com
>
>-----Original Message-----
>From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
>Jason Madsen
>Sent: Friday, 30 January 2009 9:01 PM
>To: ciscozest
>Cc: Cisco certification; Cisco certification
>Subject: Re: about OSPF router ID
>
>OSPF Router IDs can be any UNIQUE IPv4 address...they don't have to be
>addresses assigned to an interface.
>
>On Fri, Jan 30, 2009 at 6:56 PM, ciscozest <ciscozest@gmail.com> wrote:
>
>> Hi all,
>>
>>
>>
>> I read Cisco press book stated that OSPF router ID do not need to be
>> pingable. In this case if I use a router ID which is not assigned to any
>> interface on that router, would this cause any issue such as OSPF
>> adjacency,
>> LSA table advertisement, etc? Has anyone do this before and can enlighten
>> me? Thanks.
>>
>>
>> Blogs and organic groups at http://www.ccie.net
>>
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