Re: about OSPF router ID

From: Roy Waterman (roy.waterman@gmail.com)
Date: Sat Jan 31 2009 - 19:57:16 ARST

Id err love to say i "forgot" about that one too lol, but in my case Id be
lying :)

Thanks for the "reminder" Narbik ;)

Feel free to "remind" me about a lot of other aspects of routing that ive
"forgotten"

On Sat, Jan 31, 2009 at 8:03 PM, swm@emanon.com <swm@emanon.com> wrote:

> heheheh... Yup, forgot about that one. 'No sync' is the default command
> now, but you're right, if you need to turn it on, the BGP RFC states that
> the
> router-id's must match.
>
> Thanks for reminding me! :)
>
> Scott
>
>
> ---- Message from Narbik Kocharians <narbikk@gmail.com> at 2009-01-31
> 10:26:01
> ------
> >
> >I totally agree with Scott, the OSPF router id is a 32 bit dotted decimal
> number, it can be an IPv4 address, but it can also be any dotted decimal
> number like "0.0.0.1" for R1 and so forth.
> >
> >One problem that you may run in to (In a CCIE LAB) is when you have OSPF
> and
> BGP with synchronization enabled in an AS, the router that redistributes
> the
> BGP routes into OSPF must have the same router-id configured on both
> routing
> protocols (meaning OSPF and BGP router-id must be identical on that router)
> and in this case you won't be able to use anything other than a valid IP
> address, because BGP's router-id must be a valid IP address.
> >
> >Hope this helped.
> >
> >
> >On Sat, Jan 31, 2009 at 3:57 AM, ciscozest <mailto:ciscozest@gmail.com >
> wrote:
> >
> >
> >Dear Scott, Jared, Roy and Jason,
> >
> >Thank you all for the input. Really appreciate that. Have a nice weekend
> :)
> >
> >
> >-----Original Message-----
> >From: mailto:swm@emanon.com [mailto:mailto:swm@emanon.com ]
> >Sent: Saturday, 31 January 2009 3:23 PM
> >To: Jared Scrivener; 'Jason Madsen'; 'ciscozest'
> >Cc: 'Cisco certification'; 'Cisco certification'
> >
> >
> >
> >Subject: RE: about OSPF router ID
> >
> >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" <mailto: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: mailto:jscrivener@ipexpert.com
> >>
> >>-----Original Message-----
> >>From: mailto:nobody@groupstudy.com [mailto: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 <mailto: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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> >>
> >>
> >
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> 14:34
> >
> >
> >
> >
> >
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> >
> >
> >
> >
> >
> >
> >--
> >Narbik Kocharians
> >CCSI#30832, CCIE# 12410 (R&S, SP, Security)
> >http://www.MicronicsTraining.com www.MicronicsTraining.com
> >http://www.Net-Workbooks.com www.Net-Workbooks.com
> >Sr. Technical Instructor
>
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-- 
Regards
Roy

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