From: William Lijewski (ccie8642@hotmail.com)
Date: Mon Oct 06 2003 - 12:34:51 GMT-3
Correct, I was describing how OSPF works assuming that it is the first time
it was being run on the router (i.e. the first process). Thanks for
pointing that out.
Bill Lijewski
CCIE #8642
Network Learning Inc
5 Day R&S CCIE Bootcamp Instructor
>From: "Brian Dennis" <bdennis@internetworkexpert.com>
>Reply-To: "Brian Dennis" <bdennis@internetworkexpert.com>
>To: "'William Lijewski'" <ccie8642@hotmail.com>,
><nettable_walker@comcast.net>, <ccielab@groupstudy.com>
>Subject: RE: what determines the area the router ID falls into when using
>redistribute connected subnets command ?
>Date: Sun, 5 Oct 2003 22:33:50 -0700
>
>The way you explained the OSPF router ID selection process is only true
>when
>you do not have an existing OSPF process running on the router. Each
>separate OSPF process on a router will select different IP addresses for
>their router IDs.
>
>Also in a lab environment where you might have to interact with backbone
>routers that are shared with other candidates, I would recommend using a
>router ID that is unique. 1.1.1.1, 2.2.2.2 and 3.3.3.3 may not be unique.
>In
>a home lab they will be unique. In an environment with shared backbone
>routers and other candidates also doing labs you could possibly end up
>using
>the same router ID as someone else. To help guard against this possibility
>pick an existing loopback address to hard code as your OSPF, EIGRP and/or
>BGP router ID or pick X.X.Y.Y where X is your rack number and Y is the
>device number (1=R1, 2=R2, etc).
>
>Brian Dennis, CCIE #2210 (R&S/ISP-Dial/Security)
>bdennis@internetworkexpert.com
>Toll Free: 877-224-8987
>Direct: 775-745-6404 (Outside the US and Canada)
>Internetwork Expert, Inc.
>http://www.InternetworkExpert.com
>
>
>-----Original Message-----
>From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
>William Lijewski
>Sent: Sunday, October 05, 2003 9:55 PM
>To: nettable_walker@comcast.net; ccielab@groupstudy.com
>Subject: Re: what determines the area the router ID falls into when using
>redistribute connected subnets command ?
>
>It's not really in area 1. The router ID is only the way that the routers
>see one another (ID = identifier). By default OSPF will pick the highest
>Loopback, and if there are no Loopbacks it will pick the highest active
>interface. This address that it picks is just to identify itself to other
>routers. You can override this router-id selection with the 'router-id'
>command, which I would recommed to do. The router ID that you specify for
>OSPF does not have to be routable, it does not have to be pingable, it does
>not have to be in the IP routing table of any other router. It is simply
>an
>
>identifier, nothing more.
>
>Personally, when I do a lab, I use a router ID of 1.1.1.1 for R1, 2.2.2.2
>for R2, 3.3.3.3 for R3, etc... I use these numbers so when I type in 'show
>ip ospf neighbors' I can tell at a glance who I'm neighbored with. Again,
>these router identifiers do not have to be advertised in any protocol -
>they
>
>are simply the way that the other OSPF routers will identify one another.
>
>FYI: The router ID's are important in that they are used to create
>virtual-links in OSPF. If you do not statically set the router ID's you
>can
>
>run into problems. By default OSPF will pick the highest Loopback. Say
>for
>
>example we have Loopbacks set up on our routers of 150.5.X.X, where X is
>the
>
>router number. When OSPF comes up its going to pick that 150.5.X.X IP
>address as its router ID. We will use this router ID to create a virtual
>link to another router - both sides of the virtual-link will point to the
>150.5.X.X router ID's of the other side. This will all work fine, until,
>for instance, we add higher Loopbacks for BGP, say in the 200.10.X.X range
>on the same routers. Nothing will break right away. However, if we were
>to
>
>clear the OSPF process, or the proctor was to reload the router before
>grading it, we will have a problem. When the routers come back up, or the
>OSPF process restarts, it is going to again pick the highest Loopback for
>its IP address. In this case the 200.10.X.X addresses. Our virtual-links
>are still pointing to the 150.5.X.X ID's. The 150.5.X.X addresses are no
>longer the router ID's, the virtual-link will no longer work, and you
>network will not have full connectivity. Statically setting the router
>ID's
>
>will prevent any new, higher Loopback from overriding the OSPF router ID.
>
>Bill Lijewski
>CCIE #8642
>Network Learning Inc
>5 Day R&S CCIE Bootcamp Instructor
>
>
> >From: "Richard L. Pickard" <nettable_walker@comcast.net>
> >Reply-To: "Richard L. Pickard" <nettable_walker@comcast.net>
> >To: <ccielab@groupstudy.com>
> >Subject: what determines the area the router ID falls into when using
> >redistribute connected subnets command ?
> >Date: Sun, 5 Oct 2003 23:28:14 -0600
> >
> >R_5 --- frame relay --- R_3
> >
> >Router ID =
> >
> >145.7.5.5
> >
> >
> >
> >
> >
> >debug from R_3 = 00:27:12: OSPF: Rcv hello from 145.7.5.5 area 1 from
> >Serial0/0 145.7.100.2
> >
> >
> >
> >partial config from R_5:
> >
> >
> >
> >router ospf 10
> >
> >router-id 145.7.5.5
> >
> >log-adjacency-changes detail
> >
> >redistribute connected subnets
> >
> >network 145.7.25.0 0.0.0.255 area 0
> >
> >network 145.7.100.0 0.0.0.7 area 1
> >
> >
> >
> >so why is 145.7.5.5 in area 1 (as opposed to area 0)
> >
> >Just wondering about this ---
> >
> >
> >
> >clear ip ospf process on both routers made no difference -
> >
> >
> >
> >Thanks,.
> >
> >
> >
> >Richard
> >
> >
> >
> >
> >
> >//
> >
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