From: Kelly Johnson (kelly080180@hotmail.com)
Date: Tue Oct 07 2003 - 01:04:36 GMT-3
Just curious: what's gonna happen if you really have 2 identical OSPF
router-id?
----- Original Message -----
From: "Brian Dennis" <bdennis@internetworkexpert.com>
To: "'William Lijewski'" <ccie8642@hotmail.com>;
<nettable_walker@comcast.net>; <ccielab@groupstudy.com>
Sent: Sunday, October 05, 2003 10:33 PM
Subject: RE: what determines the area the router ID falls into when using
redistribute connected subnets command ?
> 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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