Ok,
I'll join the party... Of course we'll make some
assumptions(without making an .. of myself or anyone else)
My first thought here is ask another question...? "They share an Ethernet"
you say.
From the looks of it this could mean R1 E1 <--> R2 E1 is connected or
R1 E2 <--> R2 E2 is connected which would of course change the outcome of
this
little "fendish scenario". I choose do the first option simply because you
mention a
device on R1 E2 being able to reach a host on R2 E2....
My fist stab at this.. Assuming that R1 E1 <--> R2 E1 is the common shared
medium
for these two devices with R1's E1 = 10.5.0.2 being the highest
address(noting that
E0 is in a down state and will not be used) should become the DR, but when
R2's E1 interface comes online with an identical address no OSPF
relationships should
be formed because the RID would be identical on both devices, as well (with
no IP
connectivity between) these devices would not be able to see each other.
Now, once
the "heroine" corrects the problem R2's E1 interface would in effect be the
DR after the
IP connection is established. This being the case, I don't see the need for
clearing
the ospf process. A thought as to what happens once the neighbor
relationships is formed
and both routers begin to advertise a route to the 10.2.0.0 network...?
Thoughts, well within each router there will be a connected interface for
this
network (10.2.0.0 and 10.5.0.0 )which would logically replace any learned
route
for the neighboring router. The other obvious thought is that a host
trying to ping/reach
another device at R2's E2 interface would try to ping a device on the local
segment
which would not be there in effect.... time-out..!
So the answer... No.. Now, I'm off to mock this up on the home lab to
see what other fenish
occurrences I can find
So, just how far off am I..... and just how much of a fool did I make of
myself...
Nigel
----- Original Message -----
From: Howard C. Berkowitz <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Wednesday, November 29, 2000 8:37 PM
Subject: RE: About OSPF and Loopback port
> At 10:45 AM -0800 11/29/2000, Healis, Jim wrote:
> >Use loopback ports in OSPF so you can set the Router OSPF ID, otherwise
it
> >will take the highest IP address.
> >
> >Jim Healis CCNP, CCDP
> >Senior Network Administrator
> >Virata
>
> Unless there have been recent IOS changes (I'm really most current in
> 11-something), it's even more unpredictable than just the highest IP
> address:
>
> At the time of OSPF initialization, the router ID is:
>
> if there are multiple loopback interfaces, the highest IP address on
any
> loopback (i.e., not highest loopback interface number)
> if there is a single loopback interface, use its address
> if there are no loopback interfaces, use the highest IP address on any
> active interface (i.e., if all interfaces are in shutdown, OSPF
> can't initialize. Using loopbacks avoids this because a loopback
> cannot be down.)
>
> A fiendish troubleshooting scenario:
>
> R1 comes up first, then R2. They share an Ethernet. Neither has
> any loopbacks.
>
> Scenario 1 (R1 is initially misconfigured)
> R1 E0: 10.6.0.1 DOWN R2 E0: 10.1.0.1 UP/UP
> E1: 10.5.0.2 UP/UP E1: 10.5.0.2 UP/UP
> E2: 10.2.0.1 UP/UP E2: 10.2.0.2 UP/UP
>
> Admin discovers that R1 E1 is misconfigured and should have been
10.5.0.1.
> Our Heroine corrects that interface to 10.5.0.1.
>
> Assuming both routers had OSPF configured with
> network 10.0.0.0 0.255.255.255 area 0.0.0.1
>
> Will a device on R1 E2 be able to ping a host on R2 E2?
>
>
> >
> >
> > -----Original Message-----
> >From: Moerdo [mailto:[EMAIL PROTECTED]]
> >Sent: Wednesday, November 29, 2000 8:26 AM
> >To: [EMAIL PROTECTED]
> >Subject: About OSPF and Loopback port
> >
> >Does anyone here can explain to me, why me must use loopback port for
OSPF
> >configuration. Thank you for the answer for this stupid question. Thank
you.
> >
> >moerdo.
> >
>
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