OK Howard. I'm not afraid to look foolish in front of everyone.
-----------------------
Howard's scenario:
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?
----------------------
My feeble attempt at cleverness:
Assuming that there is no typo in your addressing scheme, I say you have a
real mess here and that the answer is no.
1) you have the same subnet appearing on two different routers
10.0.5.0/whatever on R1E1 and R2E1 While OSPF can handle discontiguous
subnets, I would be surprised if it can handle duplicate subnets with any
aplomb
2) on R1 the interface with the address of 10.0.5.2 has been placed into
area 0.0.0.1. when the ip address for that interface is changed, without
either reloading the router or performing a clear ip ospf process the
interface with the address 10.5.0.1 will NOT have been placed into the OSPF
process.
3) I have not done this on my routers yet. I want to see if I am in the
right ballpark so far. ( well, to be honest, as soon as I send this message
I am setting up a scenario, upon which I will report subsequently )
Well, gang - am I wise or still a fool?
Chuck
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf Of
Howard C. Berkowitz
Sent: Wednesday, November 29, 2000 12:37 PM
To: [EMAIL PROTECTED]
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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