From: John Neiberger (neiby@xxxxxxxxxx)
Date: Thu Feb 21 2002 - 13:58:25 GMT-3
Perhaps it's because the usual passive interface command
doesn't make as much sense with IS-IS. In IS-IS, we have to
specifically configure it on each interface. Maybe they
decided that--at least for IS-IS--it didn't make sense to
add 'ip router isis' to an interface only to later make it
passive.
This method is actually a pretty cool way of getting a prefix
into IS-IS. For a moment I thought this could be done in OSPF
as well, but with OSPF you'd need to have a way associate the
prefix with an area so now you're back to having a network
command plus a passive interface.
John
---- On Thu, 21 Feb 2002, Wade Edwards
(wade.edwards@powerupnetworks.com) wrote:
> This brings up something interesting I remember about the way
IS-IS does
> passive interfaces. In other routing protocols you add the
interface to
> the routing process then make it passive. With IS-IS you
make it
> passive which will add it to the IS-IS routing process
without doing the
> ip router isis command. So it seems backward from all the
other routing
> protocols. I wonder why Cisco did it this way. I could
never find out
> why it is this way on CCO. Does anyone out there know why?
>
> L8r.
>
> -----Original Message-----
> From: John Neiberger [mailto:neiby@ureach.com]=20
> Sent: Thursday, February 21, 2002 9:19 AM
> To: alee@cccis.com; ccielab@groupstudy.com
> Subject: Re: advertise loopback interface in ISIS
>
> Take a look at the following link:
>
> http://www.cisco.com/warp/public/97/is-is-ip-config.html
>
> Toward the bottom of the page it mentions the following:
>
> "The above output shows that the loopback address of this=20
> router is advertised with a value of 0. This is because the=20
> loopback is advertised with a passive-interface command
under=20
> the router IS-IS process, and the loopback interface by
itself=20
> is not enabled for IS-IS. All other IP prefixes have a value
of=20
> 10, which is the default cost on the interfaces running IS-
IS. "
>
> This seems to be saying that if you create a loopback
interface=20
> but don't add ip router isis to it, and then you add a
passive-
> interface command this will cause the loopback address to
be=20
> advertised with a metric of zero.
>
> I'm not sure what that means and I don't have a way to test
it=20
> here at work. However, that may be what you're looking for.
>
> HTH,
> John
>
>
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