From: Peter van Oene (pvo@usermail.com)
Date: Mon Feb 17 2003 - 22:11:52 GMT-3
At 04:10 PM 2/17/2003 -0600, tsiartas@ameritech.net wrote:
>As far as I know
>Ospf works with out are 0.
>However ABRs can only be between are 0 and another area. There is no
>workaround to that other than the virtual-links.
>So basically you are limiting your design for summarization. And this is
>really the main disadvantage of ospf that can be a problem when merging
>companies, IS-IS could be an alternative as you can design as many tiers
>as you like with no area 0 requirement.
Just wanted to mention that IS-IS forces a strict hierarchy in the same
manner as OSPF. This is because both OSPF and ISIS, unlike PNNI, actually
use a distance vector routing mechanism between areas (PNNI is all link
state). As with DV protocols in general, loop avoidance is critical. The
strict two level hierarchy and some split horizon like functionality handle
this in OSPF/ISIS.
Unlike OSPF however, IS-IS doesn't use a single area-identifier within its
"backbone." In IS-IS, the set of L2 speaking routers comprise the backbone.
Pete
>t
>
>
>-----Original Message-----
>From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
>Joe
>Sent: Monday, February 17, 2003 1:35 PM
>To: 'Mark Miller'; 'Sam Munzani'; ccielab@groupstudy.com
>Cc: cciesecurity@yahoogroups.com
>Subject: RE: Can you have OSPF without area 0 at all?
>
>Please send us the link you refer to. I have to say that this is simply
>not true. You will ONLY send routes from your area, whatever it may be,
>into area 0, the backbone, so you can't just arbitrarily designate any
>area as the backbone. It MUST be area 0.
>
>Joe
>
>-----Original Message-----
>From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
>Mark Miller
>Sent: Friday, February 14, 2003 6:15 PM
>To: Sam Munzani; ccielab@groupstudy.com
>Cc: cciesecurity@yahoogroups.com
>Subject: Re: Can you have OSPF without area 0 at all?
>
>
>The routing process in ospf has no concept that "area 0" is the backbone
>area. You can make it any number you want. I remember reading
>something on this. I'll try to dig it up and send you a link.
>
>Mark Miller
>
>
>----- Original Message -----
>From: "Sam Munzani" <sam@munzani.com>
>To: <ccielab@groupstudy.com>
>Cc: <cciesecurity@yahoogroups.com>
>Sent: Friday, February 14, 2003 12:56 PM
>Subject: Can you have OSPF without area 0 at all?
>
>
> > Team,
> >
> > I came across an interesting finding. I want to take everybody's
> > opinion
>on this before putting anything in production. We are building an OSPF
>network that will eventually merge with company's main OSPF backbone
>network. The core group has assigned us ospf area number 555.
> >
> > When I configure all my routers with OSPF area 555(with no area 0 at
> > all),
>it seems to be building up routing table. I always thought OSPF needs
>area 0 to function. Will this work of we add a non cisco device with
>area 555 configuration?
> >
> > What is the catch 22 in this configuration? I have started reading
> > OSPF
>RFC to figure out all technical details.
> >
> > Thanks,
> > Sam Munzani
This archive was generated by hypermail 2.1.4 : Sat Mar 01 2003 - 11:06:26 GMT-3