From: ccie2be (ccie2be@nyc.rr.com)
Date: Tue Dec 14 2004 - 10:05:19 GMT-3
Hi Brian,
Why will this work?
My guess is that ospf doesn't use area ID's in it's spf calculation. It uses
router ID's. Come to think of it, except maybe for determining if an area
is a backbone or not, ospf doesn't use the area ID for anything. If this
is true, then the area ID is primarily a convenience for people.
Am I anywhere close to being right?
I also suspect that if it's OK to have 2 non-backbone areas with the same
area ID, it's OK to have any number of non-backbone areas with the same area
ID.
For example, ospf wouldn't mind if there were 20 non-backbone areas each
with area ID 20. Is that true?
TIA, Tim
----- Original Message -----
From: "Brian Dennis" <bdennis@internetworkexpert.com>
To: "Hans None" <acsyao@hotmail.com>; <ccielab@groupstudy.com>
Sent: Monday, December 13, 2004 11:25 PM
Subject: RE: ospf discontinuous areas
> Short answer, yes it will work properly. The only problem you may run
> into is with area summarization (i.e. two area 1's summarizing the same
> address space).
>
> Long answer, see RFC 2328
> (http://www.internetworkexpert.com/rfc/rfc2328.txt)
>
> <QUOTE>
> 3.7. Partitions of areas
>
> OSPF does not actively attempt to repair area partitions. When
> an area becomes partitioned, each component simply becomes a
> separate area. The backbone then performs routing between the
> new areas. Some destinations reachable via intra-area routing
> before the partition will now require inter-area routing.
>
> However, in order to maintain full routing after the partition,
> an address range must not be split across multiple components of
> the area partition. Also, the backbone itself must not
> partition. If it does, parts of the Autonomous System will
> become unreachable. Backbone partitions can be repaired by
> configuring virtual links (see Section 15).
>
> Another way to think about area partitions is to look at the
> Autonomous System graph that was introduced in Section 2. Area
> IDs can be viewed as colors for the graph's edges.[1] Each edge
>
> of the graph connects to a network, or is itself a point-to-
> point network. In either case, the edge is colored with the
> network's Area ID.
>
> A group of edges, all having the same color, and interconnected
> by vertices, represents an area. If the topology of the
> Autonomous System is intact, the graph will have several regions
> of color, each color being a distinct Area ID.
>
> When the AS topology changes, one of the areas may become
> partitioned. The graph of the AS will then have multiple
> regions of the same color (Area ID). The routing in the
> Autonomous System will continue to function as long as these
> regions of same color are connected by the single backbone
> region.
> </QUOTE>
>
> Brian Dennis, CCIE #2210 (R&S/ISP-Dial/Security)
> bdennis@internetworkexpert.com
>
> Internetwork Expert, Inc.
> http://www.InternetworkExpert.com
> Toll Free: 877-224-8987
> Direct: 775-745-6404 (Outside the US and Canada)
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> Hans None
> Sent: Monday, December 13, 2004 8:10 PM
> To: ccielab@groupstudy.com
> Subject: ospf discontinuous areas
>
> All,
>
>
>
> Can ospf discontinuous areas work properly (non area 0).
>
>
> For example, there are multiple area 1 which are discontinuous to each
> other. Will this work properly?
>
>
> Thanks,
>
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