Chris Parker <[email protected]> writes:
Hi there Christian, Thank you very much for your comments there. Perhaps I'm not using precisely terminology, but I've configured an L1 router to be part of multiple IS-IS areas at once. I'll quote from a 2005 book to show you this topology: https:// www.networkfuntimes.com/wp-content/uploads/2018/07/ Multi-area-ISIS-router-Pt1-768x407.jpg If the following configuration is added to the bottom-left router, then both the 49.0001 and 49.0003 adjacencies come up. The result is, I was led to believe, a single L1 topology that contains two IS-IS areas. https://www.networkfuntimes.com/wp-content/uploads/2018/07/ Multi-area-ISIS-router-Pt2.jpg I think this counts as one router being in two areas at once - but if I'm not using precise language, or if I'm misunderstood you, then please forgive me.
It's easy to be confused by this; however, this is the multiple area IDs for a single area case I mentioned in my "P.S." By configuring your bottom left router with multiple area IDs you have effectively merged those 2 areas into a single area. For more information on this check out ISO 10589:2002 section 7.1.5 "Manual area addresses" which starts: 7.1.5 Manual area addresses: Within a routeing domain, it is often convenient to associate more than one area address with an area. Thanks, Chris. [as wg-member]
All the best Chris On Wed, Feb 15, 2023 at 10:16 AM Christian Hopps <[email protected]> wrote: Hi Chris, Just want to note one mis-undertanding below.. Chris Parker <[email protected]> writes: > Even if we were to talk about level 1, it is possible for an L1 > router to be in two IS-IS areas at once, which is a way of creating a > single L1 topology, a single LSP flooding domain. An IS-IS router instance can only be in one area not multiple. IS-IS differs from OSPF in that area boundaries exist "on the wire" (i.e., between routers) and not inside the router instance as they do with OSPF. An IS-IS router instance is only ever in one area. Thanks, Chris. [as wg-member] P.S. I don't think you are referring to the ability in IS-IS to refer to an area with multiple identifiers..
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