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. All the best Chris On Wed, Feb 15, 2023 at 10:16 AM Christian Hopps <cho...@chopps.org> wrote: > Hi Chris, > > Just want to note one mis-undertanding below.. > > Chris Parker <ch...@networkfuntimes.com> 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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