> On Sep 22, 2020, at 1:21 AM, Donald Eastlake <[email protected]> wrote: > > > One final question: I may be confused but my understanding of IS-IS is > that there are Level 1 links, Level 2 links, and links that are both > Level 1 and 2. A border router between Level 1 and Level 2 is a router > that has both types of links attached to it. Such a router is a part > of each Level 1 Area to which it is linked and a part of Level 2. So, > the Level 1 / Level 2 boundary is, in a real sense, internal to such a > border router.
Actually IS-IS is different than this (your last 2 sentences). This is a key conceptual difference between OSPF and IS-IS. In OSPF an OSPF router (instance) can be attached to several areas. In IS-IS an L1 or L1L2 router (instance) resides belongs to only a single L1 area. Thus in OSPF area boundaries exist within the OSPF instance, while in IS-IS the L1 area boundaries exists on the wire between L2 adjacencies. Thanks, Chris.
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