Chapter 16: Dynamic Routing Protocols
STANDARD Revision 1.0 C4® CMTS Release 8.3 User Guide
© 2016 ARRIS Enterprises LLC. All Rights Reserved. 470
IS-IS Routers
IS-IS routers may be multi-homed, implying they reside in multiple Level 1 areas (or Level 2 backbone) and therefore
require multiple NSAP addresses. Since IS-IS is an IGP, the NSAP addressing scheme need not be globally unique and
private IP addresses may be defined within an AS.
IS-IS Network Topology, Unique Level 1 Areas
IS-IS defines a multi-layered hierarchy called Level 1 and Level 2 routing.
Level 1 Routers
Level 1 routers belong to a common area and are engaged in level one routing. These routers are aware of their local
topology only and require Level 2 routers to communicate inter-area routing information.
Level 2 Routers
In practice, most Level 2 routers are also Level 1 routers; that is, they serve a local area and connect to the IS-IS backbone.
Two-Level Network Topology
The figure below depicts an IS-IS two-level network topology with both NSAP and IP addressing. NSAP addresses are based
on the defined IP loopback addresses and must be manually provisioned as such.
Note: In this example IP hosts are not assigned NSAP addresses and do not in any way participate in IS-IS routing.
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