Chapter 16: Dynamic Routing Protocols
STANDARD Revision 1.0 C4® CMTS Release 8.3 User Guide
© 2016 ARRIS Enterprises LLC. All Rights Reserved. 475
On broadcast links, periodic flooding by all IS-IS nodes is used to ensure that adjacent peers maintain a consistent view of
the LSP database for a particular IS-IS Domain. That is, all IS-IS nodes broadcast their LSPs to all attached devices. These
flooded LSPs are not acknowledged and require support from the DIS to maintain a consistent view of the LSP database.
To help support reliable flooding of LSPs, the DIS periodically sends out a CSNP that contains a summary of every known
LSP within the IS-IS domain.
To purge a LSP from the IS-IS domain, the remaining lifetime field is set to 0, and the LSP is flooded throughout the
network. Only the originator of the LSP may purge it from the domain.
IS-IS Point-to-Point
With the implementation of IS-IS point-to-point adjacencies, also referred to as point-to-point links, Broadcast links will
continue to be supported as the default configuration, with a point-to-point link being an optional configuration on an
interface or subinterface basis. IS-IS point-to-point links simplify the Shortest Path Found (SPF) calculation and reduce both
the network convergence times and the size of the topology database.
The C4/c CMTS still supports the existing IS-IS for IPv4/IPv6 and Multi-Topology as previously implemented.
Point-to-Point and Broadcast
Point-to-point and broadcast are the two predominant circuit types used by link state routing protocols such as IS-IS and
OSPF.
The most important difference between point-to-point and broadcast is that broadcast circuits utilize the concept of a
designated router, and are represented topologically as virtual nodes in the network topology graph.
From a functional aspect the IS-IS and OSPF routing protocols are treated differently with respect to:
Establishing neighbor adjacencies.
Flooding link state information.
Representing the topology.
Calculating the Shortest Path First (SPF) and protocol packets.
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