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IS-IS has always been my favourite Interior Gateway Protocol. Its elegant simplicity, its
well-structured data formats, its flexibility and easy extensibility are all appealing – IS-IS
epitomizes link-state routing. Whether for this reason or others, IS-IS is the IGP of choice
in some of the world’s largest networks. Thus, if one is at all interested in routing, it is well
worth the time and effort to learn IS-IS.
However, it is hazardous to call any routing protocol “simple”. Every design decision,
be it in architecture, implementation or deployment, has consequences, some unanticipated,
some unknowable, some dire. Interactions between different implementations, the
dynamic nature of routing, and new protocol features all contribute to making routing
protocols complex to design, write and deploy effectively in networks. For example, IS-IS
started as a link-state routing protocol for ISO networks. It has since evolved significantly:
IS-IS has IPv4 and IPv6 (and IPX) addressing; IS-IS can carry information about
multiple topologies; link attributes have expanded to include traffic engineering parameters;
a new methodology for restarting IS-IS gracefully has been developed. IS-IS even
has extensions for use in “non-packet networks”, such as SONET and optical networks,
as part of the Generalized Multi-Protocol Label Switching (G-MPLS) protocol suite.
Understanding all of what IS-IS offers and keeping abreast of the newer protocol features
is a weighty endeavour, but one that is absolutely essential for all serious networking
engineers, whether they are developing code or running networks. For a long time,
there were excellent books on OSPF, but very little on IS-IS. This encyclopaedic work
changes that. Now, at last, there is a book that does IS-IS justice, explaining the theoretical
aspects of IS-IS, practical real-life situations, and quirks in existing implementations,
and gives glimpses into some troubleshooting tools.
You couldn’t ask for a better-matched pair of guides, either. Hannes: intense, passionate,
expert; and Walter: calm, clear, expert. Between the two, they have produced a comprehensive,
up-to-date text that can be used for in-depth protocol study, as a reference, or to catch
up with the latest developments in IS-IS. |