From: Howard C. Berkowitz (hcb@gettcomm.com)
Date: Fri Nov 07 2003 - 21:53:19 GMT-3
At 3:01 PM -0800 11/7/03, Joseph Rinehart wrote:
>ISIS may be obscure, but it goes without saying that it is part and parcel
>of the core topics (i.e., EIGRP, OSPF, BGP, Frame, etc.) and as such is
>pretty important to know. One of the biggest things to note with ISIS is
>that is it NOT a native IP routing protocol, and as such has some weird
>quirks that you have to not only know but realize how to work with and in
>some cases around.
>
>Just my thoughts
And very good thoughts. ISIS confuses people because it puts them
between two extremes: remembering it is not IP-native as you
suggest, and equally, overemphasizing the OSI/CLNP aspects. With
respect to the latter point, remember you are dealing with
_Integrated_ ISIS, not pure ISIS. Integrated ISIS is intended to
handle IP.
All too often, I hear people stuck as they look for irrelevant OSI
protocols, such as ES-IS, to be running. Integrated ISIS doesn't
require any pure OSI protocols to be running.
Aside from it being on the test, another reason to study ISIS, and
indeed the characteristics of some of the OSI addressing and
protocols, becomes obvious once you start looking at IPv6.
IPv6 stateless address autoconfiguration is largely drawn from OSI
routing, perhaps with a dash of AppleTalk. IPv6 Neighbor Discovery
arguably is a superset of ES-IS, but also intended to have ES-ES
(i.e., host on same subnet) discovery. Neighbor discovery does away
with the need for ARP and some ICMP functions.
Again, let me emphasize the IPv6 address has distinct OSI ancestry.
Understanding what the high-order part of an NSAP address is doing in
ISIS (i.e., logically extending the IP to the left to make it unique
to an area) will help considerably when you look at the IPv6 address.
IPv6 does include the same sort of information (area and provider) in
the actual address, rather than logically associating it as do IPv4
protocols.
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