Subject: [Isis-wg] Help on ISIS

From: navaneeth K <[email-masked]>
Date: Thu, 23 Dec 1999 09:59:28 -0800

Hi all,

Thanx to all of you  for the immediate reaponse to my question.I'm already in the process of reading RFCs 1142,1195 ans iso10589.But i'm not able to get the clear relation between the ESH,ISH and IIH PDUs.Can anyone explain in detail as to who send ESH,ISH,IIH PDUs and when .What is the relationship between these PDUs,Which is sent in response to which etc..

Thanx for the response..
Looking forward to hear from you
Navaneeth.

Navaneetha Krishnan.N
Senior Software Engineer,
HDF, Future Software Pvt Ltd,
480 - 481, Anna Salai, Nandanam,
Chennai - 600 035
India.
Phone : +91-44-4330550 Ext.412

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From: Abe Martey <[email-masked]>
Date: Wed, 22 Dec 1999 22:07:58 -0800

Navaneetha,

There two protocols that run together to support CLNP for ISO
connectionless services.
 
1. ES-IS
2. IS-IS
 
ES-IS runs between routers (Intermediate Systems) and hosts (End Systems)
and it allows ESs and ISs learn about each other and also provides a means
for ESs to obtain configuration info from the routers...ie Area info and
preferred routers for specific destinations (via redirects).
In ES-IS routers send out Intermediate system hellos (ISH) and hosts
send out End System Hellos (ESH)
 
The other protocol, IS-IS, is meant for router to router communication.
Intermediate System to Intermediate System Hellos (IIH) are used
between routers speaking IS-IS...read on IS010589 for further details.

All this said...it may be worth mentioning that RFC1195 allows IS-IS to
be used for IP routing in a non CLNP environment...and even though ES-IS
doesn't have much relevance in this environment, it comes into play in the
IS-IS implementation. Neighboring routers in the IP only environment would
receive each others ISHs as well as IIHs...but there may not be ISO
hosts to send ESHs. IP hosts use a combinition of IP ARP, IP redirects,
default gateway, static routes and possibly IP dynamic routing protocols
to achieve the ES-IS functionality.

Hope this helps.
 
Thanks.

- abe

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