what's more amazing to me is the disproportional importance the
certification materials place on this kind of stuff. We all read the ad hoc
statement in Lammle or other guides that EIGRP is a hybrid protocol with
characteristics of both DV and LS. Of course nowhere in the materials we
read are there the kind of detailed explanations, detailed foundations,
which support these ad hoc statements.
don't even get me started about the L2 vs. L3 switching debate.
Fact is, Cisco promulgates a certain outlook, most of which is accurate
enough that it makes little difference for all practical purposes. Cisco
isn't the only one, either. As a result of an argument elsewhere, I had
reason to delve into the esoterics of OSPF virtual links, and the nature of
tunneling. My research and resulting opinion have put me square in
opposition to statements made in Doyle, Moy, and the RFC itself. I continue
to believe that certain comments were made to provide a conceptual
framework, not to state truth about how things really work. I also learned
that Moy himself, while using the term tunnel in his 1998 book, makes no
such reference in his 2001 book, leading me to believe others may have
suggested to him that there was misunderstanding due to his earlier
statement. But that debate continues because after all, there it is in print
from an expert.
I believe there are more important things to know than which protocols are
link state and which protocols are distance vector. Like what LS and DV
really are. Thanks to Howard for offering some detail here. For example, how
is the routing table created? what happens to get routes into a routing
table? And what is the basis for redistribution? How does the router ( not
routing ) process determine how and what to redistribute? Knowing that would
go a long way towards explaining some anomalies I and others have seen.
I suppose it is human nature to believe that because you have passed a test
you inherently know all there is to know. I certainly go through similar
moods myself. I also find that as I learn more I find the early readings I
did, and the early explanations, shallow and unsatisfactory.
As to whether or not any vendor certification retains or has lost value, I
leave that for other times and other places. To quote Mr. Science, "I know
more than you do, because I have a Master's degree - in Science!" Cuts to
the heart of the question, doesn't it?
Chuck
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
Howard C. Berkowitz
Sent: Sunday, July 08, 2001 7:41 AM
To: [EMAIL PROTECTED]
Subject: Re: EIGRP and IGRP network discovery [7:11273]
>Howard,
> In looking into this I was amazed by the lack of
information
>on these very specific parts of the protocol itself. However, I can't
seem
>to find anything that would seem as a source other than the Cisco
>white-paper and Don Dettmore's EIGRP white-paper on the CZone. I'm also
>using Doyle's Routing TCP/IP and Adv. IP Network Design.
I agree there is a severe lack of detail. While I don't have the
URLs, unfortunately, there were some fairly detailed presentations a
couple of Networkers ago -- I'd imagine they have been kept updated.
There are still parts of the protocol, such as the details of the
reliable multicast, that as far as I know, Cisco keeps proprietary.
Frankly, the lack of availability of detailed information is one
reason I avoid EIGRP.
Garcia-Luna-Alceves' papers get into the algorithm but not the
implementation.
>
>Could you point out some links that would provide a better reference. This
>way we could all possibly get a better understanding ourselves.
>
>TIA
>
>Nigel..
>
>----- Original Message -----
>From: Howard C. Berkowitz
>To:
>Sent: Sunday, July 08, 2001 9:13 AM
>Subject: Re: EIGRP and IGRP network discovery [7:11273]
>
>
>> >abc wrote,
>>
>>
>>
>> >IGRP use distance vector routing protocol alogorithm to discover
>neighbor.
>> >
>> >EIGRP use link state routing protocol algorithm to discover neighbor
>>
>> No, EIGRP does not use a link state mechanism for neighbor discovery.
>> It does, however, use a hello subprotocol, and the link state
>> protocols (ISIS and OSPF) use different hello subprotocols.
>>
>> Neighbor discovery in RIP and IGRP are fairly tightly coupled to
>> distance vector, because one of the first notifications of a
>> neighbor's existence is that it sends a routing update. (Actually, in
>> RIP at least -- I'd have to research IGRP -- you first hear a routing
>> table query from a neighbor, which sends its table only after you
>> respond). In EIGRP, ISIS, and OSPF, neighbor discovery is completely
>> decoupled from the topology update mechanism.
>>
>> >.
>> >
>> >Metric calaucation is basically same, but eigrp multiply 256.
>> >
>> >No wonder, cisco certification is no longer valueable.
>>
>> I question your observations, because you have not really
>> demonstrated you understand how the protocols work. Now, please
>> understand I am not trying to be overly critical. Many courses and
>> books teach it incorrectly, with marketing confusion about "hybrid"
>> protocols, and especially the erroneous association of hello
>> subprotocols with link state. To achieve real understanding, one has
>> to dig beyond the confusion and often go back to source material.
>>
>> >
>> >""John Feuerherd"" Hello all,
>> >> I'm studying for my CCIE written exam and I came across a question
on
>a
>> >> sample test that has me a little baffled. It states that EIGRP and
>IGRP
>> >use
>> >> the same network discovery method. I know they use the same metrics,
>but
>> I
>> >> am under the impression that they use different methods when
>discovering
>> >> networks. Am I correct in that statement?
>> >>
>> >> Thanks in advance,
>> >> JF
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=11357&t=11273
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