From: Howard C. Berkowitz (hcb@gettcomm.com)
Date: Fri Nov 07 2003 - 12:05:51 GMT-3
At 8:41 AM -0500 11/7/03, ccie2be wrote:
>Hi group,
>
>I'm trying to decide how much time to spend on IS-IS. I understand the basics
>and can configure level I and II areas and can set up a simple multi area ISIS
>network, but I'm weak on all the more advanced stuff. I have only a couple
>weeks left before the lab and I also want to review and practice QoS, Voice,
>and ATM.
>
>Compared to those other 3 topics, how much time should I spend practicing
>ISIS? By way of comparison, I'm very strong on OSPF. How important is it
>that I be just as strong on ISIS as I am on OSPF?
Let me answer indirectly. It would enhance your understanding of
both ISIS and OSPF to make a matrix of general protocol functions
(e.g., neighbor establishment, database synchronization, flooding,
DR/pseudonode election, etc.) and then make a matrix with a brief
note on how OSPF and ISIS each do it. You'll find the protocols tend
to have functions in common, but quite different detailed
implementation. You might even do just a single column about how
ISIS differs from OSPF (e.g., single pseudonode/DIS rather than
DR/BDR, or that ISIS L1 areas are equivalent to OSPF totally stubby
areas).
It's a tossup whether you need to be as strong in ISIS. A lot of the
complexity in ISIS deals with ISP-oriented tuning or traffic
engineering. One of the reasons OSPF is preferred in enterprises is
that it has a lot more policy/summarization/area options, which ISPs
generally don't need. THe real question is how much you'd expect
Cisco to test for ISP-oriented features, which they don't teach in
their general classes, in the fundamentally enterprise-oriented
CCIE/R&S.
>
>Also, do people think it's worthwhile to learn all the details of all the
>tuning parameters of which there seem to be many?
>
Funny you should mention that, because I've been working on some
study material updates, and just concluded that a study aid is
probably needed here.
While there are probably too many timers to memorize, these are
things that they love to test for. I think the first step is to
think of generic protocol timer functions, such as hello/periodic
update interval, processor churn protection (e.g., holddown timers in
LS protocols, exponential backoff), hello and dead intervals, etc.
Next, draw up a matrix and write in the equivalent command, when it
exists, for each routing protocol. If you're like me, you'll wind up
memorizing quite a bit by the act of writing the matrix. In high
school, one of my favorite ways to prepare for a test is to write up
what would be a cheat sheet, but leave it at home.
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