Re: can't understand BGP Theory

From: Han Ghee Chia (han_ghee@yahoo.com.sg)
Date: Wed Feb 13 2008 - 05:23:02 ARST

I believe that sort of explains why some CCIEs do not have the depth & breadth
in knowledge. But they passed the lab exam, anyway.

----- Original Message 

----
From: Scott Morris <swm@emanon.com>
To: Jersey Guy
<guy.jersey@gmail.com>; Jezz Bird <jezzbird@hotmail.com>
Cc: Cisco
certification <ccielab@groupstudy.com>
Sent: Wednesday, 13 February 2008
10:37:40
Subject: RE: can't understand BGP Theory

Most things haven't changed
that much in the past few years.  Not the basics
anyway!

Scott Morris, CCIE4
(R&S/ISP-Dial/Security/Service Provider) #4713, JNCIE-M
#153, JNCIS-ER, CISSP,
et al.
CCSI/JNCI-M/JNCI-ER
VP - Technical Training - IPexpert, Inc.
IPexpert
Sr. Technical Instructor

A Cisco Learning Partner - We Accept Learning
Credits!

smorris@ipexpert.com

Telephone: +1.810.326.1444
Fax:
+1.810.454.0130
http://www.ipexpert.com

-----Original Message-----
From:
nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Jersey Guy
Sent: Tuesday, February 12, 2008 1:50 PM
To: Jezz Bird
Cc: Cisco certification
Subject: Re: can't understand BGP Theory

Thanks everyone; great feedback
here.........much appreciated!

Good thing is that I understood the two
paragraphs this morning but was
struggling with them last night. This is good.
It means that if I persevere,
I'll eventually get it. The bad part is that it
is going to kill me, by the
time I DO understand everything. But hey, I made
it through 200 pages of
Halabi's book AND understood *most* of it....can't be
that bad....

Luan, I enjoyed your Burger King analogy. Joseph B, you're
absolutely right
about walking the walk being totally different from talking
the talk. I have
a good feeling that I'll get spanked real bad when I
eventually get down to
configuring/making/breaking BGP on a rack.

Yeah I do
have Doyle's Vol 1 & 11 but for some reason, I wanted to start
with Halabi's
book. Should I worry that all my Cisco reading material is 2-3
yrs old, or
will it suffice?

thanks, JG

On Feb 12, 2008 1:31 PM, Jezz Bird
<jezzbird@hotmail.com> wrote:

>  In a nutshell what Halabi is saying is: if
you associate the MED 
> attribute with an aggregated/summarised route AND
supress the 'component'
> routes, the MED that you use may not necessarily the
best one for ALL 
> the components. The receiving AS will not know where the
components 
> are and in fact as he suggests they could be scattered
throughout the 
> sending AS. The receiving AS will not have individual MEDs
for each of 
> the components and this is when suboptimal routing may occur.
>
> You will need to understand this before you go to the lab but don't 
> worry
about it because there are bound to be some things that you just 
> won't
understand at first. I would suggest you have a look at Routing 
> TCP/IP Vols
I & II by Jeff Doyle. He explains 
> summarisation/aggregation and BGP
brilliantly !
>
> Regards,
>
> Jezz.
>
>
> > Date: Mon, 11 Feb 2008 21:23:55
-0500
> > From: guy.jersey@gmail.com
> > To: ccielab@groupstudy.com
> >
Subject: can't understand BGP Theory
>
> >
> > From Halabi's book, Internet
Routing Architectures, 2nd edition, 
> > page
> 167:
> >
> > *MEDs are
somewhat handicapped by aggregation scenarios in which
> providers
> >
announce a given CIDR block from multiple locations in their network 
> > and
suppress the smaller routes from the block. Utilizing MEDs in 
> > this
>
scenario
> > could potentially result in suboptimal routing because the 
> >
more-specific routes of the CIDR block could be scattered throughout 
> > the
AS and MEDs associated with more-granular routes are no longer
available.
> >
> > When using MEDs to perform what's commonly referred to as best-exit
>
routing,
> > some providers leak the more-specifics of their CIDR blocks to 
>
> select
> peers
> > to remove the offshoots introduced by aggregation. The
problem with 
> > this
> is
> > that controlling the more-specific
announcements is sometimes 
> > complex,
> and
> > failure to do so can result
in some very suboptimal routing situations.
> > *
> > I read the above two
paragraphs five times but didn't understand it.
> Which
> > of the following
is true:
> >
> > a) I have no choice but to understand this stuff, to pass the
lab. I
> need to
> > understand *everything* in Halabi's book, period.
> > b)
The lab is tough but not THAT tough. I can skip certain 
> > convoluted
sections of every topic and still manage to get by.
> > c) Forget it. I am not
going to make it. MED is a piece of cake; 
> > what's
> so
> > hard to
understand??
> > d) I need to read "How to grow gray matter and raise IQ" book
before 
> > Halabi's.
> >
> > Thing is....how thoroughly do I need to pound
away at theory/reading
> before
> > hitting the equipment, lab scenarios and
excercises?
> >
> >
> > thanks, JG
> >
> >

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