From: Scott Morris (swm@emanon.com)
Date: Wed Feb 13 2008 - 00:37:40 ARST
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!
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-----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
> >
> > ____________________________________________________________________
> > ___ Subscription information may be found at:
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>
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