Re: Wanna Be a CCIE? Try This One [7:6076]

[Peter I. Slow, CCNP Voice Specialist]

Peter Slow, CCNP Voice Specialist
Network Engineer
Planetary Networks
535 West 34th Street
New York, NY
10001
Cell:    (516) 782.1535
Desk: (646) 792.2395
Mail: [EMAIL PROTECTED]
Fax:    (646) 792.2396
----- Original Message -----
From: "W. Alan Robertson" 
To: "Peter I. Slow, CCNP Voice Specialist" ;

Sent: Tuesday, May 29, 2001 1:39 PM
Subject: Re: Wanna Be a CCIE? Try This One [7:6076]


> Peter,
>
> OSPF has a distance of 110, and yes, iBGP has a distance of 200.  By
> having seperate routing domains for North America and Europe, he could
> use eBGP (Distance - 20) between his two networks.
>
> Distance wouldn't really do anything in this case, though, because
> European routes would not be learned via OSPF (Remember, we have
> theoretically split OSPF into two seperate routing domains, never the
> two shall meet).
>
> Instead, eBGP would be bridging the gap between the two OSPF networks.
> This would afford the opportunity to really take control of what
> routes were advertised between the two, and excercise strict control
> of the routing metrics, manipulating them in such a way as to ensure
> that the best path across the pond were utilized under all normal
> circumstances, but providing the redundant "less preferred" path in
> the event of some kind of outage.
>
> Can the same be accomplished via OSPF?  Yes, but because we're dealing
> with Intra-area, and Inter-area routes, it may be more complex than by
> simply manipulating the link costs.  Remember that OSPF chooses an
> Intra-area route with a Cost of 4,000,000 over an Inter-area route
> with a cost of 100.  That's just one of the quirks of the protocol.
>
> As for "Why would you want to break up an AS that small into two
> seperate private ASes?", it's called thinking outside the box.

...Watch it, spanky.

>  We
> tend to think that a small network could not be better served by
> applying the same principles that we might use for a larger
> environment.  Why is that?  Instead of letting the number of devices
> determine the right solution (Or more properly, a good solution),
> let's form a solution based on the specific requirements.
>
> A network with a small number of devices, but consisting of multiple
> sites, and redundant links, presents a unique challenge.  Forget the
> number of devices, and look at both the physical topology, and the
> problem that needs solving.  BGPs powerful policy routing tools make
> it a good fit for this environment, when viewed from a requirements
> perspective.

I think BGP is completely unecessary in this case.YES, splitting it into two
ASes ans using eBGP would work (well), but i really think that modifying the
path cost would be the right solution.
remember that i never said eBGP wouldnt work. the initial discussion was
about using BGP to do this in a SINGLE AS.

...don't get all in a tizzy, i recognize that you have a good idea.
I just don't like it =P

/me ducks

>
> It's not the only solution, but it is a valid solution, and in my
> opinion, it's a good solution.
>
> Alan
>
> ----- Original Message -----
> From: "Peter I. Slow, CCNP Voice Specialist" 
> To: "W. Alan Robertson" ;
> 
> Sent: Tuesday, May 29, 2001 1:02 PM
> Subject: Re: Wanna Be a CCIE? Try This One [7:6076]
>
>
> > Absolutely, but he has traffic going from one router to another,
> it's not
> > ever exiting the system.
> > ...why would you want to break up an AS that small into two seperate
> private
> > ASes?
> > besides... the OSPF routes are going to take precedence, not that
> the admin
> > dist. cant be changed, but ospf is 120, and BGP int routes are
> 200....
> > (right?)
> >
> > ----- Original Message -----
> > From: "W. Alan Robertson" 
> > To: "Peter I. Slow, CCNP Voice Specialist" ;
> > 
> > Sent: Tuesday, May 29, 2001 12:42 PM
> > Subject: Re: Wanna Be a CCIE? Try This One [7:6076]
> >
> >
> > > Peter,
> > >
> > > With all due respect, he doesn't have an IGP problem...  He has a
> > > routing problem, and would like the ability to influence the flow
> of
> > > traffic under certain circumstances to provide for better network
> > > performance.
> > >
> > > After hearing a better explanation of the real issue, path
> selection
> > > for an International site, the use of BGP might go a long way
> toward
> > > solving the issue.
> > >
> > > He could very simply address his issues by breaking his OSPF into
> two
> > > seperate routing domains, and utilizing BGP as a means of
> > > interconnecting them.  He could manipulate the traffic through the
> use
> > > of something as simple as AS-path prepending, or the other
> mechanisms
> > > Chuck mentioned (local preference, weight, or meds).
> > >
> > > Routing protocols are but tools, a simple means to an end.  Like
> all
> > > tools, each has it's strengths and weaknesses.  Most important is
> that
> > > you select the right one for a given situation.  In the absence of
> > > more information, the use of BGP sounds like a pretty good
> solution to
> > > the given problem.
> > >
> > > Alan
> > >
> > > ----- Original Message -----
> > > From: "Peter I. Slow, CCNP Voice Specialist"
> 
> > > To: 
> > > Sent: Tuesday, May 29, 2001 11:29 AM
> > > Subject: Re: Wanna Be a CCIE? Try This One [7:6076]
> > >
> > >
> > > > next time you recomend using bgp to fix an IGP problem, im going
> > > to.., well,
> > > > uh, just dont do it again.




Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=6267&t=6076
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