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. 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.
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=6261&t=6076
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