[c-nsp] BGP Balanced

[Hudson Delbert J Contr 61 CS/SCBN]

ejay,

why is 'med' so 'mis-understood'?

it is a metric seting, plain and simple.

it is used to when AS ZZZ and AS YYY have multi-links w/each other.

it is used to set by ZZZ to inform YYY ebgp speaker of what ZZZ's 
preferred entrance points are and is retained by YYY just in case
the preferred ZZZ POE is down upon re-entrance.

the default is usually = 0.

it is only of local to the sharing AS's as this info is reset=0 if the
traffic is
passed to a third AS.

the point of 'med' assignment is in route maps.

it is usally step #8 in BGPv4 Path Selection..

algorithm (i think) for path selection:
1=	next_hop is reachable and no others exist
2=	largest wgt.
3=	if no wgt supplied or all wgts =, use larget lcl pref.
4=	if local pref =, path .eq. route oroginated by 0.0.0.0 in next_hop.'
(whew!! had to really thing about that one)
5=	shortest AS Path
6=	if all path = len, use lowest orig code.
7=	if orig codes =, use lowest med, remember def=0 usually.
8=	if all med =, choose ext over int path.
9=	if path = internal, use path thru closest interior routing protocol
nbr
	using local routing protocol. (???? not sure aboutthis one)
10=	use lowest BGP router id, loopback always a pretty good choice.


v/r,
piranha

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net]On Behalf Of Ejay Hire
Sent: Thursday, August 26, 2004 3:05 PM
To: bep at whack.org; 'Alexandra Alvarado'
Cc: cisco-nsp at puck.nether.net
Subject: RE: [c-nsp] BGP Balanced


On an unrelated note, MED is poorly implemented and
understood on the internet at large, and should usually be
avoided.  Misconfiguration can cause route flapping and is
difficult to troubleshoot.

-ejay

> -----Original Message-----
> From: cisco-nsp-bounces at puck.nether.net 
> [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of
Bruce Pinsky
> Sent: Tuesday, August 24, 2004 7:03 PM
> To: Alexandra Alvarado
> Cc: cisco-nsp at puck.nether.net
> Subject: Re: [c-nsp] BGP Balanced
> 
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> Alexandra Alvarado wrote:
> 
> | What about BGP Multi Exit Discriminator (MED)?
> |
> 
> 
> Generally speaking, that would only apply if you actually
had 
> multiple BGP
> peers to the same provider and therefore could choose
between 
> exit points.
> ~ Here it sounds like you will simply have one exit path
and 
> need to send
> traffic over multiple physical connections.
> 
> As some have pointed out, BGP may be overkill in this
situation.
> 
> - --
> =========
> bep
> 
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