RE: BGP Question Concerning MED attribute

["Howard C. Berkowitz" <hcb@xxxxxxxxxxxx>]

At 5:36 PM -0400 9/10/03, Nordhoff, Michael G. (US - Hermitage) wrote:
> Thanks for the clarification.  The intent is to minimize the potential for
> asymmetrical routing that will most likely occur when the 2 ISPs I will be
> peering with connect to the same peering points beyond their AS's.  For
> example, I peer with Provider A and Provider B.  Provider A and Provider B
> both peer with Provider C.  My intent was to ultimately influence the path
> Provider C takes back to me.  Perhaps it was a good idea but not easily
> implemented...
>
> Thanks again for the feedback...
>
> - MN

Even if you could send MEDs, the ISP isn't required to use them.  The 
reality is that particular routing inside an ISP will only happen if 
you have a business agreement to do so.  The way to signal traffic 
under such an agreement is with a mutually-agreed-to community.

> -----Original Message-----
> From: Rob Laidlaw [mailto:laidlaw@xxxxxxxxxxxx]
> Sent: Wednesday, September 10, 2003 4:11 PM
> To: Nordhoff, Michael G. (US - Hermitage); ccielab@xxxxxxxxxxxxxx
> Subject: Re: BGP Question Concerning MED attribute
>
> Routing TCP/IP vol.2, page 246.
>
>      "When a BGP speaker learns a route from a peer, it can pass the route's
> MED to any IBGP peers, but not to EBGP peers.  As a result, the MED has
> relevance only between neighboring autonomous systems."
>
> I don't believe there is anything you can do to pass this attribute.  Why do
> you want to pass this information?  Its function is to allow a customer with
> multiple connection to the same provider to pick their entry point.  If BGP
> passed this info to the ISP's external neighbors, then the customer would be
> able to choose paths in the ISP's network rathern then the ISP.
>
> Rob
>
> ----- Original Message -----
> From: "Nordhoff, Michael G. (US - Hermitage)" <mnordhoff@xxxxxxxxxxxx>
> To: <ccielab@xxxxxxxxxxxxxx>
> Sent: Wednesday, September 10, 2003 3:39 PM
> Subject: BGP Question Concerning MED attribute
>
>
> >  A quick question concerning the BGP MED attribute...
> >
> >
> >
> >  Is it normal behavior for a BGP peer to NOT pass along MED information for
> >  prefixes learned from BGP peers in different AS's?  My scenario is this...
> >  R1 is attached to R2.  R3 is attached to R4.  R2 and R4 are attached to
> R5.
> >  R1 advertises a prefix to R2 via EBGP as does R3 to R4.  R2 and R4 then
> >  advertise these prefixes to R5 via EBGP.  The MED attributes added by R1
> and
> >  R3 are received by R2 and R4, respectively.  However, these MEDs are not
> >  being passed along to R5.  What is the reason for this behavior and what
> can
> >  be done to circumvent it?
> >
> >
> >
> >  Thanks in advance!
> >
> >
> >
> >  Mike Nordhoff - CCNP,CCDP
> >
> >  Deloitte & Touche, National WAN Services
> >
> >
> >
> >  This message (including any attachments) contains confidential information
> >  intended for a specific individual and purpose, and is protected by law.
> If
> >  you are not the intended recipient, you should delete this message.  Any
> >  disclosure, copying, or distribution of this message, or the taking of any
> >  action based on it, is strictly prohibited.
> >
> >
> >  _______________________________________________________________________
> >  You are subscribed to the GroupStudy.com CCIE R&S Discussion Group.
> >
> >  Subscription information may be found at:
> >  http://www.groupstudy.com/list/CCIELab.html
> This message (including any attachments) contains confidential information
> intended for a specific individual and purpose, and is protected by law.  If
> you are not the intended recipient, you should delete this message.  Any
> disclosure, copying, or distribution of this message, or the taking of any
> action based on it, is strictly prohibited.
>
>
> _______________________________________________________________________
> You are subscribed to the GroupStudy.com CCIE R&S Discussion Group.
>
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html