Re: IXP BGP routing

[Brian Candler <B.Candler at pobox.com>]

On Tue, May 21, 2002 at 12:04:04PM +0100, Stephane Bortzmeyer wrote:
> The problem is that he probably does not have access to the Telco's
> routers... (The original message was about the selection of routes by
> the Telco.)

In that case, I misread the posting. I thought the problem was that the ISPs
were not chosing IXP routes, since they received the same routes from their
upstream Telco via EIGRP.

Antonio, is the Telco also a member of the IXP? Does it want to peer with
its own customers? That would be a very unusual situation. Upstreams never
normally peer with their own customers for obvious commercial reasons.

I would expect the situation actually to look like this:

                                   --- ISP1 ---
                                 /              \
      Internet <---------- Telco ----- ISP2 --- IXP
                                 \              /
                                   --- ISP3 ---

In this case, there is no problem with the Telco choosing the right route,
because nothing has changed as far as they are concerned. However, ISP1
wishes to exchange traffic with ISP2/ISP3 via the IXP, in preference to the
route via the Telco.

This will be completely broken if ISP1/ISP2/ISP3 are all part of Telco's
EIGRP cloud. That is because the ISPs want to have a different routing
policy than the Telco. By definition, having a different routing policy
means that they must be a different AS. Therefore the Telco and ISPs cannot
be part of the same IGP cloud.

If the Telco *does* have its own connection into the IXP, I expect they
would only be interested in peering with other providers who have their own
independent Internet link (e.g. their own satellite connection)

So IMO, your approach should be first to decouple the Telco and ISP routing
domains as described before.

At worst: you can make the boundary a router on your own premises, assuming
that you have administrative control over that router. In other words:

                    EIGRP
        <------------------------------->
         ---- R ----------------------- RA --- RB ---- IXP
         TELCO       leased line        CUSTOMER

Router RA is the Telco border, and RB is your own border. The link between
the two is the demarcation point. RA and RB point static routes at each
other (or talk eBGP). RB is part of your own IGP and iBGP clouds.

This solution would be particularly suitable if the router RA is installed
and owned by the telco as part of their service. Otherwise, I would draw the
boundary at the leased line, as described previously.

Regards,

Brian.

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