From: Huan Pham (pnhuan@yahoo.com)
Date: Sat Feb 28 2009 - 09:24:25 ARST
Hi Shaun,
I do not see a need for using GRE tunnels.
Blocking paths with AS 1 (ISP A) to go through ISP B will remove redundancy in some scenarios, so I do not think that this is a good design either. For instance, if there're two link failures, one site with link to AS A fail, and another site with link to ISP B fails, then the two can not talk to each other.
If all sites have different private AS numbers, then you will not have to do any path filtering, because BGP will take care of preventing loops based on AS paths.
If all sites have same private AS numbers, (this is more likely the case in MPLS deployments), then on CEs, you should implement AS prepend, or community, and control the routing loops based on that prepended AS number, or the community value.
All the routing policies should be implemented on CE, and you should not need any custom policy routing config on providers' PE routers.
Cheers,
On 2/27/09, 4g1vn <shaun.gomez@gmail.com> wrote:
>
> Hi Group:
> I have quite the exercise from one of my clients. They currently have
> an MPLS WAN with SP(A). They are thinking about bringing a second SP(B)
> online with MPLS connectivity to 3 of their data center locations. The
> issue
> is that they have 300 other locations on SP(A) and would like an alternate
> path through SP(B) in the event of a link failure at one of the data
> centers. Let's say that SP(A) AS is 1 and SP(B) AS is 2, the customer
> remotes are private ASN's (63512-65535). The SP PE's BGP table
will show
> SP(A) public AS path in the BGP table and conversely SP(B) will see the
> public AS of SP(A) and will not allow those paths through. I have created
a
> GRE tunnel and eBGP peering through SP(B) and filter out the public AS
path
> on the customer CE and that seems to work. I'm just curious if this is
a
> solid solution? Does the good folks at GS have a better recommendation for
> handling this other than multi-homing every site?
>
> Thanks,
> Shaun
>
>
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