Traffic from Network B to ISP B - Design

Unanswered Question
Feb 26th, 2009
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Hi,


Before starting with the my request, Let me explain the current setup:

1. We have ISP A and ISP B connecting to a Cisco 4500 with cat4500-entservicesk9-mz.122-46.SG.bin and WS-X4516-10GE Supervisor/513 MB.

2. We have our own AS and have BGP peering with both ISPs. At present both Network A and B are routed via ISP A and B is backup simple floating static route + AS prepend on ISP B (so you can assume no routes learned from neither of the ISPs).

3. We have 2 Cisco ASA in Active/Passive.


Request:


Now we want to have Network B only via ISP B and switch back to A only on failure. What are the options other than using a route map in the existing scenario. If i use any of the BGP metrics to alter the path taken, how do i get this done without getting the routes from the ISP (considering the static routes in place now)


PLease have a look into the attachment for the sketch. Any help is greatly appreciated.


Thanks








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Mohamad Qayoom Thu, 02/26/2009 - 11:10
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Here is an excerpt from Bassam Halabi's BGP book:

"Customer Inbound Traffic

Inbound traffic is affected by how the customer advertises its networks to the providers. To affect the providers' behavior dynamically, the customer can manipulate the AS path attribute by inserting bogus entries in the AS path to affect the AS path length. The providers will receive the same prefix information with different path length and will pick the path that has the shortest length (assuming that all higher-priority attributes are the same). Note that in a multiprovider environment, it is not enough to influence the direct provider only because there is no guarantee that the adjacent provider will itself receive traffic from other providers for that customer's networks. Path manipulation will have to influence providers all the way up to the exchange point because this is where the balance (as far as path length) will be tipped one way or the other."


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