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Best approach to migrate from static ISPs to BGP multihoming

Unanswered Question
Apr 22nd, 2014
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Hello,

We currently have two ISPs for our internet connectivity and we are load sharing traffic between the two. Currently we have static routing with these ISPs. Our plan is to change that and implement BGP multihoming with the two ISPs. Also currently we have only one router which talks to both the ISP routers. We plan on implementing HSRP pair with this router and use them as WAN/Edge routers which will do BGP with the ISPs.

 

What is the best/right approach to do this? Since we will be migrating to BGP, we will get new IP space and we need some time to change the applications from current public ip space to new ip space. Should I implement HSRP pair first, do BGP with the ISPs and then migrate the applications to new ip space? Or is there a better approach? Can I have static routing and BGP peering with the ISP at the same time, until I migrate all the applications from current public ip space to new ip space?

 

Thank you.

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WILLIAM STEGMAN Tue, 04/22/2014 - 11:07
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Shivani, there a few different aspects with load balancing and dual ISP connectivity. 

  • Outbound (clients to Internet)
  • Inbound (return traffic from clients when browsing Internet)
  • Inbound (customers initiating connections from outside to applications you host)

I think HSRP on the inside interfaces of the 2 routers is a good start.  That addresses your outbound redundancy.  Outbound load balancing is a little trickier.  You could use 2 subinterfaces on your HSRP pair and make each a primary on that network while backing up the other.  Otherwise, for outbound load balancing, you'll need to learn Internet routes from each ISP and run iBGP between your 2 routers and mark certain prefixes with a higher local preference so that the exit point (the ISP gateway) is used for some prefixes and the other ISP gateway for other prefixes.  Inbound redundancy/load balancing could be achieved by advertising different networks (your source networks) out of the two ISPs, and then using a shorter mask route for redundancy should one of the ISP links go down.  You could also use AS Path prepending to make one of the ISP routers more or less preferred  for certain networks. 

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