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2 Internet Connections 1 router - NAT Rules

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  • 2 Internet Connections 1 router - NAT Rules

    I have a Cisco Router that i am going to be using to load balancing/failover between 2 ISP's. Where I am hitting a problem is with outbound NAT rules/IP Pools.

    For example: From one of our ISP's our IP block is from - and the other is - When our email server communicates with the internet we want it to use if it goes out ISP1 and if it goes out ISP2.

    I am currently using IP Pools and access lists to force traffic from our mail server to specifically use one or the other.

    ip nat pool EmailServerPool netmask
    ip nat inside source list 101 pool EmailServerPool
    access-list 101 permit ip host any

    The problem is if it were to failover to my other connection it would still be trying to use the IP address of the failed connection.

    I think i need to use a route map somehow but i can't figure out how to get it to work. I am basically trying to say if the packet is coming from the IP address of our mail server and it is going out a specific interface NAT using this IP. If it is going out the other interface NAT using this IP.

    Does this make sense?

  • #2
    Re: 2 Internet Connections 1 router - NAT Rules

    Its better if u use BGP routing protocol to maintain the redundancy and in that u also have option to route the traffic as per ur reqirement (Local prefrence).

    If u have two ISP connection and suppose one goes down then whole traffic can be shifted to another ISP with no production impact .

    I suggest start using BGP for this kind if scenario