Default gateway based on interface IP?

Discussion in 'Cisco' started by Rodre, Sep 9, 2008.

  1. Rodre

    Rodre Guest

    Hello,

    Pardon me for any indiscretions, this is my first time posting to this
    group. I have a Cisco 1720 router with IOS12.3(26) . It's Outside
    interface has a Primary IP from one carrier, and a Secondary IP from
    another carrier. I have it filtering and NAT-ing SMTP traffic for our
    email server which sits in RFC 1918 address space behind it. I have
    it's primary IP address published in our DNS as the primary MX record.
    I would like to publish it's secondary IP in our DNS as the backup MX
    record. The problem is that ISP 'A' won't route packets with the IP
    address from ISP 'B' (secondary IP) and visa versa. I am guessing that
    they both have egress filtering turned on and are silently dropping
    packets that are not part of their address space. My question is:

    How can I have packets destined for the Primary IP be routed back
    through ISP 'A's default gateway, and have packets destined for the
    Secondary IP be routed back through ISP 'B's default gateway? Is this
    possible? If so what would the NAT rules look like as well?

    Thanks in advance.

    ~Rodre
     
    Rodre, Sep 9, 2008
    #1
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