ISP addresses change address space overlaps

Discussion in 'Cisco' started by Dragec, Aug 21, 2004.

  1. Dragec

    Dragec Guest


    I have range of IP adresses assigned from my ISP. I do NAT on router to my
    internal servers. I need to change IP addressing space. How can I have both
    ranges active in my NAT? Router do no except static translation of two
    external addresses to the sam internal. Need fast hints. I have two plans

    1. To make my DNS provider set TTL of DNS records to 0 and thatn we change
    thins at the same time, both in DNS records to new addresses and me in NAT

    2. I have fw behind router and do translation from new range to local
    addresses and config router to route new range to fw

    Dragec, Aug 21, 2004
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  2. Dragec

    PES Guest

    This is the way most would do it. There still could be a little bit of
    You really cannot fix this with nat because you the following would never
    work regardless of what you were using for nat. Multiple devices would
    accept the config but the connection would break to one of the two
    addresses. Think about the return traffic on the wire inside to outside.

    insideA <> outsideA
    insideA <> outsideB

    insideA:80 <> outsideA:80
    insideA:80 <> outsideB:80

    You would have to have multiple ip addresses on the inside and do policy
    routing if using multiple devices. The following would work. This is a
    common obstacle, it is easy to over simplify it.

    insideA <> outsideA
    insideB <> outsideB

    insideA:80 <> outsideA:80
    insideA:81 <> outsideB:80

    insideA:80 <> outsideA:80
    insideB:80 <> outsideB:80
    PES, Aug 21, 2004
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  3. Configure two addresses on each of the servers. Have the old public
    address NAT to one address, and the new public address NAT to the other
    Barry Margolin, Aug 22, 2004
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