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Thread: Help setting up a Cisco 678 modem with a Linksys Wireless-G Router

  1. #1
    Newbie Master Pivot may be famous one day Master Pivot may be famous one day Master Pivot's Avatar
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    Help setting up a Cisco 678 modem with a Linksys Wireless-G Router

    I recently picked up a Cisco 678. Since the 678 doesn't have built in wireless capabilities, I am also using a Linksys Wireless-G router (4-port hub, wireless access point, and DHCP router) that I picked up some time ago.

    I know that the two systems are both are not only DHCP routers but also NAT routers. What this means, I don't really know nor what troubles it may bring.

    Does anyone have any experience with such a set up? How do I get these two systems to work together without creating a big mess?
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  2. #2
    Grouchy Old Anime Otaku LenMiyata has become well known LenMiyata has become well known LenMiyata has become well known LenMiyata's Avatar
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    Grumble Grumble Grumble

    You have the potential for a BIG MESS here... The two issues here is the Dynamic Host Control Protocol (DHCP) server, and the Network Address Translation (NAT) abilites. A short explanation of both are in order here...

    DHCP is used to assign a IP address to a computer from a pool of IP Addresss. (The automatic IP address setting in Windows XP will enable a Network port to search for a DHCP server and receive an address to use) To avoid problems, there should only be ONE DHCP server to a network...

    The Second issue is NAT. Network Address Translation is used to 'hide' one or more computer IP addresses behind a single IP address. What is usually the case is that 'Private' network address (I believe RFC 1918 is the correct IETF document) are used, with the Public Internet IP address will come from your's ISP DHCP Server.

    To get this to work, you may need to know about netmasks and subnetting as well....

    Cisco Modem ------ Linksys Hub ---- Host

    Cisco Modem has NAT turned on, DHCP off, gets 'Gateway' address from ISP. Inside address you manually set to a subnet of the allowed range (usually 192.168.something.something)

    Linksys Hub. Manually set Outside address to a setting in the same subnet as the inside address of the Cisco. set default gateway (Route) to the inside address of the Cisco. Set the DHCP address pool to a different private address subnet then the Cisco to Linksys segment.

    I've done this before myself, and if you know what your doing, it's easy. If you don't know what your doing... well....
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