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Issue with BellSouth DSL Modem IP Address Range

Posted on 2008-10-28
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Last Modified: 2013-12-14
We have a business class BellSouth DSL Modem. It is not wireless but does act as our DCHP. In my novice mind I cannot understand why the IP address range does not lease what it is set to.

when I login to the modem under 192.168.1.254 Is see under DHCP settings
modem ip: 192.168.1.254
subnet: 255.255.255.0
dhcp start: 192.168.1.1
dhcp end: 192.168.1.253

However all the client PC ipconfig list IPs as: 192.168.1.92, 192,168.1.93, 94, 95, etc. with them all showing the correct subnet and default gateway as 192.168.1.254 (the same number list for the DHCP server & DNS server under ipconfig)

We have no server all client PCs. The DSL modem plugs into a business class Linksys-Cisco switch and there is a connection from it to a SMC switch. The Linksys switch does have a web access default gateway with the same IP as 192.168.1.254 but I changed the option from static to DHCP so all the PCs can hit the web through it as well and they are. When I enter the gateway address it goes to the bellsouth dsl modem and not the Linksys as it did before the config.

I ask this question because when I boot a PC sometimes I see a warning for an IP Address Conflict and I just cannot understand why the IP address are falling in this range on the BellSouth DSL modem...

This is not my modem screen but it looks similar to this:
http://i.dslr.net/pics/faqs/image11618.gif
"mind shows a box that is checked to use the LAN IP start/end address range..."
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Question by:parcou
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Accepted Solution

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kdearing earned 350 total points
ID: 22829438
Two issues here.

1. DHCP handing out IPs in the middle of the range
    This is not really a problem, more of an annoyance.

2. IP conflicts
    This is a real problem.
    There are several possible causes:
        an unknown static IP somewhare
        a second SHCP server on the network
        the DHCP service in the router is flakey

First, you need to determine if there is a second DHCP server running on the network. Disconnect the LAN port of the router. Then either reboot or release/renew one of the PCs. It should come back with a 169.254.x.x IP address. If it's anything else, you have a second DHCP server operating in your network somewhere.

Second, try changing your DHCP scope (of course plug router LAN port back in). Narrow it down, but allow enough for all your devices. For example if you have 20 devices, set it for 192.168.1.1 - 192.168.1.25
Then either reboot or release/renew all your devices. Verify you're getting IPs within the scope.

You could also try changing your IP range completely. For example change the LAN IP to 192.168.2.254 and the DHCP to correspond.
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