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I'm trying to put my modem in bridge mode so I can plug it into a separate router but I'm having some difficulties. To try to get the facts straight on the settings required I've plugged it straight into my laptop.

The modem-router is Zyxel P660R. I've tries to get all of the settings from the router when it's still running in routing mode, they are as follows:

ZyNOS Firmware Version: V3.40(ANZ.3) | 05/16/2007

WAN Information:
DSL Mode: ADSL_G.dmt
IP Address: 77.44.75.114
IP Subnet Mask: 255.255.255.255
Default Gateway: N/A
VPI/VCI: 0/38

LAN Information:
IP Address: 192.168.1.1
IP Subnet Mask: 255.255.255.0

The IP Address was specified manually (dhcp didn't seem to work). It seems really odd to me that the Default Gateway is not assigned..? It's obviously getting this from somewhere (dhcp?) as the internet works. In the config where the static ip is entered there is no option to enter the default gateway manually.

When I change the modem-router to bridge mode and try to obtain the setting over dhcp I end up with an ip address 192.168.0.34 which again seems odd, why is the modem handing out ip's? I was expecting my static ip (77.44.75.114). So rather than dhcp I could configure it myself, specify 77.44.75.114 as ip, but then what should I use as the subnet and default gateway - when the modem-router was in router mode it said N/A.

Do I just need to go to the isp and ask for the gateway and subnet?

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2 Answers

Have you considered the possible requirements of PPPoE/PPPoA (since is appears you are on DSL) or similar authentication requirements from the ISP prior to the proper access into your ISP account (hence properly/successfully obtaining your statically assigned IP)?

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For DSL modems/routers, it's fairly common to receive a /32 IP and the device use some type of generic local/gateway addresses in the configuration (127.0.0.1/127.0.0.2 for Netopia, for instance). The actual DSL WAN is a point-to-point connection, so doesn't necessarily require proper gateway information. All it needs to do is push the traffic across the right interface - you have the local /32, so traffic gets routed back properly.

You're probably bridging to an Ethernet WAN on your router, which is not a point-to-point interface, so may not support something like an interface based default route - you could try 77.44.75.1 as the gateway and a route for that /24 to the WAN side of your router, but that would be purely a guess.

The majority of DSL connections use PPPoE to retrieve information, but if it's not working and you do not have all the details needed - regardless of whether it's static or PPPoE - you should get the correct information from the ISP, yes.

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