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I have a D-Link DSL-2500U ADSL modem. Its default IP is 192.168.1.1 and default login/password for the web interface is admin/admin. If I plug in the Ethernet cable to the NIC of a computer (that runs Windows XP), assign the IP 192.168.1.2, then I can access the web interface at http://192.168.1.1 in the browser.

My modem is configured to work in bridge mode. If I also plug in the phone line that comes from the splitter and change the NIC settings on computer to obtain an IP addres automatically over DHCP, I get a real IP (and also a default gateway, which implies a default route) from my ISP. Everything is well, Internet works, except the fact that I can't access the web interface of the modem anymore, unless I unplug the phone line, restard the modem and change the NIC settings back as described above. I assume this happens because the IP packets for 192.168.1.1 destination go to the ISP gateway via the default route instead of going to the modem.

Until now I used to have ~8Mbps download, so I know for sure that my modem and my phone line can handle it. Recently my ISP raised the download speed up to 20Mbps, but I'm still getting only ~8 as before. I know I need to have ADSL2+ support. My modem supports it and this is enabled, I can see that in the web interface. But I would want to be able to access the web interface when the modem is running in bridging mode and my Internet connection is working, so I could see the maximum link speed, just in case that my ISP forgot to increase the speed on the DSLAM port.

How can I access the web interface in this scenario?

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what is the 'Real IP' you get ? –  Revolter Dec 2 '09 at 11:36
    
By "real IP" I mean the IP I'm getting from the ISP via DHCP. It looks like 92.x.x.x, the default gateway (and the default route) has the same form. –  geek Dec 2 '09 at 12:09

4 Answers 4

up vote 2 down vote accepted
+100

When I am faced with a similar situation, I use either a Windows 2000 or Linux live CD in a virtual machine and set it to bridged mode. I set the IP to the same as the interface on the router and access the web interface that way.

The other was is simply to manually change my IP to match that of the router - as you shouldn't need to change settings to often, I do not really see this as that much hard work.

Lastly, unless you have a reason for setting it like this, you may want to enable NAT on the modem and use it as a full router for your network.

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The virtual machine approach worked. Thanks for teaching me a nice trick. –  geek Dec 7 '09 at 14:39
    
Thats cool! Thanks! –  William Hilsum Dec 7 '09 at 14:44

Add another network card and put the machine on both networks?

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I have tried to add a Microsoft Loopback Device, assigned IP 192.168.1.2 to it and still cannot access anything at 192.168.1.1 Does the modem keep the web interface accessible at this IP address when running in bridge mode? –  geek Dec 2 '09 at 9:05
    
can you not change the modem so it uses NAT rather than bridging? –  matpol Dec 2 '09 at 12:44
    
My question is if I can access the web interface without changing any modem settings. If I'd try to switch to router mode, I'd have to modify at least the firewall rules on my computer. –  geek Dec 2 '09 at 13:03
    
i don't know that the loopback device is sufficient. what you want is a second address for the physical card (ie, an alias), if possible under windows, or a second physical card. –  quack quixote Dec 4 '09 at 12:51
    
~quack, my NIC is configured to get an IP via DHCP, from the ISP, how could I add a second, static IP to the same interface? Also I don't see how a second NIC would help, since there is only one cable going from the modem to the computer (that connects the computer's NIC with the modem Ethernet interface). –  geek Dec 4 '09 at 13:28

Although windows will allow you to assign multiple IP addresses to one NIC, you can not do this if the NIC is using DHCP. Assuming you don't want to pay your ISP for a static address, then you have three choices.

1) Change you modem from bridge to NAT mode. - I am not sure why you think this should require any firewall changes on your PC. If necessary just set your PC as the DMZ machine on your modem.
2) Add a second physical NIC to your machine, one will connect to your modem, one to your access point.
3) Add a seperate router / NAT device between your modem, your PC and the access point.

I would suggest option 1. If necessary then I would buy a new modem/router that supports all the functions I require.

I don't think any of this has any bearing on your connection speed, or vice-versa.

EDIT: Sorry, I mis-understood your original post, it sounded like you had two seperate devices. With it being only one device, I can not see how you can connect to its interface while it is in bridged mode. And as others have said, there isn't going to be that much to configure anyway.
I don't think NAT is going to cause you any speed issues on a normal braodband connection. You are correct though, there is a maximum throughput that a home NAT device can handle, there are also several pretty good sites, like http://www.smallnetbuilder.com , that give throughput measurements for routers they test. Having said that, I expect your router would be able to handle 8 Mbs easy enough. There is also no gaurantee that your particular router is any faster when in bridged mode. Bear in mind its firmware will have probably been tested more for NAT mode than bridged because NAT is what they expect everyone to use.
As a last point, if you switch your router to NAT mode (and don't configure anything as DMZ) then it will do as a pretty good firewall for your PC, depending on your security requirements you could then turn off your software firewall which will ease the load on your PC's CPU.

I have a Netgear router running as a NAT device with 7 devices behind it (plus 2 smart phones sometimes), with most of them doing normal internet browsing or messenger or similarly low bandwidth use, speedtest still shows about 48Mbs down and 1.5 mbs up, I am on 50Mbs virgin broadband, so this is pretty much full speed.

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1) I'm also against NAT because I believe that this mode puts the modem under higher pressure than just forwarding IP packets when in bridge mode. So this actually might have an impact on the connection speed. 2) I don't have any access point. The modem is connected directly to the computer. 3) It is a home network, I certainly don't need one more device. –  geek Dec 4 '09 at 13:52
    
Sorry, I misunderstood, I have updated my answer. –  pipTheGeek Dec 4 '09 at 19:26

I'm pretty sure that in bridged mode the whole point is that what the modem sees is forwarded unedited to the internal network and vice versa, and the only way to do that is to that is to effectively remove yourself from the network and forward everything through.

I had a time when I used an adsl modem in bridged mode (so that a wireless router next to it became the internet gateway) and prior to selecting bridged mode it pretty much stated that the device would become invisible to the network and would essentially be an ADSL -> Ethernet converting paperweight. The only way to bring it back was to perform a hard reset to set it back to default config.

The whole idea is that you set it up as a normal router, check configs, make sure that line type is right and speeds are right then, once everything worked, click over to bridged and it vanishes from your network. If the device sees a particular line speed un unbridged mode, then that is what you'll get in bridged mode with the side effect that you'll have no way to verify it.

Basically you have a choice of seeing what speed the connection is and put up with a useless extra gateway, or you just accept that the speed is what it will be and get on with making use of it.

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