Moved to new city, DNS problems?

[jibs]

Alright, I have a Linksys E3200 router arriving in a few days that I can try. The router is also DD-WRT and Tomato capable so I can change the firmware if the stock firmware won't do the job for me.

I don't see any settings in my current E2000 router for DHCP relay or anything along those lines. I can also flash this router to DD-WRT or Tomato and give that a shot, but I would rather wait until I try the new router before I start flashing anything....and I know it's hard to do but I don't want to brick this router before the other one arrives.

Could this dhcp problem be caused by ports that I have forwarded on my router? I have ports 8080 tcp, 21 tcp, 22 tcp, 80 tcp, 43833 tcp/udp and 55536 - 56559 tcp forwarded for various network appliances.

 

[jibs]

I received my new E3200 router, powered off my cable modem, connected everything and powered on the cable modem and the new router on. I still end up receiving 192.168.100.xxx IP addresses. I checked my network and it is still showing 2 DHCP servers 192.168.100.1 and 192.168.1.1.

I flashed the E3200 to the latest shibby build of the Tomato firmware which offers substantially more admin customization options as the stock linksys firmware, but I'm still being assigned incorrect IP addresses. I've now tried 4 different wireless routers with numerous firmwares, replaced my my cable modem with a new one in bridged mode. There is obviously something I'm missing here, even with the wireless router in its basic default config it doesn't work.

There is a setting on the tomato firmware to "use internal dns" which I have enabled, and I have tried every setting combination I can think of. I'm not really sure where to go from here, I have done lots of reading about problems similar to mine but they always seem to be solved by putting the cable modem into bridge mode. There has to be a config that works for my setup...hell it worked before I moved with the exact some configs.

/end rant

Thanks

 

[owensdj]

jibs, that's one of the craziest network issues I've ever seen. The client machines shouldn't even be seeing the 192.168.100.1 DHCP server coming from the cable modem if you have it plugged into the WAN port on the router.

I don't think the cable modem is in bridged mode if it's handing out private IP addreses. It should be handing out your single public IP address. Try calling your cable ISP again and see if they can change the configuration on it. Tell them it has DHCP and NAT enabled and you need that turned off because you have a router.

 

[seepy83]

jibs, that's one of the craziest network issues I've ever seen. The client machines shouldn't even be seeing the 192.168.100.1 DHCP server coming from the cable modem if you have it plugged into the WAN port on the router.

Exactly. The DHCP server in the router should be answering any DHCP broadcasts on the LAN segment. It should not be forwarding them out the WAN port. I have never seen a SOHO router act like that.

jibs, can you verify that everything is wired correctly? Is everything in the same room and connected with patch cables, or is there any in-wall wiring to network jacks/patch panel involved?

I'm only asking you to verify the wiring because what you're describing only makes sense if everything is connected to the LAN ports on your router.

 

[jibs]

Yeah this is a strange one for sure. My setup is as follows:

From port 1 on the cable mode, that is plugged into the "internet" port on my wireless router. Then from port 1 on my wireless router it runs to port 1 on my hp 1410-8g switch which is where all my computers are connected. All of the computers are located in the same room and there is no in-wall wiring. I have removed the hp switch from the picture and the problem continues when the computers are connected directly to the wireless router. The hp switch is unmanaged and thus shouldn't do anything but route traffic

I spoke with my ISP tonight, they confirmed that the cable modem is in Bridge mode and confirmed that no DHCP or NAT should be running on the modem.

I posted this problem on another forum and I had a few recommendations that I don't fully understand. The first was to assign an access restriction that would apply to all computers at all times, from the source or destination of ports 67, 68 and destination of 192.168.1.1 which is my wireless router. I'm not sure I completely understand this, does it mean that all computers attempting to connect to my network would be directed to my router and thus have my router assign its IP addresses? I tried a basic implementation of this and it didn't appear to work...although I may not have set it up correctly

The other suggestion was to clone my MAC from my PC to my router. There wasn't really any follow up to this suggestion so i'm not too sure what this would accomplish or possibly help solve my problem

Thanks

 

[seepy83]

You need to verify that 192.168.100.1 is the cable modem.

If it is, then your ISP is wrong and it is running DHCP and NAT.

If that's the case, then maybe your best option is to just disable the DHCP service on your router, connect everything (including the cable modem) to the LAN ports, and use your router like a switch and wireless access point. You shouldn't need to do that, but it seems like the best option.

 

[AnonymouseUser]

You need to verify that 192.168.100.1 is the cable modem.

From earlier in the thread:

Alright, the new cable modem from my ISP showed up. Now before I connected everything I unplugged everything from my wireless router, disabled the wifi and connected my laptop to 1 of the LAN ports. I was assigned the proper 192.168.1.xxx IP address automatically. I ran the rogue dhcp server software and it only shows 1 dhcp server, 192.168.1.1 which is my wireless router.

I plugged in my new cable modem, let it load, plugged it into the WAN port on my wireless router, connected my laptop and was assigned a 192.168.100.xxx IP address. I ran the rouge dhcp software and it's showing 2 dhcp servers, 192.168.1.1 and 192.168.100.1. When I point my browser to 192.168.100.1 it takes me to the admin page for my new cable modem, the Cisco dpc3825.

 

[jibs]

I'm curious how this works, since it seems like I cannot win against my ISP's DHCP and NAT, i might as well look into options to continue using my router for wireless.

How would I go about configuring this? Would I have to change the IP of my router or set it to a different mode? You mention having to disable the DHCP on my router, is there anything else I have to do with it?

Thanks

You need to verify that 192.168.100.1 is the cable modem.

If that's the case, then maybe your best option is to just disable the DHCP service on your router, connect everything (including the cable modem) to the LAN ports, and use your router like a switch and wireless access point. You shouldn't need to do that, but it seems like the best option.

 

[VirtualLarry]

I would verify that your subnet mask on the router is 255.255.255.0, and NOT 255.255.0.0.

That could also be your issue.

 

[jibs]

The cable modem is handing out IP's on the 255.255.255.0 subnet and my wireless router is doing the same

I would verify that your subnet mask on the router is 255.255.255.0, and NOT 255.255.0.0.

That could also be your issue.

 

[seepy83]

I'm curious how this works, since it seems like I cannot win against my ISP's DHCP and NAT, i might as well look into options to continue using my router for wireless.

How would I go about configuring this? Would I have to change the IP of my router or set it to a different mode? You mention having to disable the DHCP on my router, is there anything else I have to do with it?

Thanks

Log in to your router and set a static IP on it. Remember what you set so that you can manage it in the future without resetting it to factory defaults if you want to make changes. The logic with this step is that you're about to turn off the DHCP server on the router, so you won't be able to just plug a device into it and then check the Default Gateway that was assigned and use that address to access the web management interface on the router.

Configure the wireless however you would like (SSID, encryption type, passphrase, channel, etc).

After that, it's as simple as disabling the DHCP server in the router and connecting all of your devices using the LAN ports. Don't connect anything to the WAN port.

As a side note, I looked up the Cisco DPC3825 users guide, and it looks like it's a complete router/switch/wireless access point. I would probably just configure that however you want and be done with it. There's really no need to use 2 routers.

 

[owensdj]

jibs, have you tried connecting a PC directly to your new Cisco DPC3825 modem to see if you can get into the setup? According to the manual it should be using 192.168.0.1 for its IP address, but maybe your ISP changed the configuration. If you can't get into the modem setup yourself to turn off the DHCP server(and the wireless too), I would call your ISP and see if they can do it on their end.

When you connect a PC directly to the modem, what IP address does it get? What DHCP server does it say it used?

 

[jibs]

I have connected directly to the Cisco modem and I can get to the setup screen which is normally located at 192.168.0.1, unless your modem is in Bridge mode like mine then it is located at 192.168.100.1 and you can't log into the modem at all, all of its functionality is disabled. I spoke with my ISP to confirm that my modem was in bridge mode and they said it was, she has me confirm that by going to 192.168.100.1 and trying to login. She said they are unable to turn off DHCP on their end.

jibs, have you tried connecting a PC directly to your new Cisco DPC3825 modem to see if you can get into the setup? According to the manual it should be using 192.168.0.1 for its IP address, but maybe your ISP changed the configuration. If you can't get into the modem setup yourself to turn off the DHCP server(and the wireless too), I would call your ISP and see if they can do it on their end.

When you connect a PC directly to the modem, what IP address does it get? What DHCP server does it say it used?

 

[jibs]

Thanks for the info. I'm keeping the option of using the Cisco modem as a wireless router as a last resort, since I live in an apartment building the 2.4gh/z spectrum is pretty packed. Even after running a program like inssider and selecting the least used channel range I still have a problem keeping a good wireless signal. Being able to use my E3200 opens up the 5gh/z spectrum and some pretty decent speeds

So just to make sure I understand how I would use my wireless router as a switch, I would log in and assign it an IP address of something like 192.168.100.5 which will be accessible from the IP range that my modem is assigning. I would then disable the DHCP server on it. That would leave me with 1 DHCP server running on my cable modem that would assign IP addresses to all my computers. I would plug the cable modem and any computers into the LAN ports on the wireless router which is now functioning as a switch.

I would also have to change any static IP's I have on my network to reflect the 192.168.100.xxx address range.

I hope that makes sense, is there anything I'm missing or not understanding to make this work?

Thanks

Log in to your router and set a static IP on it. Remember what you set so that you can manage it in the future without resetting it to factory defaults if you want to make changes. The logic with this step is that you're about to turn off the DHCP server on the router, so you won't be able to just plug a device into it and then check the Default Gateway that was assigned and use that address to access the web management interface on the router.

Configure the wireless however you would like (SSID, encryption type, passphrase, channel, etc).

After that, it's as simple as disabling the DHCP server in the router and connecting all of your devices using the LAN ports. Don't connect anything to the WAN port.

As a side note, I looked up the Cisco DPC3825 users guide, and it looks like it's a complete router/switch/wireless access point. I would probably just configure that however you want and be done with it. There's really no need to use 2 routers.

 

[seepy83]

So just to make sure I understand how I would use my wireless router as a switch, I would log in and assign it an IP address of something like 192.168.100.5 which will be accessible from the IP range that my modem is assigning. I would then disable the DHCP server on it. That would leave me with 1 DHCP server running on my cable modem that would assign IP addresses to all my computers. I would plug the cable modem and any computers into the LAN ports on the wireless router which is now functioning as a switch.

I would also have to change any static IP's I have on my network to reflect the 192.168.100.xxx address range.

I hope that makes sense, is there anything I'm missing or not understanding to make this work?

Thanks

That sounds right. You'll want to make sure that you assign your router a static IP that isn't in the DHCP range for your cable modem/residential gateway. But I think you said that you're unable to log into the cisco device at 192.168.100.1...so it doesn't sound like you can get at it to modify its DHCP scope or view what it is so you know to pick an address that it won't assign to another device. You could assign it something on a different network (192.168.200.1, just as an example), but then you would need to assign a static IP on that network (192.168.200.2, for example) on a PC that's wired to its LAN ports if you ever want to log in and make changes to it. While doing that, you wouldn't have internet access.

 

[jibs]

so if my Cisco modem is assigning IP's in the 192.168.100.xxx range, i could just turn off the DHCP on my wireless router, assign it the IP it currently uses 192.168.1.1 and it won't conflict with any of the computers on my network. Then when I want to access it I just have to connect a PC to it and assign the PC a static IP of 192.168.1.xxx and i would be able to access it again?

That sounds right. You'll want to make sure that you assign your router a static IP that isn't in the DHCP range for your cable modem/residential gateway. But I think you said that you're unable to log into the cisco device at 192.168.100.1...so it doesn't sound like you can get at it to modify its DHCP scope or view what it is so you know to pick an address that it won't assign to another device. You could assign it something on a different network (192.168.200.1, just as an example), but then you would need to assign a static IP on that network (192.168.200.2, for example) on a PC that's wired to its LAN ports if you ever want to log in and make changes to it. While doing that, you wouldn't have internet access.

 

[jibs]

Last night I disabled DHCP on my wireless router and left its IP as 192.168.1.1, had my ISP take their modem out of bridge mode so I could access the admin options 192.168.0.1. I plugged the cable modem into a LAN port on my wireless router and plugged my computers into the other LAN ports. Everything worked exactly as Seepy83 said it would and my computers were automatically assigned usable IP addresses in the IP range 192.168.0.xxx. I was able to connect to my wireless router and access the internet, everything is working perfectly. I ran the Rogue DHCP software and there is now only 1 DHCP showing up on my network.

I do have 1 question though, does my wireless router 192.168.1.1 have to be located on a diff IP range than the rest of my network or could I assign it a static IP of something like 192.168.0.250? I'm not fully understanding why it can't work on the same IP range if it doesn't have any DHCP services running and is just acting as a switch.

Thanks again to everyone for the help on this matter

 

[owensdj]

jibs, yes you can put your router on the same 192.168.0.x subnet as your Cisco cable modem now. Just look at the modem's DHCP server range and pick a static IP address that's outside the range. Maybe 192.168.0.2?

That modem tends to get bad reviewers for its wireless feature. I would turn off the wireless in the modem and turn on the wireless in your router. That would allow your wireless router to act as a wireless access point for your network. The DHCP server would be off in your router and on in your modem.

 

[jibs]

Thanks for the info. I think my subnet range starts at 192.168.0.3 right now so I will make my wireless router 192.168.0.2 and everything should be good.

Yeah the poor performance of the Cisco unit and its lack of 5gh/z is why I want to use my own wireless router.

Thanks for the help

jibs, yes you can put your router on the same 192.168.0.x subnet as your Cisco cable modem now. Just look at the modem's DHCP server range and pick a static IP address that's outside the range. Maybe 192.168.0.2?

That modem tends to get bad reviewers for its wireless feature. I would turn off the wireless in the modem and turn on the wireless in your router. That would allow your wireless router to act as a wireless access point for your network. The DHCP server would be off in your router and on in your modem.

 

[VirtualLarry]

jibs, that's one of the craziest network issues I've ever seen. The client machines shouldn't even be seeing the 192.168.100.1 DHCP server coming from the cable modem if you have it plugged into the WAN port on the router.

I don't think the cable modem is in bridged mode if it's handing out private IP addreses. It should be handing out your single public IP address. Try calling your cable ISP again and see if they can change the configuration on it. Tell them it has DHCP and NAT enabled and you need that turned off because you have a router.

See this thread. Apparently, if the CM isn't connected to the internet, it enables a local DHCP server to hand out local IPs, on 192.168.100.x.

Which then begs the question, how is the PC getting a DHCP response from the modem on that subnet, if the if router is properly wired up. (WAN to modem, LAN to PC). Something has to be mis-wired, and the OP just didn't catch it.

http://www.dslreports.com/forum/r28079499-Comcast-CS-cannot-configure-SB6141-to-bridge-mode-

 

[VirtualLarry]

I plugged the cable modem into a LAN port on my wireless router and plugged my computers into the other LAN ports.

Could this be the problem?

 

[jibs]

Could this be the problem?

Thanks for the info Larry, this was done as a recommendation by another user during a different config attempt.

I have since taken my cable modem out of bridge mode, disabled its wifi and connected it to my wireless router which has the wireless enabled and the dhcp server disabled. The DHCP is being performed by my cable modem and my wireless is being handled by my router. This has solved all the problems I was having and is giving me a strong wireless signal.

Thanks to everyone who helped me in this thread