DHCP issues on more than one router.


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Some of you may have read a post from last week about my efforts to get around an apparent DHCP bug in my D-Link DIR-825 router so I could attach my Roku device.

After trying a few things, I finally decided to bit the bullet, and I bought a Netgear WNDR3700. I figured this would do the trick in getting my wireless DHCP back on the right subnet. What happened surprised the heck out of me. The D-Link router had been handing out 192.168.17.xxx addresses though it sat at 192.168.0.1. The Netgear, once set up, started handing out... 192.168.17.xxx as well!!! Plus, I had trouble getting it to see the internet after a few minutes, and it was not easy to pull up the install webpage over ethernet.

This one has me scratching my head. I am an I.T. guy, but I am not a network guru by any means- my work is not in that area so I am not skilled in troubleshooting other than the basics. I live in an apartment which I am on this project, and I am surrounded by a number of wireless routers. I did disconnect all the other ethernet cables other than the one to my Macbook Pro (if needed, I also have Windows machines available.) Nothing seemed to really matter much. I finally put the DIR-855 back in since it did work.

Normally, I have my Apple TV, a Sprint Airave, and an older DIR-655 used for passthrough for additional ethernet connections (DHCP is off on this router.)

I am wondering if the cable modem (not sure which brand- I can look at home in case it may matter) could be interfering? Since the D-Link wants to set itself at 192.168.0.1 and the Netgear wants 192.168.1.1 it seems to me that it wouldn't be a conflict with the modem, but I am not sure.

I was sure a replacement router would solve the problem, but now I have more strange things than ever.

All help and suggestions are appreciated.

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"The Netgear, once set up, started handing out... 192.168.17.xxx as well!!!"

Nonsense plain and simple - come on your an IT guy??

You clearly have rouge dhcp server on the network if your getting and address other than what your routers dhcp servers are setup for.

On your box getting this 192.168.17 address, just look to see the mac of its dhcp server.

ipconfig /all

will show you your dhcp server

arp -a will show you the mac of that IP. What device is it? Post the output of these commands - and just look on your routers to verify to yourself that they are not handing out the 192.168.17 addresses.

example

C:\Windows\System32>ipconfig /all

Windows IP Configuration

Host Name . . . . . . . . . . . . : ts

Primary Dns Suffix . . . . . . . : local.lan

Node Type . . . . . . . . . . . . : Hybrid

IP Routing Enabled. . . . . . . . : No

WINS Proxy Enabled. . . . . . . . : No

DNS Suffix Search List. . . . . . : local.lan

Ethernet adapter Local Area Connection 2:

Connection-specific DNS Suffix . : local.lan

Description . . . . . . . . . . . : vmxnet3 Ethernet Adapter #2

Physical Address. . . . . . . . . : 00-0C-29-53-2C-03

DHCP Enabled. . . . . . . . . . . : Yes

Autoconfiguration Enabled . . . . : Yes

IPv4 Address. . . . . . . . . . . : 192.168.1.210(Preferred)

Subnet Mask . . . . . . . . . . . : 255.255.255.0

Lease Obtained. . . . . . . . . . : Monday, July 02, 2012 3:49:30 PM

Lease Expires . . . . . . . . . . : Tuesday, July 03, 2012 3:51:45 PM

Default Gateway . . . . . . . . . : 192.168.1.253

DHCP Server . . . . . . . . . . . : 192.168.1.253

DNS Servers . . . . . . . . . . . : 192.168.1.253

NetBIOS over Tcpip. . . . . . . . : Enabled

C:\Windows\System32>arp -a

Interface: 192.168.1.210 --- 0xe

Internet Address Physical Address Type

192.168.1.97 00-1c-c3-09-05-7a dynamic

192.168.1.98 00-26-24-08-8a-ed dynamic

192.168.1.99 00-06-dc-43-ad-78 dynamic

192.168.1.253 00-50-56-00-00-02 dynamic

192.168.1.255 ff-ff-ff-ff-ff-ff static

224.0.0.22 01-00-5e-00-00-16 static

224.0.0.252 01-00-5e-00-00-fc static

239.255.255.250 01-00-5e-7f-ff-fa static

255.255.255.255 ff-ff-ff-ff-ff-ff static

From the MAC of the dhcp server we should be able to look up the maker, mine is a virtual which is why the odd looking 00-00-002, I set it that on purpose.

But we can look up the first 3 00-50-56, and find that is vmware

http://www.coffer.com/mac_find/?string=00-50-56

So this can help us find at least what brand this rouge dhcp server is.

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Like I said, I'm an IT guy, but NOT in networking. And I do note the DD-WRT is supported on them both.

Could the cable modem be acting as a DCHP server? Using BudMan's instructions, It seems the DHCP is served by 192.168.17.1, which must be the modem since the router comes up, as expected, at 192.168.0.1. I need to look into this modem and see what can be done about turning off the DHCP server in it. Or, would I be better off using the modem's DHCP?

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All the cable modems I've seen just provide a connection to the Internet, nothing else. No DHCP or anything. That being said, what model is the modem?

Also, do what Budman suggested in his last post.

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That's how I discovered the DHCP is coming in as 192.168.17.1

I need to see what that device is. It seems to be a phantom device.

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192.168.17.1 is the Sprint Airave device... You must have your network wiring configured wrong.

Should be <Modem> into Router WAN port, devices into Router LAN Ports.

The Airave unit needs to have the power and yellow port plugged into the router, don't pass any devices through it's LAN ports. Hook it up that way and reset everything's power.

Here look at this - http://community.sprint.com/baw/thread/59464

Also you should be able to login to 17.1 and turn off the DHCP server in it.

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And did you look at your arp table to see the mac? So we could verify the maker of the device, etc.

And yes if its a soho router type device than sure you should be able to log into it. With the .1 address that would seem likely, let me guess thats your gateway as well.

What is the MAC?? Ping it if you don't see it in your arp table. Then look in the table again.

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I tried signing in to 17.1 and got nowhere. Will try again when home. I usually can get in from work, but I don't have my VMs on this machine yet- I changed from one laptop to another.

I had no idea that the dang Airave would have a DHCP server. Darn thing doesn't work anyway. Maybe that's why...

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Powered off the Airave. DHCP issues resolved. Thanks for that input- I wouldn't have thought it would have a DHCP server.

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