TCP/IP Problems at Work

win2k8

Hello All,
My problem is that my windows xp laptop which is connected through eithernet not wirelessly to the network through a switch is not picking up the network which uses a DHCP server from ISP to assign IP addresses. The problem started when the power went out yesterday, the internet however was working fine for everybody, EXCEPT me. I got this "Limited or No Connectiviy" icon on my desktop tray. I went into ipconfig and it gave me a 169.* ip. Well i thought i should release and renew from DHCP server.. well i did /release and ip changed to 0.0.0.0. Then when i tried to do /renew it gave me error saying: Somebody on network already has that assigned ip and i wont be given a new?!! Anyways, i tried pluggin directly into the router then... still same message, "Limited or no connectivity" and again wont let me renew ip says same thing, somebody eles has the ip already assigned to them and i wont be able to get a new ip from the DHCP server. I took my laptop around the office building and plugged it into all the ports that were open, same thing... So i'm guessing its not cable issue, not a swtich or router issue.. for everyone elses internet works just fine. So that narrows it down to a TCP/IP stack corruption? So what should i do? Please any help will be appreciated!!

Thanks

Danman32

Do you have an account with your ISP that lets you obtain multiple IP's? ISPs usually delegate the IPs based on the mac address of the modem, which tells the ISP who you are for accounting purposes. If your account only allows for one IP, and another machine already has an IP obtained through that modem and MAC, you won't be able to get a new one until the device that got the IP releases it, or the lease times out.

My dad and uncle also tried to share an internet connection with only a switch, and considering the level of understanding my uncle has, he probably only has a 1 dynamic IP residential account. In order to share such a connection, you need a broadband router.

win2k8

I already tried pluggin it in the router it says same error. The switch is connected to the router too i think. but i tried directly to router also.

win2k8

This is the specific error i get: An error occurred while renewing the interface Local Area Connection: The
DHCP client has obtained an IP address that is already in use on the network. The local interface will be disabled until the DHCP client can obtain a new address."

Olajuwon

Go to network connections, disable and reenable the lan interface or right click on and click repair. Try it!

blargoe

I don't think you have tcp/ip stack corruption. Can you plug in your laptop to a different network?

I think there is a problem with your network. The problem is there is another computer that is assigned the same IP address as the DHCP server is leasing to you. If you have access to the dhcp server logs you could find more info.

royal

See the weird thing is, is that the client will request an ip address that it had previously when it attempts to renew its license with the DHCP server. If that ip is already leased and the dhcp knows about it, it'll send a NACK back and the client should automatically request for a new ip address and the DHCP should send back an Offer. Like blargoe said, try checking the DHCP logs. If everything seems fine there, perhaps there is an issue with your NIC or even the protocol stack.

Megadeth4168

I've had NICs go bad before and do this exact thing. In everycase I was able to assign a static IP and get it to work though. I eventually would pick up a new NIC in every case and replace the old one... After that everything would work fine.

win2k8

Thanks for all the suggestions everybody. I got finally got connected to the network today, the day after problem... I guess when the other person with same ip shut down computer and restarted next day the DHCP server gave it a new ip.. and that fixed all.. I guess its one of those wierd things.

Another wierd thing that happend today was an employee who uses Outlook wasnt able to send or recieve any email for like 3 hours... it kept saying found server but cannot send or something. What finally worked was i re-installed Norton Anti-virus of all things and that made it work... so yea some things are just wierd but thing is to never give up and it will eventually go away.. atleast thats what i'm learning in my new I.T support job.

JDMurray

The DHCP client attempt to renew using the same IP address it had before. If the DHCP server has already assigned the address the DHCP client requests, the server gives the client a different address.

If the address the DHCP server was giving your client was already present on the network, the DHCP server didn't assign it. Someone either assigned it to a NIC as a static address, or you have multiple DHCP servers running on your network with overlapping address pools.

It is possible to clear the IP address a Windows DHCP client uses by searching for the IP address in the Registry and removing it from the DHCP section of the network keys. You will then need to restart the DHCP Client service to flush the old address and obtain a new IP.

Olajuwon

jdmurray wrote:

The DHCP client attempt to renew using the same IP address it had before. If the DHCP server has already assigned the address the DHCP client requests, the server gives the client a different address.

If the address the DHCP server was giving your client was already present on the network, the DHCP server didn't assign it. Someone either assigned it to a NIC as a static address, or you have multiple DHCP servers running on your network with overlapping address pools.

Exactly

royal

Hence the reason conflict detection exists on the dhcp server. If you turn that on, it'll basically ping an ip when a client requests an ip and if the ping is successful, the dhcp will send back a NACK and the client will attempt to obtain a new ip address. Conflict detection is also good if you're switching to a new dhcp sserver or a new scope which doesn't contain any information on leases so if you load the new scope/server you're going to have conflicts all over the place.

keatron

icroyal wrote:

Hence the reason conflict detection exists on the dhcp server. If you turn that on, it'll basically ping an ip when a client requests an ip and if the ping is successful, the dhcp will send back a NACK and the client will attempt to obtain a new ip address. Conflict detection is also good if you're switching to a new dhcp sserver or a new scope which doesn't contain any information on leases so if you load the new scope/server you're going to have conflicts all over the place.

Keep in mind all DHCP is not created equally. The DHCP server mechanism usually will not "ping" to see if someone has the address (because if it did, the machine with the address already assigned would respond). DHCP leases have an expiration. The DHCP server will not assign a given address again until the lease expires (in most cases). It is a common mis-conception to assume that the DHCP service will actually "check" the rest of the network before assigning an address. It just doesn't happen that way. It checks it's own records for leased addresses and lease expirations. If there's no conflict there, the next address in the pool is leased. Since your DHCP server is probably set with a default lease time of something like 8 days, a given machine disconnecting then re-connecting (as long as it's inside 8 days) will get the same IP address by design. If the expiration is 3 days then the same applies except the window of opportunity is now 3 days instead of 8. And part of this mis-conception leads to another mis-conception. I've heard people say the the command ipconfig /release followed by ipconfig /renew will give you a new ip address. Again this is wrong, the second command in itself explains it all. RENEW is not synonomous with NEW. If I had a contract with Techexams.net for one year and I renewed that contract after the 1st year, it wouldn't be the same as getting a new contract. I'd basically be extending the terms and validity of my existing contract. Same with DHCP.

sprkymrk

keatron wrote:

icroyal wrote:

Hence the reason conflict detection exists on the dhcp server. If you turn that on, it'll basically ping an ip when a client requests an ip and if the ping is successful, the dhcp will send back a NACK and the client will attempt to obtain a new ip address. Conflict detection is also good if you're switching to a new dhcp sserver or a new scope which doesn't contain any information on leases so if you load the new scope/server you're going to have conflicts all over the place.

Keep in mind all DHCP is not created equally. The DHCP server mechanism usually will not "ping" to see if someone has the address (because if it did, the machine with the address already assigned would respond). DHCP leases have an expiration. The DHCP server will not assign a given address again until the lease expires (in most cases). It is a common mis-conception to assume that the DHCP service will actually "check" the rest of the network before assigning an address. It just doesn't happen that way.

Correct, by default W2K/W2K3 DHCP Server does not use ICMP Echo Request messages (pings) to attempt to detect an IP address conflict before assigning an address. You can change this by opening the Properties for a DHCP server and clicking the Advanced tab. In the Conflict Detection Attempts, you can then specify the number of pings you want the server to do before assigning an address. I think I was told that each ping attempt creates a delay of about a second or so while the server waits for the ping message to time out. Microsoft recommends a value no higher than 2 for this setting.
I'm not trying to post redundant information, as both of you know this already. I just wanted to clarify for other readers who may not be aware of the default operation vs. the option to configure a DHCP server to ping an address before assigning.

royal

Correct, but that's why I said "if you turn it on" (meaning it's off by default).

win2k8

Thanks for the feedback, just curious though I read some where if you run the ipconfig /flushdns that will reset records, and might resolve the ip conflict?

royal

No, that only flushes the cache. An example of when you would want to use that is if you lets say connect to computer2.domain.com often and that computer gets its ip address changed and gets his dns record updated to point to his new ip address. The computer you're on wont be able to connect to computer2.domain.com because it is cached on your local system to point to the old ip. An ipconfig /flushdns will flush the dns cache on your local system so it will use the server instead of its local cache (the server has the correct record).

IP conflicts don't have anything to do with dns. It means 2 ips exist on the same network which don't have anything to do with dns. It has to do with TCP/IP configuration issues.

sprkymrk

icroyal wrote:

Correct, but that's why I said "if you turn it on" (meaning it's off by default).

As I said - I know you know...