Problem NIC with No IP Address Assigned to It?

[Jay Bollyn]

Can a NIC cause a problem on a Ethernet network if it does not have an IP address assigned to it? For instance, if it has been incorrectly configured, can the NIC cause excessive or unusual network traffic?

We use bootp to assign IP addresses. This particular PC has been commented out in the bootp table. The winXP PC is configured to use DHCP.

I know a new NIC tries to contact a DHCP server in order to obtain an IP address. So clearly some packets can be sent by a NIC with no IP address assigned to it. What else might such a NIC try to do on the network?

Any links that discuss this appreciated.

Thanks for any info.

- Jay

[Ivan Ferreira · Accepted solution]

Besides DHCP discovering and broadcast, the interface shold not be harmful. You could have problems on multi homed servers that are connected to the same network segment, unwanted wins or dns registrations if obtains an IP address may cause some problems, but, if you want to know the TRUTH, you should start a network scanner like "ethereal" and capture the packets on that interface.

[Jay Bollyn]

Thanks Ivan,

I have been relying on other people who are looking at this PC remotely over the network, but I tend to have more questions than answers. I agree the best way to check this out is to run Ethereal on the local PC.

I have always thought that a PC w/o an IP address is fairly harmless on a network, but recently I began to question that idea, for no particular reason.

- Jay

[Jim Kisco]

Another way to look at things is physical layer 1.

Is the wall ethernet port terminated properly?
Are the ethernet cables good?
Is the port it's using on the switch or router good?

Can a new NIC be put into the PC to see if the packets are affected by the chipset?

Also, is there a time of day this occurs or does it happen all the time?

Are any systems using Static IPs?

I assume you are using the "ipconfig /all command to see the current IP address.

Jim

[Hugo Tigre]

Hi Jay,

Using ethereal is off course the best way, if you want to be sure.

But another thing you have to consider, if that computer is connected to a HUB, if so, just the fact that it's connected can generate excessive traffic for all your collision domain (all computers connected to the hub), and because off broadcast for dhcp, it can cause more collisions. This is manly because in this case you'll have half duplex connections.

But if that computer is connected to a Switch, you'll probably have full duplex connections, and so, you wont have collisions because any connection to the switch is considered a pointo-to-point connection, and works at full-duplex.

Even so, you will still have broadcast traffic from that NIC send to all your subnet, but this generaly doesn't cause problems.

Also, you should considered, disabling the NIC, you can still have it connected, but if you disable it, it wont send any kind of traffic.

Finaly, the reason using ethereal is always the best way, even you have a complete understanding of how everything works, it because that NIC could be faulty, and causing unpredictable problems.

Regards,
Hugo

[Alan_152]

It should be harmless, unless:

1) there is another protocol (like netbeui or ipx/spx) assigned to it. In fact, if you aren't using it, you should refrain from assigning a client, protocol, or service to it at all.

2) it goes bad and starts jabbering

3) somebody turns it on and addresses it in an incorrect manner

4) somebody turns it on and addresses it for the purpose of breaching security

BTW, unused cards do consume electricity and generate waste heat.

[Jay Bollyn]

Thanks for these good suggestions.

As it turns out, this Dell workstation is running software RAID, and was broadcasting on a UDP port. OpenManage Array Manager has been uninstalled, and I think this resolves the problem.

- Jay