IP conflict question

790 Views | 14 Replies | Last: 5 yr ago by TexasAg2002
Dr T and the Women
How long do you want to ignore this user?
AG
Texags network experts,

I hope you can give me some advice. In my office we have 2 Samsung ultrasounds connected by ethernet to our network. I have assigned static ip to each.
The images transfer to our electronic system through a dicom tech

I often get error messages on one machine saying IP conflict. I called the company and they can't figure it out and say it is a network issue.

I don't know how it could be since each is assigned a static ip. I don't have any issues with any other hardware.

Is there any way this can be a network issue knowing these parameters?
No material on this site is intended to be a substitute for professional medical advice, diagnosis or treatment. See full Medical Disclaimer.
chigger
How long do you want to ignore this user?
AG
It sounds like some other device on the network has the same IP. Could be any internet connected device. You have to reserve the IP on the router/switch to guarantee DHCP will not assign a duplicate.
OldArmyBrent
How long do you want to ignore this user?
AG
How did you assign the static IP? My totally unprofessional opinion is that if the router is assigning everything else dynamic IP and somehow assigns the same IP, you could have a problem.

Is it possible to give your ultrasounds a static IP outside the range being used for DHCP to assign other devices?
saw em off
How long do you want to ignore this user?
Depends on how the DHCP scope is set up. For example, if you have a 192.168.1.0 subnet, you can set a dynamic range of 192.168.1.100-200 and have your US devices at 192.168.1.98 & 99. Like an above poster said, if you have statics assigned, but it's still in the DHCP scope range, it's likely a conflict can occur. The best thing to do is set everything dynamic and reserve the ones you want to never change.
UmustBKidding
How long do you want to ignore this user?
Depends also on the DHCP server. The windows one if you make a reservation it will not assign even if its in the DHCP block. Basically need to understand the DHCP infrastructure and LAN addressing scheme. Also have seen cases where people outside of IT end up sticking a home network type router in an ethernet jack and you get multiple devices responding to DHCP discover packets.
Dr T and the Women
How long do you want to ignore this user?
AG
I actually just used dhcp initially and it was having the issue. I tried the static just to see if it would solve the problem.

No material on this site is intended to be a substitute for professional medical advice, diagnosis or treatment. See full Medical Disclaimer.
91AggieLawyer
How long do you want to ignore this user?
AG
Can you assign all devices a static IP?
eric76
How long do you want to ignore this user?
AG
When a dhcp server assigns an address, it remembers the it assigned the address and the Mac address of the device.

Depending on the server, if it is powered down, it may or may not retain the information when started back up and may reassign the address to another device.

I think that many servers will make some attempt to see if the address is in use, for example by pinging the address or by checking its own arp table to see if the address is already there.

There are also differences in the way the Mac addresses are selected. Some will just start with the first address in the range and continue through. For example, if the range is 192.168.100.2 to 192.168.100.200, then it will try to assign 192.168.100.2 first, then 192.168.100.3, then 192.168.100.4, and so on.

Others will use a scheme to assign addresses across a range to try to make the assignments less predictable to attackers. If your dhcp server does this, it is much less likely to accidentally assign an address to another device after a reboot.

One thing you can do to look for which devices are being used by which devices is to check the arp table. Just open a command window and type:

arp -a -n

and note which addresses are assigned to what. You'll also need to determine which device has which MAC address.

Also, sign onto the dhcp server (I assume it is on a router) and check the dhcp assignment table.
immortal_kumquat
How long do you want to ignore this user?
You need to reserve the IP addresses on your router/switch as a previous poster mentioned, so that other devices aren't automatically assigned the same IP addresses.
eric76
How long do you want to ignore this user?
AG
By the way, how long is the address reservation time?

In some cases, I can help to set it to just a few minutes.

For what it's worth, I used to set it on our equipment to one year. That ran into problem with SonicWall appliance which can't seem to handle addresses that long. Currently I use one week for SonicWall, ten minutes for everything that isn't expected, and two weeks for everything else.

(By the way, one time for grins, I once set to give out leases of 10 years. Some devices didn't like that.)
saw em off
How long do you want to ignore this user?
91AggieLawyer said:

Can you assign all devices a static IP?
You can, but that's a pain to keep track of. You'll have to document and note the next address that's available as new devices enter your network. Also most devices have DHCP turned on by default. Chances are you'll conflict as soon as you fire it up to go assign it a static.
Dr T and the Women
How long do you want to ignore this user?
AG
thanks everyone. very helpful.
No material on this site is intended to be a substitute for professional medical advice, diagnosis or treatment. See full Medical Disclaimer.
eric76
How long do you want to ignore this user?
AG
saw em off said:

91AggieLawyer said:

Can you assign all devices a static IP?
You can, but that's the pain to keep track of. You'll have to document and note the next address that's available as new devices enter your network. Also most devices have DHCP turned on by default. Chances are you'll conflict as soon as you fire it up to go assign it a static.
One alternative is to use the 10/8 block.

Set the gateway to 10.0.0.1

Provide DHCP addresses in the range of 10.0.1.0 to 10.0.255.255.

When assigning IP addresses just give some random address between 10.1.0.0 and 10.255.255.254. If picked randomly, the odd of a conflict unless you have a really huge network is pretty close to zero.
Dr T and the Women
How long do you want to ignore this user?
AG
eric76 said:

saw em off said:

91AggieLawyer said:



Can you assign all devices a static IP?
You can, but that's the pain to keep track of. You'll have to document and note the next address that's available as new devices enter your network. Also most devices have DHCP turned on by default. Chances are you'll conflict as soon as you fire it up to go assign it a static.
One alternative is to use the 10/8 block.

Set the gateway to 10.0.0.1

Provide DHCP addresses in the range of 10.0.1.0 to 10.0.255.255.

When assigning IP addresses just give some random address between 10.1.0.0 and 10.255.255.254. If picked randomly, the odd of a conflict unless you have a really huge network is pretty close to zero.
Great idea. Ty
No material on this site is intended to be a substitute for professional medical advice, diagnosis or treatment. See full Medical Disclaimer.
UmustBKidding
How long do you want to ignore this user?
There are a huge number of ways to mask this problem, but masking it can hide a real problem that would be better off discovered and repaired. While unlikely a bad actor could be injecting addresses/gateways that cause traffic to traverse a host that could copy traffic for nefarious purposes. Knowing what host has what address is not rocket science and determining how it got that address if pretty straight forward also. At this point I have seen no real network configuration data, lots of assumptions about using NAT and RFC1918 addresses, but are those guesses or fact. I survived the conversion of the net from NCP to TCP/IP in the early 80's, long before DHCP, RARP and things people did to hide error messages came back to bite them constantly. My suggestion to hide the problem is to convert to the ipv6 local link address: fd78:07f9:86ac:ff0a::/64 so that will give you enough for 18446744073709551616 hosts.

TexasAg2002
How long do you want to ignore this user?
You could connect a laptop with a network sniffer like Wireshark to the network or one at a time to each device to view the traffic in real time. Use that to determine source IP's coming out of each system.
Refresh
Page 1 of 1
 
×
subscribe Verify your student status
See Subscription Benefits
Trial only available to users who have never subscribed or participated in a previous trial.