User getting IP conflict continuously

[balamurugan48011]

Hi Team,

               we are using AIR-CT5760 controller in our network, almost 800 users connected, but some users (only) getting IP conflict again and again, Kindly advise what could be the issue?

Regards,

Bala

Regards

[Mark Malone]

What way is the DHCP scope setup , is the controller the only device giving out ip addresses in the network , usually duplicate ips come from 2 scopes giving out address same range or somebody has set static ips from the dhcp scope and not excluded them and then there also given out in dhcp causing duplicate ips in the network

[balamurugan48011]

WLC doesn't have any dhcp scope, we have a separate DHCP server, 

[Mark Malone]

so why do you believe the issue is with the controller if a server is giving out the dhcp ips , the controller would only pass the dhcp information it shouldn't alter it , ip conflicts come from dhcp issues generally

[balamurugan48011]

yeah understand dude, but some users getting disconnected from the network when they doing work in live network, they are telling that ""suddenly ip conflict messages is coming while working and not able to work continuously, whenever its coming we need to disconnect from network and connect, this is affecting the production""

Even we having mobility network.

[Mark Malone]

I would be looking at the server as that's responsible for giving out the addresses not the wlc, check what addresses these users get when the conflict occurs are they supposed to be reserved/static addresses etc

once an address is duplicate on the network it can black hole half the traffic for that ip address

the network switches and wlc etc will just forward on what the server sends out

[balamurugan48011]

i checked dude, but these ip's not assigned by static and not reserved for anything,

i had disconnected that particular laptop and tried to ping, it is not ping and no one using this ip, i couldn't assume anything for this issue

[Mark Malone]

Have you got the exact alert the users were receiving when the issue happened

Is there multiple scopes having the same issue duplicates been seen or is this all seen on just one scope

If all scopes are effected you could check its not a server issues by removing a scope and setting a temporary dhcp scope on one of your Cisco switches and see if you see the same behaviour while the dhcp is being sent fro the switch rather than the server as a test

If you put a wireshark on one the effected pcs and capture the traffic as well while the issue is happening it will give you a better idea of whats going on with the dhcp offers and requests or else debug on Cisco devices dhcp dhcp det