how ip helper work to avoid ip conflict between static and dhcp ip.

[syjeon]

Hi, simple question here.

We configured dhcp server and have configured ip helper on interface vlan. and set the dynamic ip range from x.x.x.100 - x.x.x.200 for example.

if the client accidentally configure ip address x.x.x.x.120 as static ip, then how does IP helper work? 

remote DHCP doesn't know if x.x.x.120 is in use or not, then the traffic return from dhcp server with ip x.x.x.120, and the router identify x.x.x.120 is in use from its arp table, then discard it, and retry to get the another ip address to avoid IP conflict? 

Thanks.

[johnd2310 · Accepted solution]

Hi,

Ip helper does not prevent conflicts. Ip helper only forwards dhcp messages between dhcp server and dhcp client.Conflict detection is configured on the dhcp server i.e. the dhcp server is configured to ping the ip address before assigning the address.

You can configure conflict detection on most dhcp servers.

Thanks

John