DHCP Seconds Field Limits Forwarding of Packets by Relay Agents

This article was previously published under Q130929

In Windows NT 3.51, Dynamic Host Configuration Protocol (DHCP) clients set the seconds field in the DHCP message to zero in the initial DHCP packet. This field is incremented for every subsequent DHCP packet retransmitted by the client.

The DHCP relay agents may be configured with a non-zero threshold value for the seconds field (a value of 4 is recommended). This prevents relay agents from forwarding all DHCP packets with the seconds field set to a value less than the threshold value. If there is a DHCP server in the local subnet that has an available address for lease, it will respond to the initial DHCP packet. The client then does not have to retransmit that DHCP packet with a higher number in the seconds field which will be forwarded by the relay agent. This considerably reduces the number of DHCP packets forwarded to other subnets by the relay agent.