DHCP Client Does Not Immediately Renew Address

• Microsoft Windows NT Workstation versions 3.5 and 3.51
• Microsoft Windows NT Server versions 3.5 and 3.51

SUMMARY

When a DHCP client initiates a renewal of an IP address, and the DHCP server which leased the address is unavailable, the client may indicate an IP address of 0.0.0.0 after the lease expires, and take five minutes to receive an address from another DHCP server.

MORE INFORMATION

When 50 percent of the lease time has expired for a leased address, the client tries to renew the lease with the DHCP server that originally assigned it. If the client is unable to communicate with the original DHCP server, and 87.5 percent of the lease time has expired, the client tries to renew the lease by broadcasting a request to any available DHCP server. However, this broadcast contains a request to renew the IP address currently held by the client, and is not equivalent to a request made by a client which has no current IP address. If the lease expires, the client discontinues the use of the IP address previously leased, waits for five minutes, and begins again with a new IP Lease Request.

The following scenario illustrates how a DHCP client responds when attempting to renew an address where the DHCP server that originally leased the address to the client becomes unavailable.

1. The client successfully leases an address from DHCP server 1 (example: 1.1.10.8). At this point, DHCP server 2 is down.

2. DHCP server 1's DHCP service is stopped, and DHCP server 2 is brought up.

3. At 50 percent lease expiration, the client attempts to contact the DHCP server that originally leased the address. Inside this packet, the IP address currently being leased is included.

4. No response is received from DHCP server 1.

5. At 87.5 percent lease expiration, the client attempts to broadcast to any DHCP server; however, the IP address currently being leased is included in the packet.

6. At lease expiration, the client ceases to use the IP address originally leased from DHCP server 1.

7. Five minutes later, TCP/IP re-initializes and sends a broadcast for any DHCP server. (The DHCPDISCOVER packet here includes an IP address of "0.0.0.0".)