We are using Dhcp on our DC windows 2003 SP1. In Dhcp all ip adresses are excluded, and we are only using reservations for our Pc's, printers, switches, routers. Our cisco routers and 3com switches are not able to get IP from dhcp reservation when all ip adresses are excluded from distribution. Windows xp pc's and printers are able to get their configuration, but not switches(e.g 4500 3com)and routers (cisco 2600).In network monitor i can see that e.g. router is sending brodcast discovery message but dhcp do not respond to it at all.Any idea why?

According to your description, normal Windows XP clients and printers can get IP address properly. This indicates that the DHCP reservation is working properly. Meanwhile, switches and routers can get IP address properly if not all IP address are excluded. It seems that routers and switches have not built the DCHP packets properly with its physical address included.When only DHCP reservation is configured, a DHCP server only responds to a DHCP client request when the MAC address of the client matches one of the DHCP reservation. In DHCP Discover packet,the client identifies itself in two places using the physical address of the network card. Note the values in the CHADDR field and the DHCP: Client Identifier field are identicalwhich containing the physical address of the client network adapter as illustrated in the following.I understand that you have used Network Monitor to track the DHCP issue process. Please check theCHADDR field and the DHCP: Client Identifier field for the router's packet to ensure that it contains the correct physical address of the network adapter. You may also compare the two network monitor traces from a good and bad DHCP client to see whether there are any differences.DHCP: Discover (xid=21274A1D) DHCP: Op Code (op) = 1 (0x1) DHCP: Hardware Type (htype) = 1 (0x1) 10Mb Ethernet DHCP: Hardware Address Length (hlen) = 6 (0x6) DHCP: Hops (hops) = 0 (0x0) DHCP: Transaction ID (xid) = 556223005 (0x21274A1D) DHCP: Seconds (secs) = 0 (0x0) DHCP: Flags (flags) = 0 (0x0) DHCP: 0............... = No Broadcast DHCP: Client IP Address (ciaddr) = 0.0.0.0 DHCP: Your IP Address (yiaddr) = 0.0.0.0 DHCP: Server IP Address (siaddr) = 0.0.0.0 DHCP: Relay IP Address (giaddr) = 0.0.0.0 DHCP: Client Ethernet Address (chaddr) = 08002B2ED85E DHCP: Server Host Name (sname) = <Blank> DHCP: Boot File Name (file) = <Blank> DHCP: Magic Cookie = [OK] DHCP: Option Field (options) DHCP: DHCP Message Type = DHCP Discover DHCP: Client-identifier = (Type: 1) 08 00 2b 2e d8 5e DHCP: Host Name = JUMBO-WS DHCP: Parameter Request List = (Length: 7) 01 0f 03 2c 2e 2f 06 DHCP: End of this option fieldLaura Zhang - MSFT