DHCP & BootP
General
The DHCP (Dynamic Host Configuration Protocol) and BootP (Bootstrap Protocol) pass network configuration information to a host during startup. In NetDB3, DHCP is configured on Node and Network records. For Node records, a unique hardware address must be entered to configure DHCP.
DHCP is also described in Internet RFCs 2131 and 2132. Note that BOOTP is a subset of DHCP commands.
DHCP information is updated from NetDB approximately every 10 minutes.
DHCP Flag (Node Record)
If the DHCP box is checked and a hardware address is entered, the campus DHCP servers will reply to a DHCP request from that hardware address. Default DHCP options will be returned. If specified in the NetDB record, additional DHCP options will also be returned.
Roaming Flag (Node Records)
Roaming DHCP was implemented to allow machines to move to other networks without requiring manual configuration of IP addresses, etc. If the Roaming box is checked, Roaming DHCP is enabled for that hardware address. If the machine now moves to another network that has available roaming DHCP addresses, the DHCP server will give one of these addresses to the mobile machine.
Default Node DHCP Options
The default Node DHCP options at Stanford University are IP address, subnet mask, gateway, domain name and domain name servers. The option numbers come from RFCs 2131 and 2132.
| DHCP Option | Option Number | Description |
|---|---|---|
| IP Address | 50 | returns IP address assigned to requesting hardware address |
| Subnet mask | 1 | returns 255.255.0.0, in general |
| Gateway | 3 | for 171.64 addresses, returns 171.64.1.1; for 171.65 addresses, returns 171.65.1.1 |
| Domain name | 15 | returns domain name asssigned to the Node |
| Domain name servers | 6 | 171.64.7.77, 171.64.7.55 and 171.64.7.99 returned in random order |
Additional DHCP Options
In NetDB, the following additional DHCP options may be set for Node interfaces, Networks or address spaces. Note: Use with caution as improper use may cause networking problems. The syntax for options is <dhcp option> = <value>.
| DHCP Option | Option Number | Node Interface | Net | Address Space | Description |
|---|---|---|---|---|---|
| next-server | Y | Y | Y | boot/config server | |
| tftp-server-name | 66 | Y | Y | Y | TFTP boot/config server |
| filename | 67 | Y | N | Y | boot/config file - e.g. thin clients |
| log-servers | 7 | Y | Y | Y | |
| domain-name | 15 | Y | Y | Y | e.g., stanford.edu |
| domain-name-servers | 5 | Y | Y | Y | DNS servers |
| netbios-name-servers | 44 | Y | Y | Y | WINS servers |
| netbios-node-type | 46 | Y | Y | Y | 1=B, 2=P, 4=M, 8=H |
| option-144 | 144 | Y | N | N | for HP printers |
| permit |
N | N | Y | see below | |
| max-lease-time | Y | Y | Y | ||
| default-lease-time | 51 | Y | Y | Y | DHCP lease time (currently 2 days) |
*By default, the DHCP service only responds to known clients, i.e., nodes with their hardware addresses listed in NetDB. The permit DHCP option can be used to override this default on a per address space basis. A value of unknown-clients will allow both known and unknown clients to use DHCP in a particular address space; a value of only-unknown-clients will allow only unknown clients to use DHCP in a particular address space. The latter is useful for setting up networks with separate address spaces for known and unknown DHCP clients.
For more information, enter ticket to HelpSU.
