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DHCP and BootP


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)

When you check the DHCP box and enter a hardware address in NetDB, the campus DHCP servers will reply to a DHCP request from that address. The servers also return default DHCP options or additional options if they're specified in the NetDB record.

Roaming flag (node records)

Roaming DHCP allows machines to move to other networks without requiring manual configuration of IP addresses. If you check the Roaming box, you enable Roaming DHCP for that hardware address. If the machine moves to another network that offers 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, in general
Gateway 3 for 171.64 addresses, returns; for 171.65 addresses, returns
Domain name 15 returns domain name assigned to the Node
Domain name servers 6, and returned in random order

Additional DHCP options

In NetDB, you can also set the following additional DHCP options 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.,
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 — for example, nodes with their hardware addresses listed in NetDB. The permit DHCP option can override this default on a per-address space basis. A value of unknown-client allows both known and unknown clients to use DHCP in a particular address space; a value of only-unknown-client allows 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, please submit a HelpSU ticket.

Last modified July 12, 2021