Host Database Field: BOOTP-PARAMETERS, ADDITIONAL-BOOTP-PARAMS

[This document describes a field in the Princeton University Host Database. You may also view descriptions of other fields.]

The optional BOOTP-PARAMETERS (a.k.a. ADDITIONAL-BOOTP-PARAMS) field is used to provide additional information to our Bootp and DHCP servers. Unless you know exactly what you are doing, you should leave this field empty.

Strings entered in this field will be used by OIT's BootP and DHCP servers when responding to BootP and DHCP requests from your device, when the response is for an IP address that appears in your device's Host Database entry. By default, OIT's BootP and DHCP servers respond to such with requests as described in DHCP and DHCP Services. If you need the DHCP or BootP servers to provide additional values, you specify them here, using the syntax required by our current DHCP/BOOTP servers.

When OIT DHCP Service respond to your device with an IP address that is not in your device's Host Database entry (e.g. because your device is using OIT Mobile Service, for example), information in this field is not used. That's because the values in this field are associated with the IP addresses assigned to your device, not with your device's hardware address. E.g. if you were to specify special DNS servers in this field, then when your device is using the static IP addresses in its Host Database entry, OIT DHCP and BootP Services will provide your device with the special DNS servers you specify. When your device is using an OIT Mobile Address (e.g. because it is visiting another network), OIT DHCP Service will provide your device with the DNS servers associated with the OIT Mobile Address it is leased.

The string you specify should contain no spaces, except if spaces are required within the value of one of the tags you specify. Fields must be colon-delimited, and there should be no leading colon.

If you enter a value in this field, it completely replaces any previous value for the BOOTP-PARAMETERS field. So if the field contains special settings for DNS servers and a TFTP server, and you wish to remove just the TFTP server, then change the field to specify the DNS servers but omit the TFTP server. To completely clear the BOOTP-PARAMETERS field, specify the value NONE.

For a description of the tags understood by our DHCP/BootP servers, see the bootptab(5) manual page for CMU dhcpd version 3.3.7 with the PU patches applied. Note that the data is case-sensitive.

The Host Database provides only limited syntax checking on the value you specify; it does not duplicate all the parsing performed by our BootP/DHCP servers. Therefore, it is possible to enter some syntactically incorrect values into this Host Database field. If you do so, our BootP/DHCP servers will either ignore the value, or more likely, ignore the entire entry for your Host Database entry. (The latter would cause your device to stop receiving any BootP and DHCP service.) Therefore, be careful when completing this field, paying close attention to the manual page mentioned above.) If you do enter a value that is so incorrect as to be unparseable by our BootP/DHCP servers, hostmaster will contact you via email, typically within a few business days.

Before using this feature, you may wish to inspect your host's current entry in the bootptab file; on any OIT UNIX System, you may view /u/nocnoc/hostmaster/bootptab. Be sure to also review the contents of any templates that your entry inherits from (e.g. a subnet template). You should also have a basic familiarity with the BootP and DHCP protocols; see RFC 951, RFC 1534, RFC 1542, RFC 2131, RFC 2132, RFC 2241, RFC 2242, RFC 2485, RFC 2489.

When parsing the values you specify in the BOOTP-PARAMETERS field, we provide the following special features:

• Normally your bootptab entry contains a dn tag that specifies your DNS-DOMAIN. You may specify :dn=: to cause your bootptab entry to not contain any dn tag. (You may not use this tag to specify a different DNS domain.)

• By default your bootptab entry contains a tc tag that points to a template based upon your device's IP subnet. You may specify :tc=: to cause your bootptab entry to not contain any tc tag.

• By default your bootptab entry contains a ht=ethernet tag. If you specify an ht tag, yours will be used instead.

• By default we include an ro tag to enable Mobile IP service for devices eligible for this service. You cannot specify this tag yourself. You also may not specify the dy tag; we use this tag for OIT-administered dynamically-assigned IP addresses.

• You may not specify tags associated with DHCP lease times: dl, rb, or rn. We provide these tags for DHCP leases with appropriate values.

• You may not specify the cl tag; the server derives your device's DHCP Client Identifier from your device's hardware type (ht) and hardware address (ha).

• You may not specify the ha tag; the server uses the hardware (Ethernet, Wireless, or FDDI) address in your Host Database entry for this value.

• You may not specify the ip tag; the server uses the IP address in your Host Databsae entry for this value.

• Assuming your entry inherits from a typical subnet template entry, it will inherit a be tag that instructs it to exclude the following tags from packets sent to BootP clients: ws, no, rd, and nt. (Packets sent to DHCP clients are not affected by the be tag.) If you wish to return any of these fields to BootP clients, you will need to override the entire be tag in your entry. Be careful if you do so, as the be tag was specified to reduce the amount of data returned to BootP clients, to try to avoid exceeding the 64-byte limit on the "Vendor-Specific Area" (a.k.a "Options") field that may be returned to clients speaking the BootP protocol.

• If you enter tags that would cause a BOOTREPLY to exceed the BootP protocol's 64-byte limit on the "Vendor-Specific Area" (a.k.a "Options") field, the BootP server will arbitrarily leave out options from the BOOTPREPLY it sends. (This does not apply to DHCP clients, as the DHCP protocol supports a larger "Options" field.)

Note that if the entry contains multiple interfaces which are eligible for BootP or DHCP service, then any BOOTP-PARAMETERS field you specify will affect all the interfaces. You cannot use the BOOTP-PARAMETERS field to specify values that should only apply to a single interface.

Because we cannot change the characteristics of a current (unexpired) DHCP lease, any change you make to the BOOTP-PARAMETERS field may not be reliably propagated to a DHCP client until any current DHCP lease for this client has been expired or been invalidated on all OIT DHCP servers. See DHCP and BootP Services: Forcing a DHCP Lease to Be Discarded.

Examples

The examples below are only to illustrate typical use of the BOOTP-PARAMETERS field; the specific values are only for illustrative purposes.

• For a device that needs to be told that its TFTP Server Address is 1.2.3.4 and its Boot File name is foobar.config: sa=1.2.3.4:bf=foobar.config

• To override the default DNS servers with ones of your own: ds=192.168.1.2 192.168.1.3 192.168.1.4

• For a device that needs to be told of no DNS servers: ds@

• To clear all values from the BOOTP-PARAMETERS field: NONE

• If you want to override the be tag typically inherited from a subnet template first cancel the inherited tag, then supply any new value you would like it to have. For example, assuming the inherited be tag specified "ws no rd nt", and you wanted it to instead specify "rd ba", use: be@:be="rd ba"