BOOTP Vendor Information Extensions
Extracted elements (27)
IP multicast was considered as an alternative to BOOTP extensions for locating network services; multicast eliminates dependence on a BOOTP server, reduces administrative overhead, and can be more efficient. The main drawback cited is that IP multicasting was not widely implemented at the time of this RFC.
The BOOTP approach is most efficient when all configuration information needed by a client host is returned in a single BOOTP reply, allowing each software module to read from a local table rather than issuing individual service discovery requests.
Use of undefined generic tag types (range 18-127) without registration may conflict with other BOOTP implementations. Nonessential options such as hostname and quote-of-the-day server may be omitted and discovered later via RLP or DNS WKS records.
Implementation-specific use of undefined generic tag types in the range 18-127 may conflict with other implementations, and registration with IANA is required before using these tags.
The Subnet Mask field (Tag 1) MUST precede the Gateway field (Tag 3) in the vendor information area if both are present.
When selecting information for the vendor-specific area, care must be taken not to exceed the 64-byte length restriction of the BOOTP vendor information field.
Boot File Size Field (Tag 13, 2 bytes): A two-octet network-order value specifying the number of 512-octet blocks in the default boot file, informing the BOOTP client of the boot image size.
Domain Name Server Field (Tag 6, N address bytes): Specifies the IP addresses of N/4 DNS domain name servers per RFC-1034.
Domain Name (Tag 15, N bytes): Specifies the domain name of the client for DNS resolution per RFC-1034. Introduced in this edition of the RFC.
End Field (Tag 255, no data): Marks the end of usable data in the vendor information area; the remainder of the field should be filled with PAD (zero) octets.
Gateway Field (Tag 3, N address bytes): Specifies the IP addresses of N/4 gateways for the subnet; if one gateway is preferred, it should appear first in the list.
Hostname Field (Tag 12, N bytes): Specifies the name of the client; the name may or may not be domain-qualified, which is a site-specific decision.
IEN-116 Name Server Field (Tag 5, N address bytes): Specifies the IP addresses of N/4 IEN-116 name servers.
Log Server Field (Tag 7, N bytes), Cookie/Quote Server Field (Tag 8, N bytes), LPR Server Field (Tag 9, N bytes), Impress Server Field (Tag 10, N bytes), and RLP Server Field (Tag 11, N bytes) each specify the IP addresses of N/4 servers of their respective type.
Merit Dump File (Tag 14, N bytes): Specifies the name of a file to which this client's core should be dumped. Introduced in this edition of the RFC.
Pad Field (Tag 0, no data): A single-octet padding tag with no associated data, used to align subsequent fields to word boundaries required by the target machine.
Reserved Fields (Tags 128-254, N bytes): Reserved for additional site-specific information interpreted on an implementation-specific basis; these should follow all data using generic tags 0-127.
Root Path (Tag 17, N bytes): A string specifying a pathname to mount as a root disk. Introduced in this edition of the RFC.
Subnet Mask Field (Tag 1, 4 bytes): Specifies the net and local subnet mask per RFC-950. This field must precede the Gateway field if both are present.
Swap Server (Tag 16, 4 bytes): Carries the IP address of a swap server for the client. Introduced in this edition of the RFC.
Time Offset Field (Tag 2, 4 bytes): Specifies the signed 32-bit integer offset of the local subnet in seconds from Coordinated Universal Time (UTC).
Time Server Field (Tag 4, N address bytes): Specifies the IP addresses of N/4 time servers per RFC-868.
Additional generic data field tags may be registered by contacting IANA (iana@isi.edu). Registration is required for any use of generic tag types in the range 18-127 to avoid implementation conflicts.
Security issues are explicitly not discussed in this memo; no authentication or integrity mechanisms are specified for BOOTP vendor information extensions.
Fixed-length fields with no data consist of a single tag octet only (e.g., Pad, End); fixed-length fields with data consist of one tag octet, one length octet, and length octets of data.
The 64-octet vendor information field uses a free-format, length-tagged sub-field encoding. Each variable-length sub-field consists of one tag octet, one length octet, and length octets of data; lengths are exclusive of tag and length octets; all multi-byte quantities are in network byte order.
The vendor information area begins with a 4-octet 'magic cookie' with value 99.130.83.99 (hex 63.82.53.63) in network byte order, identifying the interpretation mode for the subsequent vendor data.