📄 rfc1533.txt
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RFC 1533 DHCP Options and BOOTP Vendor Extensions October 19935.8. Static Route Option This option specifies a list of static routes that the client should install in its routing cache. If multiple routes to the same destination are specified, they are listed in descending order of priority. The routes consist of a list of IP address pairs. The first address is the destination address, and the second address is the router for the destination. The default route (0.0.0.0) is an illegal destination for a static route. See section 3.5 for information about the router option. The code for this option is 33. The minimum length of this option is 8, and the length MUST be a multiple of 8. Code Len Destination 1 Router 1 +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+ | 33 | n | d1 | d2 | d3 | d4 | r1 | r2 | r3 | r4 | +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+ Destination 2 Router 2 +-----+-----+-----+-----+-----+-----+-----+-----+--- | d1 | d2 | d3 | d4 | r1 | r2 | r3 | r4 | ... +-----+-----+-----+-----+-----+-----+-----+-----+---6. Link Layer Parameters per Interface This section lists the options that affect the operation of the data link layer on a per-interface basis.6.1. Trailer Encapsulation Option This option specifies whether or not the client should negotiate the use of trailers (RFC 893 [14]) when using the ARP protocol. A value of 0 indicates that the client should not attempt to use trailers. A value of 1 means that the client should attempt to use trailers. The code for this option is 34, and its length is 1. Code Len Value +-----+-----+-----+ | 34 | 1 | 0/1 | +-----+-----+-----+Alexander & Droms [Page 16]RFC 1533 DHCP Options and BOOTP Vendor Extensions October 19936.2. ARP Cache Timeout Option This option specifies the timeout in seconds for ARP cache entries. The time is specified as a 32-bit unsigned integer. The code for this option is 35, and its length is 4. Code Len Time +-----+-----+-----+-----+-----+-----+ | 35 | 4 | t1 | t2 | t3 | t4 | +-----+-----+-----+-----+-----+-----+6.3. Ethernet Encapsulation Option This option specifies whether or not the client should use Ethernet Version 2 (RFC 894 [15]) or IEEE 802.3 (RFC 1042 [16]) encapsulation if the interface is an Ethernet. A value of 0 indicates that the client should use RFC 894 encapsulation. A value of 1 means that the client should use RFC 1042 encapsulation. The code for this option is 36, and its length is 1. Code Len Value +-----+-----+-----+ | 36 | 1 | 0/1 | +-----+-----+-----+7. TCP Parameters This section lists the options that affect the operation of the TCP layer on a per-interface basis.7.1. TCP Default TTL Option This option specifies the default TTL that the client should use when sending TCP segments. The value is represented as an 8-bit unsigned integer. The minimum value is 1. The code for this option is 37, and its length is 1. Code Len TTL +-----+-----+-----+ | 37 | 1 | n | +-----+-----+-----+Alexander & Droms [Page 17]RFC 1533 DHCP Options and BOOTP Vendor Extensions October 19937.2. TCP Keepalive Interval Option This option specifies the interval (in seconds) that the client TCP should wait before sending a keepalive message on a TCP connection. The time is specified as a 32-bit unsigned integer. A value of zero indicates that the client should not generate keepalive messages on connections unless specifically requested by an application. The code for this option is 38, and its length is 4. Code Len Time +-----+-----+-----+-----+-----+-----+ | 38 | 4 | t1 | t2 | t3 | t4 | +-----+-----+-----+-----+-----+-----+7.3. TCP Keepalive Garbage Option This option specifies the whether or not the client should send TCP keepalive messages with a octet of garbage for compatibility with older implementations. A value of 0 indicates that a garbage octet should not be sent. A value of 1 indicates that a garbage octet should be sent. The code for this option is 39, and its length is 1. Code Len Value +-----+-----+-----+ | 39 | 1 | 0/1 | +-----+-----+-----+8. Application and Service Parameters This section details some miscellaneous options used to configure miscellaneous applications and services.8.1. Network Information Service Domain Option This option specifies the name of the client's NIS [17] domain. The domain is formatted as a character string consisting of characters from the NVT ASCII character set. The code for this option is 40. Its minimum length is 1. Code Len NIS Domain Name +-----+-----+-----+-----+-----+-----+--- | 40 | n | n1 | n2 | n3 | n4 | ... +-----+-----+-----+-----+-----+-----+---Alexander & Droms [Page 18]RFC 1533 DHCP Options and BOOTP Vendor Extensions October 19938.2. Network Information Servers Option This option specifies a list of IP addresses indicating NIS servers available to the client. Servers SHOULD be listed in order of preference. The code for this option is 41. Its minimum length is 4, and the length MUST be a multiple of 4. Code Len Address 1 Address 2 +-----+-----+-----+-----+-----+-----+-----+-----+-- | 41 | n | a1 | a2 | a3 | a4 | a1 | a2 | ... +-----+-----+-----+-----+-----+-----+-----+-----+--8.3. Network Time Protocol Servers Option This option specifies a list of IP addresses indicating NTP [18] servers available to the client. Servers SHOULD be listed in order of preference. The code for this option is 42. Its minimum length is 4, and the length MUST be a multiple of 4. Code Len Address 1 Address 2 +-----+-----+-----+-----+-----+-----+-----+-----+-- | 42 | n | a1 | a2 | a3 | a4 | a1 | a2 | ... +-----+-----+-----+-----+-----+-----+-----+-----+--8.4. Vendor Specific Information This option is used by clients and servers to exchange vendor- specific information. The information is an opaque object of n octets, presumably interpreted by vendor-specific code on the clients and servers. The definition of this information is vendor specific. The vendor is indicated in the class-identifier option. Servers not equipped to interpret the vendor-specific information sent by a client MUST ignore it (although it may be reported). Clients which do not receive desired vendor-specific information SHOULD make an attempt to operate without it, although they may do so (and announce they are doing so) in a degraded mode. If a vendor potentially encodes more than one item of information in this option, then the vendor SHOULD encode the option using "Encapsulated vendor-specific options" as described below: The Encapsulated vendor-specific options field SHOULD be encoded as a sequence of code/length/value fields of identical syntax to the DHCP options field with the following exceptions:Alexander & Droms [Page 19]RFC 1533 DHCP Options and BOOTP Vendor Extensions October 1993 1) There SHOULD NOT be a "magic cookie" field in the encapsulated vendor-specific extensions field. 2) Codes other than 0 or 255 MAY be redefined by the vendor within the encapsulated vendor-specific extensions field, but SHOULD conform to the tag-length-value syntax defined in section 2. 3) Code 255 (END), if present, signifies the end of the encapsulated vendor extensions, not the end of the vendor extensions field. If no code 255 is present, then the end of the enclosing vendor-specific information field is taken as the end of the encapsulated vendor-specific extensions field. The code for this option is 43 and its minimum length is 1. Code Len Vendor-specific information +-----+-----+-----+-----+--- | 43 | n | i1 | i2 | ... +-----+-----+-----+-----+--- When encapsulated vendor-specific extensions are used, the information bytes 1-n have the following format: Code Len Data item Code Len Data item Code +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+ | T1 | n | d1 | d2 | ... | T2 | n | D1 | D2 | ... | ... | +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+8.5. NetBIOS over TCP/IP Name Server Option The NetBIOS name server (NBNS) option specifies a list of RFC 1001/1002 [19] [20] NBNS name servers listed in order of preference. The code for this option is 44. The minimum length of the option is 4 octets, and the length must always be a multiple of 4. Code Len Address 1 Address 2 +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+---- | 44 | n | a1 | a2 | a3 | a4 | b1 | b2 | b3 | b4 | ... +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+----Alexander & Droms [Page 20]RFC 1533 DHCP Options and BOOTP Vendor Extensions October 19938.6. NetBIOS over TCP/IP Datagram Distribution Server Option The NetBIOS datagram distribution server (NBDD) option specifies a list of RFC 1001/1002 NBDD servers listed in order of preference. The code for this option is 45. The minimum length of the option is 4 octets, and the length must always be a multiple of 4. Code Len Address 1 Address 2 +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+---- | 45 | n | a1 | a2 | a3 | a4 | b1 | b2 | b3 | b4 | ... +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+----8.7. NetBIOS over TCP/IP Node Type Option The NetBIOS node type option allows NetBIOS over TCP/IP clients which are configurable to be configured as described in RFC 1001/1002. The value is specified as a single octet which identifies the client type as follows: Value Node Type ----- --------- 0x1 B-node 0x2 P-node 0x4 M-node 0x8 H-node In the above chart, the notation '0x' indicates a number in base-16 (hexadecimal). The code for this option is 46. The length of this option is always 1. Code Len Node Type +-----+-----+-----------+ | 46 | 1 | see above | +-----+-----+-----------+Alexander & Droms [Page 21]RFC 1533 DHCP Options and BOOTP Vendor Extensions October 19938.8. NetBIOS over TCP/IP Scope Option The NetBIOS scope option specifies the NetBIOS over TCP/IP scope parameter for the client as specified in RFC 1001/1002. See [19], [20], and [8] for character-set restrictions. The code for this option is 47. The minimum length of this option is 1. Code Len NetBIOS Scope +-----+-----+-----+-----+-----+-----+---- | 47 | n | s1 | s2 | s3 | s4 | ... +-----+-----+-----+-----+-----+-----+----8.9. X Window System Font Server Option This option specifies a list of X Window System [21] Font servers available to the client. Servers SHOULD be listed in order of preference. The code for this option is 48. The minimum length of this option is 4 octets, and the length MUST be a multiple of 4. Code Len Address 1 Address 2 +-----+-----+-----+-----+-----+-----+-----+-----+--- | 48 | n | a1 | a2 | a3 | a4 | a1 | a2 | ... +-----+-----+-----+-----+-----+-----+-----+-----+---8.10. X Window System Display Manager Option This option specifies a list of IP addresses of systems that are running the X Window System Display Manager and are available to the client. Addresses SHOULD be listed in order of preference. The code for the this option is 49. The minimum length of this option is 4, and the length MUST be a multiple of 4. Code Len Address 1 Address 2 +-----+-----+-----+-----+-----+-----+-----+-----+--- | 49 | n | a1 | a2 | a3 | a4 | a1 | a2 | ... +-----+-----+-----+-----+-----+-----+-----+-----+---Alexander & Droms [Page 22]RFC 1533 DHCP Options and BOOTP Vendor Extensions October 19939. DHCP Extensions This section details the options that are specific to DHCP.9.1. Requested IP Address This option is used in a client request (DHCPDISCOVER) to allow the client to request that a particular IP address be assigned. The code for this option is 50, and its length is 4. Code Len Address +-----+-----+-----+-----+-----+-----+ | 50 | 4 | a1 | a2 | a3 | a4 | +-----+-----+-----+-----+-----+-----+9.2. IP Address Lease Time This option is used in a client request (DHCPDISCOVER or DHCPREQUEST) to allow the client to request a lease time for the IP address. In a server reply (DHCPOFFER), a DHCP server uses this option to specify the lease time it is willing to offer. The time is in units of seconds, and is specified as a 32-bit unsigned integer.
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