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IP OPTION NUMBERS (last updated 2001 Jun 29) The Internet Protocol (IP) has provision for optional header fields identified by an option type field. Options 0 and 1 are exactly one octet which is their type field. All other options have their one octet type field, followed by a one octet length field, followed by length-2 octets of option data. The option type field is sub-divided into a one bit copied flag, a two bit class field, and a five bit option number. These taken together form an eight bit value for the option type field. IP options are commonly refered to by this value. Copy Class Number Value Name Reference ---- ----- ------ ----- ------------------------------- --------- 0 0 0 0 EOOL - End of Options List [RFC791,JBP] 0 0 1 1 NOP - No Operation [RFC791,JBP] 1 0 2 130 SEC - Security [RFC1108] 1 0 3 131 LSR - Loose Source Route [RFC791,JBP] 0 2 4 68 TS - Time Stamp [RFC791,JBP] 1 0 5 133 E-SEC - Extended Security [RFC1108] 1 0 6 134 CIPSO - Commercial Security [???] 0 0 7 7 RR - Record Route [RFC791,JBP] 1 0 8 136 SID - Stream ID [RFC791,JBP] 1 0 9 137 SSR - Strict Source Route [RFC791,JBP] 0 0 10 10 ZSU - Experimental Measurement [ZSu] 0 0 11 11 MTUP - MTU Probe [RFC1191]* 0 0 12 12 MTUR - MTU Reply [RFC1191]* 1 2 13 205 FINN - Experimental Flow Control [Finn] 1 0 14 142 VISA - Expermental Access Control [Estrin] 0 0 15 15 ENCODE - ??? [VerSteeg] 1 0 16 144 IMITD - IMI Traffic Descriptor [Lee] 1 0 17 145 EIP - Extended Internet Protocol[RFC1385] 0 2 18 82 TR - Traceroute [RFC1393] 1 0 19 147 ADDEXT - Address Extension [Ullmann IPv7] 1 0 20 148 RTRALT - Router Alert [RFC2113] 1 0 21 149 SDB - Selective Directed Broadcast[Graff] 1 0 22 150 NSAPA - NSAP Addresses [Carpenter] 1 0 23 151 DPS - Dynamic Packet State [Malis] 1 0 24 152 UMP - Upstream Multicast Pkt. [Farinacci] [Note, an asterisk (*) denotes an obsoleted IP Option Number.] IP TIME TO LIVE PARAMETER The current recommended default time to live (TTL) for the Internet Protocol (IP) is 64 [RFC791, RFC1122]. IP TOS PARAMETERS This documents the default Type-of-Service values that are currently recommended for the most important Internet protocols. TOS Value Description Reference --------- -------------------------- --------- 0000 Default [Obsoleted by RFC2474] 0001 Minimize Monetary Cost [Obsoleted by RFC2474] 0010 Maximize Reliability [Obsoleted by RFC2474] 0100 Maximize Throughput [Obsoleted by RFC2474] 1000 Minimize Delay [Obsoleted by RFC2474] 1111 Maximize Security [Obsoleted by RFC2474] The TOS value is used to indicate "better". Only one TOS value or property can be requested in any one IP datagram. Generally, protocols which are involved in direct interaction with a human should select low delay, while data transfers which may involve large blocks of data are need high throughput. Finally, high reliability is most important for datagram-based Internet management functions. Application protocols not included in these tables should be able to make appropriate choice of low delay (8 decimal, 1000 binary) or high throughput (4 decimal, 0100 binary). The following are recommended values for TOS: ----- Type-of-Service Value ----- Protocol TOS Value TELNET (1) 1000 (minimize delay) FTP Control 1000 (minimize delay) Data (2) 0100 (maximize throughput) TFTP 1000 (minimize delay) SMTP (3) Command phase 1000 (minimize delay) DATA phase 0100 (maximize throughput) Domain Name Service UDP Query 1000 (minimize delay) TCP Query 0000 Zone Transfer 0100 (maximize throughput) NNTP 0001 (minimize monetary cost) ICMP Errors 0000 Requests 0000 (4) Responses (4) Any IGP 0010 (maximize reliability) EGP 0000 SNMP 0010 (maximize reliability) BOOTP 0000 Notes: (1) Includes all interactive user protocols (e.g., rlogin). (2) Includes all bulk data transfer protocols (e.g., rcp). (3) If the implementation does not support changing the TOS during the lifetime of the connection, then the recommended TOS on opening the connection is the default TOS (0000). (4) Although ICMP request messages are normally sent with the default TOS, there are sometimes good reasons why they would be sent with some other TOS value. An ICMP response always uses the same TOS value as was used in the corresponding ICMP request message. An application may (at the request of the user) substitute 0001 (minimize monetary cost) for any of the above values. REFERENCES ---------- [RFC791] Postel, J., "Internet Protocol - DARPA Internet Program Protocol Specification", STD 5, RFC 791, DARPA, September 1981. [RFC1108] Kent, S., "U.S. Department of Defense Security Options for the Internet Protocol", RFC 1108, BBN Communications, November 1991. [RFC1122] R. Braden, Ed., "Requirements for Internet Hosts -- Communication Layers," IETF Host Requirements Working Group, RFC-1122, October 1989. [RFC1191] Mogul, J., and S. Deering, "Path MTU Discovery", RFC 1191, DECWRL, Stanford University, November 1990. [RFC1349] Almquist, P., "Type of Service in the Internet Protocol Suite", RFC 1349, Consultant, July 1992. [RFC1385] Wang, Z., "EIP: The Extended Internet Protocol", RFC 1385, University College London, November 1992. [RFC1393] Malkin, G., "Traceroute Using an IP Option", RFC 1393, Xylogics, Inc., January 1993. [RFC1455] Eastlake, D., "Physical Link Security Type of Service", RFC 1455, Digital Equipment Corporation, May 1993. [Ullmann IPv7] [RFC2113] Katz, D., "IP Router Alert Option", RFC 2113, Cisco Systems, February 1997. PEOPLE ------ [Carpenter] Brian Carpenter, , June 1995. [Estrin] Deborah Estrin October 1994. [Farinacci] Dino Farinacci , May 1999. [Finn] Greg Finn October 1994. [Graff] Charles "Bud" Graff, , March 1995. [Katz] Dave Katz November 1994. [JBP] Jon Postel October 1994. [Malis] Andy Malis , April 1999. [Ullmann] Robert Ullmann []