2012-11-30 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. 0 0 0 0 EOOL - End of Options List 0 0 1 1 NOP - No Operation 1 0 2 130 SEC - Security 1 0 3 131 LSR - Loose Source Route 0 2 4 68 TS - Time Stamp 1 0 5 133 E-SEC - Extended Security 1 0 6 134 CIPSO - Commercial Security 0 0 7 7 RR - Record Route 1 0 8 136 SID - Stream ID 1 0 9 137 SSR - Strict Source Route 0 0 10 10 ZSU - Experimental Measurement ZSu 0 0 11 11 MTUP - MTU Probe 0 0 12 12 MTUR - MTU Reply 1 2 13 205 FINN - Experimental Flow Control 1 0 14 142 VISA - Experimental Access Control 0 0 15 15 ENCODE - ??? VerSteeg 1 0 16 144 IMITD - IMI Traffic Descriptor Lee 1 0 17 145 EIP - Extended Internet Protocol 0 2 18 82 TR - Traceroute 1 0 19 147 ADDEXT - Address Extension Ullmann IPv7 1 0 20 148 RTRALT - Router Alert 1 0 21 149 SDB - Selective Directed Broadcast 1 0 22 150        - Unassigned (Released 18 October 2005) 1 0 23 151 DPS - Dynamic Packet State 1 0 24 152 UMP - Upstream Multicast Pkt. 0 0 25 25 QS - Quick-Start 0 0 30 30 EXP - RFC3692-style Experiment 0 2 30 94 EXP - RFC3692-style Experiment 1 0 30 158 EXP - RFC3692-style Experiment 1 2 30 222 EXP - RFC3692-style Experiment obsoleted IP Option Number It is only appropriate to use these values in explicitly-configured experiments; they MUST NOT be shipped as defaults in implementations. See RFC 3692 for details. The current recommended default time to live (TTL) for the Internet Protocol (IP) is 64 , . This documents the default Type-of-Service values that are currently recommended for the most important Internet protocols. 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. An application may (at the request of the user) substitute 0001 (minimize monetary cost) for any of the below values. TELNET 1000 (minimize delay) FTP   Control 1000 (minimize delay)   Data 0100 (maximize throughput) TFTP 1000 (minimize delay) SMTP   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   Responses <same as request> Any IGP 0010 (maximize reliability) EGP 0000 SNMP 0010 (maximize reliability) BOOTP 0000 Includes all interactive user protocols (e.g., rlogin). Includes all bulk data transfer protocols (e.g., rcp). 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). 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. Andy Malis mailto:malis&casc.com 1999-04 Charles "Bud" Graff mailto:bud&fotlan.army.mil 1995-03 Deborah Estrin mailto:Estrin&usc.edu 1994-10 Dino Farinacci mailto:dino&cisco.com 1999-05 Greg Finn mailto:Finn&isi.edu 1994-10 Jon Postel mailto:postel&isi.edu 1994-10