23], with a key size of 128 bits. The foreign agent MUST also support authentication using HMAC-MD5 and key sizes of 128 bits or greater, with manual key distribution. Keys with arbitrary binary values MUST be supported. The "prefix+suffix" use of MD5 to protect data and a shared secret is considered vulnerable to attack by the cryptographic community. Where backward compatibility with existing Mobile IP implementations that use this mode is needed, new implementations SHOULD include keyed MD5  as one of the additional authentication algorithms for use when producing and verifying the authentication data that is supplied with Mobile IP registration messages, for instance in the extensions specified in sections 3.5.2, 3.5.3, and 3.5.4. More authentication algorithms, algorithm modes, key distribution methods, and key sizes MAY also be supported for all of these extensions.
instance as performed by the mobile registration protocol, is widely understood to be a security problem in the current Internet if not authenticated . Moreover, the Address Resolution Protocol (ARP) is not authenticated, and can potentially be used to steal another host's traffic. The use of "Gratuitous ARP" (Section 4.6) brings with it all of the risks associated with the use of ARP. 14] provides more information on generating pseudo-random numbers.
15] that do not allow forwarding of packets that have a Source Address which appears topologically incorrect. In environments where this is a problem, mobile nodes may use reverse tunneling  with the foreign agent supplied care-of address as the Source Address. Reverse tunneled packets will be able to pass normally through such routers, while ingress filtering rules will still be able to locate the true topological source of the packet in the same way as packets from non-mobile nodes.
security association between the nodes, a default value of 7 seconds MAY be used to limit the time difference. This value SHOULD be greater than 3 seconds. Obviously the two nodes must have adequately synchronized time-of-day clocks. As with any messages, time synchronization messages may be protected against tampering by an authentication mechanism determined by the security context between the two nodes. If timestamps are used, the mobile node MUST set the Identification field to a 64-bit value formatted as specified by the Network Time Protocol . The low-order 32 bits of the NTP format represent fractional seconds, and those bits which are not available from a time source SHOULD be generated from a good source of randomness. Note, however, that when using timestamps, the 64-bit Identification used in a Registration Request from the mobile node MUST be greater than that used in any previous Registration Request, as the home agent uses this field also as a sequence number. Without such a sequence number, it would be possible for a delayed duplicate of an earlier Registration Request to arrive at the home agent (within the clock synchronization required by the home agent), and thus be applied out of order, mistakenly altering the mobile node's current registered care-of address. Upon receipt of a Registration Request with an authorization-enabling extension, the home agent MUST check the Identification field for validity. In order to be valid, the timestamp contained in the Identification field MUST be close enough to the home agent's time of day clock and the timestamp MUST be greater than all previously accepted timestamps for the requesting mobile node. Time tolerances and resynchronization details are specific to a particular mobility security association. If the timestamp is valid, the home agent copies the entire Identification field into the Registration Reply it returns the Reply to the mobile node. If the timestamp is not valid, the home agent copies only the low-order 32 bits into the Registration Reply, and supplies the high-order 32 bits from its own time of day. In this latter case, the home agent MUST reject the registration by returning Code 133 (identification mismatch) in the Registration Reply. As described in Section 184.108.40.206, the mobile node MUST verify that the low-order 32 bits of the Identification in the Registration Reply are identical to those in the rejected registration attempt, before using the high-order bits for clock resynchronization.
14]. It inserts a new nonce as the high-order 32 bits of the identification field of every Registration Reply. The home agent copies the low-order 32 bits of the Identification from the Registration Request message into the low-order 32 bits of the Identification in the Registration Reply. When the mobile node receives an authenticated Registration Reply from the home agent, it saves the high-order 32 bits of the identification for use as the high-order 32 bits of its next Registration Request. The mobile node is responsible for generating the low-order 32 bits of the Identification in each Registration Request. Ideally it should generate its own random nonces. However it may use any expedient method, including duplication of the random value sent by the home agent. The method chosen is of concern only to the mobile node, because it is the node that checks for valid values in the Registration Reply. The high-order and low-order 32 bits of the identification chosen SHOULD both differ from their previous values. The home agent uses a new high-order value and the mobile node uses a new low-order value for each registration message. The foreign agent uses the low-order value (and the mobile host's home address) to correctly match registration replies with pending Requests (Section 3.7.1). If a registration message is rejected because of an invalid nonce, the Reply always provides the mobile node with a new nonce to be used in the next registration. Thus the nonce protocol is self- synchronizing.
- types of extensions to Registration Request and Registration Reply messages (see sections 3.3 and 3.4, and also consult [27, 29, 6, 7, 12]) - values for the Code in the Registration Reply message (see section 3.4, and also consult [27, 29, 6, 7, 12]) - Mobile IP defines so-called Agent Solicitation and Agent Advertisement messages. These messages are in fact Router Discovery messages  augmented with mobile-IP specific extensions. Thus, they do not define a new name space, but do define additional Router Discovery extensions as described below in Section 6.2. Also see Section 2.1 and consult [7, 12]. There are additional Mobile IP numbering spaces specified in . Information about assignment of mobile-ip numbers derived from specifications external to this document is given by IANA at http://www.iana.org/numbers.html. From that URL, follow the hyperlinks to [M] within the "Directory of General Assigned Numbers", and subsequently to the specific section for "Mobile IP Numbers". 30]. The currently standardized message types have the following numbers, and are specified in the indicated sections. Type Name Section ---- -------------------------------------------- --------- 1 Registration Request 3.3 3 Registration Reply 3.4 RFC 1256 defines two ICMP message types, Router Advertisement and Router Solicitation. Mobile IP defines a number space for extensions to Router Advertisement, which could be used by protocols other than Mobile IP. The extension types currently standardized for use with Mobile IP have the following numbers.
Type Name Reference ---- -------------------------------------------- --------- 0 One-byte Padding 2.1.3 16 Mobility Agent Advertisement 2.1.1 19 Prefix-Lengths 2.1.2 Approval of new extension numbers for use with Mobile IP is subject to Expert Review, and a specification is required . 30]. Type Name Reference ---- -------------------------------------------- --------- 0 One-byte Padding 32 Mobile-Home Authentication 3.5.2 33 Mobile-Foreign Authentication 3.5.3 34 Foreign-Home Authentication 3.5.4 30].
18, 19, 17]. Thanks also to Kannan Alaggapan, Greg Minshall, Tony Li, Jim Solomon, Erik Nordmark, Basavaraj Patil, and Phil Roberts for their contributions to the group while performing the duties of chairperson, as well as for their many useful comments. Thanks to the active members of the Mobile IP Working Group, particularly those who contributed text, including (in alphabetical order) - Ran Atkinson (Naval Research Lab), - Samita Chakrabarti (Sun Microsystems) - Ken Imboden (Candlestick Networks, Inc.) - Dave Johnson (Carnegie Mellon University), - Frank Kastenholz (FTP Software), - Anders Klemets (KTH), - Chip Maguire (KTH), - Alison Mankin (ISI) - Andrew Myles (Macquarie University), - Thomas Narten (IBM) - Al Quirt (Bell Northern Research), - Yakov Rekhter (IBM), and - Fumio Teraoka (Sony). - Alper Yegin (NTT DoCoMo) Thanks to Charlie Kunzinger and to Bill Simpson, the editors who produced the first drafts for of this document, reflecting the discussions of the Working Group. Much of the new text in the later revisions preceding RFC 2002 is due to Jim Solomon and Dave Johnson. Thanks to Greg Minshall (Novell), Phil Karn (Qualcomm), Frank Kastenholz (FTP Software), and Pat Calhoun (Sun Microsystems) for their generous support in hosting interim Working Group meetings. Sections 1.10 and 1.11, which specify new extension formats to be used with aggregatable extension types, were included from a specification document (entitled "Mobile IP Extensions Rationalization (MIER)", which was written by
- Mohamed M.Khalil, Nortel Networks - Raja Narayanan, nVisible Networks - Haseeb Akhtar, Nortel Networks - Emad Qaddoura, Nortel Networks Thanks to these authors, and also for the additional work on MIER, which was contributed by Basavaraj Patil, Pat Calhoun, Neil Justusson, N. Asokan, and Jouni Malinen.
24], and changes in cell or administration. The mechanisms will be specific to the particular link-layer technology, and are outside the scope of this document. The Point-to-Point-Protocol (PPP)  and its Internet Protocol Control Protocol (IPCP) , negotiates the use of IP addresses. The mobile node SHOULD first attempt to specify its home address, so that if the mobile node is attaching to its home network, the unrouted link will function correctly. When the home address is not accepted by the peer, but a transient IP address is dynamically assigned to the mobile node, and the mobile node is capable of supporting a co-located care-of address, the mobile node MAY register that address as a co-located care-of address. When the peer specifies its own IP address, that address MUST NOT be assumed to be a foreign agent care-of address or the IP address of a home agent.
PPP extensions for Mobile IP have been specified in RFC 2290 . Please consult that document for additional details for how to handle care-of address assignment from PPP in a more efficient manner. RFC 2988  when implementing TCP retransmission timers. Vendors of systems designed for low-bandwidth, high-delay links should consult RFCs 2757 and 2488 [28, 1]. Designers of applications targeted to operate on mobile nodes should be sensitive to the possibility of timer-related difficulties. 21]. Now, when a packet is dropped, the correspondent node's TCP implementation is likely to react as if there were a source of network congestion, and initiate the slow-start mechanisms  designed for controlling that problem. However, those mechanisms are inappropriate for overcoming errors introduced by the links themselves, and have the effect of magnifying the discontinuity introduced by the dropped packet. This problem has been analyzed by Caceres, et al. . TCP approaches to the problem of handling errors that might interfere with congestion management are discussed in documents from the [pilc] working group [3, 9]. While such approaches are beyond the scope of this document, they illustrate that providing performance transparency to mobile nodes involves understanding mechanisms outside the network layer. Problems introduced by higher media error rates also indicate the need to avoid designs which systematically drop packets; such designs might otherwise be considered favorably when making engineering tradeoffs.
13] for use as a co-located care-of address. The mobile node supports all forms of encapsulation (IP-in-IP, minimal encapsulation, and GRE), desires a copy of broadcast datagrams on the home network, and does not want simultaneous mobility bindings:
IP fields: Source Address = care-of address obtained from DHCP server Destination Address = IP address of home agent Time to Live = 64 UDP fields: Source Port = <any> Destination Port = 434 Registration Request fields: Type = 1 S=0,B=1,D=1,M=1,G=1 Lifetime = 1800 (seconds) Home Address = the mobile node's home address Home Agent = IP address of mobile node's home agent Care-of Address = care-of address obtained from DHCP server Identification = Network Time Protocol timestamp or Nonce Extensions: The Mobile-Home Authentication Extension
RFC 2002 that are intended to improve interoperability by resolving ambiguities contained in the earlier text. Implementations that perform authentication according to the new more precisely specified algorithm would be interoperable with earlier implementations that did what was originally expected for producing authentication data. That was a major source of non- interoperability before. However, this specification does have new features that, if used, would cause interoperability problems with older implementations. All features specified in RFC 2002 will work with the new implementations, except for V-J compression . The following list details some of the possible areas of compatibility problems that may be experienced by nodes conforming to this revised specification, when attempting to interoperate with nodes obeying RFC 2002. - A client that expects some of the newly mandatory features (like reverse tunneling) from a foreign agent would still be interoperable as long as it pays attention to the `T' bit.
- Mobile nodes that use the NAI extension to identify themselves would not work with old mobility agents. - Mobile nodes that use a zero home address and expect to receive their home address in the Registration Reply would not work with old mobility agents. - Mobile nodes that attempt to authenticate themselves without using the Mobile-Home authentication extension will be unable to successful register with their home agent. In all of these cases, a robust and well-configured mobile node is very likely to be able to recover if it takes reasonable actions upon receipt of a Registration Reply with an error code indicating the cause for rejection. For instance, if a mobile node sends a registration request that is rejected because it contains the wrong kind of authentication extension, then the mobile node could retry the registration with a mobile-home authentication extension, since the foreign agent and/or home agent in this case will not be configured to demand the alternative authentication data. RFC 2002 and ff.) that have been made as part of this revised protocol specification for Mobile IP.
- Specification that foreign agents SHOULD support reverse tunneling, and home agents MUST support decapsulation of reverse tunnels. - Changed the preconfiguration requirements in section 3.6 for the mobile node to reflect the capability, specified in RFC 2794 , for the mobile node to identify itself by using its NAI, and then getting a home address from the Registration Reply. - Changed section 220.127.116.11 so that a foreign agent is not required to discard Registration Replies that have a Home Address field that does not match any pending Registration Request. - Allowed registrations to be authenticated by use of a security association between the mobile node and a suitable authentication entity acceptable to the home agent. Defined "Authorization-enabling Extension" to be an authentication extension that makes a registration message acceptable to the recipient. This is needed according to specification in . - Mandated that HMAC-MD5 be used instead of the "prefix+suffix" mode of MD5 as originally mandated in RFC 2002. - Specified that the mobile node SHOULD take the first care-of address in a list offered by a foreign agent, and MAY try each subsequent advertised address in turn if the attempted registrations are rejected by the foreign agent - Clarification that a mobility agent SHOULD only put its own addresses into the initial (i.e., not mobility-related) list of routers in the mobility advertisement. RFC 2002 suggests that a mobility agent might advertise other default routers. - Specification that a mobile node MUST ignore reserved bits in Agent Advertisements, as opposed to discarding such advertisements. In this way, new bits can be defined later, without affecting the ability for mobile nodes to use the advertisements even when the newly defined bits are not understood. Furthermore, foreign agents can set the `R' bit to make sure that new bits are handled by themselves instead of some legacy mobility agent. - Specification that the foreign agent checks to make sure that the indicated home agent address does not belong to any of its network interfaces before relaying a Registration Request. If
the check fails, and the foreign agent is not the mobile node's home agent, then the foreign agent rejects the request with code 136 (unknown home agent address). - Specification that, while they are away from the home network, mobile nodes MUST NOT broadcast ARP packets to find the MAC address of another Internet node. Thus, the (possibly empty) list of Router Addresses from the ICMP Router Advertisement portion of the message is not useful for selecting a default router, unless the mobile node has some means not involving broadcast ARP and not specified within this document for obtaining the MAC address of one of the routers in the list. Similarly, in the absence of unspecified mechanisms for obtaining MAC addresses on foreign networks, the mobile node MUST ignore redirects to other routers on foreign networks. - Specification that a foreign agent MUST NOT use broadcast ARP for a mobile node's MAC address on a foreign network. It may obtain the MAC address by copying the information from an Agent Solicitation or a Registration Request transmitted from a mobile node. - Specification that a foreign agent's ARP cache for the mobile node's IP address MUST NOT be allowed to expire before the mobile node's visitor list entry expires, unless the foreign agent has some way other than broadcast ARP to refresh its MAC address associated to the mobile node's IP address. - At the end of section 4.6, clarified that a home agent MUST NOT make any changes to the way it performs proxy ARP after it rejects an invalid deregistration request. - In section 4.2.3, specification that multihomed home agents MUST use the the address sent to the mobile node in the home agent field of the registration reply as the source address in the outer IP header of the encapsulated datagram. - Inserted 'T' bit into its proper place in the Registration Request message format (section 3.3).
- Specification that the foreign agent MAY configure a maximum number of pending registrations that it is willing to maintain (typically 5). Additional registrations SHOULD then be rejected by the foreign agent with code 66. The foreign agent MAY delete any pending Registration Request after the request has been pending for more than 7 seconds; in this case, the foreign agent SHOULD reject the Request with code 78 (registration timeout). - Relaxation of the requirement that, when a mobile node has joined a multicast group at the router on the foreign network, the mobile node MUST use its home address as the source IP address for multicast packets, - Clarification that a mobility agent MAY use different settings for each of the 'R', 'H', and 'F' bits on different network interfaces. - Replacement of the terminology "recursive tunneling" by the terminology "nested tunneling". - Specification that the mobile node MAY use the IP source address of an agent advertisement as its default router address. - Clarification that keys with arbitrary binary values MUST be supported as part of mobility security associations. - Specification that the default value may be chosen as 7 seconds, for allowable time skews between a home agent and mobile node using timestamps for replay protection. Further specification that this value SHOULD be greater than 3 seconds. - Specification that Registration Requests with the 'D' bit set to 0, and specifying a care-of address not offered by the foreign agent, MUST be rejected with code 77 (invalid care-of address). - Clarification that the foreign agent SHOULD consider its own maximum value when handling the Lifetime field of the Registration Reply. - Clarification that the home agent MUST ignore the 'B' bit (as opposed to rejecting the Registration Request) if it does not support broadcasts.
- Advice about the impossibility of using dynamic home agent discovery in the case when routers change the IP destination address of a datagram from a subnet-directed broadcast address to 255.255.255.255 before injecting it into the destination subnet. - Clarified that when an Agent Advertisement is unicast to a mobile node, the specific IP home address of a mobile node MAY be used as the destination IP address. - Included a reference to RFC 2290 within appendix B, which deals with PPP operation. - Created IANA Considerations section - In section 3.8.3, clarified that a home agent SHOULD arrange the selection of a home address for a mobile node when the Registration Reply contains a zero Home Address. RFC 2290 within appendix B, which deals with PPP operation. - Revamped IANA Considerations section - Revamped Changes section - Replaced Patents section with wording mandated from RFC 2026. - Updated citations.
1] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Preference Level | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Router Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Preference Level | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | .... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = 16 | Length | Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Registration Lifetime |R|B|H|F|M|G|r|T| reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Care-of Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Care-of Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | .... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ : Optional Extensions : : .... ...... ...... : +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Allman, M., Glover, D. and L. Sanchez, "Enhancing TCP Over Satellite Channels using Standard Mechanisms", BCP 28, RFC 2488, January 1999.  S. M. Bellovin. Security Problems in the TCP/IP Protocol Suite. ACM Computer Communications Review, 19(2), March 1989.  Border, J., Kojo, M., Griner, J., Montenegro, G. and Z. Shelby, "Performance Enhancing Proxies", RFC 3135, June 2001.  Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
 Ramon Caceres and Liviu Iftode. Improving the Performance of Reliable Transport Protocols in Mobile Computing Environments. IEEE Journal on Selected Areas in Communications, 13(5):850-- 857, June 1995.  Calhoun P. and C. Perkins, "Mobile IP Network Access Identifier Extension for IPv4", RFC 2794, January 2000.  Calhoun, P. and C. Perkins, "Mobile IP Foreign Agent Challenge/Response Extension", RFC 3012, December 2000.  Cong, D., Hamlen, M. and C. Perkins, "The Definitions of Managed Objects for IP Mobility Support using SMIv2", RFC 2006, October 1996.  Dawkins, S., Montenegro, G., Kojo, M., Magret, V. and N. Vaidya, "End-to-end Performance Implications of Links with Errors", BCP 50, RFC 3155, August 2001.  Deering, S., "ICMP Router Discovery Messages", RFC 1256, September 1991.  Deering, S., "Host Extensions for IP Multicasting", STD 5, RFC 1112, August 1989.  Dommety, G. and K. Leung, "Mobile IP Vendor/Organization- Specific Extensions", RFC 3115, April 2001.  Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997.  Eastlake, D., Crocker, S. and J. Schiller, "Randomness Recommendations for Security", RFC 1750, December 1994.  Ferguson P. and D. Senie, "Network Ingress Filtering: Defeating Denial of Service Attacks which employ IP Source Address Spoofing", BCP 38, RFC 2827, May 2000.  Hanks, S., Li, T., Farinacci, D. and P. Traina, "Generic Routing Encapsulation (GRE)", RFC 1701, October 1994.  J. Ioannidis. Protocols for Mobile Internetworking. PhD Dissertation - Columbia University in the City of New York, July 1993.
 John Ioannidis, Dan Duchamp, and Gerald Q. Maguire Jr. IP- Based Protocols for Mobile Internetworking. In Proceedings of the SIGCOMM '91 Conference: Communications Architectures & Protocols, pages 235--245, September 1991.  John Ioannidis and Gerald Q. Maguire Jr. The Design and Implementation of a Mobile Internetworking Architecture. In Proceedings of the Winter USENIX Technical Conference, pages 489--500, January 1993.  Jacobson, V., "Compressing TCP/IP headers for low-speed serial links", RFC 1144, February 1990.  Jacobson, V., "Congestion Avoidance and Control. In Proceedings, SIGCOMM '88 Workshop, pages 314--329. ACM Press, August 1988. Stanford, CA.  Kent, S. and R. Atkinson, "IP Authentication Header", RFC 2402, November 1998.  Krawczyk, H., Bellare, M. and R. Canetti, "HMAC: Keyed-Hashing for Message Authentication", RFC 2104, February 1997.  McCloghrie, K. and F. Kastenholz, "The Interfaces Group MIB", RFC 2863, June 2000.  McGregor, G., "The PPP Internet Protocol Control Protocol (IPCP)", RFC 1332, May 1992.  Mills, D., "Network Time Protocol (Version 3) Specification, Implementation", RFC 1305, March 1992.  Montenegro, G., "Reverse Tunneling for Mobile IP (revised)", RFC 3024, January 2001.  Montenegro, G., Dawkins, S., Kojo, M., Magret, V. and N. Vaidya, "Long Thin Networks", RFC 2757, January 2000.  Montenegro, G. and V. Gupta, "Sun's SKIP Firewall Traversal for Mobile IP", RFC 2356, June 1998.  Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", RFC 2434, October 1998.  Paxson, V. and M. Allman, "Computing TCP's Retransmission Timer", RFC 2988, November 2000.
 Perkins, C., "IP Encapsulation within IP", RFC 2003, October 1996.  Perkins, C., "IP Mobility Support", RFC 2002, October 1996.  Perkins, C., "Minimal Encapsulation within IP", RFC 2004, October 1996.  Perkins, C. and P. Calhoun, "AAA Registration Keys for Mobile IP", Work in Progress, July 2001.  Plummer, D., "Ethernet Address Resolution Protocol: Or converting network protocol addresses to 48.bit Ethernet address for transmission on Ethernet hardware", STD 37, RFC 826, November 1982.  Postel, J., "User Datagram Protocol", STD 6, RFC 768, August 1980.  Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981.  Postel, J., "Multi-LAN Address Resolution", RFC 925, October 1984.  Reynolds, J. and J. Postel, "Assigned Numbers", STD 2, RFC 1700, October 1994.  Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, April 1992.  Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51, RFC 1661, July 1994.  Solomon, J., "Applicability Statement for IP Mobility Support" RFC 2005, October 1996.  Solomon J. and S. Glass, "Mobile-IPv4 Configuration Option for PPP IPCP", RFC 2290, February 1998.  Stevens, W., "TCP/IP Illustrated, Volume 1: The Protocols" Addison-Wesley, Reading, Massachusetts, 1994.
Full Copyright Statement Copyright (C) The Internet Society (2002). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society.