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INTERNET-DRAFT                                               H. Kitamura<draft-kitamura-ipv6-record-route-00.txt>                NEC CorporationExpires in six months                                   17 November 2000Record Route for IPv6 (RR6)Hop-by-Hop Option Extension               <draft-kitamura-ipv6-record-route-00.txt>Status of this Memo   This document is an Internet-Draft and is in full conformance with   all provisions ofSection 10 of RFC2026.   Internet-Drafts are working documents of the Internet Engineering   Task Force (IETF), its areas, and its working groups.  Note that   other groups may also distribute working documents as Internet-   Drafts.   Internet-Drafts are draft documents valid for a maximum of six months   and may be updated, replaced, or obsoleted by other documents at any   time.  It is inappropriate to use Internet- Drafts as reference   material or to cite them other than as "work in progress."   The list of current Internet-Drafts can be accessed athttp://www.ietf.org/ietf/1id-abstracts.txt   The list of Internet-Draft Shadow Directories can be accessed athttp://www.ietf.org/shadow.html.Abstract   This document proposes a "Record Route for IPv6 (RR6)" mechanism.  It   is composed of one new IPv6 hop-by-hop option (RR6 option) extension.   The RR6 mechanism is redesigned to establish an optimized record   route mechanism for IPv6. Two types of new features are introduced.   1. In order to prevent scalability problems and to make the mechanism   flexible, the beginning and ending points of the data recording range   are controlled by using their specifiers.   2. In order to record long IPv6 addresses efficiently, a simple   address compression method is introduced. Since the compression is   achieved by utilizing characteristics of recorded IPv6 addresses   effectively, the mechanism is efficient and optimized for IPv6.H. Kitamura                                                    [Page 1]

INTERNET-DRAFT         Record Route for IPv6 (RR6)         November 20001. Introduction   This document proposes a "Record Route for IPv6 (RR6)" mechanism.  It   is composed of one new IPv6 Hop-by-Hop option (RR6 option) extension.   In the IPv6 specifications [IPv6], no record route function is   defined, and the record route function for IPv4 is less flexible and   has scalability problems.   The RR6 mechanism is redesigned to establish an optimized record   route mechanism for IPv6 and fix the problems of the record route   function for IPv4. Two types of new features are introduced to   achieve this goal.   1. In order to prevent scalability problems and to make the mechanism   flexible, the beginning and ending points of the data recording range   are controlled by using their specifiers.   2. In order to record long IPv6 addresses efficiently, a simple   address compression method is introduced. Since the compression is   achieved by utilizing characteristics of recorded IPv6 addresses   effectively, the mechanism is efficient and optimized for IPv6.2. Design of the Record Route for IPv6 (RR6) Mechanism   Since a record route operation runs on each node along a   communication path, it is appropriate to achieve the record route   operation as a hop-by-hop option operation. One IPv6 hop-by-hop   option (RR6 option) is introduced to establish the RR6 mechanism.2.1 Roles of the RR6 Option Operations   The RR6 option has the following roles.   1. Provide Data Storing Space      A Data Space is prepared in the RR6 option header. All of the data      recorded by the RR6 option operation is written into the Data      Space in the RR6 option header.      Changing the length of the packet on an intermediate node makes      the mechanism complex, so that the length of the Data Space is not      changed by the RR6 address data recording operations on each node.      When the packet in which the RR6 option is set is prepared for      sending, the Data Space is preallocated in it.H. Kitamura                                                    [Page 2]

INTERNET-DRAFT         Record Route for IPv6 (RR6)         November 2000      (Since the length of the Data Space is limited, the data recording      or carrying capacity of one packet in which the RR6 option is set      is limited. This scalability issue is discussed inSection 2.2)   2. Record Address Information      When a packet in which the RR6 option is set passes through nodes      along the communication path, the RR6 option operation routine on      each node records (incoming interface's) address information of      the node. The address information is written into the Data Space      in the RR6 option header.      Exception:      On the source node, outgoing interface's address information of      the source node is recorded.   3. Carry the Recorded Data      The recorded data is carried by packets in which the RR6 option is      set. This is easy to achieve, because the Data Space exists in the      RR6 option header.      (Since recorded data is normally analyzed on a source node that      issues the packet in which RR6 option is set, the recorded data      must be carried back to the source node. Namely, the RR6 option      must be set to the packet that returns to the source node. This      issue is discussed inSection 2.4)2.2 Data Recording Range Control   Since the length of the Data Space is limited, the data recording or   carrying capacity of one packet in which the RR6 option is set is   limited.   To prevent scalability problems and to make the mechanism flexible,   the beginning and ending points (nodes) of data recording range are   controlled by using their specifiers.   When a packet in which the RR6 option is set can not record or carry   all of address information of nodes along the communication path   (because the number of nodes is larger than the capacity), an   additional packet(s) whose data recording beginning point specifier   is set appropriately is issued and the remaining address information   is recorded and carried by it.   This RR6 mechanism does not cause any scalability problems. Details   of the data recording range control are explained inSection 3.3.H. Kitamura                                                    [Page 3]

INTERNET-DRAFT         Record Route for IPv6 (RR6)         November 20002.3 Address Recording with Compression   The maximum length of one hop-by-hop option is 255 octets, and the   IPv6 address is long in length (16 octets). If address information is   recorded as a plain (non-compressed) address format, one hop-by-hop   option can record and carry only 15 record entries.   When the RR6 mechanism is applied to a large-scale network   environment, 15 entries are insufficient. Thus, it is necessary to   provide a compressed address recording method.   It is requested that a compressed address recording method of the RR6   mechanism must be sufficiently simple and efficient, because the RR6   mechanism is achieved as a hop-by-hop option operation that runs on   each node along the communication path. A complex and heavy operation   is not suitable for the compressed address recording method.   A series of recorded addresses is composed of successive neighbor   addresses, and is not a series of random numbers. It is strongly   assumed that each address is correlated with its previous or   succeeding address in the series. In other words, two neighboring   addresses will have the same leading part (prefix). This special   characteristic can be used for a simple and efficient address   compression method.   Generally speaking, compression methods are categorized into two   types, intra-compression and inter-compression.   Since inter-compression methods work efficiently for a series of   successive neighbor addresses, the RR6 mechanism adopts one of the   inter-compression methods to achieve a compressed address recording   mechanism. Details are explained inSection 3.3,2.4 Loop Communication Path   Since recorded data is normally analyzed on a source node that issues   a packet in which the RR6 option is set, the recorded data must be   carried back to the source node. Namely, the RR6 option must be set   to the packet that returns to the source node.   There are two ways of making a loop communication path.   One is to utilize an ICMPv6 Echo Request/Reply (ping6) mechanism.      In order to run the RR6 mechanism appropriately on the ping6      mechanism, the following two operations must be implemented on the      ping6's target node.H. Kitamura                                                    [Page 4]

INTERNET-DRAFT         Record Route for IPv6 (RR6)         November 2000      1. All of the RR6 option fields must be copied from         an Echo Request message to an Echo Reply message.      2. The Hop Limit field of the IPv6 header of these messages         must be copied as a continuous sequence.   The other is to prepare a packet in which a Route option is set.      The source node must be set to the final destination of the Route      option, and the target node must be set to one of the intermediate      nodes that are specified in the Route option.      No special operations are required to run the RR6 mechanism in      this method.3. Record Route for IPv6 (RR6) Option Format: IPv6 Hop-by-Hop Option     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     |  Option Type  |  Opt Data Len |    RR6_Type   |  Rec_Pointer  |     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     |  Begin_Hop_L  |   End_Hop_L   |    Reserved   |               |     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               +     |                                                               |     |                                                               |     |                           Data Space                          |     |                                                               |     |                                                               |   Option Type:    8-bit.                   Identifier of the type of option (RR6 option)                   Value is 001xxxxx. 0x20+TBA                   (Tentatively 0x23)                   RR6 Option Type must be started as 00 to avoid                   discarding the packet at the RR6 feature disabled                   node, and the third bit must be set to 1 to record                   data into the [Data Space].                   [seeSection 4.2 of RFC2460]   Opt Data Len:   8-bit unsigned integer.                   Length of the [Option Data] field of this option                   Max: 255                   Depends on the length of [Data Space]H. Kitamura                                                    [Page 5]

INTERNET-DRAFT         Record Route for IPv6 (RR6)         November 2000   RR6_Type:       8-bit.                   Identifier of the data recording type                   =0 Plain (non-compressed) address record type                   [seeSection 3.2]                   =1 Compressed address record type                   [seeSection 3.3]   Rec_Pointer:    8-bit unsigned integer.                   Pointer that shows next data recording point                   in the [Data Space] in octet                   Initial: 0                   Data recording status can be checked by Rec_Pointer                   (=0 means that no data has been recorded yet)   Begin_Hop_L:    8-bit unsigned integer.                   Data recording beginning point specifier                   (In a model case, it shows Hop Limit value of                    the node that begins the data recording on the path)                   default: 255                   [seeSection 3.1]   End_Hop_L:      8-bit unsigned integer.                   Data recording ending point specifier                   (In a model case, it shows Hop Limit value of                    the node that ends the data recording on the path)                   default: 0                   End_Hop_L has another role to indicate that                   [Data Space] is filled on the communication path.                   When it is detected that [Data Space] is fully filled                   and there is no space left to record new data,                   [End_Hop_L] is set with the Hop Limit value of the                   last data record node.                   [seeSection 3.1]   Reserved:       8-bit. (Reserved Octet)                   Reserved octet for future use.   Data Space:     [Opt Data Len]-5 octets                   Buffer space to record the address information data.                   Length of [Data Space] must be longer than or                   equal to 17 (length of one fixed length record).H. Kitamura                                                    [Page 6]

INTERNET-DRAFT         Record Route for IPv6 (RR6)         November 20003.1 Procedure of Data Recording Range Control   As described inSection 2.2, the data recording range can be   controlled by specifying the data recording beginning and ending   points. Begin_Hop_L and End_Hop_L are used to specify these points.   When a packet the RR6 option is set passes through a node, the   current Hop Limit value (Hop_L) of the node is initially compared   with Begin_Hop_L and End_Hop_L. If Hop_L is located between them, an   address recording operation is started.   End_Hop_L has another role. If the Data Space is fully filled on an   intermediate node on the communication path, End_Hop_L is set with   the Hop Limit value of the last data record node to indicate its   location.   The following describes an algorithm of data recording range control.    while (Begin_Hop_L >= Hop_L && Hop_L >= End_Hop_L) {      Prepare a data record to write into the Data Space;      // Check the remaining space in the Data Space      if (there is enough space to record address information) {        Record the prepared data record into the Data Space;        if (Data Space has been fully filled without odd remains) {            End_Hop_L is set by the Hop Limit value of the current node;        }      } else { // there is no space left to record new data         End_Hop_L is set with the Hop Limit value of         the last (previous) data record node;         // End_Hop_L = Prev_Rec_HopL;         // in the compressed address record type [seeSection 3.3]      }    }3.1.1 Example of Data Recording Range Control   Examples of data recording range control behavior are shown here.    INI: Hop Limit value of the source node that issues a packet                    [Source]-[Node1]-[Node2]-[Node3]-[Node4]-[Node5]-...    Hop Limit value     INI   INI-1   INI-2   INI-3   INI-4   INI-5  ...    (ex. INI=64)         64      63      62      61      60      59  ...    default (w/o Cont.)   x       x       x       x       x       x  ...    (Begin=(64=INI))    w/ Record Range Cont. -       -       -       x       x       x  ...    (ex. Begin=61)    w/ Record Range Cont. -       -       x       x       x       -  ...    (ex. Begin=62, End=60)H. Kitamura                                                    [Page 7]

INTERNET-DRAFT         Record Route for IPv6 (RR6)         November 20003.2 Plain (Non-Compressed) Address Record Type   In this section, a plain (non-compressed) address record type is   explained.   When [RR6_Type] = 0, a plain (non-compressed) address record type is   used to record address information.   This record type is the simplest method to record address information   into the [Data Space]. Address information of a node is recorded as   plain format (without compression).   Each node provides one data record that contains address information.   The length of the data record is fixed (17 octets). When a packet in   which the RR6 option is set passes through a node, one data record   space is consumed in the [Data Space].   The following is the format of one fixed-length data record.                                                     +-+-+-+-+-+-+-+-+                                                     |   Hop_Lim_A   |     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     |                                                               |     |                Address of Node A  (16 octets)                 |     |                            (Hop_Lim_A= Hop Limit of Node A)   |     |                                                               |     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   One fixed-length data record comprises the Hop Limit (1 octet) and   the (incoming interface's) address (16 octets) information of the   node.   Hop Limit information of the node is used to identify the location on   the communication path.   Exception:   If [Begin_Hop_L] >= Hop Limit value of the source node, the source   node must record its address information. Since there is no incoming   operation on the source node, outgoing interface's address   information is recorded into the [Address of Node] field instead of   incoming interface's address information.H. Kitamura                                                    [Page 8]

INTERNET-DRAFT         Record Route for IPv6 (RR6)         November 2000   3.2.1 Example of Data-Filled Format (Plain Address Record Type)   The following shows an example of how the [Data Space] is filled with   fixed-length data records.     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     |  Option Type  |  Opt Data Len |   RR6_Type=0  |  Rec_Pointer  |     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     |  Begin_Hop_L  |  Max_Records  |    Reserved   |   Hop_Lim_A   |     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     |                                                               |     |                Address of Node A  (16 octets)                 |     |                            (Hop_Lim_A= Hop Limit of Node A)   |     |                                                               |     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     |   Hop_Lim_B   |                                               |     +-+-+-+-+-+-+-+-+                                               |     |                Address of Node B  (16 octets)                 |     |                            (Hop_Lim_B= Hop Limit of Node B)   |     |               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     |               |   Hop_Lim_C   |                               |     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |     |                Address of Node C  (16 octets)                 |     |                            (Hop_Lim_C= Hop Limit of Node C)   |     |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     |                               |   Hop_Lim_D   |               |     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               |     |                Address of Node D  (16 octets)                 |     |                            (Hop_Lim_D= Hop Limit of Node D)   |     |                                               +-+-+-+-+-+-+-+-+     |                                               |               |     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               +     |                                                               |     |                                                               |   Some nodes on the communication path do not record address   information for some reason (e.g., not implementing or intentionally   disabling the RR6 feature).   Thus, Node A, B, C, D, ... are not always successive neighbor nodes,   and Hop_Lim_A, Hop_Lim_B, Hop_Lim_C, Hop_Lim_D, ...  are not always   consecutive descending numbers.H. Kitamura                                                    [Page 9]

INTERNET-DRAFT         Record Route for IPv6 (RR6)         November 20003.3 Compressed Address Record Type   In this section, a compressed address record type is explained.   (This document defines one simple and efficient compressed address   record type. Since there are various address compression methods,   other compressed address record types may be proposed in other   documents in future).   When [RR6_Type] = 1, a compressed address record type is used to   record address information.   Address information of a node is recorded into the [Data Space] as a   compressed format. Each node provides one data record. Since address   information is compressed, the length of the record is variable (max   17 octets). When the packet in which the RR6 option is set passes   through a node, its RR6 operation consumes one variable-length data   record space in the [Data Space].3.3.1 Compression Method   Series of recorded addresses have a special characteristic. It is   composed of successive neighbor addresses. It is strongly assumed   that each address is correlated with its previous or succeeding   address in the series. Specifically, it is assumed that two   neighboring addresses have the same leading part (prefix).   By omitting the same leading part, address information can be   compressed. This simple compression method utilizes the special   characteristic efficiently, and it is adopted for this record type.   (This method is categorized into inter-compression methods. In order   to simplify the mechanism, intra-compression methods are not used in   this record type.)   To establish a simplified compression mechanism, the same leading   part is omitted in octet unit (not bit unit).   The compression is composed of the following operations.   1. Compare current address with previous address.   2. Find the same leading part between them in octet   3. Omit the same leading part in octet, and calculate the length      of the remaining part of the current address information.H. Kitamura                                                   [Page 10]

INTERNET-DRAFT         Record Route for IPv6 (RR6)         November 20003.3.2 Data Space Format Extension for Compressed Address Record Type   In order to compare current and previous information, the leading 17   octets of the [Data Space] are used to keep Hop Limit and Address   information of the previous (last data recorded) node.   The following format is used in the compressed address record type.   (This format is an upper compatible format from the basic RR6 format)     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     |  Option Type  |  Opt Data Len |   RR6_Type=1  |  Rec_Pointer  |     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     |  Begin_Hop_L  |   End_Hop_L   |    Reserved   | Prev_Rec_HopL |     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     |                                                               |     |                Previous Record Address                        |     |                                                               |     |                                                               |     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     |                                                               |     |                Data Space (for Variable Length Data Records)  |     |                                                               |   Prev_Rec_HopL:  8-bit unsigned integer.                   Hop Limit value of the previous (last data recorded)                   node   Previous Record Address: 16-octet                   (Incoming interface's) address of the previous                   (last data recorded) node   (If [Begin_Hop_L] >= Hop Limit value of the source node, the source   node fills [Prev_Rec_HopL] with Hop Limit value of the source node,   fills [Previous Record Address] with outgoing interface's address   information of the source node, and sets [Rec_Pointer] with 17)3.3.3 Variable Length Data Record Format   The following is a format of one variable-length data record.     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...     | DHop  |  Len  |     Compressed Address     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...     (Maximum length: 17 octets)H. Kitamura                                                   [Page 11]

INTERNET-DRAFT         Record Route for IPv6 (RR6)         November 2000   DHop:           4bit.                   Hop difference that is calculated by the following                   formula   [Prev_Rec_HopL] - [Current Hop Limit]                   (=0 means more than 15 hop difference)   Len:            4bit.                   Length of the following [Compressed Address]                   (=0 means 16)   Compressed Address:                   Compressed current address                   (The same leading part in octet is omitted)                   (Max length 16)   Note:   In usual cases (hop differences are smaller than 16), [DHop] can show   accurate hop difference. Only when some hop difference on the path is   larger than 15, a situation ([DHop] = 0) appears in the [Data Space],   and this causes a Hop Limit counting ambiguity.   If the situation ([DHop] = 0) appears only once in the [Data Space],   such an ambiguity can be cleared by checking the initial Hop Limit   value and the Hop Limit value of the received packet.   If the situation ([DHop] = 0) appears more than once in the [Data   Space], such ambiguities are not cleared in the compressed address   record type. If it is necessary to count Hop Limit values of nodes   accurately, the plain (non-compressed) address record type   accompanied with appropriate data recording range control is used.3.3.4 Operation Steps at Each Node   1. Prepare a variable-length data record      Calculate "DHop", "Compressed Address" and "Len"   2. Write the data record into [Data Space (for Variable Length      Data Records)].  Writing start point in [Data Space] is      indicated by [Rec_Pointer]   3. Update [Rec_Pointer]    ([Rec_Pointer] += (1+[Len]))   4. Update [Prev_Rec_HopL] with Hop Limit value of current node   5. Update [Previous Record Address] with address information      of current nodeH. Kitamura                                                   [Page 12]

INTERNET-DRAFT         Record Route for IPv6 (RR6)         November 2000   Note:   Only step 4 and 5 are executed on an initial data record node, and no   data is recoded into [Data Space (for Variable Length Data Records)].3.3.5 Example of Data-Filled Format (Compressed Address Record Type)   The followings show an example how the [Data Space] is filled with   variable-length data records.     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     |  Option Type  |  Opt Data Len |   RR6_Type=1  |  Rec_Pointer  |     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     |  Begin_Hop_L  |   End_Hop_L   |    Reserved   | Prev_Rec_HopL |     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     |                                                               |     |                Previous Record Address  (16 octets)           |     |                                                               |     |                                                               |     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     | DHop_A| Len=13|                                               |     +-+-+-+-+-+-+-+-+                                               |     |                   Compressed Address A  (13 octets)           |     |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     |                               | DHop_B| Len=12|               |     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               |     |                   Compressed Address B  (12 octets)           |     |                                               +-+-+-+-+-+-+-+-+     |                                               | DHop_C| Len=9 |     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     |                   Compressed Address C   (9 octets)           |     |                                                               |     |               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     |               | DHop_D| Len=10|                               |     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |     |                   Compressed Address D  (10 octets)           |     |                                                               |     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     |                                                               |H. Kitamura                                                   [Page 13]

INTERNET-DRAFT         Record Route for IPv6 (RR6)         November 20004. IANA Considerations   The RR6 mechanism has introduced one IPv6 Hop-by-Hop option. In order   to implement the RR6 mechanism, one IPv6 Hop-by-Hop option type value   is tentatively assigned from unassigned spaces as follows.      IPv6 Hop-by-Hop Option: RR6 Type:    0x23 (Tentatively)   This number must be assigned by IANA officially.5. Security Considerations   Since address information is not secret information of nodes, the   Record Route for IPv6 (RR6) mechanism not have any direct impact on   Internet infrastructure security.Appendix A. Recorded Hop Limit value of the Node   A node deals with two Hop Limit values on it. One is set to receiving   packets; the other is set to transmitting packets. The timing when   Hop Limit value is changed (decremented) on the node is not clearly   defined. It is necessary that which values is appropriate to be   recorded by the RR6 option operations.   Since the recorded Hop Limit value of the node is used to identify   its location on the communication path, it must be unique and   different from Hop Limit values of other nodes on the path.   The initial Hop Limit value is not decremented on the source node, so   that the initial Hop Limit value is adopted for the recorded Hop   Limit value of the source node. Thus, the first node (succeeding node   from the source node on the path) can not use the initial Hop Limit   value, and the decremented initial Hop Limit value is adopted for the   recorded Hop Limit value of the first node.   Therefore, the rule is inductively defined. The recorded Hop Limit   value of the node is the Hop Limit value that is set to transmitting   (outgoing) packets. In other words, the decremented Hop Limit value   that is set to receiving (incoming) packets is used for the recorded   Hop Limit value of the node.H. Kitamura                                                   [Page 14]

INTERNET-DRAFT         Record Route for IPv6 (RR6)         November 2000Appendix B. RR6 Implementation   The main RR6 operations are implemented at incoming operations (e.g.,   ip6_input()). Some RR6 operations, however, are implemented at   outgoing operations (e.g., ip6_output()), because the RR6 mechanism   must run on the source node.References   [IPv6]    S. Deering, R. Hinden, "Internet Protocol, Version 6 (IPv6)             Specification,"RFC2460, December 1998.   [ICMPv6]  A. Conta, S. Deering, "Internet Control Message Protocol             (ICMPv6) for the Internet Protocol Version 6 (IPv6)             Specification,"RFC2463, December 1998.Author's Address:   Hiroshi Kitamura   NEC Corporation   Development Laboratories   (Igarashi Building 4F) 11-5, Shibaura 2-Chome,   Minato-Ku, Tokyo 108-8557, JAPAN   Phone: +81 (3) 5476-1071   Fax:   +81 (3) 5476-1005   Email: kitamura@da.jp.nec.comH. Kitamura                                                   [Page 15]
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