As per Relevance of the word processing, we have this rfc below:
Network Working Group C.
Request for Comments: 2711
Category: Standards Track A.
October 1999
IPv6 Router Alert
Status of this
This document specifies an Internet standards track protocol for
Internet community, and requests discussion and suggestions
improvements. Please refer to the current edition of the "
Official Protocol Standards" (STD 1) for the standardization
and status of this protocol. Distribution of this memo is unlimited
Copyright
Copyright (C) The Internet Society (1999). All Rights Reserved
This memo describes a new IPv6 Hop-by-Hop Option type that
transit routers to more closely examine the contents of an
datagram. This option is useful for situations where a
addressed to a particular destination contains information that
require special processing by routers along the path
1.0
New protocols, such as RSVP, use control datagrams which,
addressed to a particular destination, contain information that
to be examined, and in some case updated, by routers along the
between the source and destination. It is desirable to
regular datagrams as rapidly as possible, while ensuring that
router processes these special control datagrams appropriately
Currently, however, the only way for a router to determine if
needs to examine a datagram is to at least partially parse
layer data in all datagrams. This parsing is expensive and slow
This situation is undesirable
This document defines a new option within the IPv6 Hop-by-Hop Header
The presence of this option in an IPv6 datagram informs the
that the contents of this datagram is of interest to the router
to handle any control data accordingly. The absence of this
in an IPv6 datagram informs the router that the datagram does
contain information needed by the router and hence can be
Partridge & Jackson Standards Track [Page 1]
RFC 2711 IPv6 Router Alert Option October 1999
routed without further datagram parsing. Hosts originating IPv
datagrams are required to include this option in
circumstances
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
document are to be interpreted as described in [RFC-2119].
2.0
The goal is to provide an efficient mechanism whereby routers
know when to intercept datagrams not addressed to them without
to extensively examine every datagram. The described solution is
define a new IPv6 Hop-by-Hop Header option having the
"routers should examine this datagram more closely" and
protocols such as RSVP to use this option. This approach
little or no performance penalty on the forwarding of
datagrams. Not including this option tells the router that there
no need to closely examine the contents of the datagram
2.1
The router alert option has the following format
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0|0 0 1 0 1|0 0 0 0 0 0 1 0| Value (2 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
length = 2
The first three bits of the first byte are zero and the value 5
the remaining five bits is the Hop-by-Hop Option Type number
[RFC-2460] specifies the meaning of the first three bits.
zeroing all three, this specification requires that nodes
recognizing this option type should skip over this option
continue processing the header and that the option must not
en route
There MUST only be one option of this type, regardless of value
per Hop-by-Hop header
Partridge & Jackson Standards Track [Page 2]
RFC 2711 IPv6 Router Alert Option October 1999
Value: A 2 octet code in network byte order with the
values
0 Datagram contains a Multicast Listener
message [RFC-2710].
1 Datagram contains RSVP message
2 Datagram contains an Active Networks message
3-65535 Reserved to IANA for future use
Alignment requirement: 2n+0
Values are registered and maintained by the IANA. See section 5.0
for more details
2.2
The option indicates that the contents of the datagram may
interesting to the router. The router's interest and the
taken by employing Router Alert MUST be specified in the RFC of
protocol that mandates or allows the use of Router Alert
The final destination of the IPv6 datagram MUST ignore this
upon receipt to prevent multiple evaluations of the datagram
Unrecognized value fields MUST be silently ignored and the
of the header continued
Routers that recognize the option will examine datagrams carrying
more closely to determine whether or not further processing
necessary. The router only needs to parse the packet in
detail to decide whether the packet contains something of interest
The value field can be used by an implementation to speed
of the datagram within the transit router
Observe that further processing can involve protocol layers
IPv6. E.g., for RSVP messages, the datagram will have to undergo
and RSVP protocol processing. Once the datagram leaves the IPv
layer, there is considerable ambiguity about whether the router
acting as an IPv6 host or an IPv6 router. Precisely how the
handles the contents is value-field specific. However, if
processing required for the datagram involves examining the
of the IPv6 datagram, then the interim router is performing a
function and SHOULD interpret the data as a host
Partridge & Jackson Standards Track [Page 3]
RFC 2711 IPv6 Router Alert Option October 1999
3.0 Impact on Other
For this option to be effective, its use MUST be mandated
protocols that expect routers to perform significant processing
datagrams not directly addressed to them. Routers are not
to examine the datagrams not addressed to them unless the
include the router alert option
All IPv6 datagrams containing an RSVP message MUST contain
option within the IPv6 Hop-by-Hop Options Header of such datagrams
4.0 Security
Gratuitous use of this option can cause performance problems
routers. A more severe attack is possible in which the router
flooded by bogus datagrams containing router alert options
The use of the option, if supported in a router, MAY therefore
limited by rate or other means by the transit router
5.0 IANA
The value field described in Section 2.1 is registered and
by IANA. New values are to be assigned via IETF Consensus as
in RFC 2434 [RFC-2434].
6.0 Notice on Intellectual
The IETF takes no position regarding the validity or scope of
intellectual property or other rights that might be claimed
pertain to the implementation or use of the technology described
this document or the extent to which any license under such
might or might not be available; neither does it represent that
has made any effort to identify any such rights. Information on
IETF's procedures with respect to rights in standards-track
standards-related documentation can be found in BCP-11. Copies
claims of rights made available for publication and any assurances
licenses to be made available, or the result of an attempt made
obtain a general license or permission for the use of
proprietary rights by implementors or users of this specification
be obtained from the IETF Secretariat
The IETF invites any interested party to bring to its attention
copyrights, patents or patent applications, or other
rights which may cover technology that may be required to
this standard. Please address the information to the IETF
Director
Partridge & Jackson Standards Track [Page 4]
RFC 2711 IPv6 Router Alert Option October 1999
7.0
[RFC-2119] Bradner, S., "Key words for use in RFC's to
Requirement Levels", BCP 14, RFC 2119, March 1977.
[RFC-2205] Braden, B. (ed.), Zhang, L., Berson, S., Herzog, S. and S
Jamin, "Resource ReSerVation Protocol (RSVP)", RFC 2205,
September 1997.
[RFC-2434] Narten, T. and H. Alvestrand, "Guidelines for Writing
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[RFC-2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC-2710] Deering, S., Fenner, W. and B. Haberman, "
Listener Discovery (MLD) for IPv6", RFC 2710,
1999.
6.0 Authors'
Craig
BBN
10 Moulton
Cambridge, MA 02138
Phone: +1 (617) 873-3000
EMail: craig@bbn.
Alden
BBN
10 Moulton
Cambridge, MA 02138
Phone: +1 (617) 873-3000
EMail: awjacks@bbn.
Partridge & Jackson Standards Track [Page 5]
RFC 2711 IPv6 Router Alert Option October 1999
7.0 Full Copyright
Copyright (C) The Internet Society (1999). All Rights Reserved
This document and translations of it may be copied and furnished
others, and derivative works that comment on or otherwise explain
or assist in its implementation may be prepared, copied,
and distributed, in whole or in part, without restriction of
kind, provided that the above copyright notice and this paragraph
included on all such copies and derivative works. However,
document itself may not be modified in any way, such as by
the copyright notice or references to the Internet Society or
Internet organizations, except as needed for the purpose
developing Internet standards in which case the procedures
copyrights defined in the Internet Standards process must
followed, or as required to translate it into languages other
English
The limited permissions granted above are perpetual and will not
revoked by the Internet Society or its successors or assigns
This document and the information contained herein is provided on
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED,
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE
Funding for the RFC Editor function is currently provided by
Internet Society
Partridge & Jackson Standards Track [Page 6]
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