Network Working Group M. Andrews
Internet-Draft ISC
Updates: RFC 3542 December 13, 2011
(if approved)
Intended status: Informational
Expires: June 15, 2012
Forcing Fragmentation of IPv6 Packets
draft-andrews-6man-force-fragmentation-00
Abstract
Extend The Advanced Sockets API for IPv6 (RFC 3542) to provide a
mechanism to force a Fragment header to be added to a packet.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
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This Internet-Draft will expire on June 15, 2012.
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Table of Contents
1. Background . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Reserved Words . . . . . . . . . . . . . . . . . . . . . . 3
2. Extend IPV6_USE_MIN_MTU . . . . . . . . . . . . . . . . . . . . 3
3. Extend IPV6_DONTFRAG . . . . . . . . . . . . . . . . . . . . . 3
4. Add IPV6_DOFRAG . . . . . . . . . . . . . . . . . . . . . . . . 3
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 4
7. Normative References . . . . . . . . . . . . . . . . . . . . . 4
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 4
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1. Background
In order to avoid PMTUD [RFC 1191] in IPv6 an application must not
only force packets to be fragmented at the network MTU it must also
force the addition of a Fragment header to unfragmented packets
otherwise PTB ICMPv6 may be sent if the packet goes through a IPv6 to
IPv4 translating router [RFC 2460].
The Advanced Sockets API for IPv6 [RFC 3542] provides mechanisms to
force fragmentation of packet greater than the network MTU
(IPV6_USE_MIN_MTU). It also provides mechanisms to prevent
fragmentation of a packet (IPV6_DONTFRAG). It however does not
provide a mechanism to force a fragmentation header to be added.
This document intends to add such a mechanism.
There appears to be 3 viable alternatives. 1) extend IPV6_USE_MIN_MTU
to force the inclusion of a Fragment header. 2) extend IPV6_DONTFRAG
to signal that a Fragment header needs to be included. 3) add a new
socket option like IPV6_DOFRAG.
1.1. Reserved Words
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC 2119].
2. Extend IPV6_USE_MIN_MTU
If IPV6_USE_MIN_MTU is set to 1 then a Fragment header MUST be added
to both multicast and unicast packets.
If IPV6_USE_MIN_MTU is set to -1 then a Fragment header MUST be added
to multicast packets.
3. Extend IPV6_DONTFRAG
If IPV6_DONTFRAG is set to -1 (new value) then a Fragment header MUST
be added to the packet.
4. Add IPV6_DOFRAG
This is similar to IPV6_USE_MIN_MTU in that it is a tri-state flag.
When set to -1 a Fragment header MUST be added to multicast packets.
When set to 1 a Fragment header MUST be added to both multicast and
unicast packets. When set to 0 a Fragment header is only added if
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fragmentation would otherwise happen.
int on = 1;
setsockopt(fd, IPPROTO_IPV6, IPV6_DOFRAG, &on, sizeof(on));
Setting IPV6_DONTFRAG to 1 will force IPV6_DOFRAG to 0.
Setting IPV6_DOFRAG to 1 or -1 will force IPV6_DONTFRAG to 0.
5. IANA Considerations
No IANA Considerations.
6. Security Considerations
TBA
7. Normative References
[RFC 1191]
Mogul, J. and S. Deering, "Path MTU Discovery", RFC 1191,
November 1990.
[RFC 2119]
Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC 2460]
Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC 3542]
Stevens, W., Thomas, M., Normark, E., and T. Jinmei,
"Advanced Sockets Application Program Interface (API) for
IPv6", RFC 2003, May 2003.
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Author's Address
Mark Andrews
Internet Systems Consortium
950 Charter Street
Redwood City, CA 94063
US
Email: marka@isc.org
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