Specification", RFC 2473, December 1998.
[4] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. Traina,
"Generic Routing Encapsulation (GRE)", RFC 2784, March 2000.
[5] Lau, J., Townsley, M., and I. Goyret, "Layer Two Tunneling
Protocol - Version 3 (L2TPv3)", RFC 3931, March 2005.
[6] Kent, S. and K. Seo, "Security Architecture for the Internet
Protocol", RFC 4301, December 2005.
[7] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
November 1990.
[8] McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery for
IP version 6", RFC 1981, August 1996.
[9] Braden, R., "Requirements for Internet Hosts - Communication
Layers", STD 3, RFC 1122, October 1989.
[10] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
Specification", RFC 2460, December 1998.
7.2. Informative References
[11] Mamakos, L., Lidl, K., Evarts, J., Carrel, D., Simone, D., and
R. Wheeler, "A Method for Transmitting PPP Over Ethernet
(PPPoE)", RFC 2516, February 1999.
[12] Mathis, M., "Fragmentation Considered Very Harmful", Work in
Progress, July 2004.
[13] Mathis, M. and J. Heffner, "Path MTU Discovery", Work in
Progress, March 2006.
[14] Medina, A., Allman, M., and S. Floyd, "Measuring the Evolution
of Transport Protocols in the Internet", Computer
Communications Review, Apr 2005, <http://www.icir.org/tbit/>.
[15] Miller, I., "Protection Against a Variant of the Tiny Fragment
Attack (RFC 1858)", RFC 3128, June 2001.
[16] Gont, F., "ICMP attacks against TCP", Work in Progress,
February 2006.
Appendix A. MTU of the Tunnel
Different tunneling mechanisms may treat the tunnel links as having
different kinds of MTU values. Some might use the same default MTU
as for other interfaces; some others might use the default MTU minus
the expected IP overhead (e.g., 20, 28, or 40 bytes); some others
might even treat the tunnel as having an "infinite MTU", e.g., 64
kilobytes.
As [2] describes, having an infinite MTU, i.e., always fragmenting
the outer packet (and never the inner packet) and never performing
PMTUD for the tunnel path, is a very bad idea, especially in
host-to-router scenarios. (It could be argued that if the nodes are
sure that this is a host-to-host tunnel, a larger MTU might make
sense if fragmentation and reassembly are more efficient than just
sending properly sized packets -- but this seems like a stretch.)
Author’s Address
Pekka Savola
CSC/FUNET
Espoo
Finland
EMail: psavola@funet.fi
Full Copyright Statement
Copyright (C) The Internet Society (2006).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM 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.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Acknowledgement
Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).