Generic UDP Encapsulation for IP Tunneling
draft-ietf-tsvwg-gre-in-udp-encap-02
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| Document | Type | Active Internet-Draft (tsvwg WG) | |
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| Authors | Edward Crabbe , Lucy Yong , Xiaohu Xu | ||
| Last updated | 2014-07-01 | ||
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draft-ietf-tsvwg-gre-in-udp-encap-02
Network Working Group E. Crabbe, Ed.
Internet-Draft Google
Intended status: Standard Track L. Yong, Ed.
Huawei USA
X. Xu, Ed.
Huawei Technologies
Expires: January 2015 July 1, 2014
Generic UDP Encapsulation for IP Tunneling
draft-ietf-tsvwg-gre-in-udp-encap-02
Abstract
This document describes a method of encapsulating arbitrary
protocols within GRE and UDP headers. In this encapsulation, the
source UDP port may be used as an entropy field for purposes of load
balancing while the payload protocol may be identified by the GRE
Protocol Type.
Status of This Document
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
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."
This Internet-Draft will expire on January 1, 2015.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with
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respect to this document. Code Components extracted from this
document must include Simplified BSD License text as described in
Section 4.e of the Trust Legal Provisions and are provided without
warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction...................................................3
1.1. Applicability Statement...................................3
2. Terminology....................................................4
2.1. Requirements Language.....................................4
3. Procedures.....................................................4
4. Encapsulation Considerations...................................8
5. Backward Compatibility.........................................9
6. IANA Considerations............................................9
7. Security Considerations.......................................10
7.1. Vulnerability............................................10
8. Acknowledgements..............................................10
9. Contributors..................................................10
10. References...................................................11
10.1. Normative References....................................11
10.2. Informative References..................................12
11. Authors' Addresses...........................................13
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1. Introduction
Load balancing, or more specifically, statistical multiplexing of
traffic using Equal Cost Multi-Path (ECMP) and/or Link Aggregation
Groups (LAGs) in IP networks is a widely used technique for creating
higher capacity networks out of lower capacity links. Most existing
routers in IP networks are already capable of distributing IP
traffic flows over ECMP paths and/or LAGs on the basis of a hash
function performed on flow invariant fields in IP packet headers and
their payload protocol headers. Specifically, when the IP payload is
a User Datagram Protocol (UDP)[RFC0768] or Transmission Control
Protocol (TCP) packet, router hash functions frequently operate on
the five-tuple of the source IP address, the destination IP address,
the source port, the destination port, and the protocol/next-header
Several tunneling techniques are in common use in IP networks, such
as Generic Routing Encapsulation (GRE) [RFC2784], MPLS [RFC4023] and
L2TPv3 [RFC3931]. GRE is an increasingly popular encapsulation
choice, especially in environments where MPLS is unavailable or
unnecessary. Unfortunately, use of common GRE endpoints may reduce
the entropy available for use in load balancing, especially in
environments where the GRE Key field [RFC2890] is not readily
available for use as entropy in forwarding decisions.
This document defines a generic GRE-in-UDP encapsulation for
tunneling arbitrary network protocol payloads across an IP network
environment where ECMP or LAGs are used. The GRE header provides
payload protocol de-multiplexing by way of it's protocol type field
[RFC2784] while the UDP header provides additional entropy by way of
it's source port.
This encapsulation method requires no changes to the transit IP
network. Hash functions in most existing IP routers may utilize and
benefit from the use of a GRE-in-UDP tunnel is without needing any
change or upgrade to their ECMP implementation. The encapsulation
mechanism is applicable to a variety of IP networks including Data
Center and wide area networks.
1.1. Applicability Statement
It is recommended to use the GRE-in-UDP encapsulation technology in
a Service Provider (SP) network and/or DC network where the
congestion control is not a concern, rather than over the Internet
where the congestion control is a must.
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2. Terminology
The terms defined in [RFC768] are used in this document.
2.1. Requirements Language
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 [RFC2119].
3. Procedures
When a tunnel ingress device conforming to this document receives a
packet, the ingress MUST encapsulate the packet in UDP and GRE
headers and set the destination port of the UDP header to [TBD]
Section 6. The ingress device must also insert the payload protocol
type in the GRE Protocol Type field. The ingress device SHOULD set
the UDP source port based on flow invariant fields from the payload
header, otherwise it should be set to a randomly selected constant
value, e.g. zero, to avoid packet flow reordering. How a tunnel
ingress generates entropy from the payload is outside the scope of
this document. The tunnel ingress MUST encode its own IP address as
the source IP address and the egress tunnel endpoint IP address.
The TTL field in the IP header must be set to a value appropriate
for delivery of the encapsulated packet to the tunnel egress
endpoint.
When the tunnel egress receives a packet, it must remove the outer
UDP and GRE headers. Section 5 describes the error handling when
this entity is not instantiated at the tunnel egress.
To simplify packet processing at the tunnel egress, packets destined
to this assigned UDP destination port [TBD] MAY have their UDP
checksum set to zero. In the environment where the UDP packets may
be mis-delivered [RFC5405], UDP checksum SHOULD be used. Upon
receiving a packet with a non-zero checksum, tunnel egress MUST
perform the UDP checksum verification. For an IPv6 network, UDP
checksum SHOULD be used.
The tunnel ingress may set the GRE Key Present, Sequence Number
Present, and Checksum Present bits and associated fields in the GRE
header defined by [RFC2784] and [RFC2890].
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Congestion control is a critical aspect of proper network operation.
If only IP traffic is carried by a tunnel, there is no need to apply
any congestion control mechanism at tunnel endpoints as the end
hosts already have congestion control mechanisms available. If the
traffic end points do not provide any congestion control, but the
tunnel is used in an environment where congestion on the underlying
IP network is mitigated by some form of end to end traffic
engineering or scheduling, additional congestion control at tunnel
endpoints may be unnecessary. In the absence of either, a congestion
control mechanism SHOULD be implemented at the tunnel ingress and
egress. This is particularly important in the case of inter-domain
tunnels. Any potential congestion control mechanism [CB] to be
applied at tunnel endpoints is outside the scope of this draft.
The format of the GRE-in-UDP encapsulation for both IPv4 and IPv6
outer headers is shown in the following figures:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
IPv4 Header:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| IHL |Type of Service| Total Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification |Flags| Fragment Offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time to Live |Protcol=17(UDP)| Header Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
UDP Header:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port = XXXX | Dest Port = TBD |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| UDP Length | UDP Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
GRE Header:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|C| |K|S| Reserved0 | Ver | Protocol Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Checksum (optional) | Reserved1 (Optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number (Optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1 UDP+GRE IPv4 headers
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
IPv6 Header:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| Traffic Class | Flow Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload Length | NxtHdr=17(UDP)| Hop Limit |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Outer Source IPv6 Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Outer Destination IPv6 Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
UDP Header:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port = XXXX | Dest Port = TBD |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| UDP Length | UDP Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
GRE Header:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|C| |K|S| Reserved0 | Ver | Protocol Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Checksum (optional) | Reserved1 (Optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number (Optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2 UDP+GRE IPv6 headers
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The total overhead increase for a UDP+GRE tunnel without use of
optional GRE fields, representing the lowest total overhead increase,
is 32 bytes in the case of IPv4 and 52 bytes in the case of IPv6.
The total overhead increase for a UDP+GRE tunnel with use of GRE Key,
Sequence and Checksum Fields, representing the highest total
overhead increase, is 44 bytes in the case of IPv4 and 64 bytes in
the case of IPv6.
4. Encapsulation Considerations
GRE-in-UDP encapsulation is single tunnel mechanism where both GRE
and UDP header are required. The mechanism allows the tunneled
traffic to be unicast, broadcast, or multicast traffic. Entropy may
be generated from the header of tunneled unicast or
broadcast/multicast packets at tunnel ingress. The mapping mechanism
between the tunneled multicast traffic and the multicast capability
in the IP network is transparent and independent to the
encapsulation and is outside the scope of this document.
Tunnel ingress SHOULD perform the fragmentation [GREMTU] on a packet
before the encapsulation and factor in both GRE and UDP overhead
bytes in the effective Maximum Transmission Unit (MTU) size. Tunnel
ingress MUST use the same source UDP port for all packet fragments
to ensure that the transit routers will forward the packet fragments
on the same path. An operator should factor in the addition overhead
bytes when considering an MTU size for the payload to reduce the
likelihood of fragmentation.
To ensure the tunneled traffic gets the same treatment over the IP
network, prior to the encapsulation process, tunnel ingress should
process the payload to get the proper parameters to fill into the IP
header such as DiffServ [RFC2983]. Tunnel end points that support
ECN MUST use the method described in [RFC6040] for ECN marking
propagation. This process is outside of the scope of this document.
Note that the IPv6 header [RFC2460] contains a flow label field that
may be used for load balancing in an IPv6 network [RFC6438]. Thus
in an IPv6 network, either GRE-in-UDP or flow labels may be used for
improving load balancing performance. Use of GRE-in-UDP
encapsulation provides a unified hardware implementation for load
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balancing in an IP network independent of the IP version(s) in use.
However IPv6 network require performing the checksum, which may
impact network performance and user experience. Thus, a flow label
based load balancing may be a better approach in an IPv6 network.
5. Backward Compatibility
It is assumed that tunnel ingress routers must be upgraded in order
to support the encapsulations described in this document.
No change is required at transit routers to support forwarding of
the encapsulation described in this document.
If a router that is intended for use as a tunnel egress does not
support the GRE-in-UDP encapsulation described in this document, it
will not be listening on destination port [TBD]. In these cases,
the router will conform to normal UDP processing and respond to the
tunnel ingress with an ICMP message indicating "port unreachable"
according to [RFC792]. Upon receiving this ICMP message, the tunnel
ingress MUST NOT continue to use GRE-in-UDP encapsulation toward
this tunnel egress without management intervention.
6. IANA Considerations
IANA is requested to make the following allocation:
Service Name: GRE-in-UDP
Transport Protocol(s): UDP
Assignee: IESG <iesg@ietf.org>
Contact: IETF Chair <chair@ietf.org>
Description: GRE-in-UDP Encapsulation
Reference: [This.I-D]
Port Number: TBD
Service Code: N/A
Known Unauthorized Uses: N/A
Assignment Notes: N/A
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7. Security Considerations
7.1. Vulnerability
Neither UDP nor GRE encapsulation effects security for the payload
protocol. When using GRE-in-UDP, Network Security in a network is
the same as that of a network using GRE.
Use of ICMP for signaling of the GRE-in-UDP encapsulation capability
adds a security concern. Tunnel ingress devices may want to
validate the origin of ICMP Port Unreachable messages before taking
action. The mechanism for performing this validation is out of the
scope of this document.
In an instance where the UDP src port is not set based on the flow
invariant fields from the payload header, a random port SHOULD be
selected in order to minimize the vulnerability to off-path attacks.
[RFC6056] How the src port randomization occurs is outside scope of
this document.
Using one standardized value in UDP destination port for an
encapsulation indication may increase the vulnerability of off-path
attack. To overcome this, tunnel egress may request tunnel ingress
using a different and specific value [RFC6056] in UDP destination
port for the GRE-in-UDP encapsulation indication. How the tunnel end
points communicate the value is outside scope of this document.
8. Acknowledgements
Authors like to thank Vivek Kumar, Ron Bonica, Joe Touch, Ruediger
Geib, Gorry Fairhurst, David Black, Lar Edds, Lloyd, and many others
for their review and valuable input on this draft.
9. Contributors
The following people all contributed significantly to this document
and are listed below in alphabetical order:
John E. Drake
Juniper Networks
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Email: jdrake@juniper.net
Adrian Farrel
Juniper Networks
Email: adrian@olddog.co.uk
Vishwas Manral
Hewlett-Packard Corp.
3000 Hanover St, Palo Alto.
Email: vishwas.manral@hp.com
Carlos Pignataro
Cisco Systems
7200-12 Kit Creek Road
Research Triangle Park, NC 27709 USA
EMail: cpignata@cisco.com
Yongbing Fan
China Telecom
Guangzhou, China.
Phone: +86 20 38639121
Email: fanyb@gsta.com
10. References
10.1. Normative References
[RFC768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
August 1980.
[RFC791] DARPA, "Internet Protocol", RFC791, September 1981
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC2119, March 1997.
[RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
March 2000.
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[RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE",
RFC2890, September 2000.
[RFC2983] Black, D., "Differentiated Services and Tunnels", RFC2983,
October 2000.
[RFC5405] Eggert, L., "Unicast UDP Usage Guideline for Application
Designers", RFC5405, November 2008.
[RFC6040] Briscoe, B., "Tunneling of Explicit Congestion
Notification", RFC6040, November 2010
[RFC6438] Carpenter, B., Amante, S., "Using the IPv6 Flow Label for
Equal Cost Multipath Routing and Linda Aggregation in
tunnels", RFC6438, November, 2011
[RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and
UDP Checksums for Tunneled Packets", RFC 6935, April 2013.
[RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement
for the Use of IPv6 UDP Datagrams with Zero Checksums",
RFC 6936, April 2013.
10.2. Informative References
[RFC792] Postel, J., "Internet Control Message Protocol", STD 5, RFC
792, September 1981.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC3931] Lau, J., Townsley, M., and I. Goyret, "Layer Two Tunneling
Protocol - Version 3 (L2TPv3)", RFC 3931, March 2005.
[RFC4023] Worster, T., Rekhter, Y., and E. Rosen, "Encapsulating
MPLS in IP or Generic Routing Encapsulation (GRE)", RFC
4023, March 2005.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, February 2006.
[RFC4884] Bonica, R., Gan, D., Tappan, D., and C. Pignataro,
"Extended ICMP to Support Multi-Part Messages", RFC 4884,
April 2007.
[RFC6056] Larsen, M. and Gont, F., "Recommendations for Transport-
Protocol Port Randomization", RFC6056, January 2011
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[RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and
L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
RFC 6790, November 2012.
[GREMTU] Bonica, R., "A Fragmentation Strategy for Generic Routing
Encapsulation (GRE)", draft-bonica-intara-gre-mtu, work in
progress
[CB] Fairhurst, G., "Network Transport Circuit Breakers",
draft-fairhurst-tsvwg-circuit-breaker-01, work in progress
11. Authors' Addresses
Edward Crabbe (editor)
Google
1600 Amphitheatre Parkway
Mountain View, CA 94102
US
Lucy Yong (editor)
Huawei Technologies, USA
Email: lucy.yong@huawei.com
Xiaohu Xu (editor)
Huawei Technologies,
Beijing, China
Email: xuxiaohu@huawei.com
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