Network Working Group E. Crabbe, Ed.
Internet-Draft
Intended status: Standard Track L. Yong, Ed.
Huawei USA
X. Xu, Ed.
Huawei Technologies
Expires: April 2015 October 27, 2014
Generic UDP Encapsulation for IP Tunneling
draft-ietf-tsvwg-gre-in-udp-encap-03
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
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This Internet-Draft will expire on April 27, 2015.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Provisions Relating to IETF Documents
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publication of this document. Please review these documents
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respect to this document. Code Components extracted from this
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Table of Contents
1. Introduction...................................................3
1.1. Applicability Statement...................................3
2. Terminology....................................................4
2.1. Requirements Language.....................................4
3. Procedures.....................................................4
3.1. UDP checksum usage with IPv6..............................5
3.2. Middlebox Considerations for IPv6 UDP Zero Checksums......7
3.3. GRE-in-UDP Encapsulation Format...........................8
4. Encapsulation Considerations..................................10
5. Congestion Considerations.....................................11
6. Backward Compatibility........................................13
7. IANA Considerations...........................................13
8. Security Considerations.......................................13
8.1. Vulnerability............................................13
9. Acknowledgements..............................................14
10. Contributors.................................................14
11. References...................................................16
11.1. Normative References....................................16
11.2. Informative References..................................16
12. Authors' Addresses...........................................17
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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 GRE-in-UDP encapsulation within a Service
Provider (SP) network and/or DC network where the congestion control
is not a concern. However the encapsulation can apply to ISP
networks and/or Internet. Some environments request GRE-in-UDP
tunnel to run more functions than others.
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GRE-in-UDP encapsulation may be used to tunnel the tunneled traffic,
i.e. tunnel-in-tunnel. The tunneled traffic may use GRE-in-UDP or
other tunnel encapsulation. In this case, GRE-in-UDP tunnel end
points treat other tunnel endpoints as of the end hosts for the
traffic and do not differentiate such end hosts from other end hosts.
The use case and applicability for a GRE-in-UDP tunnel egress and
stacked tunnel egress terminate on the same IP address is for
further study.
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. In the case that ingress is unable to get the flow entropy
from the payload header, it should set a randomly selected constant
value for UDP source port to avoid payload packet flow reordering.
The value, for example, may be simply a result of boot-up time. 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.
For IPv4 UDP encapsulation, this field is RECOMMENDED to be set to
zero because the IPv4 header includes a checksum, and use of the UDP
checksum is optional with IPv4, unless checksum protection of
tunneled payload is important, see Section 6.
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For IPv6 UDP encapsulation, the IPv6 header does not include a
checksum, so this field MUST contain a UDP checksum that MUST be
used as specified in [RFC0768] and [RFC2460] unless one of the
exceptions that allows use of UDP zero-checksum mode (as specified
in [RFC6935]) applies. See Section 3.1 for specification of these
exceptions and additional requirements that apply when UDP zero-
checksum mode is used for GRE-in-UDP traffic over IPv6.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].
3.1. UDP checksum usage with IPv6
When UDP is used over IPv6, the UDP checksum is relied upon to
protect the IPv6 header from corruption, and MUST be used unless the
requirements in [RFC 6935] and [RFC 6936] for use of UDP zero-
checksum mode with a tunnel protocol are satisfied. Therefore, the
UDP checksum MUST be implemented and MUST be used in accordance with
[RFC0768] and [RFC2460] for GRE in UDP traffic over
IPv6 unless one of the following exceptions applies and the
additional requirements stated below are complied with. In addition,
use of the UDP checksum with IPv6 MUST be the default configuration
of all GRE-in-UDP implementations.
There are two exceptions that allow use of UDP zero-checksum mode
for IPv6 with GRE-in-UDP, subject to the additional requirements
stated below in this section. The two exceptions are:
o Use of GRE-in-UDP within a single service provider that utilizes
careful provisioning (e.g., rate limiting at the entries of the
network while over-provisioning network capacity) to ensure
against congestion and that actively monitors encapsulated
traffic for errors; or
o Use of GRE-in-UDP within a limited number of service providers
who closely cooperate in order to jointly provide this same
careful provisioning and monitoring.
As such, for IPv6, the UDP checksum for GRE-in-UDP MUST be used as
specified in [RFC0768] and [RFC2460] over the general Internet, and
over non-cooperating ISPs, even if each non-cooperating ISP
independently satisfies the first exception for UDP zero-checksum
mode usage with GRE-in-UDP over IPv6 within the ISP's own network.
Section 5 of RFC6936 [RFC6936] specifies the additional requirements
that implementation of UDP zero-checksum over IPv6 MUST compliant
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with. To compliant with it, the following additional requirements
apply to GRE-in-UDP implementation and use of UDP zero-checksum mode
over IPv6:
a. A GRE-in-UDP implementation MUST comply with all requirements
specified in Section 4 of [RFC6936] and with requirement 1
specified in Section 5 of [RFC6936].
b. A GRE-in-UDP receiver MUST check that the source and destination
IPv6 addresses are valid for the GRE-in-UDP tunnel and discard
any packet for which this check fails.
c. A GRE-in-UDP sender SHOULD use different IPv6 addresses for each
GRE-in-UDP tunnel that uses UDP zero-checksum mode in order to
strengthen the receiver's check of the IPv6 source address. When
this is not possible, it is RECOMMENDED to use each source IPv6
address for as few UDP zero-checksum mode MPLS-in-UDP tunnels as
is feasible.
d. GRE-in-UDP sender and receiver MUST agree the key(s) used over
the tunnel. The sender MUST insert a key on GRE header, and the
receiver MUST check if the key in GRE header is valid for the
tunnel and drop invalid packet.
e. A GRE-in-UDP receiver node SHOULD only enable the use of UDP
zero-checksum mode on a single UDP port and SHOULD NOT support
any other use UDP zero-checksum mode on any other UDP port.
f. A GRE-in-UDP sender SHOULD send GRE keepalive messages with a
zero UDP checksum. GRE-in-UDP receiver that discovers an
appreciable loss rate for keepalive packets MAY terminate the
tunnel.
g. GRE keepalive messages SHOULD include both UDP datagrams with a
checksum and datagrams with a zero UDP checksum. This will
enable the remote endpoint to distinguish between a path failure
and the dropping of datagrams with a zero UDP checksum.
h. Any middlebox support for MPLS-in-UDP with UDP zero-checksum mode
for IPv6 MUST comply with requirements 1 and 8-10 in Section 5 of
RFC 6936.
(Editor note: the design team and authors need further discuss above
requirements text)
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The above requirements are intended to be in addition to the
requirements specified in [RFC2460] as modified by [RFC6935] and the
requirements specified in [RFC6936].
GRE-in-UDP over IPv6 does not include an additional integrity check
because the above requirements in combination with the exceptions
that restrict use of UDP zero-checksum mode to well-managed networks
should not significantly increase the rate of corruption of UDP/GRE-
encapsulated traffic by comparison to GRE-encapsulated traffic over
similar well-managed networks and because GRE does not accumulate
incorrect state as a consequence of GRE header corruption.
Editor Note: The preceding paragraph addresses requirements 2-4 in
Section 5 of [RFC 6936]. Requirement 5 in that section is addressed
by the requirement e in this section. Requirements 6 and 7 in that
section are covered by the requirements f and g in this section.
Requirement 8-10 in that section is addressed by the requirement h
in this section.
In summary, UDP zero-checksum mode for IPv6 is allowed to be used
with GRE-in-UDP when one of the two exceptions specified above
applies, provided that additional requirements stated above are
complied with. Otherwise the UDP checksum MUST be used for IPv6 as
specified in [RFC0768] and [RFC2460].
This entire section and its requirements apply only to use of UDP
zero-checksum mode for IPv6; they can be avoided by using the UDP
checksum as specified in [RFC0768] and [RFC2460].
3.2. Middlebox Considerations for IPv6 UDP Zero Checksums
IPv6 datagrams with a zero UDP checksum will not be passed by any
middlebox that validates the checksum based on [RFC2460] or that
updates the UDP checksum field, such as NATs or firewalls. Changing
this behavior would require such middleboxes to be updated to
correctly handle datagrams with zero UDP checksums. The GRE-in-UDP
encapsulation does not provide a mechanism to safely fall back to
using a checksum when a path change occurs redirecting a tunnel over
a path that includes a middlebox that discards IPv6 datagrams with a
zero UDP checksum. In this case the GRE-in-UDP tunnel will be
black-holed by that middlebox. Recommended changes to allow
firewalls, NATs and other middleboxes to support use of an IPv6 zero
UDP checksum are described in Section 5 of [RFC6936].
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3.3. GRE-in-UDP Encapsulation Format
The format of the GRE-in-UDP encapsulation for both IPv4 and IPv6
outer headers is shown in the following figures:
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 used for 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.
The tunnel ingress SHOULD perform the fragmentation [GREMTU] on a
packet before the encapsulation and factor in both GRE and UDP
header bytes in the effective Maximum Transmission Unit (MTU) size.
Not performing the fragmentation will cause the packets exceeding
network MTU size to be dropped in the network. The 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
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improving load balancing performance. Use of GRE-in-UDP
encapsulation provides a unified hardware implementation for load
balancing in an IP network independent of the IP version(s) in use.
However IPv6 network require performing the UDP 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. Congestion Considerations
Section 3.1.3 of RFC 5405 [RFC5405] discussed the congestion
implications of UDP tunnels. As discussed in RFC 5405, because other
flows can share the path with one or more UDP tunnels, congestion
control [RFC2914] needs to be considered.
A major motivation for encapsulating GRE in UDP is to provide a
generic UDP tunnel protocol to tunnel a network protocol over IP
network and improve the use of multipath (such as Equal Cost
MultiPath, ECMP) in cases where traffic is to traverse routers which
are able to hash on UDP Port and IP address. As such, in many cases
this may reduce the occurrence of congestion and improve usage of
available network capacity. However, it is also necessary to ensure
that the network, including applications that use the network,
responds appropriately in more difficult cases, such as when link or
equipment failures have reduced the available capacity.
The impact of congestion must be considered both in terms of the
effect on the rest of the network of a UDP tunnel that is consuming
excessive capacity, and in terms of the effect on the flows using
the UDP tunnels. The potential impact of congestion from a UDP
tunnel depends upon what sort of traffic is carried over the tunnel,
as well as the path of the tunnel.
GRE in UDP as a generic UDP tunnel mechanism can be used to carry a
network protocol and traffic. If tunneled traffic is already
congestion controlled, GRE in UDP tunnel generally does not need
additional congestion control mechanisms. As specified in RFC 5405:
IP-based traffic is generally assumed to be congestion-controlled,
i.e., it is assumed that the transport protocols generating IP-based
traffic at the sender already employ mechanisms that are sufficient
to address congestion on the path. Consequently, a tunnel carrying.
IP-based traffic should already interact appropriately with other
traffic sharing the path, and specific congestion control mechanisms
for the tunnel are not necessary.
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For this reason, where GRE in UDP tunneling is used to carry IP
traffic that is known to be congestion controlled, the tunnel MAY be
used across any combination of a single service provider, multiple
cooperating service providers, or across the general Internet.
Internet IP traffic is generally assumed to be congestion-controlled.
However, GRE in UDP tunneling is also used in many cases to carry
traffic that is not necessarily congestion controlled. In such cases
service providers and data center operators may avoid congestion by
careful provisioning of their networks, by rate limiting of user
data traffic, and/or by using Traffic Engineering tools to monitor
the network segments and dynamically steers traffic away from the
potential congested link in time.
For this reason, where the GRE payload traffic is not congestion
controlled, GRE in UDP tunnels MUST only be used within a single
service provider that utilizes careful provisioning (e.g., rate
limiting at the entries of the network while over-provisioning
network capacity) to ensure against congestion, or within a limited
number of service providers who closely cooperate in order to
jointly provide this same careful provisioning.
As such, GRE in UDP MUST NOT be used over the general Internet, or
over non-cooperating ISPs, to carry traffic that is not congestion-
controlled.
Measures SHOULD be taken to prevent non-congestion-controlled GRE-
over-UDP traffic from "escaping" to the general Internet, e.g.:
o physical or logical isolation of the links carrying GRE-over-UDP
from the general Internet,
o deployment of packet filters that block the UDP ports assigned
for GRE-over-UDP,
o imposition of restrictions on GRE-over-UDP traffic by software
tools used to set up GRE-over-UDP tunnels between specific end
systems (as might be used within a single data center), and
o use of a "Managed Circuit Breaker" for the tunneled traffic as
described in [I-D.-tsvwg-circuit-breaker].
[Editor: the text in this section was derived from the text for
mpls-in-udp. More work necessary to make general for this]
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6. 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.
7. 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
8. Security Considerations
8.1. 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. Upon receiving an ICMP message and before
taking an action on it, the ingress MUST validate the IP address
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originating against tunnel egress address and MUST evaluate the
packet header returned in the ICMP payload to ensure the source port
is the one used for this tunnel. 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.
This document does not require that the tunnel egress validates the
IP source address of the tunneled packets (with the exception that
the IPv6 source address MUST be validated when UDP zero-checksum
mode is used with IPv6), but it should be understood that failure to
do so presupposes that there is effective destination-based (or a
combination of source-based and destination-based) filtering at the
boundaries.
9. 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.
Thank the design team led by David Black (members: Ross Callon,
Gorry Fairhurst, Xiaohu Xu, Lucy Yong) to efficiently work out the
descriptions for the congestion considerations and IPv6 UDP zero
checksum.
10. Contributors
The following people all contributed significantly to this document
and are listed below in alphabetical order:
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Ross Callon
Juniper Networks
10 Technology Park Drive
Westford, MA 01886
USA
Email: rcallon@juniper.net
David Black
EMC Corporation
176 South Street
Hopkinton, MA 01748
USA
Email: david.black@emc.com
John E. Drake
Juniper Networks
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.
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Phone: +86 20 38639121
Email: fanyb@gsta.com
11. References
11.1. 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.
[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 Link Aggregation in
tunnels", RFC6438, November, 2011
11.2. 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.
Crabbe, et al. [Page 16]
Internet-Draft Generic UDP Encapsulation for IP Tunneling October 2014
[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
[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
12. Authors' Addresses
Edward Crabbe (editor)
Email: edward.crabbe@gmail.com
Lucy Yong (editor)
Huawei Technologies, USA
Email: lucy.yong@huawei.com
Xiaohu Xu (editor)
Huawei Technologies,
Beijing, China
Email: xuxiaohu@huawei.com
Crabbe, et al. [Page 17]
Internet-Draft Generic UDP Encapsulation for IP Tunneling October 2014
Gorry's comments
- give an example of random constant value selection for UDP
source port in the case where tunnel ingress can't get flow
entropy
- use "MUST" instead of "SHOULD" for requesting use of UDP
checksum in IPv6 network
- more concise text for congestion description; use some text
in [RFC5405]
- State what consequence without doing fragmentation
- tunnel ingress actions upon receiving an ICMP msg
- tunnel-in-tunnel case
- CB does not describe the protocol to support CB, only the
mechanism. UDP report protocol may be good fit.
Crabbe, et al. [Page 18]
