Internet Engineering Task Force (IETF) X. Xu
Request for Comments: 7510 Huawei Technologies
Category: Standards Track N. Sheth
ISSN: 2070-1721 Juniper Networks
L. Yong
Huawei USA
R. Callon
Juniper Networks
D. Black
EMC Corporation
April 2015
Encapsulating MPLS in UDP
Abstract
This document specifies an IP-based encapsulation for MPLS, called
MPLS-in-UDP for situations where UDP (User Datagram Protocol)
encapsulation is preferred to direct use of MPLS, e.g., to enable
UDP-based ECMP (Equal-Cost Multipath) or link aggregation. The MPLS-
in-UDP encapsulation technology must only be deployed within a single
network (with a single network operator) or networks of an adjacent
set of cooperating network operators where traffic is managed to
avoid congestion, rather than over the Internet where congestion
control is required. Usage restrictions apply to MPLS-in-UDP usage
for traffic that is not congestion controlled and to UDP zero
checksum usage with IPv6.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7510.
Xu, et al. Standards Track [Page 1]RFC 7510 Encapsulating MPLS in UDP April 2015
Copyright Notice
Copyright (c) 2015 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 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. Existing Encapsulations . . . . . . . . . . . . . . . . . 3
1.2. Motivations for MPLS-in-UDP Encapsulation . . . . . . . . 4
1.3. Applicability Statements . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Encapsulation in UDP . . . . . . . . . . . . . . . . . . . . 5
3.1. UDP Checksum Usage with IPv6 . . . . . . . . . . . . . . 6
3.2. Middlebox Considerations for IPv6 UDP Zero Checksums . . 10
4. Processing Procedures . . . . . . . . . . . . . . . . . . . . 10
5. Congestion Considerations . . . . . . . . . . . . . . . . . . 11
6. Security Considerations . . . . . . . . . . . . . . . . . . . 13
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
8.1. Normative References . . . . . . . . . . . . . . . . . . 15
8.2. Informative References . . . . . . . . . . . . . . . . . 16
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 17
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
Xu, et al. Standards Track [Page 2]RFC 7510 Encapsulating MPLS in UDP April 2015
1. Introduction
This document specifies an IP-based encapsulation for MPLS, i.e.,
MPLS-in-UDP, which is applicable in some circumstances where IP-based
encapsulation for MPLS is required and further fine-grained load
balancing of MPLS packets over IP networks over Equal-Cost Multipath
(ECMP) and/or Link Aggregation Groups (LAGs) is required as well.
There are already IP-based encapsulations for MPLS that allow for
fine-grained load balancing by using some special field in the
encapsulation header as an entropy field. However, MPLS-in-UDP can
be advantageous since networks have used the UDP port number fields
as a basis for load-balancing solutions for some time.
Like other IP-based encapsulation methods for MPLS, this
encapsulation allows for two Label Switching Routers (LSR) to be
adjacent on a Label Switched Path (LSP), while separated by an IP
network. In order to support this encapsulation, each LSR needs to
know the capability to decapsulate MPLS-in-UDP by the remote LSRs.
This specification defines only the data-plane encapsulation and does
not concern itself with how the knowledge to use this encapsulation
is conveyed. Specifically, this capability can be either manually
configured on each LSR or dynamically advertised in manners that are
outside the scope of this document.
Similarly, the MPLS-in-UDP encapsulation format defined in this
document by itself cannot ensure the integrity and privacy of data
packets being transported through the MPLS-in-UDP tunnels and cannot
enable the tunnel decapsulators to authenticate the tunnel
encapsulator. Therefore, in the case where any of the above security
issues is concerned, the MPLS-in-UDP SHOULD be secured with IPsec
[RFC4301] or Datagram Transport Layer Security (DTLS) [RFC6347]. For
more details, please see Section 6 (Security Considerations).
1.1. Existing Encapsulations
Currently, there are several IP-based encapsulations for MPLS such as
MPLS-in-IP, MPLS-in-GRE (Generic Routing Encapsulation) [RFC4023],
and MPLS-in-L2TPv3 (Layer 2 Tunneling Protocol Version 3) [RFC4817].
In all these methods, the IP addresses can be varied to achieve load
balancing.
All these IP-based encapsulations for MPLS are specified for both
IPv4 and IPv6. In the case of IPv6-based encapsulations, the IPv6
Flow Label can be used for ECMP and LAGs [RFC6438]. However, there
is no such entropy field in the IPv4 header.
Xu, et al. Standards Track [Page 3]
RFC 7510 Encapsulating MPLS in UDP April 2015
For MPLS-in-GRE as well as MPLS-in-L2TPv3, protocol fields (the GRE
Key and the L2TPv3 Session ID, respectively) can be used as the load-
balancing key as described in [RFC5640]. For this, intermediate
routers need to understand these fields in the context of being used
as load-balancing keys.
1.2. Motivations for MPLS-in-UDP Encapsulation
Most existing routers in IP networks are already capable of
distributing IP traffic "microflows" [RFC2474] over ECMPs and/or LAG
based on the hash of the five-tuple of UDP [RFC768] and TCP packets
(i.e., source IP address, destination IP address, source port,
destination port, and protocol). By encapsulating the MPLS packets
into a UDP tunnel and using the source port of the UDP header as an
entropy field, the existing load-balancing capability as mentioned
above can be leveraged to provide fine-grained load balancing of MPLS
traffic over IP networks.
1.3. Applicability Statements
The MPLS-in-UDP encapsulation technology MUST only be deployed within
a single network (with a single network operator) or networks of an
adjacent set of cooperating network operators where traffic is
managed to avoid congestion, rather than over the Internet where
congestion control is required. Furthermore, packet filters SHOULD
be added to prevent MPLS-in-UDP packets from escaping from the
network due to misconfiguration or packet errors.
2. Terminology
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 [RFC2119].
Xu, et al. Standards Track [Page 4]
RFC 7510 Encapsulating MPLS in UDP April 2015
3. Encapsulation in UDP
MPLS-in-UDP encapsulation format is shown as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port = Entropy | Dest Port = MPLS |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| UDP Length | UDP Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ MPLS Label Stack ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
~ Message Body ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Source Port of UDP
This field contains a 16-bit entropy value that is generated by
the encapsulator to uniquely identify a flow. What constitutes
a flow is locally determined by the encapsulator and therefore
is outside the scope of this document. What algorithm is
actually used by the encapsulator to generate an entropy value
is outside the scope of this document.
In case the tunnel does not need entropy, this field of all
packets belonging to a given flow SHOULD be set to a randomly
selected constant value so as to avoid packet reordering.
To ensure that the source port number is always in the range
49152 to 65535 (note that those ports less than 49152 are
reserved by IANA to identify specific applications/protocols),
which may be required in some cases, instead of calculating a
16-bit hash, the encapsulator SHOULD calculate a 14-bit hash
and use those 14 bits as the least significant bits of the
source port field. Also, the most significant two bits SHOULD
be set to binary 11. That still conveys 14 bits of entropy
information, which would be enough in practice.
Destination Port of UDP
This field is set to a value (6635) allocated by IANA to
indicate that the UDP tunnel payload is an MPLS packet.
Xu, et al. Standards Track [Page 5]RFC 7510 Encapsulating MPLS in UDP April 2015
UDP Length
The usage of this field is in accordance with the current UDP
specification [RFC768].
UDP Checksum
For IPv4 UDP encapsulation, this field is RECOMMENDED to be set
to zero for performance or implementation reasons because the
IPv4 header includes a checksum and use of the UDP checksum is
optional with IPv4, unless checksum protection of VPN labels is
important (see Section 6). 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
[RFC768] 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 MPLS-in-UDP traffic over IPv6.
MPLS Label Stack
This field contains an MPLS Label Stack as defined in
[RFC3032].
Message Body
This field contains one MPLS message body.
3.1. UDP Checksum Usage with IPv6
When UDP is used over IPv6, the UDP checksum is relied upon to
protect both the IPv6 and UDP headers from corruption and MUST be
used unless the requirements in [RFC6935] and [RFC6936] for use of
UDP zero-checksum mode with a tunnel protocol are satisfied. MPLS-
in-UDP is a tunnel protocol, and there is significant successful
deployment of MPLS-in-IPv6 without UDP (i.e., without a checksum that
covers the IPv6 header or the MPLS label stack), as described in
Section 3.1 of [RFC6936]:
There is extensive experience with deployments using tunnel
protocols in well-managed networks (e.g., corporate networks and
service provider core networks). This has shown the robustness of
methods such as Pseudowire Emulation Edge-to-Edge (PWE3) and MPLS
that do not employ a transport protocol checksum and that have not
specified mechanisms to protect from corruption of the unprotected
headers (such as the VPN Identifier in MPLS).
Xu, et al. Standards Track [Page 6]RFC 7510 Encapsulating MPLS in UDP April 2015
The UDP checksum MUST be implemented and MUST be used in accordance
with [RFC768] and [RFC2460] for MPLS-in-UDP traffic over IPv6 unless
one or more of the following exceptions applies and the additional
requirements stated below are complied with. There are three
exceptions that allow use of UDP zero-checksum mode for IPv6 with
MPLS-in-UDP, subject to the additional requirements stated below in
this section. The three exceptions are:
a. Use of MPLS-in-UDP in networks under single administrative
control (such as within a single operator's network) where it is
known (perhaps through knowledge of equipment types and lower-
layer checks) that packet corruption is exceptionally unlikely
and where the operator is willing to take the risk of undetected
packet corruption.
b. Use of MPLS-in-UDP in networks under single administrative
control (such as within a single operator's network) where it is
judged through observational measurements (perhaps of historic or
current traffic flows that use a non-zero checksum) that the
level of packet corruption is tolerably low and where the
operator is willing to take the risk of undetected packet
corruption.
c. Use of MPLS-in-UDP for traffic delivery for applications that are
tolerant of misdelivered or corrupted packets (perhaps through
higher-layer checksum, validation, and retransmission or
transmission redundancy) where the operator is willing to rely on
the applications using the tunnel to survive any corrupt packets.
These exceptions may also be extended to the use of MPLS-in-UDP
within a set of closely cooperating network administrations (such as
network operators who have agreed to work together in order to
jointly provide specific services). Even when one of the above
exceptions applies, use of UDP checksums may be appropriate when VPN
services are provided over MPLS-in-UDP; see Section 6.
As such, for IPv6, the UDP checksum for MPLS-in-UDP MUST be used as
specified in [RFC768] and [RFC2460] for tunnels that span multiple
networks whose network administrations do not cooperate closely, even
if each non-cooperating network administration independently
satisfies one or more of the exceptions for UDP zero-checksum mode
usage with MPLS-in-UDP over IPv6.
The following additional requirements apply to implementation and use
of UDP zero-checksum mode for MPLS-in-UDP over IPv6:
a. Use of the UDP checksum with IPv6 MUST be the default
configuration of all MPLS-in-UDP implementations.
Xu, et al. Standards Track [Page 7]RFC 7510 Encapsulating MPLS in UDP April 2015
b. The MPLS-in-UDP implementation MUST comply with all requirements
specified in Section 4 of [RFC6936] and with requirement 1
specified in Section 5 of [RFC6936].
c. The tunnel decapsulator SHOULD only allow the use of UDP zero-
checksum mode for IPv6 on a single received UDP Destination Port
regardless of the encapsulator. The motivation for this
requirement is possible corruption of the UDP Destination Port,
which may cause packet delivery to the wrong UDP port. If that
other UDP port requires the UDP checksum, the misdelivered packet
will be discarded
d. The tunnel decapsulator MUST check that the source and
destination IPv6 addresses are valid for the MPLS-in-UDP tunnel
on which the packet was received if that tunnel uses UDP zero-
checksum mode and discard any packet for which this check fails.
e. The tunnel encapsulator SHOULD use different IPv6 addresses for
each MPLS-in-UDP tunnel that uses UDP zero-checksum mode
(regardless of decapsulator) in order to strengthen the
decapsulator's check of the IPv6 source address (i.e., the same
IPv6 source address SHOULD NOT be used with more than one IPv6
destination address, independent of whether that destination
address is a unicast or multicast 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 (i.e., with as
few destination IPv6 addresses) as is feasible.
f. 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
[RFC6936].
g. Measures SHOULD be taken to prevent IPv6 traffic with zero UDP
checksums from "escaping" to the general Internet; see Section 5
for examples of such measures.
h. IPv6 traffic with zero UDP checksums MUST be actively monitored
for errors by the network operator.
The above requirements do not change either the requirements
specified in [RFC2460] as modified by [RFC6935] or the requirements
specified in [RFC6936].
The requirement to check the source IPv6 address in addition to the
destination IPv6 address, plus the strong recommendation against
reuse of source IPv6 addresses among MPLS-in-UDP tunnels collectively
provide some mitigation for the absence of UDP checksum coverage of
the IPv6 header. In addition, the MPLS data plane only forwards
Xu, et al. Standards Track [Page 8]RFC 7510 Encapsulating MPLS in UDP April 2015
packets with valid labels (i.e., labels that have been distributed by
the tunnel egress LSR), providing some additional opportunity to
detect MPLS-in-UDP packet misdelivery when the misdelivered packet
contains a label that is not valid for forwarding at the receiving
LSR. The expected result for IPv6 UDP zero-checksum mode for MPLS-
in-UDP is that corruption of the destination IPv6 address will
usually cause packet discard, as offsetting corruptions to the source
IPv6 and/or MPLS top label are unlikely. Additional assurance is
provided by the restrictions in the above exceptions that limit usage
of IPv6 UDP zero-checksum mode to well-managed networks for which
MPLS packet corruption has not been a problem in practice.
Hence, MPLS-in-UDP is suitable for transmission over lower layers in
the well-managed networks that are allowed by the exceptions stated
above, and the rate of corruption of the inner IP packet on such
networks is not expected to increase by comparison to MPLS traffic
that is not encapsulated in UDP. For these reasons, MPLS-in-UDP does
not provide an additional integrity check when UDP zero-checksum mode
is used with IPv6, and this design is in accordance with requirements
2, 3, and 5 specified in Section 5 of [RFC6936].
MPLS does not accumulate incorrect state as a consequence of label
stack corruption. A corrupt MPLS label results in either packet
discard or forwarding (and forgetting) of the packet without
accumulation of MPLS protocol state. Active monitoring of MPLS-in-
UDP traffic for errors is REQUIRED as occurrence of errors will
result in some accumulation of error information outside the MPLS
protocol for operational and management purposes. This design is in
accordance with requirement 4 specified in Section 5 of [RFC6936].
The remaining requirements specified in Section 5 of [RFC6936] are
inapplicable to MPLS-in-UDP. Requirements 6 and 7 do not apply
because MPLS does not have an MPLS-generic control feedback
mechanism. Requirements 8-10 are middlebox requirements that do not
apply to MPLS-in-UDP tunnel endpoints, but see Section 3.2 for
further middlebox discussion.
In summary, UDP zero-checksum mode for IPv6 is allowed to be used
with MPLS-in-UDP when one of the three exceptions specified above
applies, provided that the additional requirements specified in this
section are complied with. Otherwise, the UDP checksum MUST be used
for IPv6 as specified in [RFC768] 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 [RFC768] and [RFC2460].
Xu, et al. Standards Track [Page 9]
RFC 7510 Encapsulating MPLS in UDP April 2015
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 MPLS-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 MPLS-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].
4. Processing Procedures
This MPLS-in-UDP encapsulation causes MPLS packets to be forwarded
through "UDP tunnels". When performing MPLS-in-UDP encapsulation by
the encapsulator, the entropy value would be generated by the
encapsulator and then be filled in the Source Port field of the UDP
header. The Destination Port field is set to a value (6635)
allocated by IANA to indicate that the UDP tunnel payload is an MPLS
packet. As for whether the top label of the encapsulated MPLS packet
is downstream-assigned or upstream-assigned, it is determined
according to the following criteria, which are compatible with
[RFC5332]:
a. If the tunnel destination IP address is a unicast address, the
top label MUST be downstream-assigned;
b. If the tunnel destination IP address is an IP multicast address,
either all encapsulated MPLS packets in the particular tunnel
have a downstream-assigned label at the top of the stack, or all
encapsulated MPLS packets in that tunnel have an upstream-
assigned label at the top of the stack. The means by which this
is determined for a particular tunnel is outside the scope of
this specification. In the absence of any knowledge about a
specific tunnel, the label SHOULD be presumed to be upstream-
assigned.
Intermediate routers, upon receiving these UDP encapsulated packets,
could balance these packets based on the hash of the five-tuple of
UDP packets. Upon receiving these UDP-encapsulated packets, the
decapsulator would decapsulate them by removing the UDP headers and
then process them accordingly. For other common processing
procedures associated with tunneling encapsulation technologies
including but not limited to Maximum Transmission Unit (MTU) and
Xu, et al. Standards Track [Page 10]RFC 7510 Encapsulating MPLS in UDP April 2015
preventing fragmentation and reassembly, Time to Live (TTL), and
differentiated services, the corresponding "Common Procedures"
defined in [RFC4023], which are applicable for MPLS-in-IP and
MPLS-in-GRE encapsulation formats SHOULD be followed.
Note: Each UDP tunnel is unidirectional, as MPLS-in-UDP traffic is
sent to the IANA-allocated UDP Destination Port, and in particular,
is never sent back to any port used as a UDP Source Port (which
serves solely as a source of entropy). This is at odds with a
typical middlebox (e.g., firewall) assumption that bidirectional
traffic uses a common pair of UDP ports. As a result, arranging to
pass bidirectional MPLS-in-UDP traffic through middleboxes may
require separate configuration for each direction of traffic.
5. Congestion Considerations
Section 3.1.3 of [RFC5405] discussed the congestion implications of
UDP tunnels. As discussed in [RFC5405], 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 MPLS in UDP is to improve the
use of multipath (such as ECMP) in cases where traffic is to traverse
routers that 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.
MPLS is widely used to carry an extensive range of traffic. In many
cases, MPLS is used to carry IP traffic. IP traffic is generally
assumed to be congestion controlled, and thus a tunnel carrying
general IP traffic (as might be expected to be carried across the
Internet) generally does not need additional congestion control
mechanisms. As specified in [RFC5405]:
Xu, et al. Standards Track [Page 11]
RFC 7510 Encapsulating MPLS in UDP April 2015
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.
For this reason, where MPLS-in-UDP tunneling is used to carry IP
traffic that is known to be congestion controlled, the UDP tunnels
MAY be used within a single network or across multiple networks, with
cooperating network operators. Internet IP traffic is generally
assumed to be congestion controlled. Similarly, in general, Layer 3
VPNs are carrying IP traffic that is similarly assumed to be
congestion controlled.
Whether or not Layer 2 VPN traffic is congestion controlled may
depend upon the specific services being offered and what use is being
made of the Layer 2 services.
However, MPLS is also used in many cases to carry traffic that is not
necessarily congestion controlled. For example, MPLS may be used to
carry pseudowire or VPN traffic where specific bandwidth guarantees
are provided to each pseudowire or to each VPN.
In such cases, network operators may avoid congestion by careful
provisioning of their networks, by rate limiting of user data
traffic, and/or by using MPLS Traffic Engineering (MPLS-TE) to assign
specific bandwidth guarantees to each LSP. Where MPLS is carried
over UDP over IP, the identity of each individual MPLS flow is lost,
in general, and MPLS-TE cannot be used to guarantee bandwidth to
specific flows (since many LSPs may be multiplexed over a single UDP
tunnel, and many UDP tunnels may be mixed in an IP network).
For this reason, where the MPLS traffic is not congestion controlled,
MPLS-in-UDP tunnels MUST only be used within a single operator's
network 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 networks
whose operators closely cooperate in order to jointly provide this
same careful provisioning.
As such, MPLS-in-UDP MUST NOT be used over the general Internet, or
over non-cooperating network operators, to carry traffic that is not
congestion controlled.
Xu, et al. Standards Track [Page 12]RFC 7510 Encapsulating MPLS in UDP April 2015
Measures SHOULD be taken to prevent non-congestion-controlled MPLS-
in-UDP traffic from "escaping" to the general Internet, e.g.:
a. Physical or logical isolation of the links carrying MPLS-over-UDP
from the general Internet.
b. Deployment of packet filters that block the UDP Destination Ports
used for MPLS-over-UDP.
c. Imposition of restrictions on MPLS-in-UDP traffic by software
tools used to set up MPLS-in-UDP tunnels between specific end
systems (as might be used within a single data center).
d. Use of a "Managed Circuit Breaker" for the MPLS traffic as
described in [CIRCUIT-BREAKER].
6. Security Considerations
The security problems faced with the MPLS-in-UDP tunnel are exactly
the same as those faced with MPLS-in-IP and MPLS-in-GRE tunnels
[RFC4023]. In other words, the MPLS-in-UDP tunnel as defined in this
document by itself cannot ensure the integrity and privacy of data
packets being transported through the MPLS-in-UDP tunnel and cannot
enable the tunnel decapsulator to authenticate the tunnel
encapsulator. In the case where any of the above security issues is
concerned, the MPLS-in-UDP tunnel SHOULD be secured with IPsec or
DTLS. IPsec was designed as a network security mechanism, and
therefore it resides at the network layer. As such, if the tunnel is
secured with IPsec, the UDP header would not be visible to
intermediate routers anymore in either IPsec tunnel or transport
mode. As a result, the meaning of adopting the MPLS-in-UDP tunnel as
an alternative to the MPLS-in-GRE or MPLS-in-IP tunnel is lost. By
comparison, DTLS is better suited for application security and can
better preserve network- and transport-layer protocol information.
Specifically, if DTLS is used, the destination port of the UDP header
MUST be set to an IANA-assigned value (6636) indicating MPLS-in-UDP
with DTLS, and that UDP port MUST NOT be used for other traffic. The
UDP source port field can still be used to add entropy, e.g., for
load-sharing purposes. DTLS usage is limited to a single DTLS
session for any specific tunnel encapsulator/decapsulator pair
(identified by source and destination IP addresses). Both IP
addresses MUST be unicast addresses -- multicast traffic is not
supported when DTLS is used. An MPLS-in-UDP tunnel decapsulator
implementation that supports DTLS is expected to be able to establish
DTLS sessions with multiple tunnel encapsulators. Likewise, an MPLS-
in-UDP tunnel encapsulator implementation is expected to be able to
establish DTLS sessions with multiple decapsulators. (However,
Xu, et al. Standards Track [Page 13]RFC 7510 Encapsulating MPLS in UDP April 2015
different source and/or destination IP addresses may be involved.
See Section 3.1 for discussion of one situation where use of
different source IP addresses is important.)
If the tunnel is not secured with IPsec or DTLS, some other method
should be used to ensure that packets are decapsulated and forwarded
by the tunnel tail only if those packets were encapsulated by the
tunnel head. If the tunnel lies entirely within a single
administrative domain, address filtering at the boundaries can be
used to ensure that no packet with the IP source address of a tunnel
endpoint or with the IP destination address of a tunnel endpoint can
enter the domain from outside. However, when the tunnel head and the
tunnel tail are not in the same administrative domain, this may
become difficult, and filtering based on the destination address can
even become impossible if the packets must traverse the public
Internet. Sometimes only source address filtering (but not
destination address filtering) is done at the boundaries of an
administrative domain. If this is the case, the filtering does not
provide effective protection at all unless the decapsulator of an
MPLS-in-UDP validates the IP source address of the packet.
This document does not require that the decapsulator validate 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. MPLS-based VPN services rely on a VPN label in the MPLS
label stack to identify the VPN. Corruption of that label could leak
traffic across VPN boundaries. Such leakage is highly undesirable
when inter-VPN isolation is used for privacy or security reasons.
When that is the case, UDP checksums SHOULD be used for MPLS-in-UDP
with both IPv4 and IPv6, and in particular, UDP zero-checksum mode
SHOULD NOT be used with IPv6. Each UDP checksum covers the VPN
label, thereby providing increased assurance of isolation among VPNs.
Xu, et al. Standards Track [Page 14]
RFC 7510 Encapsulating MPLS in UDP April 2015
7. IANA Considerations
One UDP destination port number indicating MPLS has been allocated by
IANA:
Service Name: MPLS-UDP
Transport Protocol(s): UDP
Assignee: IESG <iesg@ietf.org>
Contact: IETF Chair <chair@ietf.org>.
Description: Encapsulate MPLS packets in UDP tunnels.
Reference: RFC 7510
Port Number: 6635
One UDP destination port number indicating MPLS with DTLS has been
allocated by IANA:
Service Name: MPLS-UDP-DTLS
Transport Protocol(s): UDP
Assignee: IESG <iesg@ietf.org>
Contact: IETF Chair <chair@ietf.org>.
Description: Encapsulate MPLS packets in UDP tunnels with DTLS.
Reference: RFC 7510
Port Number: 6636
8. References
8.1. Normative References
[RFC768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
August 1980, <http://www.rfc-editor.org/info/rfc768>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
Xu, et al. Standards Track [Page 15]RFC 7510 Encapsulating MPLS in UDP April 2015
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998,
<http://www.rfc-editor.org/info/rfc2460>.
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, January 2001,
<http://www.rfc-editor.org/info/rfc3032>.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005,
<http://www.rfc-editor.org/info/rfc4301>.
[RFC5332] Eckert, T., Rosen, E., Ed., Aggarwal, R., and Y. Rekhter,
"MPLS Multicast Encapsulations", RFC 5332, August 2008,
<http://www.rfc-editor.org/info/rfc5332>.
[RFC5405] Eggert, L. and G. Fairhurst, "Unicast UDP Usage Guidelines
for Application Designers", BCP 145, RFC 5405, November
2008, <http://www.rfc-editor.org/info/rfc5405>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, January 2012,
<http://www.rfc-editor.org/info/rfc6347>.
[RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and
UDP Checksums for Tunneled Packets", RFC 6935, April 2013,
<http://www.rfc-editor.org/info/rfc6935>.
[RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement
for the Use of IPv6 UDP Datagrams with Zero Checksums",
RFC 6936, April 2013,
<http://www.rfc-editor.org/info/rfc6936>.
8.2. Informative References
[CIRCUIT-BREAKER]
Fairhurst, G., "Network Transport Circuit Breakers", Work
in Progress, draft-ietf-tsvwg-circuit-breaker-01, April
2015.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474, December
1998, <http://www.rfc-editor.org/info/rfc2474>.
Xu, et al. Standards Track [Page 16]RFC 7510 Encapsulating MPLS in UDP April 2015
[RFC2914] Floyd, S., "Congestion Control Principles", BCP 41, RFC
2914, September 2000,
<http://www.rfc-editor.org/info/rfc2914>.
[RFC4023] Worster, T., Rekhter, Y., and E. Rosen, Ed.,
"Encapsulating MPLS in IP or Generic Routing Encapsulation
(GRE)", RFC 4023, March 2005,
<http://www.rfc-editor.org/info/rfc4023>.
[RFC4817] Townsley, M., Pignataro, C., Wainner, S., Seely, T., and
J. Young, "Encapsulation of MPLS over Layer 2 Tunneling
Protocol Version 3", RFC 4817, March 2007,
<http://www.rfc-editor.org/info/rfc4817>.
[RFC5640] Filsfils, C., Mohapatra, P., and C. Pignataro, "Load-
Balancing for Mesh Softwires", RFC 5640, August 2009,
<http://www.rfc-editor.org/info/rfc5640>.
[RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label
for Equal Cost Multipath Routing and Link Aggregation in
Tunnels", RFC 6438, November 2011,
<http://www.rfc-editor.org/info/rfc6438>.
Acknowledgements
Thanks to Shane Amante, Dino Farinacci, Keshava A K, Ivan Pepelnjak,
Eric Rosen, Andrew G. Malis, Kireeti Kompella, Marshall Eubanks,
George Swallow, Loa Andersson, Vivek Kumar, Stewart Bryant, Wen
Zhang, Joel M. Halpern, Noel Chiappa, Scott Brim, Alia Atlas,
Alexander Vainshtein, Joel Jaeggli, Edward Crabbe, Mark Tinka, Lars
Eggert, Joe Touch, Lloyd Wood, Gorry Fairhurst, Weiguo Hao, Mark
Szczesniak, Stephen Farrell, Martin Stiemerling, Zhenxiao Liu, and
Xing Tong for their valuable comments and suggestions on this
document.
Special thanks to Alia Atlas for her insightful suggestion of adding
an applicability statement.
Thanks to Daniel King, Gregory Mirsky, and Eric Osborne for their
valuable MPLS-RT reviews on this document. Thanks to Charlie Kaufman
for his SecDir review of this document. Thanks to Nevil Brownlee for
the OPS-Dir review of this document. Thanks to Roni Even for the
Gen-ART review of this document. Thanks to Pearl Liang for the IANA
review of this document.
Xu, et al. Standards Track [Page 17]RFC 7510 Encapsulating MPLS in UDP April 2015
Contributors
Note that contributors are listed in alphabetical order according to
their last names.
Yongbing Fan
China Telecom
EMail: fanyb@gsta.com
Adrian Farrel
Juniper Networks
EMail: adrian@olddog.co.uk
Zhenbin Li
Huawei Technologies
EMail: lizhenbin@huawei.com
Carlos Pignataro
Cisco Systems
EMail: cpignata@cisco.com
Curtis Villamizar
Outer Cape Cod Network Consulting, LLC
EMail: curtis@occnc.com
Xu, et al. Standards Track [Page 18]RFC 7510 Encapsulating MPLS in UDP April 2015
Authors' Addresses
Xiaohu Xu
Huawei Technologies
No.156 Beiqing Rd
Beijing 100095
China
Phone: +86-10-60610041
EMail: xuxiaohu@huawei.com
Nischal Sheth
Juniper Networks
1194 N. Mathilda Ave
Sunnyvale, CA 94089
United States
EMail: nsheth@juniper.net
Lucy Yong
Huawei USA
EMail: Lucy.yong@huawei.com
Ross Callon
Juniper Networks
EMail: rcallon@juniper.net
David Black
EMC Corporation
176 South Street
Hopkinton, MA 01748
United States
EMail: david.black@emc.com
Xu, et al. Standards Track [Page 19]
