💾 Archived View for gmi.noulin.net › rfc › rfc5565.gmi captured on 2022-04-29 at 01:31:00. Gemini links have been rewritten to link to archived content
⬅️ Previous capture (2022-01-08)
-=-=-=-=-=-=-
Keywords: [--------]
Network Working Group J. Wu
Request for Comments: 5565 Y. Cui
Category: Standards Track Tsinghua University
C. Metz
E. Rosen
Cisco Systems, Inc.
June 2009
Softwire Mesh Framework
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (c) 2009 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 in effect on the date of
publication of this document (http://trustee.ietf.org/license-info).
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document.
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Wu, et al. Standards Track [Page 1]
RFC 5565 Softwire Mesh Framework June 2009
Abstract
The Internet needs to be able to handle both IPv4 and IPv6 packets.
However, it is expected that some constituent networks of the
Internet will be "single-protocol" networks. One kind of single-
protocol network can parse only IPv4 packets and can process only
IPv4 routing information; another kind can parse only IPv6 packets
and can process only IPv6 routing information. It is nevertheless
required that either kind of single-protocol network be able to
provide transit service for the "other" protocol. This is done by
passing the "other kind" of routing information from one edge of the
single-protocol network to the other, and by tunneling the "other
kind" of data packet from one edge to the other. The tunnels are
known as "softwires". This framework document explains how the
routing information and the data packets of one protocol are passed
through a single-protocol network of the other protocol. The
document is careful to specify when this can be done with existing
technology and when it requires the development of new or modified
technology.
Table of Contents
1. Introduction ....................................................3
2. Specification of Requirements ...................................6
3. Scenarios of Interest ...........................................7
3.1. IPv6-over-IPv4 Scenario ....................................7
3.2. IPv4-over-IPv6 Scenario ....................................9
4. General Principles of the Solution .............................10
4.1. E-IP and I-IP .............................................10
4.2. Routing ...................................................10
4.3. Tunneled Forwarding .......................................11
5. Distribution of Inter-AFBR Routing Information .................11
6. Softwire Signaling .............................................13
7. Choosing to Forward through a Softwire .........................15
8. Selecting a Tunneling Technology ...............................15
9. Selecting the Softwire for a Given Packet ......................16
10. Softwire OAM and MIBs .........................................17
10.1. Operations and Maintenance (OAM) .........................17
10.2. MIBs .....................................................18
11. Softwire Multicast ............................................18
11.1. One-to-One Mappings ......................................18
11.1.1. Using PIM in the Core .............................19
11.1.2. Using mLDP and Multicast MPLS in the Core .........20
11.2. MVPN-Like Schemes ........................................21
12. Inter-AS Considerations .......................................22
13. Security Considerations .......................................23
13.1. Problem Analysis .........................................23
13.2. Non-Cryptographic Techniques .............................24
Wu, et al. Standards Track [Page 2]
RFC 5565 Softwire Mesh Framework June 2009
13.3. Cryptographic Techniques .................................26
14. References ....................................................27
14.1. Normative References .....................................27
14.2. Informative References ...................................28
15. Contributors ..................................................30
16. Acknowledgments ...............................................30
1. Introduction
The routing information in any IP backbone network can be thought of
as being in one of two categories: "internal routing information" or
"external routing information". The internal routing information
consists of routes to the nodes that belong to the backbone, and to
the interfaces of those nodes. External routing information consists
of routes to destinations beyond the backbone, especially
destinations to which the backbone is not directly attached. In
general, BGP [RFC4271] is used to distribute external routing
information, and an Interior Gateway Protocol (IGP) such as OSPF
[RFC2328] or IS-IS [RFC1195] is used to distribute internal routing
information.
Often an IP backbone will provide transit routing services for
packets that originate outside the backbone and whose destinations
are outside the backbone. These packets enter the backbone at one of
its "edge routers". They are routed through the backbone to another
edge router, after which they leave the backbone and continue on
their way. The edge nodes of the backbone are often known as
"Provider Edge" (PE) routers. The term "ingress" (or "ingress PE")
refers to the router at which a packet enters the backbone, and the
term "egress" (or "egress PE") refers to the router at which it
leaves the backbone. Interior nodes are often known as "P routers".
Routers that are outside the backbone but directly attached to it are
known as "Customer Edge" (CE) routers. (This terminology is taken
from [RFC4364].)
When a packet's destination is outside the backbone, the routing
information that is needed within the backbone in order to route the
packet to the proper egress is, by definition, external routing
information.
Traditionally, the external routing information has been distributed
by BGP to all the routers in the backbone, not just to the edge
routers (i.e., not just to the ingress and egress points). Each of
the interior nodes has been expected to look up the packet's
destination address and route it towards the egress point. This is
known as "native forwarding": the interior nodes look into each
packet's header in order to match the information in the header with
the external routing information.
Wu, et al. Standards Track [Page 3]
RFC 5565 Softwire Mesh Framework June 2009
It is, however, possible to provide transit services without
requiring that all the backbone routers have the external routing
information. The routing information that BGP distributes to each
ingress router specifies the egress router for each route. The
ingress router can therefore "tunnel" the packet directly to the
egress router. "Tunneling the packet" means putting on some sort of
encapsulation header that will force the interior routers to forward
the packet to the egress router. The original packet is known as the
"encapsulation payload". The P routers do not look at the packet
header of the payload but only at the encapsulation header. Since
the path to the egress router is part of the internal routing
information of the backbone, the interior routers then do not need to
know the external routing information. This is known as "tunneled
forwarding". Of course, before the packet can leave the egress, it
has to be decapsulated.
The scenario where the P routers do not have external routes is
sometimes known as a "BGP-free core". That is something of a
misnomer, though, since the crucial aspect of this scenario is not
that the interior nodes don't run BGP, but that they don't maintain
the external routing information.
In recent years, we have seen this scenario deployed to support VPN
services, as specified in [RFC4364]. An edge router maintains
multiple independent routing/addressing spaces, one for each VPN to
which it interfaces. However, the routing information for the VPNs
is not maintained by the interior routers. In most of these
scenarios, MPLS is used as the encapsulation mechanism for getting
the packets from ingress to egress. There are some deployments in
which an IP-based encapsulation, such as L2TPv3 (Layer 2 Transport
Protocol) [RFC3931] or GRE (Generic Routing Encapsulation) [RFC2784]
is used.
This same technique can also be useful when the external routing
information consists not of VPN routes, but of "ordinary" Internet
routes. It can be used any time it is desired to keep external
routing information out of a backbone's interior nodes, or in fact
any time it is desired for any reason to avoid the native forwarding
of certain kinds of packets.
This framework focuses on two such scenarios.
1. In this scenario, the backbone's interior nodes support only
IPv6. They do not maintain IPv4 routes at all, and are not
expected to parse IPv4 packet headers. Yet, it is desired to
use such a backbone to provide transit services for IPv4
packets. Therefore, tunneled forwarding of IPv4 packets is
Wu, et al. Standards Track [Page 4]
RFC 5565 Softwire Mesh Framework June 2009
required. Of course, the edge nodes must have the IPv4 routes,
but the ingress must perform an encapsulation in order to get
an IPv4 packet forwarded to the egress.
2. This scenario is the reverse of scenario 1, i.e., the
backbone's interior nodes support only IPv4, but it is desired
to use the backbone for IPv6 transit.
In these scenarios, a backbone whose interior nodes support only one
of the two address families is required to provide transit services
for the other. The backbone's edge routers must, of course, support
both address families. We use the term "Address Family Border
Router" (AFBR) to refer to these PE routers. The tunnels that are
used for forwarding are referred to as "softwires".
These two scenarios are known as the "Softwire Mesh Problem"
[SW-PROB], and the framework specified in this document is therefore
known as the "Softwire Mesh Framework". In this framework, only the
AFBRs need to support both address families. The CE routers support
only a single address family, and the P routers support only the
other address family.
It is possible to address these scenarios via a large variety of
tunneling technologies. This framework does not mandate the use of
any particular tunneling technology. In any given deployment, the
choice of tunneling technology is a matter of policy. The framework
accommodates at least the use of MPLS ([RFC3031], [RFC3032]) -- both
LDP-based (Label Distribution Protocol, [RFC5036]) and RSVP-TE-based
(Resource Reservation Protocol - Traffic Engineering, [RFC3209]) --
L2TPv3 [RFC3931], GRE [RFC2784], and IP-in-IP [RFC2003]. The
framework will also accommodate the use of IPsec tunneling, when that
is necessary in order to meet security requirements.
It is expected that, in many deployments, the choice of tunneling
technology will be made by a simple expression of policy, such as
"always use IP-IP tunnels", or "always use LDP-based MPLS", or
"always use L2TPv3".
However, other deployments may have a mixture of routers, some of
which support, say, both GRE and L2TPv3, but others of which support
only one of those techniques. It is desirable therefore to allow the
network administration to create a small set of classes, and to
configure each AFBR to be a member of one or more of these classes.
Then the routers can advertise their class memberships to each other,
and the encapsulation policies can be expressed as, e.g., "use L2TPv3
to tunnel to routers in class X; use GRE to tunnel to routers in
Wu, et al. Standards Track [Page 5]
RFC 5565 Softwire Mesh Framework June 2009
class Y". To support such policies, it is necessary for the AFBRs to
be able to advertise their class memberships; a standard way of doing
this must be developed.
Policy may also require a certain class of traffic to receive a
certain quality of service, and this may impact the choice of tunnel
and/or tunneling technology used for packets in that class. This
needs to be accommodated by the Softwire Mesh Framework.
The use of tunneled forwarding often requires that some sort of
signaling protocol be used to set up and/or maintain the tunnels.
Many of the tunneling technologies accommodated by this framework
already have their own signaling protocols. However, some do not,
and in some cases the standard signaling protocol for a particular
tunneling technology may not be appropriate (for one or another
reason) in the scenarios of interest. In such cases (and in such
cases only), new signaling methodologies need to be defined and
standardized.
In this framework, the softwires do not form an overlay topology that
is visible to routing; routing adjacencies are not maintained over
the softwires, and routing control packets are not sent through the
softwires. Routing adjacencies among backbone nodes (including the
edge nodes) are maintained via the native technology of the backbone.
There is already a standard routing method for distributing external
routing information among AFBRs, namely BGP. However, in the
scenarios of interest, we may be using IPv6-based BGP sessions to
pass IPv4 routing information, and we may be using IPv4-based BGP
sessions to pass IPv6 routing information. Furthermore, when IPv4
traffic is to be tunneled over an IPv6 backbone, it is necessary to
encode the "BGP next hop" for an IPv4 route as an IPv6 address, and
vice versa. The method for encoding an IPv4 address as the next hop
for an IPv6 route is specified in [V6NLRI-V4NH]; the method for
encoding an IPv6 address as the next hop for an IPv4 route is
specified in [V4NLRI-V6NH].
2. Specification of Requirements
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].
Wu, et al. Standards Track [Page 6]
RFC 5565 Softwire Mesh Framework June 2009
3. Scenarios of Interest
3.1. IPv6-over-IPv4 Scenario
In this scenario, the client networks run IPv6 but the backbone
network runs IPv4. This is illustrated in Figure 1.
+--------+ +--------+
| IPv6 | | IPv6 |
| Client | | Client |
| Network| | Network|
+--------+ +--------+
| \ / |
| \ / |
| \ / |
| X |
| / \ |
| / \ |
| / \ |
+--------+ +--------+
| AFBR | | AFBR |
+--| IPv4/6 |---| IPv4/6 |--+
| +--------+ +--------+ |
+--------+ | | +--------+
| IPv4 | | | | IPv4 |
| Client | | | | Client |
| Network|------| IPv4 |-------| Network|
+--------+ | only | +--------+
| |
| +--------+ +--------+ |
+--| AFBR |---| AFBR |--+
| IPv4/6 | | IPv4/6 |
+--------+ +--------+
| \ / |
| \ / |
| \ / |
| X |
| / \ |
| / \ |
| / \ |
+--------+ +--------+
| IPv6 | | IPv6 |
| Client | | Client |
| Network| | Network|
+--------+ +--------+
Figure 1: IPv6-over-IPv4 Scenario
Wu, et al. Standards Track [Page 7]
RFC 5565 Softwire Mesh Framework June 2009
The IPv4 transit core may or may not run MPLS. If it does, MPLS may
be used as part of the solution.
While Figure 1 does not show any "backdoor" connections among the
client networks, this framework assumes that there will be such
connections. That is, there is no assumption that the only path
between two client networks is via the pictured transit-core network.
Hence, the routing solution must be robust in any kind of topology.
Many mechanisms for providing IPv6 connectivity across IPv4 networks
have been devised over the past ten years. A number of different
tunneling mechanisms have been used, some provisioned manually, and
others based on special addressing. More recently, L3VPN (Layer 3
Virtual Private Network) techniques from [RFC4364] have been extended
to provide IPv6 connectivity, using MPLS in the AFBRs and,
optionally, in the backbone [V6NLRI-V4NH]. The solution described in
this framework can be thought of as a superset of [V6NLRI-V4NH], with
a more generalized scheme for choosing the tunneling (softwire)
technology. In this framework, MPLS is allowed -- but not required
-- even at the AFBRs. As in [V6NLRI-V4NH], there is no manual
provisioning of tunnels, and no special addressing is required.
Wu, et al. Standards Track [Page 8]
RFC 5565 Softwire Mesh Framework June 2009
3.2. IPv4-over-IPv6 Scenario
In this scenario, the client networks run IPv4 but the backbone
network runs IPv6. This is illustrated in Figure 2.
+--------+ +--------+
| IPv4 | | IPv4 |
| Client | | Client |
| Network| | Network|
+--------+ +--------+
| \ / |
| \ / |
| \ / |
| X |
| / \ |
| / \ |
| / \ |
+--------+ +--------+
| AFBR | | AFBR |
+--| IPv4/6 |---| IPv4/6 |--+
| +--------+ +--------+ |
+--------+ | | +--------+
| IPv6 | | | | IPv6 |
| Client | | | | Client |
| Network|------| IPv6 |-------| Network|
+--------+ | only | +--------+
| |
| +--------+ +--------+ |
+--| AFBR |---| AFBR |--+
| IPv4/6 | | IPv4/6 |
+--------+ +--------+
| \ / |
| \ / |
| \ / |
| X |
| / \ |
| / \ |
| / \ |
+--------+ +--------+
| IPv4 | | IPv4 |
| Client | | Client |
| Network| | Network|
+--------+ +--------+
Figure 2: IPv4-over-IPv6 Scenario
The IPv6 transit core may or may not run MPLS. If it does, MPLS may
be used as part of the solution.
Wu, et al. Standards Track [Page 9]
RFC 5565 Softwire Mesh Framework June 2009
While Figure 2 does not show any "backdoor" connections among the
client networks, this framework assumes that there will be such
connections. That is, there is no assumption that the only path
between two client networks is via the pictured transit-core network.
Hence, the routing solution must be robust in any kind of topology.
While the issue of IPv6-over-IPv4 has received considerable attention
in the past, the scenario of IPv4-over-IPv6 has not. Yet, it is a
significant emerging requirement, as a number of service providers
are building IPv6 backbone networks and do not wish to provide native
IPv4 support in their core routers. These service providers have a
large legacy of IPv4 networks and applications that need to operate
across their IPv6 backbone. Solutions for this do not exist yet
because it had always been assumed that the backbone networks of the
foreseeable future would be dual stack.
4. General Principles of the Solution
This section gives a very brief overview of the procedures. The
subsequent sections provide more detail.
4.1. E-IP and I-IP
In the following sections, we use the term "I-IP" (Internal IP) to
refer to the form of IP (i.e., either IPv4 or IPv6) that is supported
by the transit network. We use the term "E-IP" (External IP) to
refer to the form of IP that is supported by the client networks.
In the scenarios of interest, E-IP is IPv4 if and only if I-IP is
IPv6, and E-IP is IPv6 if and only if I-IP is IPv4.
We assume that the P routers support only I-IP. That is, they are
expected to have only I-IP routing information, and they are not
expected to be able to parse E-IP headers. We similarly assume that
the CE routers support only E-IP.
The AFBRs handle both I-IP and E-IP. However, only I-IP is used on
AFBR's "core-facing interfaces", and E-IP is only used on its client-
facing interfaces.
4.2. Routing
The P routers and the AFBRs of the transit network participate in an
IGP for the purposes of distributing I-IP routing information.
The AFBRs use Internal BGP (IBGP) to exchange E-IP routing
information with each other. Either there is a full mesh of IBGP
connections among the AFBRs, or else some or all of the AFBRs are
clients of a BGP Route Reflector. Although these IBGP connections
Wu, et al. Standards Track [Page 10]
RFC 5565 Softwire Mesh Framework June 2009
are used to pass E-IP routing information (i.e., the Network Layer
Reachability Information (NLRI) of the BGP updates is in the E-IP
address family), the IBGP connections run over I-IP, and the BGP next
hop for each E-IP NLRI is in the I-IP address family.
4.3. Tunneled Forwarding
When an ingress AFBR receives an E-IP packet from a client-facing
interface, it looks up the packet's destination IP address. In the
scenarios of interest, the best match for that address will be a BGP-
distributed route whose next hop is the I-IP address of another AFBR,
the egress AFBR.
The ingress AFBR must forward the packet through a tunnel (i.e,
through a softwire) to the egress AFBR. This is done by
encapsulating the packet, using an encapsulation header that the P
routers can process and that will cause the P routers to send the
packet to the egress AFBR. The egress AFBR then extracts the
payload, i.e., the original E-IP packet, and forwards it further by
looking up its IP destination address.
Several kinds of tunneling technologies are supported. Some of those
technologies require explicit AFBR-to-AFBR signaling before the
tunnel can be used, others do not.
Transmitting a packet through a softwire always requires that an
encapsulation header be added to the original packet. The resulting
packet is therefore always longer than the encapsulation payload. As
an operational matter, the Maximum Transmission Unit (MTU) of the
softwire's path SHOULD be large enough so that (a) no packet will
need to be fragmented before being encapsulated, and (b) no
encapsulated packet will need to be fragmented while it is being
forwarded along a softwire. A general discussion of MTU issues in
the context of tunneled forwarding may be found in [RFC4459].
5. Distribution of Inter-AFBR Routing Information
AFBRs peer with routers in the client networks to exchange routing
information for the E-IP family.
AFBRs use BGP to distribute the E-IP routing information to each
other. This can be done by an AFBR-AFBR mesh of IBGP sessions, but
more likely is done through a BGP Route Reflector, i.e., where each
AFBR has an IBGP session to one or two Route Reflectors rather than
to other AFBRs.
Wu, et al. Standards Track [Page 11]
RFC 5565 Softwire Mesh Framework June 2009
The BGP sessions between the AFBRs, or between the AFBRs and the
Route Reflector, will run on top of the I-IP address family. That
is, if the transit core supports only IPv6, the IBGP sessions used to
distribute IPv4 routing information from the client networks will run
over IPv6; if the transit core supports only IPv4, the IBGP sessions
used to distribute IPv6 routing information from the client networks
will run over IPv4. The BGP sessions thus use the native networking
layer of the core; BGP messages are NOT tunneled through softwires or
through any other mechanism.
In BGP, a routing update associates an address prefix (or more
generally, NLRI) with the address of a BGP next hop (NH). The NLRI
is associated with a particular address family. The NH address is
also associated with a particular address family, which may be the
same as or different than the address family associated with the
NLRI. Generally, the NH address belongs to the address family that
is used to communicate with the BGP speaker to whom the NH address
belongs.
Since routing updates that contain information about E-IP address
prefixes are carried over BGP sessions that use I-IP transport, and
since the BGP messages are not tunneled, a BGP update providing
information about an E-IP address prefix will need to specify a next
hop address in the I-IP family.
Due to a variety of historical circumstances, when the NLRI and the
NH in a given BGP update are of different address families, it is not
always obvious how the NH should be encoded. There is a different
encoding procedure for each pair of address families.
In the case where the NLRI is in the IPv6 address family, and the NH
is in the IPv4 address family, [V6NLRI-V4NH] explains how to encode
the NH.
In the case where the NLRI is in the IPv4 address family, and the NH
is in the IPv6 address family, [V4NLRI-V6NH] explains how to encode
the NH.
If a BGP speaker sends an update for an NLRI in the E-IP family, and
the update is being sent over a BGP session that is running on top of
the I-IP network layer, and the BGP speaker is advertising itself as
the NH for that NLRI, then the BGP speaker MUST, unless explicitly
overridden by policy, specify the NH address in the I-IP family. The
address family of the NH MUST NOT be changed by a Route Reflector.
In some cases (e.g., when [V4NLRI-V6NH] is used), one cannot follow
this rule unless one's BGP peers have advertised a particular BGP
capability. This leads to the following softwire deployment
Wu, et al. Standards Track [Page 12]
RFC 5565 Softwire Mesh Framework June 2009
restriction: if a BGP capability is defined for the case in which an
E-IP NLRI has an I-IP NH, all the AFBRs in a given transit core MUST
advertise that capability.
If an AFBR has multiple IP addresses, the network administrators
usually have considerable flexibility in choosing which one the AFBR
uses to identify itself as the next hop in a BGP update. However, if
the AFBR expects to receive packets through a softwire of a
particular tunneling technology, and if the AFBR is known to that
tunneling technology via a specific IP address, then that same IP
address must be used to identify the AFBR in the next hop field of
the BGP updates. For example, if L2TPv3 tunneling is used, then the
IP address that the AFBR uses when engaging in L2TPv3 signaling must
be the same as the IP address it uses to identify itself in the next
hop field of a BGP update.
In [V6NLRI-V4NH], IPv6 routing information is distributed using the
labeled IPv6 address family. This allows the egress AFBR to
associate an MPLS label with each IPv6 address prefix. If an ingress
AFBR forwards packets through a softwire that can carry MPLS packets,
each data packet can carry the MPLS label corresponding to the IPv6
route that it matched. This may be useful at the egress AFBR, for
demultiplexing and/or enhanced performance. It is also possible to
do the same for the IPv4 address family, i.e., to use the labeled
IPv4 address family instead of the IPv4 address family. The use of
the labeled IP address families in this manner is OPTIONAL.
6. Softwire Signaling
A mesh of inter-AFBR softwires spanning the transit core must be in
place before packets can flow between client networks. Given N dual-
stack AFBRs, this requires N^2 "point-to-point IP" or "label switched
path" (LSP) tunnels. While in theory these could be configured
manually, that would result in a very undesirable O(N^2) provisioning
problem. Therefore, manual configuration of point-to-point tunnels
is not considered part of this framework.
Because the transit core is providing layer 3 transit services,
point-to-point tunnels are not required by this framework;
multipoint-to-point tunnels are all that is needed. In a multipoint-
to-point tunnel, when a packet emerges from the tunnel there is no
way to tell which router put the packet into the tunnel. This models
the native IP forwarding paradigm, wherein the egress router cannot
determine a given packet's ingress router. Of course, point-to-point
tunnels might be required for some reason beyond the basic
requirements described in this document. For example, Quality of
Wu, et al. Standards Track [Page 13]
RFC 5565 Softwire Mesh Framework June 2009
Service (QoS) or security considerations might require the use of
point-to-point tunnels. So point-to-point tunnels are allowed, but
not required, by this framework.
If it is desired to use a particular tunneling technology for the
softwires, and if that technology has its own "native" signaling
methodology, the presumption is that the native signaling will be
used. This would certainly apply to MPLS-based softwires, where LDP
or RSVP-TE would be used. An IPsec-based softwire would use standard
IKEv2 (Internet Key Exchange) [RFC4306] and IPsec [RFC4301]
signaling, as that is necessary in order to guarantee the softwire's
security properties.
A GRE-based softwire might or might not require signaling, depending
on whether various optional GRE header fields are to be used. GRE
does not have any "native" signaling, so for those cases, a signaling
procedure needs to be developed to support softwires.
Another possible softwire technology is L2TPv3. While L2TPv3 does
have its own native signaling, that signaling sets up point-to-point
tunnels. For the purpose of softwires, it is better to use L2TPv3 in
a multipoint-to-point mode, and this requires a different kind of
signaling.
The signaling to be used for GRE and L2TPv3 to cover these scenarios
is BGP-based, and is described in [RFC5512].
If IP-IP tunneling is used, or if GRE tunneling is used without
options, no signaling is required, as the only information needed by
the ingress AFBR to create the encapsulation header is the IP address
of the egress AFBR, and that is distributed by BGP.
When the encapsulation IP header is constructed, there may be fields
in the IP whose value is determined neither by whatever signaling has
been done nor by the distributed routing information. The values of
these fields are determined by policy in the ingress AFBR. Examples
of such fields may be the TTL (Time to Live) field, the DSCP
(Diffserv Service Classes) bits, etc.
It is desirable for all necessary softwires to be fully set up before
the arrival of any packets that need to go through the softwires.
That is, the softwires should be "always on". From the perspective
of any particular AFBR, the softwire endpoints are always BGP next
hops of routes that the AFBR has installed. This suggests that any
necessary softwire signaling should either be done as part of normal
system startup (as would happen, e.g., with LDP-based MPLS) or else
Wu, et al. Standards Track [Page 14]
RFC 5565 Softwire Mesh Framework June 2009
be triggered by the reception of BGP routing information (such as is
described in [RFC5512]); it is also helpful if distribution of the
routing information that serves as the trigger is prioritized.
7. Choosing to Forward through a Softwire
The decision to forward through a softwire, instead of to forward
natively, is made by the ingress AFBR. This decision is a matter of
policy.
In many cases, the policy will be very simple. Some useful policies
are:
- If routing says that an E-IP packet has to be sent out a core-
facing interface to an I-IP core, then send the packet through a
softwire.
- If routing says that an E-IP packet has to be sent out an
interface that only supports I-IP packets, then send the E-IP
packet through a softwire.
- If routing says that the BGP next hop address for an E-IP packet
is an I-IP address, then send the E-IP packet through a softwire.
- If the route that is the best match for a particular packet's
destination address is a BGP-distributed route, then send the
packet through a softwire (i.e., tunnel all BGP-routed packets).
More complicated policies are also possible, but a consideration of
those policies is outside the scope of this document.
8. Selecting a Tunneling Technology
The choice of tunneling technology is a matter of policy configured
at the ingress AFBR.
It is envisioned that, in most cases, the policy will be a very
simple one, and will be the same at all the AFBRs of a given transit
core -- e.g., "always use LDP-based MPLS" or "always use L2TPv3".
However, other deployments may have a mixture of routers, some of
which support, say, both GRE and L2TPv3, but others of which support
only one of those techniques. It is desirable therefore to allow the
network administration to create a small set of classes and to
configure each AFBR to be a member of one or more of these classes.
Then the routers can advertise their class memberships to each other,
and the encapsulation policies can be expressed as, e.g., "use L2TPv3
to talk to routers in class X; use GRE to talk to routers in class
Wu, et al. Standards Track [Page 15]
RFC 5565 Softwire Mesh Framework June 2009
Y". To support such policies, it is necessary for the AFBRs to be
able to advertise their class memberships. [RFC5512] specifies a way
in which an AFBR may advertise, to other AFBRS, various
characteristics that may be relevant to the policy (e.g., "I belong
to class Y"). In many cases, these characteristics can be
represented by arbitrarily selected communities or extended
communities, and the policies at the ingress can be expressed in
terms of these classes (i.e., communities).
Policy may also require a certain class of traffic to receive a
certain quality of service, and this may impact the choice of tunnel
and/or tunneling technology used for packets in that class. This
framework allows a variety of tunneling technologies to be used for
instantiating softwires. The choice of tunneling technology is a
matter of policy, as discussed in Section 1.
While in many cases the policy will be unconditional, e.g., "always
use L2TPv3 for softwires", in other cases the policy may specify that
the choice is conditional upon information about the softwire remote
endpoint, e.g., "use L2TPv3 to talk to routers in class X; use GRE to
talk to routers in class Y". It is desirable therefore to allow the
network administration to create a small set of classes, and to
configure each AFBR to be a member of one or more of these classes.
If each such class is represented as a community or extended
community, then [RFC5512] specifies a method that AFBRs can use to
advertise their class memberships to each other.
This framework also allows for policies of arbitrary complexity,
which may depend on characteristics or attributes of individual
address prefixes as well as on QoS or security considerations.
However, the specification of such policies is not within the scope
of this document.
9. Selecting the Softwire for a Given Packet
Suppose it has been decided to send a given packet through a
softwire. Routing provides the address, in the address family of the
transport network, of the BGP next hop. The packet MUST be sent
through a softwire whose remote endpoint address is the same as the
BGP next hop address.
Sending a packet through a softwire is a matter of first
encapsulating the packet with an encapsulation header that can be
processed by the transit network and then transmitting towards the
softwire's remote endpoint address.
Wu, et al. Standards Track [Page 16]
RFC 5565 Softwire Mesh Framework June 2009
In many cases, once one knows the remote endpoint address, one has
all the information one needs in order to form the encapsulation
header. This will be the case if the tunnel technology instantiating
the softwire is, e.g., LDP-based MPLS, IP-in-IP, or GRE without
optional header fields.
If the tunnel technology being used is L2TPv3 or GRE with optional
header fields, additional information from the remote endpoint is
needed in order to form the encapsulation header. The procedures for
sending and receiving this information are described in [RFC5512].
If the tunnel technology being used is RSVP-TE-based MPLS or IPsec,
the native signaling procedures of those technologies will need to be
used.
If the packet being sent through the softwire matches a route in the
labeled IPv4 or labeled IPv6 address families, it should be sent
through the softwire as an MPLS packet with the corresponding label.
Note that most of the tunneling technologies mentioned in this
document are capable of carrying MPLS packets, so this does not
presuppose support for MPLS in the core routers.
10. Softwire OAM and MIBs
10.1. Operations and Maintenance (OAM)
Softwires are essentially tunnels connecting routers. If they
disappear or degrade in performance, then connectivity through those
tunnels will be impacted. There are several techniques available to
monitor the status of the tunnel endpoints (AFBRs) as well as the
tunnels themselves. These techniques allow operations such as
softwire path tracing, remote softwire endpoint pinging, and remote
softwire endpoint liveness failure detection.
Examples of techniques applicable to softwire OAM include:
o BGP/TCP timeouts between AFBRs
o ICMP or LSP echo request and reply addressed to a particular AFBR
o BFD (Bidirectional Forwarding Detection) [BFD] packet exchange
between AFBR routers
Another possibility for softwire OAM is to build something similar to
[RFC4378] or, in other words, to create and generate softwire echo
request/reply packets. The echo request sent to a well-known UDP
port would contain the egress AFBR IP address and the softwire
identifier as the payload (similar to the MPLS Forwarding Equivalence
Wu, et al. Standards Track [Page 17]
RFC 5565 Softwire Mesh Framework June 2009
Class contained in the LSP echo request). The softwire echo packet
would be encapsulated with the encapsulation header and forwarded
across the same path (inband) as that of the softwire itself.
This mechanism can also be automated to periodically verify remote
softwire endpoint reachability, with the loss of reachability being
signaled to the softwire application on the local AFBR, thus enabling
suitable actions to be taken. Consideration must be given to the
trade-offs between the scalability of such mechanisms versus the time
required for detection of loss of endpoint reachability for such
automated mechanisms.
In general, a framework for softwire OAM can, for a large part, be
based on the [RFC4176] framework.
10.2. MIBs
Specific MIBs do exist to manage elements of the Softwire Mesh
Framework. However, there will be a need to either extend these MIBs
or create new ones that reflect the functional elements that can be
SNMP-managed within the softwire network.
11. Softwire Multicast
A set of client networks, running E-IP, that are connected to a
provider's I-IP transit core may wish to run IP multicast
applications. Extending IP multicast connectivity across the transit
core can be done in a number of ways, each with a different set of
characteristics. Most (though not all) of the possibilities are
either slight variations of the procedures defined for L3VPNs in
[L3VPN-MCAST].
We will focus on supporting those multicast features and protocols
that are typically used across inter-provider boundaries. Support is
provided for PIM-SM (Protocol Independent Multicast - Sparse Mode)
and PIM-SSM (PIM Source-Specific Mode). Support for BIDIR-PIM
(Bidirectional PIM), BSR (Bootstrap Router Mechanism for PIM), and
AutoRP (Automatic Rendezvous Point Determination) is not provided as
these features are not typically used across inter-provider
boundaries.
11.1. One-to-One Mappings
In the "one-to-one mapping" scheme, each client multicast tree is
extended through the transit core so that for each client tree there
is exactly one tree through the core.
Wu, et al. Standards Track [Page 18]
RFC 5565 Softwire Mesh Framework June 2009
The one-to-one scheme is not used in [L3VPN-MCAST] because it
requires an amount of state in the core routers that is proportional
to the number of client multicast trees passing through the core. In
the VPN context, this is considered undesirable because the amount of
state is unbounded and out of the control of the service provider.
However, the one-to-one scheme models the typical "Internet
multicast" scenario where the client network and the transit core are
both IPv4 or both IPv6. If it scales satisfactorily for that case,
it should also scale satisfactorily for the case where the client
network and the transit core support different versions of IP.
11.1.1. Using PIM in the Core
When an AFBR receives an E-IP PIM control message from one of its
CEs, it translates it from E-IP to I-IP, and forwards it towards the
source of the tree. Since the routers in the transit core will not
generally have a route to the source of the tree, the AFBR must
include an "RPF (Reverse Path Forwarding) Vector" [RFC5496] in the
PIM message.
Suppose an AFBR A receives an E-IP PIM Join/Prune message from a CE
for either an (S,G) tree or a (*,G) tree. The AFBR would have to
"translate" the PIM message into an I-IP PIM message. It would then
send it to the neighbor that is the next hop along the route to the
root of the (S,G) or (*,G) tree. In the case of an (S,G) tree, the
root of the tree is S; in the case of a (*,G) tree, the root of the
tree is the Rendezvous Point (RP) for the group G.
Note that the address of the root of the tree will be an E-IP
address. Since the routers within the transit core (other than the
AFBRs) do not have routes to E-IP addresses, A must put an RPF Vector
[RFC5496] in the PIM Join/Prune message that it sends to its upstream
neighbor. The RPF Vector will identify, as an I-IP address, the AFBR
B that is the egress point in the transit network along the route to
the root of the multicast tree. AFBR B is AFBR A's BGP next hop for
the route to the root of the tree. The RPF Vector allows the core
routers to forward PIM Join/Prune messages upstream towards the root
of the tree, even though they do not maintain E-IP routes.
In order to translate an E-IP PIM message into an I-IP PIM message,
the AFBR A must translate the address of S (in the case of an (S,G)
group) or the address of G's RP from the E-IP address family to the
I-IP address family, and the AFBR B must translate them back.
In the case where E-IP is IPv4 and I-IP is IPv6, it may be possible
to do this translation algorithmically. A can translate the IPv4 S
into the corresponding IPv4-mapped IPv6 address [RFC4291], and then B
can translate it back. At the time of this writing, there is no such
Wu, et al. Standards Track [Page 19]
RFC 5565 Softwire Mesh Framework June 2009
thing as an IPv4-mapped IPv6 multicast address, but if such a thing
were to be standardized, then A could also translate the IPv4 G into
IPv6, and B could translate it back. The precise circumstances under
which these translations are to be done would be a matter of policy.
Obviously, this translation procedure does not generalize to the case
where the client multicast is IPv6 but the core is IPv4. To handle
that case, one needs additional signaling between the two AFBRs.
Each downstream AFBR needs to signal the upstream AFBR that it needs
a multicast tunnel for (S,G). The upstream AFBR must then assign a
multicast address G' to the tunnel and inform the downstream of the
P-G value to use. The downstream AFBR then uses PIM/IPv4 to join the
(S',G') tree, where S' is the IPv4 address of the upstream ASBR
(Autonomous System Border Router).
The (S',G') trees should be SSM trees.
This procedure can be used to support client multicasts of either
IPv4 or IPv6 over a transit core of the opposite protocol. However,
it only works when the client multicasts are SSM, since it provides
no method for mapping a client "prune a source off the (*,G) tree"
operation into an operation on the (S',G') tree. This method also
requires additional signaling. The BGP-based signaling of
[L3VPN-MCAST-BGP] is one signaling method that could be used. Other
signaling methods could be defined as well.
11.1.2. Using mLDP and Multicast MPLS in the Core
LDP extensions for point-to-multipoint and multipoint-to-multipoint
LSPs are specified in [MLDP]; we will use the term "mLDP" to refer to
those LDP extensions. If the transit core implements mLDP and
supports multicast MPLS, then client Source-Specific Multicast (SSM)
trees can be mapped one-to-one onto P2MP (Point-to-Multipoint) LSPs.
When an AFBR A receives an E-IP PIM Join/Prune message for (S,G) from
one of its CEs, where G is an SSM group, it would use mLDP to join a
P2MP LSP. The root of the P2MP LSP would be the AFBR B that is A's
BGP next hop on the route to S. In mLDP, a P2MP LSP is uniquely
identified by a combination of its root and an "FEC (Forwarding
Equivalence Class) identifier". The original (S,G) can be
algorithmically encoded into the FEC identifier so that all AFBRs
that need to join the P2MP LSP for (S,G) will generate the same FEC
identifier. When the root of the P2MP LSP (AFBR B) receives such an
mLDP message, it extracts the original (S,G) from the FEC identifier,
creates an "ordinary" E-IP PIM Join/Prune message, and sends it to
the CE that is its next hop on the route to S.
Wu, et al. Standards Track [Page 20]
RFC 5565 Softwire Mesh Framework June 2009
The method of encoding the (S,G) into the FEC identifier needs to be
standardized. The encoding must be self-identifying so that a node
that is the root of a P2MP LSP can determine whether a FEC identifier
is the result of having encoded a PIM (S,G).
The appropriate state machinery must be standardized so that PIM
events at the AFBRs result in the proper mLDP events. For example,
if at some point an AFBR determines (via PIM procedures) that it no
longer has any downstream receivers for (S,G), the AFBR should invoke
the proper mLDP procedures to prune itself off the corresponding P2MP
LSP.
Note that this method cannot be used when the G is a Sparse Mode
group. The reason this method cannot be used is that mLDP does not
have any function corresponding to the PIM "prune this source off the
shared tree" function. So if a P2MP LSP were mapped one-to-one with
a P2MP LSP, duplicate traffic could end up traversing the transit
core (i.e., traffic from S might travel down both the shared tree and
S's source tree). Alternatively, one could devise an AFBR-to-AFBR
protocol to prune sources off the P2MP LSP at the root of the LSP.
It is recommended, though, that client SM multicast groups be
supported by other methods, such as those discussed below.
Client-side bidirectional multicast groups set up by PIM-bidir could
be mapped using the above technique to MP2MP (Multipoint-to-
Multipoint) LSPs set up by mLDP [MLDP]. We do not consider this
further, as inter-provider bidirectional groups are not in use
anywhere.
11.2. MVPN-Like Schemes
The "MVPN (Multicast VPN)-like schemes" are those described in
[L3VPN-MCAST] and its companion documents (such as
[L3VPN-MCAST-BGP]). To apply those schemes to the softwire
environment, it is necessary only to treat all the AFBRs of a given
transit core as if they were all, for multicast purposes, PE routers
attached to the same VPN.
The MVPN-like schemes do not require a one-to-one mapping between
client multicast trees and transit-core multicast trees. In the MVPN
environment, it is a requirement that the number of trees in the core
scales less than linearly with the number of client trees. This
requirement may not hold in the softwire scenarios.
The MVPN-like schemes can support SM, SSM, and Bidir groups. They
provide a number of options for the control plane:
Wu, et al. Standards Track [Page 21]
RFC 5565 Softwire Mesh Framework June 2009
- LAN-like
Use a set of multicast trees in the core to emulate a LAN (Local
Area Network) and run the client-side PIM protocol over that
"LAN". The "LAN" can consist of a single Bidir tree containing
all the AFBRs or a set of SSM trees, one rooted at each AFBR and
containing all the other AFBRs as receivers.
- NBMA (Non-Broadcast Multiple Access), using BGP
The client-side PIM signaling can be translated into BGP-based
signaling, with a BGP Route Reflector mediating the signaling.
These two basic options admit of many variations; a comprehensive
discussion is in [L3VPN-MCAST].
For the data plane, there are also a number of options:
- All multicast data sent over the emulated LAN. This particular
option is not very attractive, though, for the softwire
scenarios, as every AFBR would have to receive every client
multicast packet.
- Every multicast group mapped to a tree that is considered
appropriate for that group, in the sense of causing the traffic
of that group to go to "too many" AFBRs that don't need to
receive it.
Again, a comprehensive discussion of the issues can be found in
[L3VPN-MCAST].
12. Inter-AS Considerations
We have so far only considered the case where a "transit core"
consists of a single Autonomous System (AS). If the transit core
consists of multiple ASes, then it may be necessary to use softwires
whose endpoints are AFBRs attached to different Autonomous Systems.
In this case, the AFBR at the remote endpoint of a softwire is not
the BGP next hop for packets that need to be sent on the softwire.
Since the procedures described above require the address of a remote
softwire endpoint to be the same as the address of the BGP next hop,
those procedures do not work as specified when the transit core
consists of multiple ASes.
There are several ways to deal with this situation.
1. Don't do it; require that there be AFBRs at the edge of each AS
so that a transit core does not extend more than one AS.
Wu, et al. Standards Track [Page 22]
RFC 5565 Softwire Mesh Framework June 2009
2. Use multi-hop EBGP to allow AFBRs to send BGP routes to each
other, even if the ABFRs are not in the same or in neighboring
ASes.
3. Ensure that an ASBR that is not an AFBR does not change the
next hop field of the routes for which encapsulation is needed.
In the latter two cases, BGP recursive next hop resolution needs to
be done, and encapsulations may need to be "stacked" (i.e., multiple
layers of encapsulation may need to be used).
For instance, consider packet P with destination IP address D.
Suppose it arrives at ingress AFBR A1 and that the route that is the
best match for D has BGP next hop B1. So A1 will encapsulate the
packet for delivery to B1. If B1 is not within A1's AS, A1 will need
to look up the route to B1 and then find the BGP next hop, call it
B2, of that route. If the interior routers of A1's AS do not have
routes to B1, then A1 needs to encapsulate the packet a second time,
this time for delivery to B2.
13. Security Considerations
13.1. Problem Analysis
In the Softwire Mesh Framework, the data packets that are
encapsulated are E-IP data packets that are traveling through the
Internet. These data packets (the softwire "payload") may or may not
need such security features as authentication, integrity,
confidentiality, or replay protection. However, the security needs
of the payload packets are independent of whether or not those
packets are traversing softwires. The fact that a particular payload
packet is traveling through a softwire does not in any way affect its
security needs.
Thus, the only security issues we need to consider are those that
affect the I-IP encapsulation headers, rather than those that affect
the E-IP payload.
Since the encapsulation headers determine the routing of packets
traveling through softwires, they must appear "in the clear".
In the Softwire Mesh Framework, for each receiving endpoint of a
tunnel, there are one or more "valid" transmitting endpoints, where
the valid transmitting endpoints are those that are authorized to
tunnel packets to the receiving endpoint. If the encapsulation
header has no guarantee of authentication or integrity, then it is
possible to have spoofing attacks, in which unauthorized nodes send
Wu, et al. Standards Track [Page 23]
RFC 5565 Softwire Mesh Framework June 2009
encapsulated packets to the receiving endpoint, giving the receiving
endpoint the invalid impression the encapsulated packets have really
traveled through the softwire. Replay attacks are also possible.
The effect of such attacks is somewhat limited, though. The
receiving endpoint of a softwire decapsulates the payload and does
further routing based on the IP destination address of the payload.
Since the payload packets are traveling through the Internet, they
have addresses from the globally unique address space (rather than,
e.g., from a private address space of some sort). Therefore, these
attacks cannot cause payload packets to be delivered to an address
other than the one appearing in the destination IP address field of
the payload packet.
However, attacks of this sort can result in policy violations. The
authorized transmitting endpoint(s) of a softwire may be following a
policy according to which only certain payload packets get sent
through the softwire. If unauthorized nodes are able to encapsulate
the payload packets so that they arrive at the receiving endpoint
looking as if they arrived from authorized nodes, then the properly
authorized policies have been side-stepped.
Attacks of the sort we are considering can also be used in denial-
of-service attacks on the receiving tunnel endpoints. However, such
attacks cannot be prevented by use of cryptographic
authentication/integrity techniques, as the need to do cryptography
on spoofed packets only makes the denial-of-service problem worse.
(The assumption is that the cryptography mechanisms are likely to be
more costly than the decapsulation/forwarding mechanisms. So if one
tries to eliminate a flooding attack on the decapsulation/forwarding
mechanisms by discarding packets that do not pass a cryptographic
integrity test, one ends up just trading one kind of attack for
another.)
This section is largely based on the security considerations section
of RFC 4023, which also deals with encapsulations and tunnels.
13.2. Non-Cryptographic Techniques
If a tunnel lies entirely within a single administrative domain,
then, to a certain extent, there are certain non-cryptographic
techniques one can use to prevent spoofed packets from reaching a
tunnel's receiving endpoint. For example, when the tunnel
encapsulation is IP-based:
Wu, et al. Standards Track [Page 24]
RFC 5565 Softwire Mesh Framework June 2009
- The receiving endpoints of the tunnels can be given a distinct
set of addresses, and those addresses can be made known to the
border routers. The border routers can then filter out packets,
destined to those addresses, that arrive from outside the domain.
- The transmitting endpoints of the tunnels can be given a distinct
set of addresses, and those addresses can be made known to the
border routers and to the receiving endpoints of the tunnels.
The border routers can filter out all packets arriving from
outside the domain with source addresses that are in this set,
and the receiving endpoints can discard all packets that appear
to be part of a softwire, but whose source addresses are not in
this set.
If an MPLS-based encapsulation is used, the border routers can refuse
to accept MPLS packets from outside the domain, or they can refuse to
accept such MPLS packets whenever the top label corresponds to the
address of a tunnel receiving endpoint.
These techniques assume that, within a domain, the network is secure
enough to prevent the introduction of spoofed packets from within the
domain itself. That may not always be the case. Also, these
techniques can be difficult or impossible to use effectively for
tunnels that are not in the same administrative domain.
A different technique is to have the encapsulation header contain a
cleartext password. The 64-bit "cookie" of L2TPv3 [RFC3931] is
sometimes used in this way. This can be useful within an
administrative domain if it is regarded as infeasible for an attacker
to spy on packets that originate in the domain and that do not leave
the domain. An attacker would then not be able to discover the
password. An attacker could, of course, try to guess the password,
but if the password is an arbitrary 64-bit binary sequence, brute
force attacks that run through all the possible passwords would be
infeasible. This technique may be easier to manage than ingress
filtering is, and may be just as effective if the assumptions hold.
Like ingress filtering, though, it may not be applicable for tunnels
that cross domain boundaries.
Therefore, it is necessary to also consider the use of cryptographic
techniques for setting up the tunnels and for passing data through
them.
Wu, et al. Standards Track [Page 25]
RFC 5565 Softwire Mesh Framework June 2009
13.3. Cryptographic Techniques
If the path between the two endpoints of a tunnel is not adequately
secure, then:
- If a control protocol is used to set up the tunnels (e.g., to
inform one tunnel endpoint of the IP address of the other), the
control protocol MUST have an authentication mechanism, and this
MUST be used when the tunnel is set up. If the tunnel is set up
automatically as the result of, for example, information
distributed by BGP, then the use of BGP's MD5-based
authentication mechanism [RFC2385] is satisfactory.
- Data transmission through the tunnel should be secured with
IPsec. In the remainder of this section, we specify the way
IPsec may be used, and the implementation requirements we mention
are meant to be applicable whenever IPsec is being used.
We consider only the case where IPsec is used together with an IP-
based tunneling mechanism. Use of IPsec with an MPLS-based tunneling
mechanism is for further study.
If it is deemed necessary to use tunnels that are protected by IPsec,
the tunnel type SHOULD be negotiated by the tunnel endpoints using
the procedures specified in [RFC5566]. That document allows the use
of IPsec tunnel mode but also allows one to treat the tunnel head and
the tunnel tail as the endpoints of a Security Association, and to
use IPsec transport mode.
In order to use IPsec transport mode, encapsulated packets should be
viewed as originating at the tunnel head and as being destined for
the tunnel tail. A single IP address of the tunnel head will be used
as the source IP address, and a single IP address of the tunnel tail
will be used as the destination IP address. This technique can be
used to carry MPLS packets through an IPsec Security Association, by
first encapsulating the MPLS packets in MPLS-in-IP or MPLS-in-GRE
[RFC4023] and then applying IPsec transport mode.
When IPsec is used to secure softwires, IPsec MUST provide
authentication and integrity. Thus, the implementation MUST support
either ESP (IP Encapsulating Security Payload) with null encryption
[RFC4303] or else AH (IP Authentication Header) [RFC4302]. ESP with
encryption MAY be supported. If ESP is used, the tunnel tail MUST
check that the source IP address of any packet received on a given SA
(IPsec Security Association) is the one expected, as specified in
Section 5.2, step 4, of [RFC4301].
Wu, et al. Standards Track [Page 26]
RFC 5565 Softwire Mesh Framework June 2009
Since the softwires are set up dynamically as a byproduct of passing
routing information, key distribution MUST be done automatically by
means of IKEv2 [RFC4306]. If a PKI (Public Key Infrastructure) is
not available, the IPsec Tunnel Authenticator sub-TLV described in
[RFC5566] MUST be used and validated before setting up an SA.
The selectors associated with the SA are the source and destination
addresses of the encapsulation header, along with the IP protocol
number representing the encapsulation protocol being used.
14. References
14.1. Normative References
[RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003,
October 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
Traina, "Generic Routing Encapsulation (GRE)", RFC
2784, March 2000.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon,
"Multiprotocol Label Switching Architecture", RFC
3031, January 2001.
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, January 2001.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan,
V., and G. Swallow, "RSVP-TE: Extensions to RSVP for
LSP Tunnels", RFC 3209, December 2001.
[RFC3931] Lau, J., Ed., Townsley, M., Ed., and I. Goyret, Ed.,
"Layer Two Tunneling Protocol - Version 3 (L2TPv3)",
RFC 3931, March 2005.
[RFC4023] Worster, T., Rekhter, Y., and E. Rosen, Ed.,
"Encapsulating MPLS in IP or Generic Routing
Encapsulation (GRE)", RFC 4023, March 2005.
[RFC5512] Mohapatra, P. and E. Rosen, "The BGP Encapsulation
Subsequent Address Family Identifier (SAFI) and the
BGP Tunnel Encapsulation Attribute", RFC 5512, April
2009.
Wu, et al. Standards Track [Page 27]
RFC 5565 Softwire Mesh Framework June 2009
[RFC5566] Berger, L., White, R. and E. Rosen, "BGP IPsec Tunnel
Encapsulation Attribute", RFC 5566, June 2009.
[V4NLRI-V6NH] Le Faucheur, F. and E. Rosen, "Advertising IPv4
Network Layer Reachability Information with an IPv6
Next Hop", RFC 5549, May 2009.
[V6NLRI-V4NH] De Clercq, J., Ooms, D., Prevost, S., and F. Le
Faucheur, "Connecting IPv6 Islands over IPv4 MPLS
Using IPv6 Provider Edge Routers (6PE)", RFC 4798,
February 2007.
14.2. Informative References
[BFD] Katz, D. and D. Ward, "Bidirectional Forwarding
Detection", Work in Progress, February 2009.
[L3VPN-MCAST] Rosen, E., Ed., and R. Aggarwal, Ed., "Multicast in
MPLS/BGP IP VPNs", Work in Progress, March 2009.
[L3VPN-MCAST-BGP]
Aggarwal, R., Rosen, E., Morin, T. and Y. Rekhter,
"BGP Encodings and Procedures for Multicast in
MPLS/BGP IP VPNs", Work in Progress, April 2009.
[MLDP] Minei, I., Ed., Kompella, K., Wijnands, IJ., Ed., and
B. Thomas, "Label Distribution Protocol Extensions for
Point-to-Multipoint and Multipoint-to-Multipoint Label
Switched Paths", Work in Progress, April 2009.
[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP
and dual environments", RFC 1195, December 1990.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April
1998.
[RFC2385] Heffernan, A., "Protection of BGP Sessions via the TCP
MD5 Signature Option", RFC 2385, August 1998.
[RFC4176] El Mghazli, Y., Ed., Nadeau, T., Boucadair, M., Chan,
K., and A. Gonguet, "Framework for Layer 3 Virtual
Private Networks (L3VPN) Operations and Management",
RFC 4176, October 2005.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271, January
2006.
Wu, et al. Standards Track [Page 28]
RFC 5565 Softwire Mesh Framework June 2009
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302,
December 2005.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, December 2005.
[RFC4306] Kaufman, C., Ed., "Internet Key Exchange (IKEv2)
Protocol", RFC 4306, December 2005.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, February 2006.
[RFC4378] Allan, D., Ed., and T. Nadeau, Ed., "A Framework for
Multi-Protocol Label Switching (MPLS) Operations and
Management (OAM)", RFC 4378, February 2006.
[RFC4459] Savola, P., "MTU and Fragmentation Issues with In-
the-Network Tunneling", RFC 4459, April 2006.
[RFC5036] Andersson, L., Ed., Minei, I., Ed., and B. Thomas,
Ed., "LDP Specification", RFC 5036, October 2007.
[RFC5496] Wijnands, IJ., Boers, A., and E. Rosen, "The Reverse
Path Forwarding (RPF) Vector TLV", RFC 5496, March
2009.
[SW-PROB] Li, X., Ed., Dawkins, S., Ed., Ward, D., Ed., and A.
Durand, Ed., "Softwire Problem Statement", RFC 4925,
July 2007.
Wu, et al. Standards Track [Page 29]
RFC 5565 Softwire Mesh Framework June 2009
15. Contributors
Xing Li
Tsinghua University
Department of Electronic Engineering, Tsinghua University
Beijing 100084
P.R.China
Phone: +86-10-6278-5983
EMail: xing@cernet.edu.cn
Simon Barber
Cisco Systems, Inc.
250 Longwater Avenue
Reading, ENGLAND, RG2 6GB
United Kingdom
EMail: sbarber@cisco.com
Pradosh Mohapatra
Cisco Systems, Inc.
3700 Cisco Way
San Jose, CA 95134
USA
EMail: pmohapat@cisco.com
John Scudder
Juniper Networks
1194 North Mathilda Avenue
Sunnyvale, CA 94089
USA
EMail: jgs@juniper.net
16. Acknowledgments
David Ward, Chris Cassar, Gargi Nalawade, Ruchi Kapoor, Pranav Mehta,
Mingwei Xu, and Ke Xu provided useful input into this document.
Wu, et al. Standards Track [Page 30]
RFC 5565 Softwire Mesh Framework June 2009
Authors' Addresses
Jianping Wu
Tsinghua University
Department of Computer Science, Tsinghua University
Beijing 100084
P.R.China
Phone: +86-10-6278-5983
EMail: jianping@cernet.edu.cn
Yong Cui
Tsinghua University
Department of Computer Science, Tsinghua University
Beijing 100084
P.R.China
Phone: +86-10-6278-5822
EMail: yong@csnet1.cs.tsinghua.edu.cn
Chris Metz
Cisco Systems, Inc.
3700 Cisco Way
San Jose, CA 95134
USA
EMail: chmetz@cisco.com
Eric C. Rosen
Cisco Systems, Inc.
1414 Massachusetts Avenue
Boxborough, MA 01719
USA
EMail: erosen@cisco.com
Wu, et al. Standards Track [Page 31]