Network Working Group J. Wu
Internet Draft Y. Cui
Intended Status: Standards Track X. Li
Expires: September 31, 2008 Tsinghua University
C. Metz
E. Rosen (Editor)
S. Barber
P. Mohapatra
Cisco Systems, Inc.
J. Scudder
Juniper Networks, Inc.
March 31, 2008
Softwire Mesh Framework
draft-ietf-softwire-mesh-framework-04.txt
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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.
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Table of Contents
1 Specification of requirements ......................... 4
2 Introduction .......................................... 4
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 .................... 11
4.1 'E-IP' and 'I-IP' ..................................... 11
4.2 Routing ............................................... 11
4.3 Tunneled Forwarding ................................... 12
5 Distribution of Inter-AFBR Routing Information ........ 12
6 Softwire Signaling .................................... 14
7 Choosing to Forward Through a Softwire ................ 16
8 Selecting a Tunneling Technology ...................... 16
9 Selecting the Softwire for a Given Packet ............. 17
10 Softwire OAM and MIBs ................................. 18
10.1 Operations and Maintenance (OAM) ...................... 18
10.2 MIBs .................................................. 19
11 Softwire Multicast .................................... 19
11.1 One-to-One Mappings ................................... 20
11.1.1 Using PIM in the Core ................................. 20
11.1.2 Using mLDP and Multicast MPLS in the Core ............. 21
11.2 MVPN-like Schemes ..................................... 22
12 Inter-AS Considerations ............................... 23
13 IANA Considerations ................................... 24
14 Security Considerations ............................... 24
14.1 Problem Analysis ...................................... 24
14.2 Non-cryptographic techniques .......................... 26
14.3 Cryptographic techniques .............................. 27
15 Acknowledgments ....................................... 28
16 Normative References .................................. 28
17 Informative References ................................ 29
18 Full Copyright Statement .............................. 32
19 Intellectual Property ................................. 33
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1. 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].
2. 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 which 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 which 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.
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It is, however, possible to provide transit services without
requiring that all the backbone routers have the external routing
information. The routing information which 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 which 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
required. Of course, the edge nodes must have the IPv4 routes,
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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 draft 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
([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
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.
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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 softwires 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
which 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].
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.
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+--------+ +--------+
| 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
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.
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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, 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.
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.
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+--------+ +--------+
| 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.
While Figure 2 does not show any "backdoor" connections among the client
networks, this framework assumes that there will be such connections.
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That is, there is no assumption 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 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 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
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Reflector. Although these IBGP connections are used to pass E-IP
routing information (i.e., the 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 which the P
routers can process, and which 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.
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.
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.
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In BGP, a routing update associates an address prefix (or more
generally, "Network Layer Reachability Information", or 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 which 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 softwires deployment
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
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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 which 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 than 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 which goes beyond the basic
requirements described in this document. E.g., 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. A softwire based on IPsec would use
standard IKE (Internet Key Exchange) [RFC4306] and IPsec [RFC4301]
signaling, as that is necessary in order to guarantee the softwire's
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security properties.
A Softwire based on GRE 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 [ENCAPS-SAFI].
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 which 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 which the AFBR has installed. This suggests that any
necessary softwire signaling should be either be done as part of
normal system startup (as would happen, e.g., with LDP-based MPLS),
or else should be triggered by the reception of BGP routing
information (such as is described in [ENCAPS-SAFI]); it is also
helpful if distribution of the routing information that serves as the
trigger is prioritized.
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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, 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
packets 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 packets through a softwire
- if the route which 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
Y". To support such policies, it is necessary for the AFBRs to be
able to advertise their class memberships. [ENCAPS-SAFI] specifies a
way in which an AFBR may advertise, to other AFBRS, various
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characteristics which may be relevant to the polcy (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 2.
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 [ENCAPS-SAFI] 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 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.
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
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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 [ENCAPS-
SAFI].
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.
IPsec procedures will be discussed further in a subsequent revision
of this document.
RSVP-TE procedures will be discussed in companion documents.
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 end-points (AFBRs) as well as the
tunnels themselves. These techniques allow operations such as
softwires path tracing, remote softwire end-point pinging and remote
softwire end-point 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
the [RFC4378] or in other words creating and generating softwire echo
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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
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
softwires end-point reachability, with the loss of reachability being
signaled to the softwires application on the local AFBR thus enabling
suitable actions to be taken. Consideration must be given to the
trade offs between scalability of such mechanisms verses time to
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
which are typically used across inter-provider boundaries. Support
is provided for PIM-SM (PIM Sparse Mode) and PIM-SSM (PIM Single
Source Mode). Support for BIDIR-PIM (Bidirectional PIM), BSR
(Bootstrap Router Mechanism for PIM), AutoRP (Automatic Rendezvous
Point Determination) is not provided as these features are not
typically used across inter-provider boundaries.
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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.
The one-to-one scheme is not used in [L3VPN-MCAST], because it
requires an amount of state in the core routers which 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 are 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 would translate it from E-IP to I-IP, and forward 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
create include an "RPF (Reverse Path Forwarding) Vector" [RPF-VECTOR]
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 which 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" [RPF-VECTOR] 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.
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In order to "translate" the 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 is possible to do
this translation algorithmically. A can translate the IPv4 S and G
into the corresponding IPv4-mapped IPv6 addresses [RFC4291], and then
B can translate them back. The precise circumstances under which
these translations are 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 need 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
If the transit core implements mLDP (LDP Extensions for Point-to-
Multipoint and Multipoint-to-Multipoint LSPs, [mLDP]) and supports
multicast MPLS, then client Single-Source Multicast (SSM) trees can
be mapped one-to-one onto P2MP (Point-to-Multipoint) LSPs.
When an AFBR A receives a 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 a "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
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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 which is its next hop on the route to S.
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
which 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-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 softwires scenarios.
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The MVPN-like schemes can support SM, SSM, and Bidir groups. They
provide a number of options for the control plane:
- 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 consists 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 softwires scenarios,
as every AFBR would have to receive every client multicast
packet.
- Every multicast group mapped to a tree which 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 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.
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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.
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 which 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.
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. IANA Considerations
This document has no actions for IANA.
14. Security Considerations
14.1. Problem Analysis
In the Softwires mesh framework, the data packets that are
encapsulated are E-IP data packets that are traveling through the
Internet. These data packets (the Softwires "payload") may or may
not need such security features as authentication, integrity,
confidentiality, or playback 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 which
affect the I-IP encapsulation headers, rather than those which affect
the E-IP payload.
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Since the encapsulation headers determine the routing of packets
traveling through softwires, they must appear "in the clear", i.e.,
they do not have any confidentiality requirement.
In the Softwires mesh framework, for each tunnel receiving endpoint,
there are one or more "valid" transmitting endpoints, where the valid
transmitting endpoints are those which 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 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 intended.
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.
This section is largely based on the security considerations section
of RFC 4023, which also deals with encapsulations and tunnels.
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14.2. Non-cryptographic techniques
If a tunnel lies entirely within a single administrative domain, then
to a certain extent, then 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:
- The tunnel receiving endpoints 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, which arrive from outside the
domain.
- The tunnel transmitting endpoints can be given a distinct set of
addresses, and those addresses can be made known to the border
routers and to the tunnel receiving endpoints. 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 which 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 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 however 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 which 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
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techniques for setting up the tunnels and for passing data through
them.
14.3. 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 [ENCAPS-IPSEC]. 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 to carry MPLS packets through an IPsec Security Association,
but 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
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(IPsec Security Association) is the one expected.
Since the softwires are set up dynamically as a byproduct of passing
routing information, key distribution MUST be done automatically by
means of IKE [RFC4306], operating in main mode with preshared keys.
If a PKI (Public Key Infrastructure) is not available, the IPsec
Tunnel Authenticator sub-TLV described in [ENCAPS-IPSEC] 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.
15. Acknowledgments
David Ward, Chris Cassar, Gargi Nalawade, Ruchi Kapoor, Pranav Mehta,
Mingwei Xu and Ke Xu provided useful input into this document.
16. Normative References
[ENCAPS-IPSEC] "BGP IPSec Tunnel Encapsulation Attribute", L. Berger,
R. White, E. Rosen, draft-ietf-softwire-encaps-ipsec-00.txt, March
2008.
[ENCAPS-SAFI] "BGP Information SAFI and BGP Tunnel Encapsulation
Attribute", P. Mohapatra and E. Rosen, draft-ietf-softwire-encaps-
safi-00.txt, January 2008.
[RFC2003] "IP Encapsulation within IP", C. Perkins, October 1996.
[RFC2119] "Key words for use in RFCs to Indicate Requirement Levels",
S. Bradner, March 1997.
[RFC2784] "Generic Routing Encapsulation (GRE)", D. Farinacci, T. Li,
S. Hanks, D. Meyer, P. Traina, RFC 2784, March 2000.
[RFC3031] "Multiprotocol Label Switching Architecture", E. Rosen, A.
Viswanathan, R. Callon, RFC 3031, January 2001.
[RFC3032] "MPLS Label Stack Encoding", E. Rosen, D. Tappan, G.
Fedorkow, Y. Rekhter, D. Farinacci, T. Li, A. Conta, RFC 3032,
January 2001.
[RFC3209] D. Awduche, L. Berger, D. Gan, T. Li, V. Srinivasan, and G.
Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC 3209,
December 2001.
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[RFC3931] J. Lau, M. Townsley, I. Goyret, "Layer Two Tunneling
Protocol - Version 3 (L2TPv3)", RFC 3931, March 2005.
[RFC4023] "Encapsulating MPLS in IP or Generic Routing Encapsulation
(GRE)", T. Worster, Y. Rekhter, E. Rosen, RFC 4023, March 2005.
[V4NLRI-V6NH] F. Le Faucheur, E. Rosen, "Advertising an IPv4 NLRI
with an IPv6 Next Hop", draft-ietf-softwire-v4nlri-v6nh-00.txt,
January 2008.
[V6NLRI-V4NH] J. De Clercq, D. Ooms, S. Prevost, F. Le Faucheur,
"Connecting IPv6 Islands over IPv4 MPLS using IPv6 Provider Edge
Routers (6PE)", RFC 4798, February 2007.
17. Informative References
[BFD] D. Katz and D. Ward, "Bidirectional Forwarding Detection",
draft-ietf-bfd-base-08.txt, March 2008.
[L3VPN-MCAST], "Multicast in MPLS/BGP IP VPNs", E. Rosen, R.
Aggarwal, draft-ietf-l3vpn-2547bis-mcast-06.txt, January 2008.
[L3VPN-MCAST-BGP], "BGP Encodings and Procedures for Multicast in
MPLS/BGP IP VPNs", R. Aggarwal, E. Rosen, T. Morin, Y. Rekhter, C.
Kodeboniya, draft-ietf-l3vpn-2547bis-mcast-bgp-04.txt, November 2007.
[MLDP] "Label Distribution Protocol Extensions for Point-to-
Multipoint and Multipoint-to-Multipoint Label Switched Paths", I.
Minei, K. Kompella, IJ. Wijnands, B. Thomas, draft-ietf-mpls-ldp-
p2mp-04, February 2008.
[RFC1195] "Use of OSI IS-IS for Routing in TCP/IP and Dual
Environments", R. Callon, RFC 1195, December 1990.
[RFC2328] J. Moy, "OSPF Version 2", RFC 2328, April 1998.
[RFC2385] "Protection of BGP Sessions via the TCP MD5 Signature
Option", A. Heffernan, RFC 2385, August 1998.
[RFC4176] Y. El Mghazli, T. Nadeau, M. Boucadair, K. Chan, A.
Gonguet, "Framework for Layer 3 Virtual Private Networks (L3VPN)
Operations and Management", RFC 4176, October 2005.
[RFC4271] Rekhter, Y,, Li T., Hares, S., "A Border Gateway Protocol 4
(BGP-4)", RFC 4271, January 2006.
[RFC4291] "IP Version 6 Addressing Architecture", R. Hinden, S.
Wu, et al. [Page 29]
Internet Draft draft-ietf-softwire-mesh-framework-04.txt March 2008
Deering, RFC 4291, February 2006.
[RFC4301], "Security Architecture for the Internet Protocol", S.
Kent, K. Seo, RFC 4301, December 2005.
[RFC4302] "IP Authentication Header", S. Kent, RFC 4302, December
2005.
[RFC4303] "IP Encapsulating Security Payload (ESP)", S. Kent, RFC
4303, December 2005.
[RFC4306] "Internet Key Exchange (IKEv2) Protocol", C. Kaufman, ed.,
RFC 4306, December 2005.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, February 2006.
[RFC4378] D. Allan and T. Nadeau, "A Framework for Multi-Protocol
Label Switching (MPLS) Operations and Management (OAM)", RFC 4378,
February 2006.
[RFC5036] "LDP Specification", L. Andersson, I. Minei, B. Thomas,
October 2007.
[RPF-VECTOR], "The RPF Vector TLV", IJ. Wijnands, A. Boers, E. Rosen,
draft-ietf-pim-rpf-vector-06.txt, February 2008.
[SW-PROB] X. Li, S. Dawkins, D. Ward, A. Durand, "Softwire Problem
Statement", RFC 4925, July 2007.
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
Wu, et al. [Page 30]
Internet Draft draft-ietf-softwire-mesh-framework-04.txt March 2008
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
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
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. [Page 31]
Internet Draft draft-ietf-softwire-mesh-framework-04.txt March 2008
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, California 94089
USA
Email: jgs@juniper.net
18. Full Copyright Statement
Copyright (C) The IETF Trust (2008).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Wu, et al. [Page 32]
Internet Draft draft-ietf-softwire-mesh-framework-04.txt March 2008
19. Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at ietf-
ipr@ietf.org.
Wu, et al. [Page 33]
