Applicability Statement for BGP/MPLS IP Virtual Private Networks (VPNs)
RFC 4365
| Document | Type | RFC - Informational (February 2006; Errata) | |
|---|---|---|---|
| Author | Eric Rosen | ||
| Last updated | 2020-01-21 | ||
| Stream | Internet Engineering Task Force (IETF) | ||
| Formats | plain text html pdf htmlized with errata bibtex | ||
| Stream | WG state | (None) | |
| Document shepherd | No shepherd assigned | ||
| IESG | IESG state | RFC 4365 (Informational) | |
| Action Holders |
(None)
|
||
| Consensus Boilerplate | Unknown | ||
| Telechat date | |||
| Responsible AD | Thomas Narten | ||
| Send notices to | rcallon@juniper.net, rbonica@juniper.net, rick@rhwilder.net | ||
Network Working Group E. Rosen
Request for Comments: 4365 Cisco Systems, Inc.
Category: Informational February 2006
Applicability Statement for BGP/MPLS IP
Virtual Private Networks (VPNs)
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
This document provides an Applicability Statement for the Virtual
Private Network (VPN) solution described in RFC 4364 and other
documents listed in the References section.
Table of Contents
1. Introduction ....................................................2
2. SP Provisioning Model ...........................................4
3. Supported Topologies and Traffic Types ..........................6
4. Isolated Exchange of Data and Routing Information ...............7
5. Access Control and Authentication ...............................9
6. Security Considerations .........................................9
6.1. Protection of User Data ....................................9
6.2. SP Security Measures ......................................10
6.3. Security Framework Template ...............................12
7. Addressing .....................................................18
8. Interoperability and Interworking ..............................19
9. Network Access .................................................19
9.1. Physical/Link Layer Topology ..............................19
9.2. Temporary Access ..........................................19
9.3. Access Connectivity .......................................20
10. Service Access ................................................21
10.1. Internet Access ..........................................21
10.2. Other Services ...........................................21
11. SP Routing ....................................................22
12. Migration Impact ..............................................22
13. Scalability ...................................................23
14. QoS, SLA ......................................................26
Rosen Informational [Page 1]
RFC 4365 Applicability Statement for BGP/MPLS IP VPNs February 2006
15. Management ....................................................27
15.1. Management by the Provider ...............................27
15.2. Management by the Customer ...............................28
16. Acknowledgements ..............................................28
17. Normative References ..........................................29
18. Informative References ........................................29
1. Introduction
This document provides an Applicability Statement for the Virtual
Private Network (VPN) solution described in [BGP-MPLS-IP-VPN] and
other documents listed in the References section. We refer to these
as "BGP/MPLS IP VPNs", because Border Gateway Protocol (BGP) is used
to distribute the routes, and Multiprotocol Label Switching (MPLS) is
used to indicate that particular packets need to follow particular
routes. The characteristics of BGP/MPLS IP VPNs are compared with
the requirements specified in [L3VPN-REQS].
A VPN service is provided by a Service Provider (SP) to a customer
(sometimes referred to as an enterprise). BGP/MPLS IP VPNs are
intended for the situation in which:
- The customer:
* uses the VPN only for carrying IP packets.
* does not want to manage a routed backbone; the customer may
be using routing within his sites, but wishes to outsource
the inter-site routing to the SP.
* wants the SP to make the backbone and its routing completely
transparent to the customer's own routing.
If the customer has a routed infrastructure at his sites, he
does not want his site routing algorithms to need to be aware
of any part of the SP backbone network, other than the
Provider Edge (PE) routers to which the sites are attached.
In particular, the customer does not want his routers to need
to be aware of either the native structure of the SP backbone
or an overlay topology of tunnels through the SP backbone.
- The Service Provider:
* has an IP backbone, with MPLS-enabled edge routers, and
possibly (though not necessarily) with MPLS-enabled core
routers.
Rosen Informational [Page 2]
RFC 4365 Applicability Statement for BGP/MPLS IP VPNs February 2006
* wants to provide a service that meets the customer
requirements above.
* does not want to maintain a distinct overlay topology of
tunnels for each customer.
The basic principle is to model each VPN as a self-contained
"internet", where each site makes one or more access connections to
an SP, sends the SP its routing information, and then relies on the
SP to distribute routing information to and from the other sites in
that same VPN. The service differs from Internet service, however,
in that the SP strictly controls the distribution of this routing
information so that routes from within a VPN are not sent outside the
VPN, unless that is explicitly authorized by the customer. In fact,
even within the VPN, the distribution of routes may be controlled by
the SP so as to meet some policy of the customer.
The routers at a given customer site need not be routing peers of the
routers at other customer sites, and indeed need not know anything
about the internal structure of other customer sites. In fact,
different routing protocols may run at the different sites, with each
site using whatever protocol is most appropriate for that particular
site.
If EBGP (the BGP procedures used between BGP speakers from different
Autonomous Systems) is used on the access links that connect a
Provider Edge router (PE router) to a Customer Edge router (CE
router), then the SP and the customer do NOT peer in any Interior
Gateway Protocol (IGP), i.e., intra-domain routing algorithm).
BGP/MPLS IP VPNs are optimized for the situation in which a customer
(an enterprise) expects a service provider to operate and maintain
the customer's "backbone" (i.e., the customer's inter-site routing).
As such, the service provider becomes a "business partner" of the
enterprise. The technical mechanisms accommodate the case in which a
number of closely cooperating SPs can jointly offer the VPN service
to a customer, in that the BGP-based route distribution mechanisms
can operate between different SPs. If a set of SPs has sufficient
agreements with respect to Quality of Service (QoS), Service Level
Agreement (SLA), etc., then the customer's VPN could have sites
attached to different SPs from that set.
[BGP-MPLS-IP-VPN] specifies the inter-AS (Autonomous System)
mechanisms that allow a single VPN to have sites attached to
different SPs. However, the design center is not an environment
where a given VPN is spread among a very large number (e.g.,
hundreds) of SPs.
Rosen Informational [Page 3]
RFC 4365 Applicability Statement for BGP/MPLS IP VPNs February 2006
In cases where remote offices, individual telecommuters, etc., must
use the public Internet to access the VPN, it is possible to "tunnel"
the remote traffic to a PE router, and the PE router will treat the
traffic as if it had arrived over an interface connected to the PE.
Remote Point-to-Point Protocol (PPP) connections can be tunneled via
Layer 2 Tunneling Protocol (L2TP) to a PE router; IPsec tunnels can
also be used to tunnel traffic to a PE router across the public
Internet. Of course, when the public Internet is used, issues such
as QoS and SLAs must be carefully considered.
Some customers want to connect their sites over the public Internet,
creating a VPN "virtual backbone", purchasing connectivity for a
given site from whatever Internet Service Provider (ISP) offers the
best price for connecting that site. A BGP/MPLS IP VPN is not an
appropriate solution for such customers; they instead need to
consider solutions (either customer-managed or provider-managed) that
interconnect their sites via an overlay of secure tunnels across the
Internet. (See, for example, [IPSEC-VPN].)
Some customers who do not want to connect their sites via secure
site-to-site tunnels across the Internet may nevertheless want to
maintain complete control over the routing in their VPN backbone.
These customers will not want a "managed routing service" such as is
provided by BGP/MPLS IP VPNs, since that hides all details of the
backbone routing and topology from the customer. Rather, they may
prefer a "virtual router" service, in which the tunnels through the
SP networks are visible as links to the customer's routing algorithm.
(See, for example, [VR-VPN].)
2. SP Provisioning Model
If a particular VPN attaches to a particular PE router, the SP must
configure that PE router with a VPN Routing and Forwarding table
(VRF), a routing table that is specific to the specified VPN. (This
is known as a VPN Forwarding Instance (VFI) in the language of
[L3VPN-REQS] and [L3VPN-FRMWRK].) Each interface or sub-interface at
that PE that attaches to a site in the specified VPN (i.e., each
local access link of that VPN) must be configured so as to be
associated with that VRF. Each such interface may be unnumbered or
may be assigned an address that is unique within the VPN's address
space. In general, a routing algorithm needs to be run on each of
these links (though static routing can be used instead). The routing
algorithm can be EBGP, or an IGP such as Routing Information Protocol
(RIP) or Open Shortest Path First (OSPF). (IF OSPF is used, the
procedures of [VPN-OSPF] MUST be implemented.) If an IGP is run on
the access links, the IGP MUST be a separate IGP instance, different
Rosen Informational [Page 4]
RFC 4365 Applicability Statement for BGP/MPLS IP VPNs February 2006
than the IGP instance running among the backbone routers, and
different than the IGP instance running on the access links of any
other VPN. Static routing is also allowed.
The VRF is populated automatically with routes distributed from
locally attached CE routers via whatever routing algorithm is run on
the PE/CE links. It is also populated automatically with routes
distributed from other VRFs via BGP. Standard routing decision
processes are used to automatically select the proper routes. Static
configuration of routes in the VRF is optional.
Each PE router must run BGP, and must be pre-configured with the
identities of a small set of BGP Route Reflectors, with which it is
to peer via IBGP. ("IBGP" refers to the BGP procedures used between
BGP speakers from the same Autonomous System.)
In lieu of using Route Reflectors, one could configure each PE with
the identities of all the other PEs, and set up a full mesh of IBGP
connections. While this might be adequate for small networks, it
would not scale well to large networks; the use of Route Reflectors
is necessary to achieve scalability. See section 4.3.3 of
[BGP-MPLS-IP-VPN] for a more complete discussion of the use of Route
Reflectors, and related scalability mechanisms such as Outbound Route
Filtering.
Each VRF must be configured with three parameters:
- A Route Distinguisher. This is a globally unique 8-byte value.
Each VRF may have a unique Route Distinguisher (RD), or there may
be a single unique RD for an entire VPN. When BGP is used to
distribute VPN routing information across the SP backbone, this
value is prepended to the VPN's IPv4 address prefixes, creating a
new address family, the VPN-IPv4 address family. Thus, even when
two VPNs have overlapping IPv4 address spaces, they have unique
VPN-IPv4 address spaces.
- One or more Export Route Targets. A Route Target (RT) is a
globally unique 8-byte value that BGP carries, as the Extended
Communities Route Target attribute, along with routes that are
exported form the VRF.
- One or more Import Route Targets. This RT is used to select
routes to be imported from other VRFs into this VRF.
In the simplest cases and most common cases, the Export RT, Import
RT, and RD can be identical, and all VRFs in the same VPN will
distribute routes to each other (a typical intranet). In more
complex cases, they can be set differently, allowing a very fine
Rosen Informational [Page 5]
RFC 4365 Applicability Statement for BGP/MPLS IP VPNs February 2006
degree of control over the distribution of routes among VRFs. This
can be used to create extranets or to enforce various customer
policies. In complicated cases, particular Export RTs can be
assigned to particular routes using router management mechanisms.
One advantage to not requiring the RD to be the same as any RT is
that this may allow an RD value to be automatically determined for
each VRF; RT values, on the other hand, must always be configured.
Adding a new site to a VPN is a matter of attaching the site's CE
router to a PE router, configuring the interface, and, if a VRF for
that VPN already exists in the PE router, associating that interface
with the VRF. If a VRF for that VPN does not already exist in the
PE, then one must be configured as specified above. Changes to the
configuration of a PE are automatically reflected via BGP to the
other PEs.
The RTs and RDs are made unique by being structured as an SP
identifier followed by a number which is assigned by the identified
SP. SPs may be identified by their AS numbers, or by a registered IP
address owned by that SP.
Although RTs are encoded as BGP Extended Communities, the encoding
itself distinguishes them from any other kind of BGP Extended
Community.
3. Supported Topologies and Traffic Types
The scheme is optimized for full inter-site connectivity, in the
sense that this is what the simplest configurations provide.
However, the SP has full control, through the mechanism of Route
Targets, of the distribution of routing information among the set of
VRFs. This enables the SP to provide hub-and-spoke or partial mesh
connectivity as well as full mesh connectivity.
Note that, strictly speaking, the scheme does not create a topology,
as it does not create layer 2 connections among the sites. It does,
however, allow for control over the IP connectivity among the sites.
It is also possible to constrain the distribution of routing in
arbitrary ways, e.g., so that data from site A to site B must travel
through a third site C. (In fact, if it is desired to do so, this
level of control can be specified at the granularity of a single
route.)
It is possible for some of the routes from a particular customer site
A to be distributed to one set of remote sites, while other routes
from site A are distributed to a different set of remote sites. This
is done with the Route Target mechanism previously described.
Rosen Informational [Page 6]
RFC 4365 Applicability Statement for BGP/MPLS IP VPNs February 2006
Unicast IP traffic is fully supported. Customer IP packets are
passed transparently.
Multicast IP traffic is optionally supported, if the SP provides the
optional mechanisms of [BGP-MPLS-MCAST-VPN]. There are, however,
scaling implications to the use of these mechanisms. Discussion of
these implications is deferred.
Non-IP traffic is not supported. If support for non-IP traffic is
necessary, either the SP must additionally provide a layer 2
tunneling service or the customer must use IP tunneling.
In general, customer routers at different sites do not become routing
peers. However, a customer may, if he so desires, allow routers at
different sites to be routing peers over a link that is NOT part of
the VPN service. Such peering relationships are known as "IGP
backdoors". To ensure the proper operation of routing when IGP
backdoors are present, each VPN route that is distributed by the SP
is distributed along with a corresponding routing metric. This
enables the customer's IGP to compare the "backdoor routes" properly
with the routes that use the SP backbone. In the particular case
where a customer running OSPF within his sites wishes to have IGP
backdoors, he should run OSPF on the PE/CE link, and the PEs should
run the procedures of [VPN-OSPF]. (The CEs do NOT require any
special OSPF procedures.)
4. Isolated Exchange of Data and Routing Information
The Route Target mechanism is used to control the distribution of
routing information, so that routes from one VPN do not get sent to
another. VPN routes are treated by BGP as a different address family
than general Internet routes. Routes from a VRF do not get leaked to
the Internet unless the VRF has been explicitly configured to allow
it (and this is NOT the default).
The way in which a particular VPN is divided into sites, or the
topology of any particular VPN site, is hidden from the Internet and
from other VPNs. (Of course, if a particular site can receive
Internet traffic, and if it responds to traceroute probes from the
Internet, then any user of the Internet can learn something about the
site topology. The fact that the site is in a VPN does not make this
any easier or any harder.)
Similarly, Internet routes do not get leaked into the VPN, unless a
VRF of that VPN is explicitly configured to import the Internet
routes.
Rosen Informational [Page 7]
RFC 4365 Applicability Statement for BGP/MPLS IP VPNs February 2006
Proper configuration is essential to maintaining the isolation. In
particular, each access link must be associated with the proper VRF
for that access link, and each VRF must be configured with the proper
set of RTs.
A number of means for exchanging reachability information between the
PE and CE devices are supported: static routing, EBGP, and RIP are
supported by the procedures of [BGP-MPLS-IP-VPN]. If the procedures
of [VPN-OSPF] and [OSPF-2547-DNBIT] are implemented, OSPF may be
used. If OSPF is used between two VPN sites that are in the same
OSPF area, and if it is desired for routes over the VPN backbone to
be preferred to the OSPF intra-site routes, then the "sham link"
procedures of [VPN-OSPF] must be used.
The routing protocols used among the customer routers are not in any
way restricted by the VPN scheme, as whatever IGP is used within the
VPN, the PE/CE access links may run EBGP, or may otherwise be in a
different routing domain than the site's internal links.
BGP is used for passing routing information among SPs. BGP may be
authenticated by use of the TCP MD5 option, or by operating through
an IPsec tunnel.
Data traveling between two customer sites is encapsulated while in
transit through the backbone. The encapsulation contains sufficient
information to ensure that the packet is sent to the proper PE
router, and then, in conjunction with the VRF and related information
at that PE, to the proper CE routers.
If two VPNs attach to the same PE, there is strict separation of
forwarding at that PE, as well as strict separation of the routing
information.
Isolation of traffic is similar to that provided by classical L2 VPNs
which are based on Frame Relay or Asynchronous Transfer Mode (ATM).
As in classical L2 VPNs, the customer must rely on the SP to properly
configure the backbone network to ensure proper isolation and to
maintain the security of his communications gear.
Rosen Informational [Page 8]
RFC 4365 Applicability Statement for BGP/MPLS IP VPNs February 2006
5. Access Control and Authentication
No particular means of PE/CE authentication is specified for BGP/MPLS
IP VPNs. PE/CE mutual authentication may be done via any mechanism
supported by the routing protocol in which the CE and PE are peers
(e.g., use of the TCP MD5 authentication when the PE/CE protocol is
BGP), or by any other mechanism that may be desired. With such
mechanisms in place, a CE may not join a VPN until the CE
authenticates itself to the Service Provider.
There is, however, no standardized method that requires a CE to
authenticate itself to the customer network (rather than to the SP)
before the CE is allowed to join the VPN. This is for further study.
No particular means is specified for controlling which user data
packets can be forwarded by BGP/MPLS IP VPNs. BGP/MPLS IP VPNs are
compatible with Access Control Lists (ACLs) and any other filtering
features that are supported on the PE routers. Routing can be set up
so that extranet traffic is directly through a firewall, if that is
desired.
It is possible for various sorts of "tunnel interfaces" to be
associated with a VRF. In this case, whatever authentication is
natively used in the establishment of the tunnel interface may be
used. For example, an IPsec tunnel can be used as an "access link"
to attach a remote user or site to a VRF. The authentication
procedure in this case is part of IPsec, not part of the VPN scheme.
Where L2TP is used, each PPP session carried in an L2TP tunnel can be
associated with a VRF. The SP's Authentication, Authorization, and
Accounting (AAA) server can be used to determine the VPN to which the
PPP session belongs, and then the customer's AAA server can be given
the opportunity to authenticate that session as well.
6. Security Considerations
6.1. Protection of User Data
No particular means of ensuring user data security is specified for
BGP/MPLS IP VPNs.
The optional procedures of [MPLS/BGP-IPsec] may be used to provide
authentication and/or encryption of user data as it travels from the
ingress PE to the egress PE. However, the data is exposed at those
two PEs, as well as on the PE/CE access links.
Rosen Informational [Page 9]
RFC 4365 Applicability Statement for BGP/MPLS IP VPNs February 2006
The customer may provide his own user data security by using IPsec
tunnels that terminate within the customer sites. Such tunnels are
transparent to the VPN scheme. Schemes that discover the remote
tunnel endpoints automatically and then set up the tunnels
automatically as needed are the best fit with this VPN technology.
Note that there is no requirement in general that IPsec tunnels
between customer sites terminate at CE routers.
The use of end-to-end transport mode IPsec by the customer is also
transparent to the VPN scheme. In fact, the VPN scheme is compatible
with any use of security by the customer, as long as a cleartext IP
header is passed from CE to PE.
When data must cross the Internet to reach the ingress PE router,
IPsec tunnels between the end user and the PE router can be used; the
PE router must then associate each IPsec tunnel with the proper VRF.
This association would have to be based on user-specific information
provided by the Internet Key Exchange (IKE) protocol, such as a VPN-
id.
If data is going from one SP network to another, and must cross the
public Internet to get between those two networks, IPsec tunnels can
be used to secure the data. This would require bilateral agreement
between the two SPs. BGP connections can also be passed through an
IPsec tunnel if this is deemed necessary, in order to protect user
data, by a pair of SPs. QoS/SLA factors would have to be carefully
considered in this case.
6.2. SP Security Measures
The SP is responsible for preventing illegitimate traffic from
entering a VPN. VPN traffic is always encapsulated while traveling
on the backbone, so preventing illegitimate traffic is a matter of
ensuring that the PE routers to the encapsulation/decapsulation
correctly and that encapsulations have not been "spoofed", i.e., that
the encapsulated packets were actually encapsulated by PE routers.
This requires the SP to take various security measures. The PE and P
routers must themselves be secure against break-ins (either from
someone physically present or from the Internet), and neither P nor
PE routers should form routing adjacencies to other P or PE routers
without benefit of some kind of security. This may be authentication
in the IGP, or physical security.
Rosen Informational [Page 10]
RFC 4365 Applicability Statement for BGP/MPLS IP VPNs February 2006
The PE/CE access link should be secured in some manner, though the
provider may make it the responsibility of the customer to ensure
that the CE is secure from compromise. If the PE/CE access link is a
tunnel over the Internet, then of course some sort of authentication
protocol should always be used.
Label Distribution Protocol (LDP) sessions and BGP sessions between
PE and/or P routers should be authenticated. This can be done via
the TCP MD5 option or by use of IPsec.
If the SP is providing the VPN service over an MPLS backbone, it
should not accept MPLS packets from its external interfaces (i.e.,
interfaces to CE devices or to other providers' networks) unless the
top label of the packet was legitimately distributed to the system
from which the packet is being received. If the packet's incoming
interface leads to a different SP (rather than to a customer), an
appropriate trust relationship must also be present, including the
trust that the other SP also provides appropriate security measures.
If the SP is providing the VPN service by using an IP (rather than an
MPLS) encapsulation, or if it accepts IP-encapsulated VPN packets
from other SPs, it should apply filtering at its borders so that it
does not accept from other SPs or from customers any IP packets that
are addressed to the PE routers, unless appropriate trust
relationships are in place.
Cryptographic authentication of the encapsulated data packets is
certainly advantageous when there are multiple SPs providing a single
VPN.
When a dynamic routing protocol is run on the link between a CE
router and a PE router, routing instability in the private network
may have an effect on the PE router. For example, an unusually large
number of routing updates could be sent from the CE router to the PE
router, placing an unusually large processing load on the PE router.
This can potentially be used as a Denial-of-Service (DoS) attack on
the PE router.
This issue can be mitigated via resource partitioning in the PE, in
order to limit the amount of resources (e.g., CPU and memory) that
any one VPN is permitted to use in PE routers. Also, rate limits may
be applied to the routing traffic sent from the CE to the PE.
Alternately, when this problem is detected, the CE-to-PE interface
may be shut down.
Network management traffic from the CE to the PE may be rate limited
(for example, to prevent network management traffic from CE to PE to
be used in a DoS attack).
Rosen Informational [Page 11]
RFC 4365 Applicability Statement for BGP/MPLS IP VPNs February 2006
6.3. Security Framework Template
Section 9 of [L2VPN-SEC-FRMWRK] provides "a brief template that may
be used to evaluate and summarize how a given PPVPN [Provider-
Provisioned Virtual Private Network] approach (solution) measures up
against the PPVPN Security Framework". It further states "an
evaluation using this template should appear in the applicability
statement for each PPVPN approach". The purpose of this subsection
is to provide the information in the form required by this template.
Security requirements that are relevant only to L2VPNs are not
applicable and are not further discussed.
- Does the approach provides complete IP address space separation
for each L3VPN?
Yes.
The IP address prefixes from a particular VPN appear in their
native form only in routing tables that are specific to the
particular VPN. They are distributed in their native form only
by routing instances that are specific to the particular VPN.
When address prefixes from different VPNs are combined into a
common table, or distributed by a common mechanism, the address
prefixes are first prepended with a Route Distinguisher (RD).
The RD is a 64-bit quantity, structured so that globally unique
RD values can easily be created by an SP. As long as no two VPNs
are assigned the same RD value, complete IP address space
separation is provided. It is however possible for an SP to
misconfigure the RD assignments.
- Does the approach provide complete IP route separation for each
L3VPN?
Yes.
The distribution of routes is controlled by assigning import and
export Route Targets (RTs). A route that is exported from a VRF
carries an RT specified by the SP as an export RT for that VRF.
The route can be imported into other VRFs only if the RT that it
carries has been configured by the SP as an import RT for those
other VRFS. Thus, the SP has complete control over the set of
VRFs to which a route will be distributed. It is of course
possible for the SP to misconfigure the RT assignments.
Rosen Informational [Page 12]
RFC 4365 Applicability Statement for BGP/MPLS IP VPNs February 2006
- Does the approach provide a means to prevent improper cross-
connection of sites in separate VPNs?
This requirement is addressed in a way that is beyond the scope
of the VPN mechanisms.
In BGP/MPLS IP VPNs, an SP makes a particular site part of a
particular VPN by configuring the PE router's interface to that
site to be associated with a particular VRF in that PE. The VRF
is configured with import and export RTs, and it is the way in
which VRFs are configured with RTs in the various PEs that
results in a particular set of sites being connected as a VPN.
Connecting the sites properly in this way is regarded as a
network management function, and the VPN scheme itself does not
provide a means to prevent misconfiguration.
The VPN scheme does not provide any particular method for
ensuring that a given interface from a PE leads to the CE that is
expected to be there. If a routing algorithm is run on a
particular PE/CE interface, any security procedures that the
routing algorithm provides (e.g., MD5 authentication of BGP
sessions) can be used; this is outside the scope of the VPN
scheme. Also, a CE can attach to a PE via an IPsec tunnel, if
this is desired, for a greater degree of security.
- Does the approach provide a means to detect improper cross-
connection of sites in separate VPNs?
The base specifications for BGP/MPLS IP VPNs do not provide a
means for detecting that a site has been connected to the wrong
VPN. However, the optional procedure specified in [CE-VERIF]
does provide such a means. Basically, each PE obtains, via
protocol, a secret from each CE to which it is directly attached.
When the routes from a given CE are distributed, the secret from
that CE is attached as an attribute of the route. This secret
will ultimately be distributed to any other CE that receives any
route from the given CE. A CE that is not supposed to be part of
a given VPN will not know the right secret, and if it is
connected to the given VPN the other CEs in that VPN will realize
that a CE that doesn't know the proper secret has been connected
to the VPN.
- Does the approach protect against the introduction of
unauthorized packets into each VPN?
We must look separately at the various points at which one might
attempt to introduce unauthorized packets.
Rosen Informational [Page 13]
RFC 4365 Applicability Statement for BGP/MPLS IP VPNs February 2006
* Packets arriving at a PE over a PE/CE interface
If a given PE is directly connected to a given CE, the PE
will accept any packets that the CE sends it. The VPN scheme
has no special procedures for determining that these packets
actually came from the CE. However, various means of
securing the PE/CE connection can be used (for instance, the
PE and CE can be connected by an IPsec tunnel) if desired.
That is, this aspect of the requirement can be addressed by
means that are outside the scope of the VPN specification.
Once a packet has been accepted from a CE by a PE, the packet
is routed according to the VRF associated with that PE's
interface to that CE. Such packets can only be sent along
routes that are in that VRF. There is no way a packet from a
CE can be routed to an arbitrary VPN. In particular, there
is nothing a VPN user can do to cause any particular packet
to be sent to the wrong VPN. So this aspect of the
requirement is fully addressed.
* Packets arriving at a PE over an interface from the backbone
The optional procedures of [MPLS/BGP-IPsec] can be used to
ensure that a packet that is received by a PE from the
backbone will not be recognized as a VPN packet unless it
actually is one. Those procedures also ensure that a
received VPN packet came from a particular PE and that it
carries the MPLS label that that PE put on it. These
procedures protect the packet from ingress PE to egress PE,
but do not protect the PE/CE interfaces.
If the optional procedures of [MPLS/BGP-IPsec] are not used,
then the following considerations apply.
Undetected corruption of the routing information carried in a
packet's VPN encapsulation can result in misdelivery of the
packet, possibly to the wrong VPN.
If a packet enters an SP's network on an interface other than
a PE/CE interface, the SP should ensure that the packet
either does not look like a VPN packet or else is not routed
to a PE router. This can be done in a variety of ways that
are outside the scope of the VPN scheme. For example, IP
packets addressed to the PE routers can be filtered, MPLS
packets (or, e.g., MPLS-in-IP) from outside the SP network
can be refused, etc.
Rosen Informational [Page 14]
RFC 4365 Applicability Statement for BGP/MPLS IP VPNs February 2006
In the case of a multi-provider L3VPN backbone, the SP will
have to know which interfaces lead to SPs that are VPN
partners, so that VPN packets can be allowed to flow on those
interfaces.
If the public Internet is used as the L3VPN backbone,
protection against unauthorized packets cannot be achieved by
the above measures. IPsec tunnels should always be used to
carry VPN traffic across the public Internet.
- Does the approach provide confidentiality (secrecy) protection,
sender authentication, integrity protection, or protection
against replay attacks for PPVPN user data?
If these are desired, they must be provided by mechanisms that
are outside the scope of the VPN mechanisms. For instance, the
users can use secure protocols on an end-to-end basis, e.g.,
IPsec, Secure Shell (SSH), Secure Sockets Layer (SSL), etc.
- Does the approach provide protection against unauthorized traffic
pattern analysis for PPVPN user data?
Preventing an observer from obtaining traffic pattern analysis
from the SP network is beyond the scope of the VPN mechanisms.
- Do the control protocol(s) used for each of the following
functions provide for message integrity and peer authentication?
* VPN membership discovery
This requirement is fully satisfied. Membership discovery is
done by means of BGP. Control message integrity and peer
authentication in BGP may be achieved by use of the TCP MD5
option.
* Tunnel establishment
The answer to this question depends of course on the tunnel
protocol and tunnel establishment protocol; a variety of
different tunneling schemes can be used in BGP/MPLS IP VPNs.
Thus, this question is out of scope.
In the common case where the tunnels are MPLS Label Switching
Routers (LSRs) established by LDP, then control message
integrity and peer authentication may be achieved by use of
the TCP MD5 option.
Rosen Informational [Page 15]
RFC 4365 Applicability Statement for BGP/MPLS IP VPNs February 2006
* VPN topology and reachability advertisement
With respect to PE-PE interactions, the relevant control
protocol is BGP, so control message integrity and peer
authentication can be achieved by use of the TCP MD5 option.
With respect to CE-PE interactions, the answer depends on the
protocol used for exchanging information between PE and CE,
as the security mechanisms (if any) of those protocols would
need to be used. In the common case where the PE/CE protocol
is BGP, the TCP MD5 option can be used.
* VPN provisioning and management
The protocols procedures for provisioning VPNs and managing
the PE routers are outside the scope of the VPN scheme.
* VPN monitoring and attack detection and reporting
The protocols and procedures for monitoring the VPNs are
outside the scope of the VPN scheme.
- What protection does the approach provide against PPVPN-specific
DoS attacks (i.e., inter-trusted-zone DoS attacks)?
* Protection of the service provider infrastructure against
Data Plane or Control Plane DoS attacks originated in a
private (PPVPN user) network and aimed at PPVPN mechanisms.
The PE/CE interfaces of a given VPN will generally be
addressable from within that VPN. Apart from that, a user
within an L3VPN has no more access to the service provider
infrastructure than does any user of the Internet.
Therefore, we will focus in this section on possible DoS
attacks against a PE router that may occur when traffic from
within a VPN is addressed to a PE router.
A user within the VPN may address traffic to a PE router and
may attempt to send an excessive amount of traffic to it.
Presumably, the PE routers will not accept unauthorized TCP
connections or Simple Network Management Protocol (SNMP)
commands, so such traffic will be thrown away; the danger is
that the PE may need to use a significant proportion of its
capacity to discard such traffic. However, this case is no
different than the case of any SP access router that attaches
to subscriber equipment. The presence of the VPN mechanisms
does not make the PE any more or less vulnerable to DoS
attacks from arbitrary end users.
Rosen Informational [Page 16]
RFC 4365 Applicability Statement for BGP/MPLS IP VPNs February 2006
* Protection of the service provider infrastructure against
Data Plane or Control Plane DoS attacks originated in the
Internet and aimed at PPVPN mechanisms.
DoS attacks of this sort can be prevented if the PE routers
are not addressable from the Internet. Alternatively, an SP
can apply address filtering at its boundaries so that packets
from the Internet are filtered if they are addressed to a PE
router.
* Protection of PPVPN users against Data Plane or Control Plane
DoS attacks originated from the Internet or from other PPVPN
users and aimed at PPVPN mechanisms.
Mechanisms already discussed prevent users in a VPN from
receiving packets from the Internet, unless this is
specifically allowed. In the case where it is specifically
allowed, it is no different than any other situation in which
a network is connected to the Internet, and there is no
special vulnerability to DoS attacks due to the L3VPN
mechanisms.
There is nothing to prevent a user in a VPN from mounting a
DoS attack against other users in the VPN. However, the
L3VPN mechanisms make this neither more nor less likely.
- Does the approach provide protection against unstable or
malicious operation of a PPVPN user network?
* Protection against high levels of, or malicious design of,
routing traffic from PPVPN user networks to the service
provider network.
If a dynamic routing algorithm is running on the PE/CE
interface, it can be used to mount an attack on the PE
router, by having the CE present the PE with an excessive
number of routing events. If an end user within a VPN
successfully attacks the routing algorithm of the VPN, that
might also result in an excessive number of routing events
being seen by the PE router. This sort of attack can be
ameliorated by having the PE limit the amount of its
resources that can be expended processing routing events from
a particular VPN. If the PE/CE routing algorithm is BGP,
then such mechanisms as route flap damping may be appropriate
as well.
Rosen Informational [Page 17]
RFC 4365 Applicability Statement for BGP/MPLS IP VPNs February 2006
* Protection against high levels of, or malicious design of,
network management traffic from PPVPN user networks to the
service provider network.
A user in a BGP/MPLS IP VPN has no more ability than any
Internet user to send management traffic to the service
provider network.
* Protection against worms and probes originated in the PPVPN
user networks, sent towards the service provider network.
A user in a BGP/MPLS IP VPN has no more ability than any
Internet user to send worms or probes to the service provider
network.
7. Addressing
Overlapping customer addresses are supported. There is no
requirement that such addresses be in conformance with [RFC1918].
There is no requirement that customer VPN addresses be distinct from
addresses in the SP network.
Any set of addresses used in the VPN can be supported, irrespective
of how they are assigned, how well they aggregate, and whether they
are public or private. However, the set of addresses that are
reachable from a given site must be unique.
Network address translation for packets leaving/entering a VPN is
possible and is transparent to the VPN scheme.
There is nothing in the architecture to preclude the mechanisms from
being extended to support IPv6, provided that the appropriate IPv6-
capable routing algorithms are in place. That is, PE/CE routing must
support IPv6, and the PE-PE BGP must support the labeled IPv6 address
family. The latter has not been specified, but its specification is
obvious from the specification of the labeled IPv4 address family.
The IGP used in the SP backbone need not be IPv6 capable in order to
support customer IPv6 networks.
In theory, the same could be said of other network layers, but in
practice a customer who has non-IP traffic to carry must expect to
carry it either in site-to-site IP tunnels or using some additional
service (such as a layer 2 service) from the SP.
Layer 2 addresses and identifiers are never carried across the SP
backbone.
Rosen Informational [Page 18]
RFC 4365 Applicability Statement for BGP/MPLS IP VPNs February 2006
No restrictions are placed on the customer's addressing schemes or
policies. Note though that the SP may place restrictions on the
number of routes from a given customer site, or may charge
differentially depending on the number of such routes, and such
restrictions may have implications for the customer's addressing
scheme. In particular, addressing schemes that facilitate route
aggregation on a per-site basis will result in the most efficient use
of the SP's resources, and this may be reflected in SP charging
policies.
8. Interoperability and Interworking
Interoperability should be ensured by proper implementation of the
published standards.
Direct PE-PE interworking over the SP backbone with other VPN
solutions is not supported.
As all the different types of L3VPNs are IP networks, they can of
course interwork in the same way that any two IP networks can
interwork. For example, a single site can contain a CE router of one
VPN scheme and a CE router of another VPN scheme, and these CE
routers could be IGP peers, or they might even be the same CE router.
This would result in the redistribution of routes from one type of
VPN to the other, providing the necessary interworking.
9. Network Access
9.1. Physical/Link Layer Topology
The architecture and protocols do not restrict the link layer or the
physical layer in any manner.
9.2. Temporary Access
Temporary access via PPP is possible, using industry standard PPP-
based authentication mechanisms. For example:
- A dial-up user (or other PPP user) is authenticated by the PE,
using the SP's AAA server, based on a login string or on the
number dialed.
- The SP's AAA server returns a VPN-id to PE.
- The PE assigns the user to a VRF, based on that VPN-id.
Rosen Informational [Page 19]
RFC 4365 Applicability Statement for BGP/MPLS IP VPNs February 2006
- The user is then authenticated by a AAA server within the VPN
(i.e., managed by the customer rather than by the SP). This AAA
server would typically be addressed through the VRF (i.e., may be
in VPN's private address space).
- The user gets disconnected if either authentication step is
unsuccessful.
IPsec access to a VRF is also possible. In this case, the security
association is between the end user and the SP.
In these ways, a user can access a BGP/MPLS IP VPN via the public
Internet.
There is no explicit support for mobility, other than what is stated
above.
9.3. Access Connectivity
Homing of a CE to two or more PEs is fully supported, whether or not
the PEs are on the same SP network.
If a CE is connected to two or more PEs, all its PE/CE links can be
used to carry traffic in both directions. In particular, traffic
from different ingress PEs to a particular CE may arrive at that CE
over different PE/CE links. This depends on the backbone network
routing between the CE and the various ingress PEs.
If a VRF on a particular ingress PE contains several routes to a
particular destination, then traffic from that ingress PE can be
split among these routes. If these routes end with different PE/CE
links, then traffic from that ingress PE will be split among those
links.
BGP contains a multitude of knobs that allow an SP to control the
traffic sent on one PE/CE link as opposed to the other. One can also
make use of the Link Bandwidth extended community [BGP-EXT-COMM] to
control how traffic is distributed among multiple egress PE/CE links.
The VPN scheme is of course compatible with the use of traffic
engineering techniques, Resource Reservation Protocol - Traffic
Engineering (RSVP-TE) based or otherwise, in the backbone network.
Rosen Informational [Page 20]
RFC 4365 Applicability Statement for BGP/MPLS IP VPNs February 2006
10. Service Access
10.1. Internet Access
Internet access and VPN access are possible from the same site. This
is even possible over the same interface, as long as the VPN's
internal addresses are distinct from the addresses of the systems
that must be reached via the Internet. This requires only that
Internet routes as well as VPN routes be imported into the VRF
associated with that interface. This may be as simple as putting a
default route to the Internet into that VRF.
The "route to the Internet" that is in a particular VRF need not lead
directly to the Internet; it may lead to a firewall or other security
device at another site of the VPN. The VPN customer can cause this
to happen simply by exporting a default route from the site with the
firewall. Generally, a site with a firewall will use a different
virtual interface for Internet access than for VPN access, since the
firewall needs to distinguish the "clean interface" from the "dirty
interface".
In such a configuration, the customer would export his routes to the
Internet via the firewall's dirty interface, but would export the
same routes to the VPN via the clean interface. Thus, all traffic
from the Internet would come through the dirty interface, then
through the firewall, and possibly go to another VPN site though the
clean interface. This also allows any necessary Network Address
Translation (NAT) functionality to be done in the firewall.
10.2. Other Services
Any externally provided service can be accessed from the VPN,
provided that it can be addressed with an address that is not
otherwise in use within the VPN. Access can be firewalled or non-
firewalled. If the client accessing the service does not have a
globally unique IP address, and a single server provides a service to
multiple VPNs, NAT will have to be applied to the client's packets
before they reach the server. This can be done at a customer site,
or by a VRF-specific NAT function in a PE router.
Rosen Informational [Page 21]
RFC 4365 Applicability Statement for BGP/MPLS IP VPNs February 2006
11. SP Routing
Routing through the backbone is independent of the VPN scheme and is
unaffected by the presence or absence of VPNs. The only impact is
that the backbone routing must carry routes to the PE routers.
The VPN routes themselves are carried in BGP as a distinct address
family, different than the address family that is used to carry
"ordinary" IP routes. These routes are passed from PE router to
Route Reflector to PE router, and are never seen by the P routers.
The Route Reflectors that carry the VPN routes can be entirely
separate from the Route Reflectors that carry the "ordinary" IP
routes.
The fact that two PE routers support a common VPN does not require
those PE routers to form an IGP routing adjacency between themselves.
The number of adjacencies in the backbone IGP is independent of and
unrelated to the number of VPNs supported by any set of PE routers.
No VPN-specific protection and restoration mechanisms are needed;
these are general routing considerations, and the VPN scheme is
compatible with any protection and restoration mechanisms that may be
available.
The SP does not manage the customer's IGP in any way, and routes are
never leaked between the SP's IGP and any customer's IGP.
If the PE/CE protocol is EBGP, the SP and the customer do not ever
participate in a common IGP.
12. Migration Impact
Generally, this means replacement of an existing legacy backbone with
VPN backbone. The general migration mechanism would be to hook up
the sites one at a time to the VPN backbone, and to start giving the
routes via the VPN backbone preference to routes via the legacy
backbone. Details depend on the legacy backbone's IGP. In general,
one would have to manipulate the IGP metrics to provide the proper
route preference.
If the legacy backbone routing protocol is OSPF, then migration is
best done with OSPF as the PE/CE protocol and the PE supporting the
[VPN-OSPF] procedures, OR with BGP as the PE/CE protocol, and the CE
supporting the BGP/OSPF interaction specified in [VPN-OSPF].
With other legacy backbone routing protocols, the proper metrics must
be set at the point (PE or CE) where the BGP routes from the SP
network are being redistributed into the legacy IGP.
Rosen Informational [Page 22]
RFC 4365 Applicability Statement for BGP/MPLS IP VPNs February 2006
13. Scalability
There is no upper limit on the number of VPNs per SP network, as
there is no one box in the SP network that needs to know of all VPNs.
Knowledge of a particular VPN is confined to the PE routers that
attach to sites in that VPN, and to the BGP Route Reflectors that
receive routing data from those PEs; other systems maintain no state
at all for the VPN. Note though that there is no need for any one
Route Reflector to know of all VPNs.
If the SP is providing the VPN service over an MPLS backbone, then
the backbone IGP must carry a host route for every Label Switched
Path (LSP) egress node within the routing domain. Every PE router in
the routing domain is an LSP egress node. If there are VPNs attached
to PE routers that are within the routing domain, as well as PE
routers that are in some second routing domain, then the border
routers leading towards the second routing domain will also be LSP
egress nodes. Thus, the sum of the number of PE routers plus number
of border routers within a routing domain is limited by the number of
routes that can be carried within the domain's IGP. This does not
seem to create any practical scalability issue.
There is no upper limit on the number of site interfaces per VPN, as
state for a particular interface is maintained only at the PE router
to which that interface attaches. The number of site interfaces per
VPN at a given PE router is limited only by the number of interfaces
that that PE router can support.
The number of routes per VPN is constrained only by the number of
routes that can be supported in BGP, the number of routes that can be
maintained in the PEs that attach to that VPN, and the number of
routes that can be maintained in the BGP Route Reflectors that hold
the routes of that VPN.
The major constraint in considering scalability is the number of
routes that a given PE can support. In general, a given PE can
support as many VPNs as it has interfaces (including virtual
interfaces or "sub-interfaces", not just physical interfaces), but it
is constrained in the total number of routes it can handle. The
number of routes a given PE must handle depends on the particular set
of VPNs it attaches to, and the number of routes in each such VPN,
and the number of "non-VPN" Internet routes (if any) that it must
also handle.
The SP may need to engage in significant planning to ensure that
these limits are not often reached. If these limits are reached, it
may be necessary either to replace the PE with one of larger capacity
or to reorganize the way in which access links lead from CEs to PEs,
Rosen Informational [Page 23]
RFC 4365 Applicability Statement for BGP/MPLS IP VPNs February 2006
in order to better concentrate the set of access links from sites
that are in the same VPN. Rehoming a site to a different PE may not
involve actual rewiring; if the access technology is switched, this
is a matter of provisioning, but may still be a significant
undertaking. If it is necessary to have downtime while performing
the rehoming, the customer is impacted as well. Rehoming can also be
done "virtually", by creating a layer 2 tunnel from a CE's "old" PE
to its "new" PE.
An important consideration to remember is that one may have any
number of INDEPENDENT BGP systems carrying VPN routes. This is
unlike the case of the Internet, where the Internet BGP system must
carry all the Internet routes. The difference stems from the fact
that all Internet addresses must be reachable from each other, but a
given VPN address is only supposed to be reachable from other
addresses in the same VPN.
Scalability is also affected by the rate of changes in the
reachability advertisements from CE to PE, as changes reported by a
CE to its attached PE may be propagated to the other PEs. BGP
mechanisms to control the rate of reported changes should be used by
the SP.
Another constraint on the number of VPNs that can be supported by a
particular PE router is based on the number of routing instances that
the PE router can support. If the PE/CE routing is static, or is
done by BGP, the number of routing protocol instances in a PE device
does not depend on the number of CEs supported by the PE device. In
the case of BGP, a single BGP protocol instance can support all CEs
that exchange routing information using BGP. If the PE/CE router is
done via RIP or OSPF, then the PE must maintain one RIP or OSPF
instance per VRF. Note that the number of routing instances that can
be supported may be different for different routing protocols.
Inter-AS scenarios constructed according to option (b) of section 10
of [BGP-MPLS-IP-VPN] require BGP "border routers" to hold the routes
for a set of VPNs. If two SPs share in a small number of VPNs, a
single border router between them provides adequate capacity. As the
number of shared VPNs increases, additional border routers may be
needed to handle the increased number of routes. Again, no single
border router would handle all the routes from all the VPNs, so an
increase in the number of VPNs can always be supported by adding more
border routers.
Inter-AS scenarios constructed according to option (c) of section 10
of [BGP-MPLS-IP-VPN] eliminate the need for border routers to contain
VPN routes (thus improving scalability in that dimension), but at the
cost of requiring that each AS have a route to the PEs in the others.
Rosen Informational [Page 24]
RFC 4365 Applicability Statement for BGP/MPLS IP VPNs February 2006
(Inter-AS scenarios constructed according to option (a) of section 10
of [BGP-MPLS-IP-VPN] do not scale well.)
The solution of [BGP-MPLS-IP-VPN] is intended to simplify CE and site
operations, by hiding the structure of the rest of the VPN from a
site, and by hiding the structure of the backbone. Thus, CEs need
have only a single sub-interface to the backbone, CEs at one site
need not even be aware of the existence of CEs at another, and CEs at
one site need not be routing peers of CEs at another. CEs are never
routing peers of P routers. These factors help to scale the
customer's network, but limiting the number of adjacencies each CE
must see, and by limiting the total number of links that the
customer's IGP must handle.
The solution of [BGP-MPLS-IP-VPN] is also intended to simplify the
SP's VPN provisioning, so that potentially the SP will have to do
little more than say which sites belong to which VPNs. However, as
the system scales up, planning is needed to determine which PEs
should home which VPNs, and which BGP RRs should take which VPNs'
routing information.
P routers maintain NO per-VPN state at all; the only requirement on
them is to maintain routes to the PE routers. When MPLS is used, a P
router must also maintain one multipoint-to-point LSP for each such
route.
However, certain VPN multicast schemes require per-multicast-group
state in the P routers, summed over all VPNs. Others require only no
state in the P routers at all, but will result in sending more
unnecessary traffic. The complete set of tradeoffs for multicast is
not that well understood yet.
Note that as the scaling of a particular PE is primarily a matter of
the total number of routes that it must maintain, scalability is
facilitated if the addresses are assigned in a way that permits them
to be aggregated (i.e., if the customers have a sensible addressing
plan).
When a dynamic routing protocol is run on the link between a CE
router and a PE router, routing instability in the private network
may have an effect on the PE router. For example, an unusually large
number of routing updates could be sent from the CE router to the PE
router, placing an unusually large processing load on the PE router.
This issue can be mitigated via resource partitioning in the PE, in
order to limit the amount of resources (e.g., CPU and memory) that
any one VPN is permitted to use in PE routers. Also, rate limits may
be applied to the routing traffic sent from the CE to the PE.
Rosen Informational [Page 25]
RFC 4365 Applicability Statement for BGP/MPLS IP VPNs February 2006
Alternately, when this problem is detected, the CE-to-PE interface
may be shut down.
14. QoS, SLA
The provision of appropriate QoS capabilities may require any
combination of the following:
- QoS in the access network.
- Admission control (policing) by the PE router on the ingress
access links.
- Traffic conditioning (shaping) by the PE router on the ingress
access links.
- Traffic engineering in the backbone.
- Intserv/diffserv classification by the PE, for traffic arriving
from the CE. Once the PE classifies the user packets, this
classification needs to be preserved in the encapsulation (MPLS
or IP) used to send the packet across the backbone.
- Differentiated Services Codepoint (DSCP) mapping.
- DSCP transparency.
- Random Early Discard in the backbone.
None of these features are VPN-specific. The ability to support them
depends on whether the features are available on the edge and core
platforms, rather than on any particular VPN scheme.
MPLS support for differentiated services is detailed in RFC 3270
[MPLS-DIFFSERV]. DSCP mapping and transparency are covered in
section 2.6 of that document.
It is possible to use traffic engineering to provide, e.g.,
guaranteed bandwidth between two PEs for the traffic of a given VPN.
The VRF entries for that VPN in each PE need to be modified so that
the traffic to the other PE is directed onto the traffic-engineered
path. How this is done is a local matter.
BGP/MPLS IP VPNs can support both the "hose model" and the "pipe
model" of QoS. In the "pipe model", a particular quality of service
(e.g., a guaranteed amount of bandwidth) would be applied to all or
some of the packets traveling between a given pair of CEs. In the
"hose model", a particular quality of service (e.g., a guaranteed
Rosen Informational [Page 26]
RFC 4365 Applicability Statement for BGP/MPLS IP VPNs February 2006
amount of bandwidth) would be applied to all traffic to or from a
particular CE, irrespective of which other CE the traffic is going to
or coming from. Since BGP/MPLS IP VPNs do not usually make use of
CE-CE tunnels, the hose model is the more natural fit. Providing the
pipe model would require the use of traffic engineering to explicitly
create the necessary tunnels.
Many of the requirements specified in [L3VPN-REQS] stipulate that the
Network Monitoring System (NMS) should support SLA monitoring and
verification between the SP and the various customers by measurement
of the indicators defined within the context of the SLA. The
measurement of these indicators (i.e., counters) can be achieved when
BGP/MPLS IP VPNs are used by employing a combination of the
Management Information Base (MIB) module designed for BGP/MPLS IP
VPNs [L3VPN-MIB] as well as other standard MIB modules such as the
IF-MIB [IF-MIB]. Devices supporting these MIB modules can calculate
SLAs based on real-time performance measurements using indicators and
threshold crossing alerts. Devices can make these thresholds
configurable either via a management interface such as SNMP.
15. Management
The L3VPN Requirements document [L3VPN-REQS] stipulates that the term
"Provider Provisioned VPN" refers to VPNs for which the service
provider participates in management and provisioning of the VPN. RFC
BGP/MPLS IP VPNs can be provisioned and managed to meet these
requirements. The following subsections will outline how devices
supporting BGP/MPLS IP VPNs can satisfy these requirements.
15.1. Management by the Provider
The SP manages all the VPN-specific information in the PE device.
This can be done using the MIB designed for BGP/MPLS IP VPNs
[L3VPN-MIB], in combination with other standard MIB modules such as
IF-MIB [IF-MIB], and other MPLS MIB modules [LSRMIB], [LDPMIB],
[TEMIB], [FTNMIB].
Devices supporting BGP/MPLS IP VPNs that employ the management
interface characteristics described above will also support the ITU-T
Telecommunications Management Network Model "FCAPS" functionalities
as required in the L3VPN Requirements document. These include Fault,
Configuration, Accounting, Provisioning, and Security.
In BGP/MPLS IP VPNs, the SP is not required to manage the CE devices.
However, if it is desired for the SP to do so, the SP may manage CE
devices from a central site, provided that a route to the central
site is exported into the CE's VPN, and the central site is in a VPN
into which the routes to the managed CE devices have been imported.
Rosen Informational [Page 27]
RFC 4365 Applicability Statement for BGP/MPLS IP VPNs February 2006
This is a form of extranet.
If the central site is managing CE devices from several VPNs, those
CE devices must have mutually unique addresses. Note that this does
not enable the CE devices from different VPNs to reach each other.
The CE devices have no VPN-specific information in them. Hence the
fact that they are connected together into a VPN does not require
them to have any VPN-specific management MIB modules or capabilities.
15.2. Management by the Customer
CE devices may be managed from within the VPN, transparently to the
SP. The CE devices have no VPN-specific information in them, and the
fact that they are tied together into a VPN does not impact the
customer's management of them.
Customer access to a PE device is totally at the discretion of the
SP, but is not required by the solution. The PE device is a routing
peer of a CE device, and can be pinged, etc.
If a customer is permitted to access the PE router for management
purposes, the functions available to any particular customer need to
be strictly controlled, and the use of resource partitioning may be
appropriate.
Network management traffic from the CE to the PE may be rate limited
(for example, to prevent network management traffic from CE to PE to
be used in a DoS attack).
16. Acknowledgements
Many thanks to Jeremy De Clercq, Luyuan Fang, Dave McDysan, Ananth
Nagarajan, Yakov Rekhter, and Muneyoshi Suzuki, for their comments,
criticisms, and help in preparing this document. Thanks also to
Thomas Nadeau for his help with the section on management, to
Francois LeFaucheur for his help with the section on QoS, and to Ross
Callon for his review of the document.
Rosen Informational [Page 28]
RFC 4365 Applicability Statement for BGP/MPLS IP VPNs February 2006
17. Normative References
[BGP-EXT-COMM] Sangli, S., Tappan, D., and Y. Rekhter, "BGP
Extended Communities Attribute", RFC 4360,
February 2006.
[BGP-MPLS-IP-VPN] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual
Private Networks (VPNs)", RFC 4364, February
2006.
[L3VPN-FRMWRK] Callon, R. and M. Suzuki, "A Framework for Layer
3 Provider-Provisioned Virtual Private Networks
(PPVPNs)", RFC 4110, July 2005.
[L3VPN-REQS] Carugi, M. and D. McDysan, "Service Requirements
for Layer 3 Provider Provisioned Virtual Private
Networks (PPVPNs)", RFC 4031, April 2005.
[L2VPN-SEC-FRMWRK] Fang, L., "Security Framework for Provider-
Provisioned Virtual Private Networks (PPVPNs)",
RFC 4111, July 2005.
18. Informative References
[VPN-OSPF] Rosen, E., Psenak, P., and P. Pillay-Esnault,
"OSPF as the PE/CE Protocol in BGP/MPLS VPNs",
Work in Progress, February 2004.
[OSPF-2547-DNBIT] Rosen, E., Psenak, P., and P. Pillay-Esnault,
"Using an LSA Options Bit to Prevent Looping in
BGP/MPLS IP VPNs", Work in Progress, March 2004.
[MPLS/BGP-IPsec] Rosen, E., De Clercq, J., Paridaens, O.,
T'Joens, Y., and C. Sargor, "Architecture for
the Use of PE-PE IPsec Tunnels in BGP/MPLS IP
VPNs", Work in Progress, March 2004.
[BGP-MPLS-MCAST-VPN] Rosen, E., Cai, Y., and IJ. Wijsnands,
"Multicast in MPLS/BGP VPNs", Work in Progress,
May 2004.
[CE-VERIF] Bonica, R., Rekhter, Y., Raszuk, R., Rosen, E.,
and D. Tappan, "CE-to-CE Member Verification for
Layer 3 VPNs", Work in Progress, September 2003.
Rosen Informational [Page 29]
RFC 4365 Applicability Statement for BGP/MPLS IP VPNs February 2006
[FTNMIB] Nadeau, T., Srinivasan, C., and A. Viswanathan,
"Multiprotocol Label Switching (MPLS) Forwarding
Equivalence Class To Next Hop Label Forwarding
Entry (FEC-To-NHLFE) Management Information Base
(MIB)", RFC 3814, June 2004.
[IPSEC-VPN] De Clercq, J., Paridaens, O., Krywaniuk, A., and
C. Wang, "An Architecture for Provider
Provisioned CE-based Virtual Private Networks
using IPsec", Work in Progress, February 2004.
[LDPMIB] Cucchiara, J., Sjostrand, H., and J. Luciani,
"Definitions of Managed Objects for the
Multiprotocol Label Switching (MPLS), Label
Distribution Protocol (LDP)", RFC 3815, June
2004.
[LSRMIB] Srinivasan, C., Viswanathan, A., and T. Nadeau,
"Multiprotocol Label Switching (MPLS) Label
Switching Router (LSR) Management Information
Base (MIB)", RFC 3813, June 2004.
[MPLS-DIFFSERV] Le Faucheur, F., Wu, L., Davie, B., Davari, S.,
Vaananen, P., Krishnan, R., Cheval, P., and J.
Heinanen, "Multi-Protocol Label Switching (MPLS)
Support of Differentiated Services", RFC 3270,
May 2002.
[L3VPN-MIB] Nadeau, T. and H. Van Der Linde, "MPLS/BGP
Virtual Private Network Management Information
Base Using SMIv2", Work in Progress, August
2004.
[IF-MIB] McCloghrie, K. and F. Kastenholz, "The
Interfaces Group MIB", RFC 2863, June 2000.
[RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de
Groot, G., and E. Lear, "Address Allocation for
Private Internets", BCP 5, RFC 1918, February
1996.
[TEMIB] Srinivasan, C., Viswanathan, A., and T. Nadeau,
"Multiprotocol Label Switching (MPLS) Traffic
Engineering (TE) Management Information Base
(MIB)", RFC 3812, June 2004.
Rosen Informational [Page 30]
RFC 4365 Applicability Statement for BGP/MPLS IP VPNs February 2006
[VR-VPN] Knight, P., Ould-Brahim, H., and B. Gleeson,
"Network Based IP VPN Architecture using Virtual
Routers", Work in Progress, April 2004.
Author's Address
Eric C. Rosen
Cisco Systems, Inc.
1414 Massachusetts Avenue
Boxborough, MA 01719
EMail: erosen@cisco.com
Rosen Informational [Page 31]
RFC 4365 Applicability Statement for BGP/MPLS IP VPNs February 2006
Full Copyright Statement
Copyright (C) The Internet Society (2006).
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 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.
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.
Acknowledgement
Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).
Rosen Informational [Page 32]