Internet Engineering Task Force E. Rosen, Ed.
Internet-Draft R. Bonica
Intended status: Informational Juniper Networks, Inc.
Expires: December 13, 2018 June 11, 2018
Augmenting RFC 4364 Technology to
Provide Secure Layer L3VPNs over Public Infrastructure
draft-rosen-bess-secure-l3vpn-00
Abstract
The Layer 3 Virtual Private Network (VPN) technology described in RFC
4364 is focused on the scenario in which a network Service Provider
(SP) maintains a secure backbone network and offers VPN service over
that network to its customers. Customers access the SP's network by
attaching "Customer Edge" (CE) routers to "Provider Edge" (PE)
routers, and exchanging cleartext IP packets. PE routers generally
serve multiple customers, and prevent unauthorized communication
among customers. Customer data sent across the backbone (from one PE
to another) is encapsulated in MPLS, using an MPLS label to associate
a given packet with a given customer. The labeled packets are then
sent across the backbone network in the clear, using MPLS transport.
However, many customers want a VPN service that is secure enough to
run over the public Internet, and which does not require them to send
cleartext IP packets to a service provider. Often they want to
connect directly to edge nodes of the public Internet, which does not
provide MPLS support. Each customer may itself have multiple tenants
who are not allowed to intercommunicate with each other freely. In
this case, the customer many need to provide a VPN service for the
tenants. This document describes a way in which this can be achieved
using the technology of RFC 4364. The functionality assigned therein
to a PE router can be placed instead in Customer Premises Equipment.
This functionality can be augmented by transmitting MPLS packets
through IPsec Security Associations. The BGP control plane sessions
can also be protected by IPsec. This allows a customer to use RFC
4364 technology to provide VPN service to its internal departments,
while sending only IPsec-protected packets to the Internet or other
backbone network, and eliminating the need for MPLS transport in the
backbone.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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This Internet-Draft will expire on December 13, 2018.
Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Review of L3VPN Concepts and Terminology . . . . . . . . 3
1.2. Secured L3VPN . . . . . . . . . . . . . . . . . . . . . . 4
1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
2. Model of Operation . . . . . . . . . . . . . . . . . . . . . 6
3. How the C-PEs Advertise Red Routes . . . . . . . . . . . . . 9
3.1. Red and Black C-PE Loopback Addresses . . . . . . . . . . 9
3.2. Setting Up Red BGP Sessions Between C-PEs and RRs . . . . 10
3.3. Routes Transmited by the C-PE on Red BGP Sessions . . . . 12
3.4. Propagating Red Routes . . . . . . . . . . . . . . . . . 13
4. VPN-IP Routes and Recursive Route Resolution . . . . . . . . 13
5. MPLS-in-IPsec . . . . . . . . . . . . . . . . . . . . . . . . 15
6. Security Handle . . . . . . . . . . . . . . . . . . . . . . . 16
7. Data Plane Security Procedures . . . . . . . . . . . . . . . 16
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
10. Implementation Challenges . . . . . . . . . . . . . . . . . . 17
11. Security Considerations . . . . . . . . . . . . . . . . . . . 17
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
12.1. Normative References . . . . . . . . . . . . . . . . . . 17
12.2. Informational References . . . . . . . . . . . . . . . . 19
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction
1.1. Review of L3VPN Concepts and Terminology
In conventional Virtual Private Networks (L3VPNs) based on the
technology of [RFC4364], a Service Provider (SP) maintains a secure
private network (known as the "SP backbone"). An SP maintains a
number of "Provider Edge" (PE) routers to which customers may attach.
A customer router that attaches to a PE router is known as a
"Customer Edge" (CE) router.
Multiple customers may connect to a single PE router. Within a given
PE, each customer is associated with a routing context of its own
(known as a Virtual Routing and Forwarding table, or VRF). A
particular customer attaches to the PE via a set of one or more
interfaces or Virtual LANs (VLANs) that are not shared with other
customers. (In the subsequent text, the term "interface" will
include VLANs and other "virtual" interfaces.) Each such interface
is associated with a particular customer's VRF; thus such interfaces
are known as "VRF interfaces". These are the PE's customer-facing
interfaces. The VRF interfaces carry IP datagrams, either IPv4 or
IPv6 or both.
A given customer's VRF is automatically populated with, and only
with, routes that lead out the local VRF interfaces, and routes that
lead to remote VRF interfaces of the same customer. Routes leading
outside a customer's VPN are excluded from that customer's VRF unless
explicitly allowed by policy. Thus two customers can attach to the
same PE even if they are not allow to communicate with each other
through that PE.
The PE at which a customer data packet enters the SP backbone network
is known as the packet's "ingress PE". The PE at which a customer
data packet leaves the SP backbone is known as the packet's "egress
PE". Generally, the ingress PE pushes two MPLS labels onto each data
packet. The top label (sometimes known as the "transport label")
directs the packet to its egress PE. The second label (sometimes
known as the "VPN label") is used at the egress PE to associate a
given customer's packets with that customer's VRF at the egress PE.
These labeled packets travel across the SP backbone "in the clear"
(i.e., with no cryptographic protection to provide privacy,
authentication, or integrity), as the SP backbone is presumed to be
adequately secure.
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The control plane protocol for this type of VPN is BGP. A given
customer's routes are distributed among the PEs to which that
customer attaches by means of a BGP address family known as "VPN-IP"
(either VPN-IPv4 or VPN-IPv6). Distribution of these routes is
controlled in such a way as to ensure that a given customer's routes,
exported from one of that customer's VRFs, are imported only by other
VRFs associated with the same customer.
1.2. Secured L3VPN
For security reasons, the L3VPN technology summarized in Section 1.1
is not generally used in the following scenarios:
o Some or all of the customer sites need to be reached over the
public Internet, rather than over a secure SP backbone network.
o The customer does not want to expose any of his data in cleartext
to the SP, even if the SP backbone network is secure.
o The customer does not want to expose any of his routing control
information in cleartext to the SP, and/or wishes to hide his
internal IP addressing structure from the SP.
In such situations, the customer needs to use cryptographic methods
in order to ensure privacy, integrity, and authentication for the IP
datagrams he sends over the backbone network; the cryptography must
be applied before the datagrams are sent to the SP backbone network
or Internet. (It is presumed of course that the customer's own sites
and systems have been secured to his satisfaction; how that is
achieved is outside the scope of this document.)
In these use cases, the customer may still want the benefits of the
L3VPN service, e.g.:
o The customer may itself be providing a VPN service to multiple
"tenants". E.g.,
* The customer may be an enterprise or governmental agency that
consists of multiple internal departments or organizations that
are not allowed to communicate freely with each other, and that
may even have independent IP address spaces. We will use the
term "tenant" to refer to such a department or organization.
* The customer may be a Data Center operator that is providing a
virtual network to each of multiple Data Center tenants.
o In L3VPN, a CE router at one customer site does not have to be
provisioned with the addresses of CE routers at other sites.
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Rather, these are auto-discovered via BGP. This sort of auto-
discovery is just as valuable when the customer needs more
security than is provided by conventional L3VPN. Auto-discovery
also allows some or all of the CE routers to be mobile, changing
their IP addresses from time to time.
It is possible to adapt the L3VPN technology to handle use cases
where cryptographic methods must be applied before a packet is sent
to an SP or to a backbone network . This document describes a way in
which this may be done. We will refer to this adaptation as a
"Secured L3VPN". Section 2 outlines the way this adaptation works.
Subsequent sections of this document specify the necessary procedures
in more detail.
Secured L3VPN makes use of IPsec technology. This document does not
discuss the details of IPsec. A roadmap through the set of RFCs
describing IPsec can be found in [RFC6071]. Of particular importance
are [RFC4303] (IPsec Encapsulating Security Payload), [RFC7296]
(Internet Key Exchange Protocol version 2), and [RFC8221]
(Cryptographic Algorithm Implementation Requirements and Usage
Guidance).
1.3. Terminology
In this document we shall use the following terminology:
SP
A network service provider (possibly an Internet service
provider).
customer
An organization or other entity that obtains network service
(private network service or Internet service) from an SP.
tenant
An organization or other entity that obtains VPN service from the
customer. For example, if the customer is a governmental agency,
its tenants might be the various departments of the agency. If
the customer is an enterprise, its tenants might be the various
organizations within the enterprise. If the customer is a Data
Center provider, its tenants might be organizations to which it
sells Data Center services.
C-PE router:
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A router that performs the functions of an L3VPN PE router
([RFC4364]), but that is operated and managed not by a network
service provider, but rather by a customer of the network service
provider. The customer may use the C-PE to provide a Secured
L3VPN service to one or more of its tenants.
Red interface:
A tenant-facing interface of a C-PE device, where the tenant in
question is receiving Secured L3VPN service.
Black interface:
A C-PE interface that is not a red interface. This may be a
network-facing interface, or a tenant-facing interface to a tenant
that is not receiving any L3VPN service.
Red BGP session:
A BGP session, protected by IPsec, between two C-PEs, or between a
C-PE and a BGP Route Reflector.
Black BGP session:
A BGP session other than a red BGP session.
Local red route:
A route whose next hop interface is a local red interface.
Remote red route:
A route received, as a VPN-IPv4 or VPN-IPv6 route, over a red BGP
session.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. Model of Operation
In a Secured L3VPN, the functions conventionally performed by an
L3VPN PE router (as detailed in [RFC4364]) are instead performed by a
router that is operated and managed by the customer, rather than by
the SP. Since such a router is part of the customer's network, but
has the functionality of an L3VPN PE router, we will refer to it as a
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"C-PE router". The customer is responsible for ensuring that the
C-PE itself is properly secured. The C-PE provides L3VPN
functionality to the customer's tenants.
Each interface of a C-PE is either a "red interface" or a "black
interface":
o A red interface is a tenant-facing interface that attaches to a
tenant who is receiving Secured L3VPN service from the customer.
o A black interface is any interface that is not a red interface.
Black interfaces may be network-facing interfaces (attached to an
SP backbone), or may be tenant-facing interfaces attached to
tenants that are not receiving any L3VPN from the customer. We
assume in this document that a C-PE that provides the Secured
L3VPN service to one or more tenants does not provide a
conventional (unsecured) L3VPN service to any of the tenants.
A C-PE has one or more VRFs, one per tenant. Each VRF is associated
with a distinct set of red interfaces, the ones that lead to the
network(s), VLAN(s), or virtual network(s) that is (are) specific to
the given tenant. Standard L3VPN techniques then prevent
communication among the different tenants unless explicitly allowed
by policy. In simpler scenarios, the customer may have sites with
only a single tenant. The C-PEs at those sites require only a single
VRF, and all the red interfaces will be associated with that VRF.
The black interfaces of a C-PE can attach to an access router of the
public internet, or to a conventional L3VPN PE router belonging to an
SP, or to any other router that provides IP connectivity among the
customer's C-PE routers. (If a C-PE attaches to a conventional L3VPN
PE router, then the C-PE appears to the conventional PE to be a CE
router.)
As in any L3VPN, the VRFs are populated with a combination of local
routes and remote routes:
o The local routes in a given VRF are those routes whose "next hop
interface" is a local red interface associated with that VRF.
o The remote routes in a given VRF are those routes learned via BGP
from the customer's other C-PEs. These routes may be learned
directly via BGP sessions to those other C-PEs, or indirectly via
one or more BGP Route Reflectors (RRs).
In this document, we will use the term "red routes" to refer to
routes within a VRF. These are distinguished from the "black routes"
that exist in a C-PE's global routing table.
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A conventional PE router sends and receives MPLS packets over its
network facing interfaces. A C-PE, on the other hand, sends "MPLS-
in-IPsec" packets (see [RFC4023] and Section 5 of this document) over
its black interfaces. Since an MPLS-in-IPsec packet is an IP
datagram, there is no need for the backbone network to support MPLS
transport. IPsec is used to provide privacy, integrity and
authentication for the packets sent by the C-PE to the backbone
network.
In a Secured L3VPN, protection of the control plane is just as
important as is protection of the data plane. It is therefore
necessary to ensure that the BGP messages used to disseminate the red
routes also have privacy, integrity, and authentication. In order to
ensure this, the BGP sessions used to disseminate information about
red routes will be protected by IPsec. We will refer to such BGP
sessions as "red BGP sessions". It is recommended to use IPsec
Transport mode to protect these BGP sessions. This means that a C-PE
MUST NOT send or receive VPN-IP routes over any BGP session that is
not protected by IPsec. (A VPN-IP route is a route whose BGP Address
Family (AFI) is 1 (IPv4) or 2 (IPv6) and whose Subsequent Address
Family (SAFI) is 128, 129, or 5.)
Note that if RRs are used, the RRs must be as secure as the C-PEs.
This likely means that they are managed by the customer and located
at sites regarded by the customer as adequately secure.
Thus in a Secured L3VPN, red routes are propagated only among trusted
systems, and always in red BGP sessions. The propagation of red
routes on red BGP sessions is controlled by attaching Route Targets
to those routes, as with any [RFC4364]-based technology.
As in any L3VPN, BGP uses the VPN-IPv4 and/or VPN-IPv6 address
families when disseminating information about VPN routes from one VRF
to another. Each such route carries an MPLS label that is to be
pushed on the label stack of any tenant packet for which the address
prefix in the route's NLRI is the best match to the packet's IP
destination address.
In Secured L3VPNs, these routes MUST also carry a Tunnel
Encapsulation attribute ([tunnel_encaps]) specifying an "MPLS-in-
IPsec" tunnel type (see Section 5, as well as Sections 3 and 8.1 of
[RFC4023]). This indicates that before a tenant's MPLS packet is
sent to the backbone network, it must be encapsulated in IP and then
sent on an IPsec Transport Mode Security Association (SA).
A C-PE may have unprotected (black) BGP sessions, e.g., to gather
public Internet routes. However, the black BGP sessions MUST NOT be
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enabled for the VPN-IP AFI/SAFIs. This prevents any routes learned
over the black BGP sessions from being imported into the VRFs.
As we shall see in Section 3.3, there are also some IP routes (as
distinguished from VPN-IP routes) that MUST NOT be transmitted on
black BGP sessions, and that MUST be ignored if received on black BGP
sessions. These are known as the "red loopback routes".
The procedures of this document result in a network overlay whose
control plane consists of red BGP sessions, and whose data plane
consists of MPLS-in-IPsec Security Associations. This allows an SP's
customer to provide Secured L3VPN service to its tenants.
When RRs are used, C-PEs "register" with the RRs by setting up BGP
sessions to them, running the BGP sessions through IPsec SAs. The
necessary authentication of the C-PE is provided during the course of
setting up the IPsec SA. One C-PE learns of another other C-PE's
presence when the RR propagates routes from the latter C-PE to the
former.
The procedures specified in this document result in one MPLS-in-IPsec
SA between a given pair of C-PEs. This one SA will carry the traffic
of all the tenants that are attached to both C-PEs. That should
provide adequate security, as the tenants' data is already exposed to
the C-PEs. If for some reason it is desired to have a distinct SA
for each tenant, a method of doing so is mentioned in Section 4.
3. How the C-PEs Advertise Red Routes
3.1. Red and Black C-PE Loopback Addresses
To support the Secured L3VPN control plane, each C-PE MUST have two
loopback addresses. One of these will be known as its "red
loopback", the other as its "black loopback".
The black loopbacks MUST be addresses that are globally routable.
That is, they are public addresses. (Strictly speaking, the black
loopback only needs to be routable in any network that might be used
to carry traffic between two C-PEs. But we will assume that traffic
between two C-PEs might need to traverse the public Internet.)
Typically a C-PE's black loopback will be in the address space
administered by the network service provider to which the C-PE
attaches. The service provider may assign it dynamically, or it may
be assigned statically and configured in the C-PE by the customer.
In addition to having a globally routable black loopback, a C-PE will
of course have globally routable interface addresses for each of its
black interfaces.
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Interface addresses of the red interfaces SHOULD NOT be globally
routable.
If the C-PE attaches to multiple service providers, the black
loopback is likely to be be a provider-independent address. However,
it MUST be routable in the backbone network of both providers, and
most likely will need to be globally routable.
The C-PE may have one or more (black) BGP sessions with service
provider peers, in which case it may advertise the black loopback;
the next hop field of such an advertisement would be the interface
address of the interface over which that BGP session runs.
Each C-PE of a given customer MUST be provisioned with a red loopback
that is unique among the set of C-PEs of that customer. The red
loopback MUST NOT be a routable address in the public Internet or in
the backbone networks of any service provider to which any of the
C-PEs is attached. If a C-PE has a (black) BGP session with a
service provider peer, it MUST NOT advertise a route to its red
loopback over that session. That is, any IP route to a red loopback
is considered to be a red route, and MUST NOT be advertised or
received on a black BGP session. These "red loopback routes" can
thus be considered to be "red routes", even though they are IP rather
than VPN-IP routes.
3.2. Setting Up Red BGP Sessions Between C-PEs and RRs
The customer is expected to have two or more BGP Route Reflectors
(red RRs). The red RRs are presumed to be secure; making them so is
the responsibility of the customer. As with the C-PEs, each red RR
has a black loopback and a red loopback. If the RR is not also a
C-PE, it will have only black interfaces, each of course with a
globally routable interface address.
A customer's red RRs will form BGP sessions with that customer's
C-PEs. These BGP sessions MUST be protected by IPsec. The use of
IPsec transport mode is RECOMMENDED. If the RR's red loopback is an
IPv4 address, it may be used as the RR's BGP Identifier (see
[RFC4271]).
When a C-PE device comes up, it attempts to set up an IPsec-protected
BGP session with the red RRs. This requires first setting up an
IPsec SA with each red RR, and then using IPsec Transport Mode to
protect the BGP session.
If the C-PE's red loopback is an IPv4 address, the C-PE's BGP
Identifier (see [RFC4271]) may be the red loopback.
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The endpoint addresses of the IPsec SA are the black loopbacks of the
endpoint systems.
Therefore, in order to initiate a BGP session to a red RR, a C-PE
must be provisioned to know a publicly routable address (i.e., the
black loopback) of the RR. A C-PE must also be provisioned with
whatever additional information is needed in order to set up an IPsec
SA with each of the red RRs. Each C-PE will attempt to continuously
maintain live BGP sessions (protected by IPsec) with each red RR.
Note that the source and destination IP address fields of the IP
datagrams carrying the IPsec-encapsulated BGP messages will be
publicly routable adresses.
In some scenarios, it may be desirable to provision each red RR with
the publicly routable address and pre-shared secret of every C-PE.
This makes it easy for the C-PEs to authenticate themselves to the
RR, but requires each RR to be reprovisioned every time a new C-PE is
added to the network.
In other scenarios, it may be considered desirable to allow the RRs
to auto-discover the C-PEs, without the need for any per-C-PE pre-
provisioning of the RRs. In this case, a certificate-based
authentication method [reference?] can be used when setting up the
IPsec SAs that carry the BGP sessions.
In either type of scenario, the C-PE SHOULD NOT be assumed to have a
fixed black loopback address or fixed black interface addresses;
rather, it SHOULD be assumed that a C-PE might be a mobile device
whose globally routable addresses change from time to time.
If a customer's C-PEs support multiple VPNs (for multiple tenants),
that customer's red RRs will receive and disseminate the VPN-IP
routes of all those VPNs.
Note that according to the above procedures, the C-PEs will only have
red BGP sessions to the red RRs; the C-PEs will not have BGP sessions
to each other. Thus it is not necessary for the C-PEs to know of
each other in advance. Of course, if a particular customer deems it
desirable for the C-PEs to have red BGP sessions to each other, each
C-PE can be provisioned with a publicly routable address of each
other C-PE, along with any additional information needed to set up an
IPsec SA to each other C-PE.
It is RECOMMENDED that, for the purpose of setting up the red BGP
sessions, all the RRs and C-PEs be considered to be in the same
Autonomous System (AS). Then the red BGP sessions will all be IBGP
sessions, and the next hop field of a red route will not be modified
as the route is propagated. Note that if an implementation allows a
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given router to be attached to two different ASes, this does not
require that all the C-PEs and red RRs attach to the Internet via the
same AS. The "red overlay" may appear to be within a single AS, but
the "black underlay" need not be within a single AS.
If it is necessary to use an EBGP session between a C-PE and an RR,
the RR SHOULD have a configured policy to leave the next hop
unchanged when propagating red VPN-IP routes on an EBGP session. See
Section 3.4.
In some scenarios, the C-PEs may set up red BGP sessions to
Autonomous System Border Routers (ASBRs), rather than to RRs. This
is transparent to the C-PE.
3.3. Routes Transmited by the C-PE on Red BGP Sessions
A C-PE MUST transmit its local VPN-IP routes on the red BGP sessions,
and only on the red BGP sessions. The next hop of each local VPN-IP
route MUST be set to the red loopback of the C-PE. The choice to
transmit a particular VPN-IP route on a particular session may of
course be influenced by the route's Route Targets.
A C-PE MUST NOT transmit its local VPN-IP routes on black BGP
sessions. VPN-IP routes MUST NOT be accepted from black BGP
sessions.
In all other respects, the handling of VPN-IP routes is done by
normal L3VPN procedures.
Each C-PE MUST also transmit the following IP (IPv4 or IPv6) route on
the red BGP sessions. We refer to this route as the C-PE's "red
loopback route":
o The address prefix field of the route's Network Layer Reachability
Information (NLRI) contains the C-PE's red loopback as a host
address.
o The Next Hop of the route is the C-PE's black loopback.
o The route carries a Tunnel Encapsulation Attribute [tunnel_encaps]
with the the following parameters:
* Tunnel Type = "MPLS-in-IPsec" (see Section 5.)
* Remote Endpoint = the C-PE's black loopback
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* A "Security Handle" (see Section 6). This provides any
information needed by another C-PE to set up an MPLS-in-IPsec
Security Association with the advertising C-PE.
A C-PE MUST NOT transmit, on any black BGP session, an IP route whose
NLRI contains its red loopback.
A given C-PE's red loopback route must be propagated to all other the
C-PEs belonging to the same customer. Therefore, such routes SHOULD
NOT carry Route Targets.
3.4. Propagating Red Routes
A route that is received over a red BGP session may need to be
propagated to other red BGP sessions. A route that is received over
a red BGP session MUST NOT be propagated over a black BGP session.
Similarly, a route that is received over a black BGP session MUST NOT
be propagated over a red BGP session.
When a route is propagated from one red BGP session to another, its
next hop SHOULD be left unchanged. As specified in Section 4, this
will ensure that a data packet sent on the path advertised by that
route are sent on an IPsec SA between its ingress C-PE and its egress
C-PE. Changing the next hop will change the IPsec SA endpoint.
This may be useful in certain deployments. For instance, the path
from an ingress C-PE to an egress C-PE may traverse several ASBRS.
If these ASBRs are secure, it may be desirable to set up a sequence
of IPsec SAs, (e.g., C-PE1--ASBR1, ASBR1--ASBR2, ASBR2--C-PE2)
instead of using a single IPsec SA between C-PE1 and C-PE2. If this
is not the intention, the red BGP sessions MUST leave the next hop
unchanged, even if those sessions are EBGP sessions.
In all other respects, propagation of red routes is governed by the
normal procedures for propagating routes. If the route carries one
or more Route Targets, these may affect its propagation. However,
note that propagation of a route between a red BGP session and a
black BGP session MUST NOT be done, irrespective of the Route
Targets.
4. VPN-IP Routes and Recursive Route Resolution
Suppose a C-PE, say C-PE1, receives a packet, say packet P, on one of
its local red interfaces. Suppose that packet P is addressed to a
system that is reachable via one of the red interfaces at another
C-PE, say C-PE2. C-PE1 looks up packet P's destination address in
the VRF associated with P's incoming interface. The matching route
will be a "Labeled VPN-IP route" [RFC4364] originated by C-PE2, and
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disseminated to C-PE1 over a red BGP session. Per Section 3.3, the
next hop of that route will be C-PE2's red loopback.
The labeled VPN-IP route matched by packet P's destination address
will contain an MPLS label, the "VPN label". C-PE1 pushes the VPN
label onto packet P's MPLS label stack. Then C-PE1 needs to
determine how to transmit the resulting MPLS packet to the next hop
of the VPN-IP route. The next hop of the labeled VPN-IP route will
be the red loopback address C-PE2. So C-PE1 looks for the route to
that red loopback address. This will be the red loopback route
(i.e., the red IP route, see Section 3.3) originated by C-PE2.
C-PE2's red loopback will then be recursively resolved by means of
C-PE2's red loopback route. By virtue of the Tunnel Encapsulation
attribute carried by that route, C-PE1 will realize that to send
packet P, it must set up an MPLS-in-IPsec SA (see Section 5, as well
as Sections 3 and 8.1 of [RFC4023]) with C-PE2. Per the route's
Tunnel Encapsulation attribute, the remote endpoint of this IPsec SA
will be C-PE2's black loopback, and the Security Handle in the Tunnel
Encapsulation attribute will carry any other information needed to
set up the Security Association.
Note that the remote endpoint of the IPsec SA is determined by the
Tunnel Encapsulation attribute of the red loopback route, rather than
by the next hop field of that route. This ensures that the SA is
made to the proper endpoint, even if the next hop field of the red
loopback route was modified while the route was propagated.
IMPORTANT: A VPN-IP route MUST NOT be recursively resolved by an IP
route that was received over a black BGP session. If a VPN-IP
route's next hop resolves to a route received over a black BGP
session, the existence of the latter route MUST be regarded as the
result of an attempt to spoof the location of the egress C-PE. That
is, the latter route MUST be considered to be a spoofed route. Note
that it may not be possible to detect this spoofing attack until the
attempt is made to recursively resolve the VPN-IP route.
Implementors should take special care to ensure that their
implementations are not vulnerable to this sort of spoofing attack.
IF an implementation cannot detect this sort of attack during the
recursive route resolution process, then the C-PE MUST NOT have any
black BGP sessions.
When packet P is transmitted, it is transmitted through an MPLS-in-
IPsec SA. Thus the only information that appears in the clear is the
IP header needed to get the packet across the network. The IP source
and destination addresses of that packet will be the black loopbacks
of C-PE1 and C-PE2 respectively. The red loopback addresses do not
appear in the packets at all, and no part of the payload packet
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(neither the VPN label nor the IP datagram following the VPN label)
appears in the clear.
The MPLS-in-IPsec SA between C-PE1 and C-PE2 may be initiated by
C-PE1 as soon as it receives a red loopback route originated by
C-PE2. Alternatively, the initiation of the setup of the Security
Association may be delayed until the SA is actually needed for
transmitting packets.
These procedures will result in a single IPsec SA between a pair of
C-PEs, with the data of multiple tenants carried on that single SA.
If for some reason it is considered preferable to have an SA per
tenant, the following procedures can be used:
o On each C-PE, provision a distinct red loopback for each tenant.
o Each C-PE will originate a red loopback route for each red
loopback.
o Each red loopback route will have its own Tunnel Encapsulation
attribute. The respective Security Handle sub-TLVs (if present)
MUST be distinct.
5. MPLS-in-IPsec
Packets traveling from one C-PE to another travel through "MPLS-in-
IPsec" tunnels. To transmit an MPLS packet through an MPLS-in-IPsec
tunnel, one does the following:
o Encapsulate the MPLS packet in IP, as specified in Section 3 of
[RFC4023].
o Use an IPsec transport mode Security Association to send the MPLS-
in-IP packet from one C-PE to the other. This is specified in
Section 8.1 of [RFC4023].
The result of encapsulating MPLS in IP and then transmitting the
MPLS-in-IP packet on an IPsec transport mode Security Association is
known as an MPLS-in-IPsec packet.
On the wire, an MPLS-in-IPsec packet consists of a cleartext IP
header followed by a payload. The IP source and destination
addresses of an MPLS-in-IPsec packet will be the black loopbacks of
the source and destination C-PEs. The payload will be an MPLS
packet. If the IPsec Security Association is providing privacy,
authentication, and integrity, the payload is protected from
inspection or alteration.
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When the packet arrives at the destination C-PE, any necessary
decryption is done, and packet appears to be an MPLS-in-IP packet
addressed to the black address of the destination C-PE. The IP
encapsulation is removed, yielding an MPLS packet. Per the usual
L3VPN procedures, the label at the top of the MPLS label stack will
be used to govern the further disposition of the packet. However, if
a packet received over a black interface was not received though an
IPsec SA, the packet MUST NOT be sent out any VRF interface.
MPLS-in-IP packets received in the clear (i.e., not received over an
IPsec SA) MUST be discarded.
Note that this section is not intended to describe an implementation
strategy.
6. Security Handle
This document defines a new BGP Tunnel Encapsulation attribute sub-
TLV, the "Security Handle". This sub-TLV has a one-octet length
field. It is intended for use in the Tunnel Encapsulation attribute
carried by the red loopback routes. Its use is deployment specific.
As an example, in some deployments, this sub-TLV might be used to
carry the IPsec Security Parameters Index (SPI). When setting up an
SA to the originator of a particular Tunnel Encapsulation attribute,
the SPI would be used as part of the SA setup procedure.
In deployments where the C-PEs auto-discover each other through RRs,
and authenticate via certificate-based mechanisms, the Security
Handle may not be needed at all. If a given deployment does not make
use of the Security Handle, the sub-TLV SHOULD be omitted from the
Tunnel Encapsulation attribue.
7. Data Plane Security Procedures
If a C-PE receives data over one of its local red interfaces, it may
forward the data out another of its local red interfaces, as long as
those two interfaces are associated with the same VRF, or if there is
policy allowing communication ("extranet") between those two
interfaces.
However, data received by a C-PE over one of its red interfaces MUST
NOT be forwarded out a black interface, unless that data is being
sent over the black interface through an IPsec SA.
Similarly, data received by a C-PE over one of its black interfaces
MUST NOT be forwarded out a red interface unless the data arrived
through an IPsec SA.
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Typically an IPsec implementation has procedures to prevent
unauthorized red-to-black or black-to-red forwarding. However, the
conventional procedures are based on filtering of IP addresses, and
hence do not apply directly if MPLS-in-IPsec is used. Implementors
should take care to ensure that unauthorized red-to-black or black-
to-red forwarding is prohibited.
8. Acknowledgments
The authors wish to thank John Scudder for his ideas and
contributions to this work.
9. IANA Considerations
IANA is requested to create a new entry in the "BGP Tunnel
Encapsulation Attribute Sub-TLVs" registry, "Security Handle". This
sub-TLV is defined in Section 6 to have a one-octet length field.
Thus it needs to be assigned a codepoint in the range 0-127
inclusive.
10. Implementation Challenges
This document specifies an architecture for Secured L3VPNs, but a
successful implementation faces a number of challenges.
This document specifies a recursive route resolution process that
makes use of the Tunnel Encapsulation attribute. This is a new
feature.
This document specifies that during recurisve route resolution,
resolution of a red route via a route received over a black BGP
session must be prohibited. This is a new feature that may present
challenges.
Ultimately, success will require a highly scalable IPsec
implementation, that can set up SAs dynamically based on information
disseminated by BGP. This presents a number of implementation
challenges.
11. Security Considerations
12. References
12.1. Normative References
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC4023] Worster, T., Rekhter, Y., and E. Rosen, Ed.,
"Encapsulating MPLS in IP or Generic Routing Encapsulation
(GRE)", RFC 4023, DOI 10.17487/RFC4023, March 2005,
<https://www.rfc-editor.org/info/rfc4023>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, DOI 10.17487/RFC4303, December 2005,
<https://www.rfc-editor.org/info/rfc4303>.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
2006, <https://www.rfc-editor.org/info/rfc4364>.
[RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
Kivinen, "Internet Key Exchange Protocol Version 2
(IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
2014, <https://www.rfc-editor.org/info/rfc7296>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8221] Wouters, P., Migault, D., Mattsson, J., Nir, Y., and T.
Kivinen, "Cryptographic Algorithm Implementation
Requirements and Usage Guidance for Encapsulating Security
Payload (ESP) and Authentication Header (AH)", RFC 8221,
DOI 10.17487/RFC8221, October 2017,
<https://www.rfc-editor.org/info/rfc8221>.
[tunnel_encaps]
Rosen, E., Patel, K., and G. Van de Velde, "The BGP Tunnel
Encapsulation Attribute VPN", internet-draft draft-ietf-
idr-tunnel-encaps-09, February 2018.
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12.2. Informational References
[RFC6071] Frankel, S. and S. Krishnan, "IP Security (IPsec) and
Internet Key Exchange (IKE) Document Roadmap", RFC 6071,
DOI 10.17487/RFC6071, February 2011,
<https://www.rfc-editor.org/info/rfc6071>.
Authors' Addresses
Eric C. Rosen (editor)
Juniper Networks, Inc.
10 Technology Park Drive
Westford, Massachusetts 01886
United States
Email: erosen@juniper.net
Ron Bonica
Juniper Networks, Inc.
2251 Corporate Park Drive
Herndon, Virginia 20171
United States
Email: rbonica@juniper.net
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