Internet DRAFT - draft-rosen-bess-secure-l3vpn
draft-rosen-bess-secure-l3vpn
Internet Engineering Task Force E. Rosen, Ed.
Internet-Draft R. Bonica
Intended status: Informational Juniper Networks, Inc.
Expires: December 22, 2018 June 20, 2018
Augmenting RFC 4364 Technology to
Provide Secure Layer L3VPNs over Public Infrastructure
draft-rosen-bess-secure-l3vpn-01
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, which exchange 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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working documents as Internet-Drafts. The list of current Internet-
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This Internet-Draft will expire on December 22, 2018.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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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 . . . . . . . . . . . . . . . . . . . . . 7
3. How the C-PEs Advertise Red Routes . . . . . . . . . . . . . 10
3.1. Red and Black C-PE Loopback Addresses . . . . . . . . . . 10
3.2. Setting Up Red BGP Sessions Between C-PEs and RRs . . . . 11
3.3. Routes Transmited by the C-PE on Red BGP Sessions . . . . 13
3.4. Propagating Red Routes . . . . . . . . . . . . . . . . . 13
4. Resolving the Next Hop of a Red VPN-IP Route . . . . . . . . 14
5. MPLS-in-IPsec . . . . . . . . . . . . . . . . . . . . . . . . 16
6. Security Handle . . . . . . . . . . . . . . . . . . . . . . . 17
7. Data Plane Security Procedures . . . . . . . . . . . . . . . 17
8. Implementation Challenges . . . . . . . . . . . . . . . . . . 18
9. Security Considerations . . . . . . . . . . . . . . . . . . . 18
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 19
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
12.1. Normative References . . . . . . . . . . . . . . . . . . 19
12.2. Informational References . . . . . . . . . . . . . . . . 20
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
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:
o routes that lead out the local VRF interfaces, and
o 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 allowed 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,
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authentication, or integrity), as the SP backbone is presumed to be
adequately secure.
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 a
network that is untrusted (e.g., the public Internet).
o The customer wants to be very sure that its SP is not able to read
or modify its data.
o The customer does not want to expose any of its routing control
information 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 sent 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 satisfactorily secured; how that is achieved is
outside the scope of this document.)
In these use cases, the customer may still want some of 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, and
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needs to extend some or all of those virtual networks over a
non-secured backbone network.
(Of course, the same technology works when there is only a single
tenant.)
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.
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; for some customers, this is
a mission-critical need.
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:
o SP:
A network service provider (possibly an Internet service
provider).
o customer:
An organization or other entity that obtains network service
(private network service or Internet service) from an SP.
o tenant:
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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.
o C-PE router:
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.
o Red interface:
A tenant-facing interface of a C-PE device, where the tenant in
question is receiving Secured L3VPN service.
o Black interface:
A C-PE interface that is not a red interface. This may be an
interface to the Internet, to an SP backbone network, or to a
tenant that is not receiving the Secure L3VPN service.
o Red BGP session:
A BGP session, protected by IPsec, between two C-PEs, or between a
C-PE and a BGP Route Reflector.
o Black BGP session:
A BGP session other than a red BGP session.
o Black Network:
The part of the communications infrastructure that is not trusted
or not regarded as adequately secure. E.g., the public Internet
is a black network.
o Red Route:
* Local red route:
A route whose next hop interface is a local red interface.
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* Remote red route:
A route received, as a VPN-IPv4 or VPN-IPv6 route, over a red
BGP session.
* Red Loopback Route: This term is defined in Section 3.3.
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
"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 backbone-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.
(Note that a black interface could also be attached to an
"Internet Gateway", owned by a single tenant or shared by multiple
tenants, that provides controlled access to the Internet for that
tenant or tenants. This scenario is not further discussed in this
document.)
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
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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 secure 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.
A conventional PE router sends and receives MPLS packets over its
backbone-facing interfaces. A C-PE, on the other hand, sends "MPLS-
in-IPsec" packets (see [RFC4023] and Section 5 of this document) over
its backbone-facing 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
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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 only via 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 the "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
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
procedures for setting up IPsec SAs between a C-PE and an RR will
authenticate the C-PE to the RR, and vice versa. One C-PE learns of
another other C-PE's presence when the RR propagates routes from the
latter C-PE to the former.
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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.
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. In some
scenarios, it may be sufficient to advertise the black loopback via
an IGP.
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 SHOULD NOT be a routable address in the public Internet or
in the backbone networks of any service provider to which any of the
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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] and [RFC6286]).
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] and [RFC6286]) may be the red loopback.
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 addresses.
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
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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 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
given router to be part of 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
(perhaps because the implementation does not allow one router to be
part of two different ASes), 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,
creating what is sometimes known as an "option B interconnect"
(Section 10 of [RFC4364]). This is transparent to the C-PE.
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3.3. Routes Transmited by the C-PE on Red BGP Sessions
A C-PE MUST propagate 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
* An optional "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.
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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 would change the IPsec SA endpoint.
Changing the next hop 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. (This reduces the number of IPsec sessions
supported by a C-PE, at the cost of requiring secure ASBRs along the
path.) 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. Resolving the Next Hop of a Red VPN-IP Route
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 reached via one of the red interfaces of 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
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 resolved through C-PE2's red
loopback route. By virtue of the Tunnel Encapsulation attribute
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carried by the latter 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: The next hop of a VPN-IP route MUST NOT be resolved
through an IP route that was not received over a red BGP session.
If a VPN-IP route's next hop resolves to a route that was not
received over a red 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. The next hop of a VPN-IP route should always be a
red loopback. However, since the full set of red loopbacks is not
necessarily known in advance, it may not be possible to detect this
spoofing attack until the attempt is made to resolve the VPN-IP
route's next hop. Implementors should take special care to ensure
that their implementations are not vulnerable to this sort of
spoofing attack. Implementors should also take care to consider
various corner cases, such as:
o There is a black route to the next hop of a VPN-IP route, but no
red route to that next hop. In this case the next hop MUST be
considered to be unreachable.
o There is both a black route and a red route to the next hop of a
VPN-IP route. In this case, the red route MUST be preferred to
the black route for the purpose of resolving the next hop.
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
(neither the VPN label nor the IP datagram following the VPN label)
appears in the clear.
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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.
Note that this section is not intended to describe an implementation
strategy.
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 through 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 attribute.
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.
Note that this rule has an important side-effect. A C-PE will not be
able to forward packets received on a red interface to destinations
that are outside the VPN, such as destinations on the public
Internet. However, nothing prevents the customer from having an
"Internet Gateway" at one or more sites, and attaching the Gateways
to the C-PEs via black interfaces. If the routing at the customer
site is such that intra-VPN traffic goes to the C-PE via a red
interface, but traffic to the Internet goes via the Gateway, the C-PE
can serve as an Internet access point without compromising the VPN's
security (assuming of course that the Gateway provides the necessary
security for traffic to/from the Internet).
8. Implementation Challenges
This document specifies an architecture for Secured L3VPNs, but a
successful implementation faces a number of challenges.
This document specifies a route resolution process that makes use of
the Tunnel Encapsulation attribute. This is a new feature.
This document specifies that during resolution of the next hop of a
VPN-IP route, routes received over black BGP sessions must be
disregarded. 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.
9. Security Considerations
Security considerations are discussed throughout this document.
As long as the C-PE devices and the Route Reflectors are physically
secure, and not compromised, the techniques of this document provide
privacy, integrity, and authentication for customer data and customer
routing information.
The techniques of this document do not protect against attacks on the
network backbone that make the black addresses unreachable, or that
spoof the routes to the black addresses. Such attacks can disrupt or
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disable the customer's ability to communicate over the unsecured
network infrastructure. However, such attacks cannot expose the
customer's routing or data.
Proper security depends on the correct implementation of such
policies as "do not forward packets between red and black interfaces
unless the packets are protected by IPsec on the black interfaces"
and "do not resolve the next hop of a VPN-IP red route using a route
that was not received over a red BGP session".
Attacks that are based on traffic analysis are not prevented by the
techniques of this document.
10. 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.
11. Acknowledgments
We wish to thank John Scudder for his ideas and contributions to this
work.
The idea of integrating IPsec into L3VPN is not new to this document.
This document has been influenced by earlier work such as
[PE-PE_IPsec], and we wish to thank the authors of the earlier work.
12. References
12.1. Normative References
[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>.
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[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>.
[RFC6286] Chen, E. and J. Yuan, "Autonomous-System-Wide Unique BGP
Identifier for BGP-4", RFC 6286, DOI 10.17487/RFC6286,
June 2011, <https://www.rfc-editor.org/info/rfc6286>.
[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.
12.2. Informational References
[PE-PE_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", internet-draft draft-ietf-
l3vpn-ipsec-2547-05, August 2005.
[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>.
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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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