Network Working Group S. Yamamoto
Internet-Draft C. Williams
Expires: April 25, 2007 KDDI R&D Labs
F. Parent
consultant
H. Yokota
KDDI R&D Labs
October 22, 2006
Softwire Security Analysis and Requirements
draft-ietf-softwire-security-requirements-01
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Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
This document provides the security Guidelines for the Softwire "Hubs
and Spokes" and "Mesh" solutions. Together with the discussion of
the Softwire deployment scenarios, the vulnerability to the security
attacks is analyzed to provide the security protection mechanism such
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as authentication, integrity and confidentiality to the softwire
control and data packets.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Hubs and Spokes Security Guidelines . . . . . . . . . . . . . 4
3.1 Deployment Scenarios . . . . . . . . . . . . . . . . . . . 4
3.2 Trust Relationship . . . . . . . . . . . . . . . . . . . . 6
3.3 Softwire Security Threat Scenarios . . . . . . . . . . . . 7
3.3.1 Softwire Blackhole Attacks . . . . . . . . . . . . . . 8
3.4 Softwire Security Guidelines . . . . . . . . . . . . . . . 9
3.5 Guidelines for Usage of Security Protection Mechanism . . 10
3.5.1 Softwire Security Protocol . . . . . . . . . . . . . . 10
3.5.2 Authentication . . . . . . . . . . . . . . . . . . . . 11
3.5.3 Inter-operability guidelines . . . . . . . . . . . . . 12
3.5.4 IPsec filtering details . . . . . . . . . . . . . . . 12
3.5.5 IPsec SPD entries example . . . . . . . . . . . . . . 12
4. Mesh Security Guidelines . . . . . . . . . . . . . . . . . . . 13
4.1 Deployment Scenario . . . . . . . . . . . . . . . . . . . 13
4.2 Trust Relationship . . . . . . . . . . . . . . . . . . . . 14
4.3 Softwire Security Threat Scenarios . . . . . . . . . . . . 15
4.3.1 Attacks on the Control Plane . . . . . . . . . . . . . 15
4.3.2 Attacks on the Data Plane . . . . . . . . . . . . . . 16
4.4 Softwire Security Guidelines . . . . . . . . . . . . . . . 16
4.5 Guidelines for Usage of Security Protection Mechanism . . 16
4.5.1 Security Protection Mechanism for Control Plane . . . 16
4.5.2 Security Protection Mechanism for Data Plane . . . . . 19
5. Security Considerations . . . . . . . . . . . . . . . . . . . 20
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
6.1 Normative References . . . . . . . . . . . . . . . . . . . 20
6.2 Informative References . . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 23
Intellectual Property and Copyright Statements . . . . . . . . 24
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1. Introduction
The Softwire Working Group is developing discovery, control and
encapsulation methods for connecting IPv4 networks across IPv6
networks and IPv6 networks across IPv4 networks. Such IP based
protocols were defined as softwire. This document provides the
security Guidelines based on the softwire problem statement by
analyzing security threat scenarios for the Softwire "Hubs and
Spokes" and "Mesh" solutions [I-D.softwire-problem-statement].
The Softwire protocol itself does not implement full security
protection mechanism in the control plane and data plane and
vulnerable for potential security attacks. Thus, the Softwire MUST
be able to prevent the security threat. This means that the Softwire
protocol for control and data planes SHOULD be capable of preventing
the security threat. The feature that prevent the security threat
may or may not be used depending on the Softwire deployment. This
document provides the guidelines for the usage of the security
protection mechanism in terms of the softwire deployment scenarios.
2. Terminology
The terminology is based on the softwire problem statement document
[I-D.softwire-problem-statement].
AF(i) - Address Family. IPv4 or IPv6. Notation used to indicate
that prefixes, a node or network only deal with a single IP AF.
AF(i,j) - Notation used to indicate that a node is dual-stack or that
a network is composed of dual-stack nodes.
Address Family Border Router (AFBR) -A dual-stack router that
interconnects two networks that use either the same or different
address families. An AFBR forms peering relationships with other
AFBRs, adjacent core routers and attached CE routers, perform
softwire discovery and signaling, advertises client ASF(i)
reachability information and encapsulates/decapsulates customer
packets in softwire transport headers.
Customer Edge (CE) - A router located inside AF access island that
peers with other CE routers within the access island network and with
one or more upstream AFBRs.
Customer Premise Equipment (CPE) - An equipment, host or router,
located at a subscriber's premises and connected with a carrier's
access network.
Provider Edge (PE) - A router located at the edge of transit core
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network that interfaces with CE in access island.
Softwire Concentrator (SC) - The node terminating the softwire in the
service provider network.
Softwire Initiator (SI) - The node initiating the softwire within the
customer network.
Softwire Encapsulation Set (SW-Encap) - A softwire encapsulation set
contains tunnel header parameters, order of preference of the tunnel
header types and the expected payload types (e.g. IPv4) carried
inside the softwire.
Softwire Next_Hop (SW-NHOP) - This attribute accompanies client AF
reachability advertisements and is used to reference a softwire on
the ingress AFBR leading to the specific prefixes. It contains a
softwire identifier value and a softwire next_hop IP address denoted
as <SW ID:SW-NHOP address>. Its existence in the presence of client
AF prefixes (in advertisements or entries in a routing table) infers
the use of softwire to reach that prefix.
3. Hubs and Spokes Security Guidelines
3.1 Deployment Scenarios
To provide the security Guidelines, the discussion of the possible
deployment scenario and the trust relationship in the network is
important.
The Softwire initiator always resides in the customer network. The
node, in which the softwire initiator resides, can be the CPE access
device, another dedicated CPE router behind the original CPE access
device or any kind of host device such as PC, appliance, sensor etc.
However, the host device may not always have direct access to its
home carrier network, to which the user has subscribed. For example,
the softwire initiator in the laptop PC can access various access
networks such as Wi-Fi hot-spots, visited office network. This is
the nomadic case, which the Softwire SHOULD support., the following
three use cases should be considered:
As the softwire deployment models, the following three cases as shown
in Figure 1 should be considered. In these cases, the automated
discovery of the softwire concentrator may be used. But in this
document, the information on the softwire concentrator such as the
DNS name or IP address is assumed to be configured by the user, or by
the provider of the softwire initiator in advance.
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Case 1: The softwire initiator connects to the softwire concentrator
that belongs to the home network service provider via the home access
provider network. The IP address of the host may be changed
periodically due to the home network service provider's policy.
Case 2: The softwire initiator connects to the softwire concentrator
that belongs to the home network service provider via the visited
access network. This is typical of nomadic access use case. The
host does not subscribe to the visited access provider, but this
provider has some roaming agreement with the home network service
provider of the host. The IP address of the host may be changed
periodically due to the home network service provider's policy.
Case 3: The softwire initiator connects to the softwire concentrator
that belongs to the visited network service provider via the visited
access network. This is also typical of nomadic access use case.
The host does not subscribe to the visited network service provider,
but this provider has some roaming agreement with the home network
service provider of the host. If this is the case, the IP address of
the host is determined by the visited network service provider's
policy.
The trust relationship for these three cases will also be different.
The security consideration must take them into account. In
particular, to allow cases 2 and 3, AAA interactions between the home
network service provider and visited access/service provider should
be considered. The details of this scenario are given in Section
Section 3.2.
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visited network visited network
access provider service provider
+---------------------------------+
+......|......+ +.....................|......+
. v . . v .
+------+ . . . +------+ +--------+ .
| |=====================.==| | | | .
| SI |__.________ . . | SC |<---->| AAAp | .
| |---------- \ . . | | | | .
+------+ . \\ . . +------+ +--------+ .
. \\ . . ^ .
^ +..........\\.+ +.....................|......+
| \\ |
| \\ |
| \\ |
| \\ |
| +............+ \\ +.....................|......+
. . \\. v .
+------+ . . \\__+------+ +--------+ .
| | . . ---| | | | .
| SI |=====================.==| SC |<---->| AAAh | .
| | . . . | | | | .
+------+ . . . +------+ +--------+ .
. . . .
+............+ +............................+
home network home network
access provider service provider
Figure 1: Hubs and Spokes model
3.2 Trust Relationship
To perform authentication between the SC and the SI, the AAA server
needs to be involved. One or more AAA servers should reside in the
same administrative domain as the SC to authenticate the SI. When
the SI is mobile, it may roam from the home ISP network to another,
e.g. a WIFI hot-spot network. In such a situation, the SI may not
always connect to the same SC. From the SI's viewpoint, the AAA
server that is in the same administrative domain is called the home
AAA server and those not in the same administrative domain are called
visited AAA servers. The trust relationships between those nodes are
as follows:
It can be assumed that the SC and the AAA in the same administrative
domain share a trust relationship. When the SC needs to authenticate
the SI, the SC communicates with the AAA server to request
authentication and/or to obtain security information. If the SI
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roams into a network that is not in the same administrative domain,
the AAA server (the visited AAA server) communicates with the home
AAA server that has the SI's security information. Therefore, the
communication between the SC and the AAA server must be protected.
It can be usually assumed that the home and visited AAA servers share
a trust relationship and the connection between them is protected.
It can be assumed that the SI and the home AAA server share a trust
relationship. The home AAA server provides security information on
the SI when it is requested by the visited AAA server. The SI and
the visited AAA server do not usually have a trust relationship;
however, if the SI can confirm that the home AAA server is involved
with the authentication of the SI and the visited AAA server does not
alter security information from the home AAA server, the visited AAA
server can be trusted by the SI. The communication between the SI,
the home and visited AAA servers must be protected.
The SI and the SC do not necessarily share a trust relationship
especially when the SI roams into a different administrative domain.
When they are mutually authenticated by means of e.g. AAA servers,
they can start trusting each other. Unless authentication is
successfully performed, the softwire protocol should not be
initiated.
3.3 Softwire Security Threat Scenarios
Softwire can be used to connect IPv4 networks across public IPv6
networks and IPv6 networks across public IPv4 networks. The control
and data packets used during the softwire session are vulnerable to
attack.
A complete threat analysis of softwire requires examination of the
protocols used for the softwire setup, the encapsulation method used
to transport the payload, and other protocols used for configuration
(e.g., router advertisements, DHCP).
Threat analysis done for other protocols L2TP using IPsec [RFC3193],
PANA [RFC4016], NSIS [RFC4081], [I-D.rpsec-routing-threats] are
applicable here as well and should be used as reference.
Examples of attacks on softwire include:
1. An adversary may try to discover identities by snooping data
packets.
2. An adversary may try to modify packets (both control and data).
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3. An adversary may try to hijack the softwire tunnel.
4. An adversary can launch denial of service attacks by terminating
softwire created tunnels.
5. An adversary may attempt to disrupt the softwire negotiation in
order to weaken or remove confidentiality protection.
6. An adversary may impersonate the softwire concentrator to
intercept traffic ("rogue" softwire concentrator).
7. If ingress filtering is not in place within the access network, a
number of DoS attack can happen:
* A malicious user can impersonate someone else's IPv4 address
during the set-up phase and redirect a tunnel to that IP
address. A then can, for example, start a high bandwidth
multimedia flow across that tunnel and saturate its victim's
uplink.
* A malicious user impersonates a large number of IPv4 addresses
and request tunnel of their behalf. That would quickly
saturate the ISP tunnel server infrastructure.
8. If ingress filtering is in place in the core ISP backbone but not
in the access network, the potential victims of the above
problems will be limited to the ISP's own customers.
9. If specific filtering is not in place in the ISP core network,
another kind of attack can happen. Customers from another ISP
could start using its tunneling infrastructure to get free IPv6
connectivity, transforming effectively the ISP into a IPv6
transit provider.
For the Hubs and Spokes model, the SI needs to discover the softwire
concentrator. This involves sending solicitations (setup protocol).
Once the client has discovered the concentrator, the two will enter
authentication exchange. Once the access is granted, the client will
most likely exchange data with other nodes in the Internet. These
steps are vulnerable to man-in-the-middle (MITM), denial of service
(DoS), and service theft attacks, which are discussed in this
document. Among them, so called blackhole attacks defined in
[RFC4593] are discussed in the next section.
3.3.1 Softwire Blackhole Attacks
A Softwire blackhole attack is a threat by which an internal Attacker
captures all of the necessary information (including keys if security
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is present) of a legitimate Softwire node and remove the messages of
the subgroup of the network. The attacker may also be able to change
a legitimate Softwire Control message. The aim of the internal
attacker is to Deceive the receiving nodes of Softwire service that
its Path to the concentrator is different. In this way the Attacker
may accumulate traffic to itself but it does Not forward any data
towards the Softwire Concentrator. Here the attacker is able to
divert the traffic to a "black hole" where it is discarded. The
attack here is local and the rest of the network may not be
compromised.
Countermeasure: In order to overcome the confidentiality problem,
each node requesting Softwire service can send data encrypted with
the key that it shares with the concentrator. Therefore, the
attacker will not be able to read data packets but will be able to
drop them. This problem can be solved by employing an authenticated
acknowledgment mechanism after the Softwire tunnel is established.
3.4 Softwire Security Guidelines
Based on the security threat analysis in other sections in this
document, an enumeration of security requirements are summarized
below:
1. The tunnel set-up protocol MUST not introduce any new
vulnerability to the network.
2. The softwire protocol MUST NOT assume that the discovery process
is protected.
3. The Softwire MUST BE able to mutually authenticate the initiator
and the concentrator. The softwire protocol MUST be able to
establish keys between the initiator and the concentrator to
protect the Softwire messages.
4. The Softwire signaling communication between the client and the
concentrator MUST BE protected against eavesdropping and spoofing
attacks.
5. The Softwire protocol MUST be able to protect itself against
replay attacks.
6. The Softwire protocol MUST be able to protect the device
identifier against spoofing when it is exchanged between the
initiator and the concentrator.
7. The Softwire protocol MUST be able to protect disconnect-type and
revocation-type messages.
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8. The Softwire protocol MUST be able to securely bind the
authenticated session to the device identifier of the client, to
prevent service theft.
9. Softwire security MUST meet the key management requirements of
the IPsec protocol suite. IKE SHOULD be supported for
authentication, security association negotiation, and key
management
3.5 Guidelines for Usage of Security Protection Mechanism
The Softwire security requirements state that control and/or data
plane must be able to provide full payload security when desired
[I-D.softwire-problem-statement, section 2.11.2]. [RFC3193]
discusses how L2TP can use IPsec to provide tunnel authentication,
privacy protection, integrity checking and replay protection.
[RFC3193] can be applied in the softwire "Hubs and Spokes" model
context. New additions to IPsec ([RFC3947],[RFC3948],[RFC4306]) are
necessary to meet the softwire requirements were published after
[RFC3193].
The following sections will discuss [RFC3193] as applied in the
softwire "Hubs and Spokes" model.
In softwire, L2TP is used in a voluntary tunneling model only. The
Softwire Initiator (SI) acts as a L2TP Access Concentrator (LAC) and
PPP endpoint. The L2TP tunnel is always initiated from the SI.
The scope of the security is on the L2TP tunnel between the SI and
SC. If end to end security is required, a security protocol should
be used in the payload packets (out of scope of this document for
now).
3.5.1 Softwire Security Protocol
[RFC3193] section 2.1 defines the security requirement for L2TP. The
same requirements are used for the "Hubs and Spokes" softwire model.
A softwire security compliant implementation MUST implement the
security protocol requirements as defined in [RFC3193] section 2.1:
o IPsec ESP [RFC4303] in transport mode to secure both the L2TP
control and data packets.
o IKE MUST be supported for authentication, security association
negotiation and key management for IPsec (this is a SHOULD in
[RFC3193])
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o Since softwire must support NAT traversal, UDP encapsulation of
IPsec ESP packets [RFC3948] and negotiation of NAT-traversal in
IKE [RFC3947] MUST be supported.
IKEv2 [RFC4306] supports legacy authentication methods that may be
useful in environments where username and password based
authentication is already deployed.
3.5.2 Authentication
The softwire protocol MUST support customer authentication in the
control plane, in order to authorize access to the service, and
provide adequate logging of activity. However, in some
circumstances, the service provider may decide to turn it off. For
example, when the customer is already authenticated by some other
means, such as closed networks, cellular networks at Layer 2, etc.
The protocol SHOULD offer mutual authentication in scenarios where
the SI requires identity proof from the SC.
In addition, the SC MAY allow non-authenticated connection. In that
case, the SC acts as a gateway for anonymous connections. This
approach is better than an open relay implementation since ingress
filtering is performed on established tunnels. If non-authenticated
connections are supported by the SC, enabling this function MUST be
configurable by the SC administrator.
3.5.2.1 PPP authentication
PPP can provide mutual authentication between the SI and SC using
CHAP [RFC1994] during the connection establishment phase (Link
Control Protocol, LCP). PPP CHAP authentication can be used when the
SI and SC are on a trusted, non-public IP network.
Since CHAP does not provide per-packet authentication, integrity, or
replay protection, PPP CHAP authentication MUST NOT be used
unprotected on a public IP network.
Optionally, other authentication methods such as PAP, MS-CHAP EAP MAY
be supported.
3.5.2.2 L2TPv2 authentication
L2TPv2 provides an optional CHAP-like [RFC1994] tunnel authentication
during the control connection establishment [RFC2661, 5.1.1]. The
same restrictions apply to L2TPv2 authentication and PPP CHAP.
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3.5.2.3 IPsec authentication
Authentication using shared secrets can be used when the number of
softwire initiators is small. When the number of SI increases,
shared secrets becomes difficult to manage. Public-key digital
signature or key encryption authentication with certificates is
preferable [RFC3193, 4.1].
3.5.3 Inter-operability guidelines
The inter-operability guidelines in [RFC3193] concerning tunnel
teardown, fragmentation and per-packet security checks must be
followed. [Note: nothing specific to softwire.]
3.5.4 IPsec filtering details
The IPsec filtering details from [RFC3193] section 4 are applicable
to softwire "Hubs and Spokes" model.
Although the L2TP specification allows the responder (SC in softwire)
to use a new IP address when sending the Start-Control-Connection-
Request-Reply (SCCRP), a softwire concentrator implementation SHOULD
NOT do this ([RFC3193] section 4). Note that this feature may be
needed for "load-balancing" between SCs.
3.5.5 IPsec SPD entries example
The SPD examples in [RFC3193] appendix A can be applied to softwire
model. In that case, the initiator is always the client (SI), and
responder is the SC.
3.5.5.1 IPv6 over IPv4 Softwire with L2TPv2 example
In this example, the softwire initiator and concentrator are denoted
with IPv4 addresses IPv4-SI and IPv4-SC respectively.
Next Layer
src dst Protocol Action
----- ------ ---------- --------
IPV4-SI IPV4-SC ESP BYPASS
IPV4-SI IPV4-SC IKE BYPASS
IPv4-SI IPV4-SC UDP, src 1701, dst 1701 PROTECT(ESP,transport)
IPv4-SC IPv4-SI UDP, src * , dst 1701 PROTECT(ESP,transport)
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Next Layer
src dst Protocol Action
----- ------ ---------- --------
* IPV4-SC ESP BYPASS
* IPV4-SC IKE BYPASS
* IPV4-SC UDP, src * , dst 1701 PROTECT(ESP,transport)
3.5.5.2 IPv4 over IPv6 Softwire with example
In this example, the softwire initiator and concentrator are denoted
with IPv6 addresses IPv6-SI and IPv6-SC respectively.
Next Layer
src dst Protocol Action
----- ------ ---------- --------
IPV6-SI IPV6-SC ESP BYPASS
IPV6-SI IPV6-SC IKE BYPASS
IPv4-SI IPV6-SC UDP, src 1701, dst 1701 PROTECT(ESP,transport)
IPv4-SC IPv4-SI UDP, src * , dst 1701 PROTECT(ESP,transport)
Next Layer
src dst Protocol Action
----- ------ ---------- --------
* IPV6-SC ESP BYPASS
* IPV6-SC IKE BYPASS
* IPV6-SC UDP, src * , dst 1701 PROTECT(ESP,transport)
4. Mesh Security Guidelines
4.1 Deployment Scenario
In the "Mesh" model, it is required to establish connectivity to
access network islands of one address family type across a transit
core of a differing address family type. To provide reachability
across the transit core, AFBRs are installed between access network
island and transit core network. These AFBRs can peer across
autonomous systems or perform as Provider Edge routers (PE) within an
autonomous system. The AFBRs establish and encapsulate softwires in
a mesh to the other islands across the transit core network. The
transit core network consists of one or more service providers.
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In the softwire "Mesh" solution, point to multi-point connectivity
among AFBRs is dynamically established by announcing the reachability
and the encapsulation method using Multiprotocol Extensions for BGP-4
(MP-BGP)[RFC2858].
AFBR nodes are Internal BGP speakers and will peer with each other
(directly or via a route reflector) to exchange SW-encap sets,
perform softwire signaling, and advertise AF access island
reachability information and SW-NHOP information. If such
information is advertised within an autonomous system, the AFBR node
receiving them from other AFBRs does not forward them to other AFBR
nodes. To exchange the information among AFBRs, the full mesh
connectivity is required.
BGP speakers can inject bogus routing information, either by
masquerading as any other legitimate BGP speaker, or by distributing
unauthorized routing information as themselves. The damage due to
this bogus information is limited rather than eBGP case but cannot be
ignored.
AFBRs are PE routers located at the edge of the provider core
networks. This is similar architecture of Provider Provisioned PE-
based VPN. CE-PE connectivity is established by static way or using
routing protocol i.e. eBGP. AFBRs form a peering relationship with
one or more CE routers located inside the AF access island to AF
access island reachability information. Note that the security
threat on CE-PE is not specific to Softwire Mesh solution.
As alternative model to make the AFBR a single-stack AF(j) PE node,
the dual-stack AF(i,j) processing is moved to CE routers located at
the edge of a customer site and may or may not be provided by the
core network provider. This is the dual-stack CE model. This model
might evolve inter-CE BGP peering to exchange client AF prefixes/
next-hops. The CE-PE connection includes dedicated physical
circuits, logical circuits (such as Frame Relay and ATM), and shared
medium access (such as Ethernet-based access). The CE device has the
IP connectivity with SP's PE device over the Access connection.
4.2 Trust Relationship
All the ASBRs in the transit core MUST have a trust relationship or
an agreement with each other to establish softwires. Within an
autonomous system, it is assumed that all the nodes (e.g. the ASBR,
PE or Route Reflector, if applicable) are trusted with each other so
that the AFBR can be collocated in the ASBR or PE. If the transit
core consists of multiple autonomous systems, intermediate routers
between ASBRs may not be trusted.
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There MUST be a trust relationship between the PE in the transit core
and the CE in the corresponding island; however, the link(s) between
the PE and CE may not be protected.
4.3 Softwire Security Threat Scenarios
In terms of Softwire mesh solution, the security threats are common
to those of PPVPN. [RFC4111] But in this document, the security
threats on PE-PE are specifically discussed.
The security attacks on the control plane and the data plane can be
mounted. In Mesh Solution, Softwires will be established by using
MP-BGP. MP-BGP does not change the security issues inherent in the
existing BGP. In terms of the control plane security, the general
BGP security vulnerabilities are applicable[RFC4272].
4.3.1 Attacks on the Control Plane
BGP, in and of itself, is subject to the following attacks [RFC4272].
1. The routing data carried in BGP is carried in cleartext, so
eavesdropping is a possible attack against routing data
confidentiality. (confidentiality violations)
2. BGP does not provide for replay protection of its message.
(replay)
3. BGP does not provide protection against insertion of messages.
However, because BGP uses TCP, when the connection is fully
established, message insertion by an outsider would require
accurate sequence number prediction or session-stealing
attacks.(message insertion)
4. BGP does not provide protection against deletion messages. This
attack is more difficult against a mature TCP implementation, but
is not entirely out of question. (message deletion)
5. BGP does not provide protection against modification of messages.
A modification that was syntactically correct and did not change
the length of the TCP payload would in general not be detectable.
(message modification)
6. 6. BGP does not provide protection against man-in-the-middle
attacks. As BGP does not perform peer entity authentication, it
is vulnerable to a man-in-the-middle attack. (man-in-the-middle)
7. While bogus routing data can present a DoS attack on the end
systems that are trying to transmit data through network and on
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the network infrastructure itself, certain bogus information can
present a DoS on the BGP routing protocol. (denial-of-service)
4.3.2 Attacks on the Data Plane
Examples of attacks include:
1. An adversary may try to discover confidential information by
sniffing softwire packets.
2. An adversary may try to modify the contents of softwire packets.
3. An adversary may try to spoof the softwire packets that do not
belong there and to insert of copies of once-legitimate packets
that have been recorded and replayed.
4. An adversary can launch Denial-of-Service attack by deleting
softwire data traffic. DoS attacks of the resource exhaustion
type can be mounted against the data plane by spoofing a large
amount of non-authenticated data into the softwire from the
outside of the softwire tunnel.
5. An adversary may try to sniff softwire packets and to examine
aspects or meta-aspects of them that may be visible even when the
packets themselves are encrypted. An attacker might gain useful
information based on the amount and timing of traffic, packet
sizes, sources and destination addresses, etc.
4.4 Softwire Security Guidelines
Given that security is generally a compromise between expense and
risk, it is also useful to consider the likelihood of different
attacks. There is at least a perceived difference in the likelihood
of most types of attacks being successfully mounted in different
deployment.
The trust model between the access network islands and the transit
core networks is a key element in determining the applicability of
encryption for the specific Mesh softwire implementation.
4.5 Guidelines for Usage of Security Protection Mechanism
4.5.1 Security Protection Mechanism for Control Plane
A BGP has the three fundamental vulnerabilities to the security
threats [RFC4272].
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1. BGP has no internal mechanism that provides strong protection of
the integrity, freshness, and peer authenticity of the message in
peer-peer BGP communications.
2. No mechanism has been specified within BGP to validate the
authority of a BGP peer to announce NLRI information.
3. No mechanism has been specified within BGP to ensure the
authenticity of the path attributes announced by a BGP peer.
A BGP implementation MUST support the authentication mechanism
specified in RFC 2385. The authentication provided by this mechanism
could be done on a peer-peer basis.
The mechanism defined in RFC 2385 is based on a one-way hash function
(MD5) and use of a secret key. The key is shared between peer
routers and is used to generate 16-byte message authentication code
values that are not readily computed by an attacker who does not have
access to the key.
RFC 2385, however, does not specify a means of managing the keys use
to compute the MAC although RFC3562 provides some Guidelines in the
key management.
Key management can be especially onerous for operators. The number
of keys required and the maintenance of keys (issue/revoke/renew) has
had an additive effect as a barrier to deployment. Thus automated
means of managing keys, to reduce operational burdens, MUST be
available in BGP security systems.[I-D.rpsec-bgpsecrec]
Automated key management will be provided by IKE/IPsec.
4.5.1.1 TCP MD5
The mandatory-to-support mechanism of TCP MD5 will counter message
insertion, deletion, and modification, man-in-the-middle and denial
of service attacks from outsiders. The use of TCP MD5 does not
protect against eavesdropping attacks, (but routing data
confidentiality is not a goal of BGP) The mechanism of TCP MD5 does
not protect against replay attacks, so the only protection against
replay is provided by the TCP sequence number processing. Therefore,
a replay attack could be mounted against a BGP connection protected
with TCP MD5 but in very carefully timed circumstances.
In addition, lack of an automated key distribution protocol
complicates management and encourages overly long-term use of
symmetric keys.
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4.5.1.2 IPsec
Use of TCP MD5 counters the message insertion, deletion, and
modification attacks, as well as man-in-the-middle attacks by
outsiders. If routing data confidentiality is desired, the use of
IPsec ESP could provide that service. But routing data
confidentiality is not a goal of BGP.
IPsec, transport mode is used to protect BGP session between peers.
If eavesdropping attack against the data plane is identified as a
threat, ESP can be used to provide confidentiality (encryption),
integrity and authentication for the BGP session. Where
eavesdropping is not a threat, ESP without confidentiality or AH may
be used.
To provide replay protection, automated key management system using
IKE must be used. IKE main mode can be used using shared secrets for
authentication when the number of BGP peers is small. When the
number of BGP peers is large managing the shared secrets on all peers
does not scale. In this scenario, public-key digital signature or
key encryption authentication in IKE should be used, assuming that
the peers have the necessary computation available.
4.5.1.3 Secure BGP
The deeper security issues raised by BGP are not addressed by IPsec
or any other transmission security mechanism.
As cryptographic-based mechanism, Both TCP MD5 and IPsec assume that
the cryptographic algorithms are secure, that secrets used are
protected from exposure and are chosen well so as not to be
guessable, that the platforms are securely managed and operated to
prevent break-ins, etc.
These mechanisms do not prevent attacks that arise from a router's
legitimate BGP peers [RFC4272].
The S-BGP countermeasures use IPsec, Public Key Infrastructure (PKI)
technology,a nd a new BGP path attribute ("attestations") to ensure
the authenticity and integrity of BGP communication on a point-to-
point basis, and to validate BGP routing UPDATE's on a source to
destination basis[I-D.clynn-s-bgp-protocol].
To implement the secure BGP, Secure Origin BGP (soBGP) and Pretty
Secure BGP (psBGP) are also proposed. The detail comparison was made
in[Wan05].
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4.5.2 Security Protection Mechanism for Data Plane
The protection mechanisms discussed are intended to describe methods
by which some security threats can be mitigated. They are not
intended as requirements for all softwire implementations.
The several of the attacks outlined in Section 4.3.2. In order to
protect against such threats, the softwire SHOULD provide for replay
and integrity protection for softwire data packets and MAY protect
confidentiality of data packets. Automated key management in the
softwire mesh solution may be necessary per [RFC4107].
4.5.2.1 Cryptographic Techniques
IPsec can provide replay protection, integrity and confidentiality of
IP data packets, which would protect against most threats identified
in 4.3.2.
In Softwire Mesh framework solution, IPsec connections can be
established on selective basis using Tunnel SAFI advertised by AFBRs.
The softwire mesh framework [wu-softwire-mesh-framework] currently
supports many tunnel encapsulation type using a "Softwire Mesh
Encasulation attribute" advertised as a BGP Tunnel SAFI [nalawade-
softwire-mesh-encap-attribute], [nalawade-kapoor-tunnel-safi].
To protect the data packets using IPsec, AFBRs must be configured
with the proper IPsec parameters: ESP (with or without
confidentiality), transport or tunnel mode, key management (IKE
phase1 mode and ID), selectors and SPD.
[nalawade-kapoor-tunnel-safi] describes an IPsec Tunnel Information
TLV that contains an IKE Identifier. The SPD and selectors must also
be defined. These are directly related to the encapsulation type
used between the AFBRs (e.g., selectors for L2TP will be different
from IPv6-over-IPv4 tunnels).
(to be completed)
4.5.2.2 Access Control Techniques
Access control techniques include packet-by-packet or packet flow-by
-packet flow access control by means of filters as well as by means
of admitting a session for a control/signaling/management protocol
that is being used to implement softwires.
It is relatively common for routers to filter data packets. That is,
routers can look for particular values in certain fields of the IP or
higher level (e.g., TCP or UDP) headers. Packets that match the
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criteria associated with a particular filter may be either discarded
or given special treatment to prevent an attack or to mitigate the
effect of a possible future attack.
5. Security Considerations
This document is about the IETF's requirement that security be
considered in the deployment of softwire. The entire document
consider the security.
The several of the attacks outlined in 4.3.2. In order to protect
against such threats, the softwire SHOULD provide for replay and
integrity protection for softwire data packets and MAY protect
confidentiality of data packets. Automated key management in the
softwire mesh solution may be necessary per[RFC4107].
6. References
6.1 Normative References
[I-D.softwire-hs-framework-l2tpv2]
Sorer, B., Pignataro, C., Dos Santos, M., Tremblay, J.,
and L. Toutain, "Softwire Hub & Spoke Deployment Framework
with L2TPv2", draft-softwire-hs-framework-l2tpv2 (work in
progress), August 2006.
[I-D.softwire-problem-statement]
Li, X., Durand, A., Ward, D., and S. Dawkins, "Softwire
Problem Statement",
draft-ietf-softwire-problem-statement-02 (work in
progress), May 2006.
[I-D.v6ops-tunneling-requirements]
Durand, A. and F. Parent, "Requirements for assisted
tunneling",
draft-durand-v6ops-assisted-tunneling-requirements-00
(work in progress), September 2004.
[I-D.wu-softwire-mesh-framework]
Wu, J., Cui, Y., LI, X., Metz, C., and G. Nalawade, "A
Framework for Softwire Mesh Signaling, Routing and
Encapsulation across IPv4 and IPv6 Backbone Networks",
draft-wu-softwire-mesh-framework-00 (work in progress),
June 2006.
[RFC1994] Simpson, W., "PPP Challenge Handshake Authentication
Protocol (CHAP)", RFC 1994, August 1996.
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[RFC2385] Heffernan, A., "Protection of BGP Sessions via the TCP MD5
Signature Option", RFC 2385, August 1998.
[RFC2409] Harkins, D. and D. Carrel, "The Internet Key Exchange
(IKE)", RFC 2409, November 1998.
[RFC2661] Townsley, W., Valencia, A., Rubens, A., Pall, G., Zorn,
G., and B. Palter, "Layer Two Tunneling Protocol "L2TP"",
RFC 2661, August 1999.
[RFC2858] Bates, T., Rekhter, Y., Chandra, R., and D. Katz,
"Multiprotocol Extensions for BGP-4", RFC 2858, June 2000.
[RFC3365] Schiller, J., "Strong Security Requirements for Internet
Engineering Task Force Standard Protocols", BCP 61,
RFC 3365, August 2002.
[RFC3947] Kivinen, T., Swander, B., Huttunen, A., and V. Volpe,
"Negotiation of NAT-Traversal in the IKE", RFC 3947,
January 2005.
[RFC3948] Huttunen, A., Swander, B., Volpe, V., DiBurro, L., and M.
Stenberg, "UDP Encapsulation of IPsec ESP Packets",
RFC 3948, January 2005.
[RFC4107] Bellovin, S. and R. Housley, "Guidelines for Cryptographic
Key Management", BCP 107, RFC 4107, June 2005.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, December 2005.
[RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
RFC 4306, December 2005.
[RFC4593] Barbir, A., Murphy, S., and Y. Yang, "Generic Threats to
Routing Protocols", RFC 4593, October 2006.
6.2 Informative References
[I-D.bellovin-useipsec]
Bellovin, S., "Guidelines for Mandating the Use of IPsec",
draft-bellovin-useipsec-04 (work in progress),
September 2005.
[I-D.clynn-s-bgp-protocol]
Lynn, C. and K. Seo, "Secure BGP (S-BGP)",
draft-clynn-s-bgp-protocol-01 (work in progress),
June 2003.
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[I-D.rpsec-bgpsecrec]
Christian, B. and T. Tauber, "BGP Security Requirements",
draft-ietf-rpsec-bgpsecrec-06 (work in progress),
April 2006.
[I-D.rpsec-routing-threats]
Barbir, A., Murphy, S., and Y. Yang, "Generic Threats to
Routing Protocols", draft-ietf-rpsec-routing-threats-07
(work in progress), October 2005.
[I-D.white-sobgp-architecture]
White, R., "Architecture and Deployment Considerations for
Secure Origin BGP (soBGP)",
draft-white-sobgp-architecture-02 (work in progress),
June 2006.
[RFC3193] Patel, B., Aboba, B., Dixon, W., Zorn, G., and S. Booth,
"Securing L2TP using IPsec", RFC 3193, November 2001.
[RFC3562] Leech, M., "Key Management Considerations for the TCP MD5
Signature Option", RFC 3562, July 2003.
[RFC4016] Parthasarathy, M., "Protocol for Carrying Authentication
and Network Access (PANA) Threat Analysis and Security
Requirements", RFC 4016, March 2005.
[RFC4081] Tschofenig, H. and D. Kroeselberg, "Security Threats for
Next Steps in Signaling (NSIS)", RFC 4081, June 2005.
[RFC4111] Fang, L., "Security Framework for Provider-Provisioned
Virtual Private Networks (PPVPNs)", RFC 4111, July 2005.
[RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis",
RFC 4272, January 2006.
[Wan05] Wan, T., Wan, P., and S. Kranakis, "A Selective
Introduction to Border Gateway Protocol (BGP) Security
Issues", URL http://www.scs.carleton.ca/research/
tech_reports/2005/TR-05-08.pdf, August 2005.
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Authors' Addresses
Shu Yamamoto
KDDI R&D Labs
2-1-15 Fujimino-shi
Saitama, 356-8502
Japan
Phone: 81 (49) 278-7311
Email: shu@kddilabs.jp
Carl Williams
KDDI R&D Labs
Palo Alto, CA 94301
USA
Phone: +1.650.279.5903
Email: carlw@mcsr-labs.org
Florent Parent
consultant
Quebec, QC
Canada
Phone: +1 418 265 7357
Email: Florent.Parent@mac.com
Hidetoshi Yokota
KDDI R&D Labs
2-1-15 Ohara
Fujimino, Saitama 356-8502
Japan
Phone: 81 (49) 278-7894
Email: yokota@kddilabs.jp
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Yamamoto, et al. Expires April 25, 2007 [Page 24]
