Segment Routing IPv6 Security Considerations
draft-ietf-spring-srv6-security-00
| Document | Type | Active Internet-Draft (spring WG) | |
|---|---|---|---|
| Authors | Nick Buraglio , Tal Mizrahi , tongtian124 , Luis M. Contreras , Fernando Gont | ||
| Last updated | 2024-08-22 | ||
| Replaces | draft-bdmgct-spring-srv6-security | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Proposed Standard | ||
| Formats | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Document shepherd | (None) | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Yes | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | aretana.ietf@gmail.com |
draft-ietf-spring-srv6-security-00
Source Packet Routing in Networking N. Buraglio
Internet-Draft Energy Sciences Network
Intended status: Standards Track T. Mizrahi
Expires: 22 February 2025 Huawei
T. Tong
China Unicom
L. M. Contreras
Telefonica
F. Gont
SI6 Networks
21 August 2024
Segment Routing IPv6 Security Considerations
draft-ietf-spring-srv6-security-00
Abstract
SRv6 is a traffic engineering, encapsulation and steering mechanism
utilizing IPv6 addresses to identify segments in a pre-defined
policy. This document discusses security considerations in SRv6
networks, including the potential threats and the possible mitigation
methods. The document does not define any new security protocols or
extensions to existing protocols.
About This Document
This note is to be removed before publishing as an RFC.
The latest revision of this draft can be found at
https://buraglio.github.io/draft-bdmgct-spring-srv6-security/draft-
bdmgct-spring-srv6-security.html. Status information for this
document may be found at https://datatracker.ietf.org/doc/draft-ietf-
spring-srv6-security/.
Discussion of this document takes place on the Source Packet Routing
in Networking Working Group mailing list (mailto:spring@ietf.org),
which is archived at https://mailarchive.ietf.org/arch/browse/
spring/. Subscribe at https://www.ietf.org/mailman/listinfo/spring/.
Source for this draft and an issue tracker can be found at
https://github.com/buraglio/draft-bdmgct-spring-srv6-security.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Copyright Notice
Copyright (c) 2024 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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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Scope of this Document . . . . . . . . . . . . . . . . . . . 4
3. Conventions and Definitions . . . . . . . . . . . . . . . . . 4
3.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
3.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
4. Threat Model . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Impact . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6. Attacks . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.1. Attack Abstractions . . . . . . . . . . . . . . . . . . . 8
6.2. SR Modification Attack . . . . . . . . . . . . . . . . . 9
6.2.1. Overview . . . . . . . . . . . . . . . . . . . . . . 9
6.2.2. Scope . . . . . . . . . . . . . . . . . . . . . . . . 9
6.2.3. Impact . . . . . . . . . . . . . . . . . . . . . . . 9
6.2.4. Overview . . . . . . . . . . . . . . . . . . . . . . 11
6.2.5. Scope . . . . . . . . . . . . . . . . . . . . . . . . 11
6.2.6. Impact . . . . . . . . . . . . . . . . . . . . . . . 11
6.3. Packet Insertion . . . . . . . . . . . . . . . . . . . . 11
6.3.1. Overview . . . . . . . . . . . . . . . . . . . . . . 11
6.3.2. Scope . . . . . . . . . . . . . . . . . . . . . . . . 11
6.3.3. Impact . . . . . . . . . . . . . . . . . . . . . . . 12
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6.4. Control and Management Plane Attacks . . . . . . . . . . 12
6.4.1. Overview . . . . . . . . . . . . . . . . . . . . . . 12
6.4.2. Scope . . . . . . . . . . . . . . . . . . . . . . . . 12
6.4.3. Impact . . . . . . . . . . . . . . . . . . . . . . . 12
6.5. Other Attacks . . . . . . . . . . . . . . . . . . . . . . 13
7. Mitigation Methods . . . . . . . . . . . . . . . . . . . . . 13
7.1. Filtering . . . . . . . . . . . . . . . . . . . . . . . . 13
7.1.1. SRH Filtering . . . . . . . . . . . . . . . . . . . . 13
7.1.2. Address Range Filtering . . . . . . . . . . . . . . . 13
7.2. Encapsulation of Packets . . . . . . . . . . . . . . . . 14
7.3. Hashed Message Authentication Code (HMAC) . . . . . . . . 14
8. Implications on Existing Equipment . . . . . . . . . . . . . 14
8.1. Limitations in Filtering Capabilities . . . . . . . . . . 15
8.2. Middlebox Filtering Issues . . . . . . . . . . . . . . . 15
9. Security Considerations . . . . . . . . . . . . . . . . . . . 16
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
11. Topics for Further Consideration . . . . . . . . . . . . . . 16
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
12.1. Normative References . . . . . . . . . . . . . . . . . . 17
12.2. Informative References . . . . . . . . . . . . . . . . . 18
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
1. Introduction
Segment Routing (SR) [RFC8402] utilizing an IPv6 data plane is a
source routing model that leverages an IPv6 underlay and an IPv6
extension header called the Segment Routing Header (SRH) [RFC8754] to
signal and control the forwarding and path of packets by imposing an
ordered list of path details that are processed at each hop along the
signaled path. Because SRv6 is fundamentally bound to the IPv6
protocol, and because of the reliance on a new header there are
security considerations which must be noted or addressed in order to
operate an SRv6 network in a reliable and secure manner.
Specifically, some primary properties of SRv6 that affect the
security considerations are:
* SRv6 may use the SRH which is a type of Routing Extension Header
defined by [RFC8754]. Some security considerations of the SRH are
discussed in [RFC5095] section 5 and [RFC8754] section 7.
* SRv6 uses the IPv6 data-plane, and therefore known security
considerations of IPv6 [RFC9099] are applicable to SRv6 as well.
* While SRv6 uses what appear to be typical IPv6 addresses, the
address space is processed differently by segment endpoints. A
typical IPv6 unicast address is composed of a network prefix, host
identifier, and a subnet mask. A typical SRv6 segment identifier
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(SID) consists of a locator, a function identifier, and
optionally, function arguments (LOC:FUNCT:ARG [RFC8986]). The
locator must be routable, which enables both SRv6 capable and
incapable devices to participate in forwarding, either as normal
IPv6 unicast or SRv6. The capability to operate in environments
that may have gaps in SRv6 support allows the bridging of islands
of SRv6 devices with standard IPv6 unicast routing.
This document describes various threats to SRv6 networks and also
presents existing approaches to avoid or mitigate the threats.
2. Scope of this Document
The following IETF RFCs were selected for security assessment as part
of this effort:
* [RFC8402] : "Segment Routing Architecture"
* [RFC8754] : "IPv6 Segment Routing Header (SRH)"
* [RFC8986] : "Segment Routing over IPv6 (SRv6) Network Programming"
* [RFC9020] : "YANG Data Model for Segment Routing"
* [RFC9256] : "Segment Routing Policy Architecture"
* [RFC9491] : "Integration of the Network Service Header (NSH) and
Segment Routing for Service Function Chaining (SFC)"
* [RFC9524] : "Segment Routing Replication for Multipoint Service
Delivery"
We note that SRv6 is under active development and, as such, the above
documents might not cover all protocols employed in an SRv6
deployment.
3. Conventions and Definitions
3.1. Requirements Language
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.
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3.2. Terminology
* HMAC TLV: Hashed Message Authentication Code Type Length Value
[RFC8754]
* SID: Segment Identifier [RFC8402]
* SRH: Segment Routing Header [RFC8754]
* SRv6: Segment Routing over IPv6 [RFC8402]
4. Threat Model
This section introduces the threat model that is used in this
document. The model is based on terminology from the Internet threat
model [RFC3552], as well as some concepts from [RFC9055], [RFC7384]
and [RFC9416]. Details regarding inter-domain segment routing (SR)
are out of scope for this document.
Internal vs. External: An internal attacker in the context of SRv6
is an attacker who is located within an SR domain. Specifically,
an internal attacker either has access to a node in the SR domain,
or is located on an internal path between two nodes in the SR
domain. External attackers, on the other hand, are not within the
SR domain.
On-path vs. Off-path: On-path attackers are located in a position
that allows interception, modification or dropping of in-flight
packets, as well as insertion (generation) of packets. Off-path
attackers can only attack by insertion of packets.
The following figure depicts the attacker types according to the
taxonomy above. As illustrated in the figure, on-path attackers are
located along the path of the traffic that is under attack, and
therefore can listen, insert, delete, modify or replay packets in
transit. Off-path attackers can insert packets, and in some cases
can passively listen to some traffic, such as multicast
transmissions.
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on-path on-path off-path off-path
external internal internal external
attacker attacker attacker attacker
| | |__ |
| SR __ | __ _/| \ |
| domain / \_/ | \_/ v \__ v
| \ | X \ X
v / v \
----->X---------->O------>X------->O------->O---->
^\ ^ /^
| \___/\_ /\_ | _/\__/ |
| \__/ | |
| | |
SR SR SR
ingress endpoint egress
node node
Figure 1: Threat Model Taxonomy
In the current threat model the SR domain defines the boundary that
distinguishes internal from external threats. As specified in
[RFC8402]:
By default, SR operates within a trusted domain. Traffic MUST be
filtered at the domain boundaries.
The use of best practices to reduce the risk of tampering within the
trusted domain is important. Such practices are discussed in
[RFC4381] and are applicable to both SR-MPLS and SRv6.
In the context of the current document it is assumed that SRv6 is
deployed within a limited domain [RFC8799] with filtering at the
domain boundaries, forming a trusted domain with respect to SRv6.
Thus, external attackers are outside the trusted domain.
Specifically, an attack on one domain that is invoked from within a
different domain is considered an external attack in the context of
the current document.
Following the spirit of [RFC8402], the current document mandates a
filtering mechanism that eliminates the threats from external
attackers. This approach limits the scope of the attacks described
in this document to within the domain (i.e., internal attackers).
It should be noted that in some threat models the distinction between
internal and external attackers depends on whether an attacker has
access to a cryptographically secured (encrypted or authenticated)
domain. Specifically, in some of these models there is a distinction
between an attacker who becomes internal by having physical access,
for example by plugging into an active port of a network device, and
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an attacker who has full access to a legitimate network node,
including for example encryption keys if the network is encrypted.
The current model does not distinguish between these two types of
attackers and there is no assumption about whether the SR domain is
cryptographically secured or not. Thus, some of the attacks that are
described in the next section can be mitigated by cryptographic
means, as further discussed in Section 7.3.
5. Impact
One of the important aspects of a threat analysis is the potential
impact of each threat. SRv6 allows for the sending of IPv6 packets
via arbitrary paths. An attack on SRv6 may cause packets to traverse
arbitrary paths within an SR domain. This may allow an attacker to
perform a number of attacks on the victim networks and hosts that
would be mostly unfeasible for a non-SRv6 environment.
The threat model in [ANSI-Sec] classifies threats according to their
potential impact, defining six categories. For each of these
categories we briefly discuss its applicability to SRv6 attacks.
* Unauthorized Access: an attack that results in unauthorized access
might be achieved by having an attacker leverage SRv6 to
circumvent security controls as a result of security devices being
unable to enforce security policies in the presence of IPv6
Extension Headers (see [RFC9098]), or by directing packets through
paths where packet-filtering policies are not enforced.
* Masquerade: various attacks that result in spoofing or
masquerading are possible in IPv6 networks (e.g., [RFC9098]).
However, these attacks are not specific to SRv6, and are therefore
not within the scope of this document.
* System Integrity: attacks on SRv6 can manipulate the path and the
processing that the packet is subject to, thus compromising the
integrity of the system. Furthermore, an attack that compromises
the control plane and/or the management plane is also a means of
impacting the system integrity.
* Communication Integrity: SRv6 attacks may cause packets to be
forwarded through paths that the attacker controls, which may
facilitate other attacks that compromise the integrity of user
data. Integrity protection of user data, which is implemented in
higher layers, avoids these aspects, and therefore communication
integrity is not within the scope of this document.
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* Confidentiality: as in communication integrity, packets forwarded
through unintended paths may traverse nodes controlled by the
attacker. Since eavesdropping to user data can be avoided by
using encryption in higher layers, it is not within the scope of
this document. However, eavesdropping to a network that uses SRv6
allows the attacker to collect information about SR endpoint
addresses, SR policies, and network topologies, is a specific form
of reconnaissance
* Denial of Service: the availability aspects of SRv6 include the
ability of attackers to leverage SRv6 as a means for compromising
the performance of a network or for causing Denial of Service
(DoS). Compromising the availability of the system can be
achieved by sending multiple SRv6-enabled packets to/through
victim nodes, where the SRv6-enabled packets result in a negative
performance impact of the victim systems (see [RFC9098] for
further details). Alternatively, an attacker might achieve attack
amplification by causing packets to "bounce" multiple times
between a set of victim nodes, with the goal of exhausting
processing resources and/or bandwidth (see [CanSecWest2007] for a
discussion of this type of attack).
Section 6 discusses specific implementations of these attacks, and
possible mitigations are discussed in Section 7.
6. Attacks
6.1. Attack Abstractions
Packet manipulation and processing attacks can be implemented by
performing a set of one or more basic operations. These basic
operations (abstractions) are as follows:
* Passive listening: an attacker who reads packets off the network
can collect information about SR endpoint addresses, SR policies
and the network topology. This information can then be used to
deploy other types of attacks.
* Packet replaying: in a replay attack the attacker records one or
more packets and transmits them at a later point in time.
* Packet insertion: an attacker generates and injects a packet to
the network. The generated packet may be maliciously crafted to
include false information, including for example false addresses
and SRv6-related information.
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* Packet deletion: by intercepting and removing packets from the
network, an attacker prevents these packets from reaching their
destination. Selective removal of packets may, in some cases,
cause more severe damage than random packet loss.
* Packet modification: the attacker modifies packets during transit.
This section describes attacks that are based on packet manipulation
and processing, as well as attacks performed by other means.
6.2. SR Modification Attack
6.2.1. Overview
An attacker can modify a packet while it is in transit in a way that
directly affects the packet's SR policy. The modification can affect
the destination address of the IPv6 header and/or the SRH. In this
context SRH modification may refer to inserting an SRH, removing an
SRH, or modifying some fields of an existing SRH.
Modification of an existing SRH can be further classified into
several possible attacks. Specifically, the attack can include
adding one or more SIDs to the segment list, removing one or more
SIDs or replacing some SIDs with different SIDs. Another possible
type of modification is by adding, removing or modifying TLV fields
in the SRH.
When an SRH is present modifying the destination address (DA) of the
IPv6 header affects the active segment. However, DA modification can
affect the SR policy even in the absence of an SRH. One example is
modifying a DA which is used as a Binding SID [RFC8402]. Another
example is modifying a DA which represents a compressed segment list
[I-D.ietf-spring-srv6-srh-compression]. SRH compression allows
encoding multiple compressed SIDs within a single 128-bit SID, and
thus modifying the DA can affect one or more hops in the SR policy.
6.2.2. Scope
An SR modification attack can be performed by on-path attackers. As
discussed in Section 4, it assumed that filtering is deployed at the
domain boundaries, thus limiting the ability of implementing SR
modification attacks to on-path internal attackers.
6.2.3. Impact
The SR modification attack allows an attacker to change the SR policy
that the packet is steered through and thus to manipulate the path
and the processing that the packet is subject to.
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Specifically, the SR modification attack can impact the network and
the forwarding behavior of packets in one or more of the following
ways:
Avoiding a specific node or path: An attacker can manipulate the DA
and/or SRH in order to avoid a specific node or path. This
approach can be used, for example, for bypassing the billing
service or avoiding access controls and security filters.
Preferring a specific path: The packet can be manipulated to avert
packets to a specific path. This attack can result in allowing
various unauthorized services such as traffic acceleration.
Alternatively, an attacker can avert traffic to be forwarded
through a specific node that the attacker has access to, thus
facilitating more complex on-path attacks such as passive
listening, recon and various man-in-the-middle attacks. It is
noted that the SR modification attack is performed by an on-path
attacker who has access to packets in transit, and thus can
implement these attacks directly. However, SR modification is
relatively easy to implement and requires low processing resources
by an attacker, while it facilitates more complex on-path attacks
by averting the traffic to another node that the attacker has
access to and has more processing resources.
Forwarding through a path that causes the packet to be discarded: SR
modification may cause a packet to be forwarded to a point in the
network where it can no longer be forwarded, causing the packet to
be discarded.
Manipulating the SRv6 network programming: An attacker can trigger a
specific endpoint behavior by modifying the destination address
and/or SIDs in the segment list. This attack can be invoked in
order to manipulate the path or in order to exhaust the resources
of the SR endpoint.
Availability: An attacker can add SIDs to the segment list in order
to increase the number hops that each packet is forwarded through
and thus increase the load on the network. For example, a set of
SIDs can be inserted in a way that creates a forwarding loop
([RFC8402], [RFC5095]) and thus loads the nodes along the loop.
Network programming can be used in some cases to manipulate
segment endpoints to perform unnecessary functions that consume
processing resources. Path inflation, malicious looping and
unnecessary instructions have a common outcome, resource
exhaustion, which may in severe cases cause Denial of Service
(DoS).
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6.2.4. Overview
An on-path attacker can passively listen to packets and specifically
to the SRv6-related information that is conveyed in the IPv6 header
and the SRH. This approach can be used for collecting information
about SIDs and policies, and thus to facilitate mapping the structure
of the network and its potential vulnerabilities.
6.2.5. Scope
A recon attack is limited to on-path internal attackers.
It is assumed that the SRv6 domain is filtered in a way that prevents
any leaks of explicit SRv6 routing information through the boundaries
of the administrative domain. External attackers can only collect
SRv6-related data in a malfunctioning network in which SRv6-related
information is leaked through the boundaries of an SR domain.
6.2.6. Impact
While the information collected in a recon attack does not compromise
the confidentiality of the user data, it allows an attacker to gather
information about the network which in turn can be used to enable
other attacks.
6.3. Packet Insertion
6.3.1. Overview
In this attack packets are inserted (injected) into the network with
a segment list that defines a specific SR policy. The attack can be
applied either by using synthetic packets or by replaying previously
recorded packets.
6.3.2. Scope
Packet insertion can be performed by internal attackers, either on-
path or off-path. In the case of a replay attack, recording packets
in-flight requires on-path access and the recorded packets can later
be injected either from an on-path or an off-path location.
SRv6 domains are assumed to be filtered in a way that mitigates
insertion attacks from external attackers.
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6.3.3. Impact
The main impact of this attack is resource exhaustion which
compromises the availability of the network, as described in
Section 6.2.3.
6.4. Control and Management Plane Attacks
6.4.1. Overview
Depending on the control plane protocols used in a network, it is
possible to use the control plane as a way of compromising the
network. For example, an attacker can advertise SIDs in order to
manipulate the SR policies used in the network. A wide range of
attacks can be implemented, including injecting control plane
messages, selectively removing legitimate messages, replaying them or
passively listening to them.
A compromised management plane can also facilitate a wide range of
attacks, including manipulating the SR policies or compromising the
network availability.
6.4.2. Scope
Control plane attacks can be performed by internal attackers.
Injection can be performed by off-path attackers, while removal,
replaying and listening require on-path access. The scope of
management attacks depends on the specific management protocol and
architecture.
It is assumed that SRv6 domain boundary filtering is used for
mitigating potential control plane and management plane attacks from
external attackers. Segment routing does not define any specific
security mechanisms in existing control plane or management plane
protocols. However, existing control plane and management plane
protocols use authentication and security mechanisms to validate the
authenticity of information.
6.4.3. Impact
A compromised control plane or management plane can impact the
network in various possible ways. SR policies can be manipulated by
the attacker to avoid specific paths or to prefer specific paths, as
described in Section 6.2.3. Alternatively, the attacker can
compromise the availability, either by defining SR policies that load
the network resources, as described in Section 6.2.3, or by
blackholing some or all of the SR policies. A passive attacker can
use the control plane or management plane messages as a means for
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recon, similarly to Section 6.2.3.
6.5. Other Attacks
Various attacks which are not specific to SRv6 can be used to
compromise networks that deploy SRv6. For example, spoofing is not
specific to SRv6, but can be used in a network that uses SRv6. Such
attacks are outside the scope of this document.
Because SRv6 is completely reliant on IPv6 for addressing,
forwarding, and fundamental networking basics, it is potentially
subject to any existing or emerging IPv6 vulnerabilities [RFC9099],
however, this is out of scope for this document.
7. Mitigation Methods
This section presents methods that can be used to mitigate the
threats and issues that were presented in previous sections. This
section does not introduce new security solutions or protocols.
7.1. Filtering
7.1.1. SRH Filtering
SRv6 packets rely on the routing header in order to steer traffic
that adheres to a defined SRv6 traffic policy. Thus, SRH filtering
can be enforced at the ingress and egress nodes of the SR domain, so
that packets with an SRH cannot be forwarded into the SR domain or
out of the SR domain. Specifically, such filtering is performed by
detecting Next Header 43 (Routing Header) with Routing Type 4 (SRH).
Because of the methodologies used in SID compression
[I-D.ietf-spring-srv6-srh-compression], SRH compression does not
necessarily use an SRH. In practice this means that when compressed
segment lists are used without an SRH, filtering based on the Next
Header is not relevant, and thus filtering can only be applied based
on the address range, as described below.
7.1.2. Address Range Filtering
The IPv6 destination address can be filtered at the SR ingress node
in order to mitigate external attacks. An ingress packet with a
destination address that defines an active segment with an SR
endpoint in the SR domain is filtered.
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In order to apply such a filtering mechanism the SR domain needs to
have an allocated address range that can be detected and enforced by
the SR ingress, for example by using ULA addresses, or preferably, by
using the IANA special use prefix [IANAIPv6SPAR] for SRv6, 5f00::/16.
Note that the use of GUA addressing in data plane programming could
result in an fail open scenario when appropriate border filtering is
not implemented or supported.
7.2. Encapsulation of Packets
Packets steered in an SR domain are often encapsulated in an IPv6
encapsulation. This mechanism allows for encapsulation of both IPv4
and IPv6 packets. Encapsulation of packets at the SR ingress node
and decapsulation at the SR egress node mitigates the ability of
external attackers to impact SR steering within the domain.
7.3. Hashed Message Authentication Code (HMAC)
The SRH can be secured by an HMAC TLV, as defined in [RFC8754]. The
HMAC is an optional TLV that secures the segment list, the SRH flags,
the SRH Last Entry field and the IPv6 source address. A pre-shared
key is used in the generation and verification of the HMAC.
Using an HMAC in an SR domain can mitigate some of the SR
Modification Attacks (Section 6.2). For example, the segment list is
protected by the HMAC.
The following aspects of the HAMC should be considered:
* The HMAC TLV is OPTIONAL.
* While it is presumed that unique keys will be employed by each
participating node, in scenarios where the network resorts to
manual configuration of pre-shared keys, the same key might be
reused by multiple systems as an (incorrect) shortcut to keeping
the problem of pre-shared key configuration manageable.
* An internal attacker who does not have access to the pre-shared
key can capture legitimate packets, and later replay the SRH and
HMAC from these recorded packets. This allows the attacker to
insert the previously recorded SRH and HMAC into a newly injected
packet. An on-path internal attacker can also replace the SRH of
an in-transit packet with a different SRH that was previously
captured.
8. Implications on Existing Equipment
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8.1. Limitations in Filtering Capabilities
[RFC9288] provides recommendations on the filtering of IPv6 packets
containing IPv6 extension headers at transit routers. SRv6 relies on
the routing header (RH4). Because the technology is reasonably new,
many platforms, routing and otherwise, do not possess the capability
to filter and in some cases even provide logging for IPv6 next-header
43 Routing type 4.
8.2. Middlebox Filtering Issues
When an SRv6 packet is forwarded in the SRv6 domain, its destination
address changes constantly, the real destination address is hidden.
Security devices on SRv6 network may not learn the real destination
address and fail to take access control on some SRv6 traffic.
The security devices on SRv6 networks need to take care of SRv6
packets. However, the SRv6 packets usually use loopback address of
the PE device as a source address. As a result, the address
information of SR packets may be asymmetric, resulting in improper
filter traffic problems, which affects the effectiveness of security
devices. For example, along the forwarding path in SRv6 network, the
SR-aware firewall will check the association relationships of the
bidirectional VPN traffic packets. And it is able to retrieve the
final destination of SRv6 packet from the last entry in the SRH.
When the <source, destination> tuple of the packet from PE1 to PE2 is
<PE1-IP-ADDR, PE2-VPN-SID>, and the other direction is <PE2-IP-ADDR,
PE1-VPN-SID>, the source address and destination address of the
forward and backward VPN traffic are regarded as different flow.
Eventually, the legal traffic may be blocked by the firewall.
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SRv6 is commonly used as a tunneling technology in operator networks.
To provide VPN service in an SRv6 network, the ingress PE
encapsulates the payload with an outer IPv6 header with the SRH
carrying the SR Policy segment List along with the VPN service SID.
The user traffic towards SRv6 provider backbone will be encapsulated
in SRv6 tunnel. When constructing an SRv6 packet, the destination
address field of the SRv6 packet changes constantly and the source
address field of the SRv6 packet is usually assigned using an address
on the originating device, which may be a host or a network element
depending on configuration. This may affect the security equipment
and middle boxes in the traffic path. Because of the existence of
the SRH, and the additional headers, security appliances, monitoring
systems, and middle boxes could react in different ways if do not
incorporate support for the supporting SRv6 mechanisms, such as the
IPv6 Segment Routing Header (SRH) [RFC8754]. Additionally,
implementation limitations in the processing of IPv6 packets with
extension headers may result in SRv6 packets being dropped
[RFC7872],[RFC9098].
9. Security Considerations
The security considerations of SRv6 are presented throughout this
document.
10. IANA Considerations
This document has no IANA actions.
11. Topics for Further Consideration
This section lists topics that will be discussed further before
deciding whether they need to be included in this document, as well
as some placeholders for items that need further work.
* The following references may be used in the future: RFC9256
[RFC8986]
* SRH compression
* Spoofing
* Path enumeration
* Infrastructure and topology exposure: this seems like a non-issue
from a WAN perspective. Needs more thought - could be problematic
in a host to host scenario involving a WAN and/or a data center
fabric.
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* Terms that may be used in a future version: Locator Block, FRR,
uSID
* L4 checksum: [RFC8200] specifies that when the Routing header is
present the L4 checksum is computed by the originating node based
on the IPv6 address of the last element of the Routing header.
When compressed segment lists
[I-D.ietf-spring-srv6-srh-compression] are used, the last element
of the Routing header may be different than the Destination
Address as received by the final destination. Furthermore,
compressed segment lists can be used in the Destination Address
without the presence of a Routing header, and in this case the
IPv6 Destination address can be modified along the path. As a
result, some existing middleboxes which verify the L4 checksum
might miscalculate the checksum. This issue is currently under
discussion in the SPRING WG.
* Segment Routing Header figure: the SRv6 Segment Routing Header
(SRH) is defined in [RFC8754].
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | Routing Type | Segments Left |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Last Entry | Flags | Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Segment List[0] (128 bits IPv6 address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
...
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Segment List[n] (128 bits IPv6 address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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/rfc/rfc2119>.
[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/rfc/rfc8174>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/rfc/rfc8402>.
[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/rfc/rfc8754>.
[RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
(SRv6) Network Programming", RFC 8986,
DOI 10.17487/RFC8986, February 2021,
<https://www.rfc-editor.org/rfc/rfc8986>.
[RFC9020] Litkowski, S., Qu, Y., Lindem, A., Sarkar, P., and J.
Tantsura, "YANG Data Model for Segment Routing", RFC 9020,
DOI 10.17487/RFC9020, May 2021,
<https://www.rfc-editor.org/rfc/rfc9020>.
[RFC9256] Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
A., and P. Mattes, "Segment Routing Policy Architecture",
RFC 9256, DOI 10.17487/RFC9256, July 2022,
<https://www.rfc-editor.org/rfc/rfc9256>.
[RFC9491] Guichard, J., Ed. and J. Tantsura, Ed., "Integration of
the Network Service Header (NSH) and Segment Routing for
Service Function Chaining (SFC)", RFC 9491,
DOI 10.17487/RFC9491, November 2023,
<https://www.rfc-editor.org/rfc/rfc9491>.
[RFC9524] Voyer, D., Ed., Filsfils, C., Parekh, R., Bidgoli, H., and
Z. Zhang, "Segment Routing Replication for Multipoint
Service Delivery", RFC 9524, DOI 10.17487/RFC9524,
February 2024, <https://www.rfc-editor.org/rfc/rfc9524>.
12.2. Informative References
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[ANSI-Sec] "Operations, Administration, Maintenance, and Provisioning
Security Requirements for the Public Telecommunications
Network: A Baseline of Security Requirements for the
Management Plane", 2003, <https://www.ieee802.org/1/ecsg-
linksec/meetings/July03/3m150075.pdf>.
[CanSecWest2007]
"IPv6 Routing Header Security", 2007, <https://airbus-
seclab.github.io/ipv6/IPv6_RH_security-csw07.pdf>.
[I-D.ietf-spring-srv6-srh-compression]
Cheng, W., Filsfils, C., Li, Z., Decraene, B., and F.
Clad, "Compressed SRv6 Segment List Encoding", Work in
Progress, Internet-Draft, draft-ietf-spring-srv6-srh-
compression-18, 22 July 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-spring-
srv6-srh-compression-18>.
[IANAIPv6SPAR]
"IANA IPv6 Special-Purpose Address Registry", n.d.,
<https://www.iana.org/assignments/iana-ipv6-special-
registry/iana-ipv6-special-registry.xhtml>.
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552,
DOI 10.17487/RFC3552, July 2003,
<https://www.rfc-editor.org/rfc/rfc3552>.
[RFC5095] Abley, J., Savola, P., and G. Neville-Neil, "Deprecation
of Type 0 Routing Headers in IPv6", RFC 5095,
DOI 10.17487/RFC5095, December 2007,
<https://www.rfc-editor.org/rfc/rfc5095>.
[RFC7384] Mizrahi, T., "Security Requirements of Time Protocols in
Packet Switched Networks", RFC 7384, DOI 10.17487/RFC7384,
October 2014, <https://www.rfc-editor.org/rfc/rfc7384>.
[RFC7855] Previdi, S., Ed., Filsfils, C., Ed., Decraene, B.,
Litkowski, S., Horneffer, M., and R. Shakir, "Source
Packet Routing in Networking (SPRING) Problem Statement
and Requirements", RFC 7855, DOI 10.17487/RFC7855, May
2016, <https://www.rfc-editor.org/rfc/rfc7855>.
[RFC7872] Gont, F., Linkova, J., Chown, T., and W. Liu,
"Observations on the Dropping of Packets with IPv6
Extension Headers in the Real World", RFC 7872,
DOI 10.17487/RFC7872, June 2016,
<https://www.rfc-editor.org/rfc/rfc7872>.
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[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/rfc/rfc8200>.
[RFC8799] Carpenter, B. and B. Liu, "Limited Domains and Internet
Protocols", RFC 8799, DOI 10.17487/RFC8799, July 2020,
<https://www.rfc-editor.org/rfc/rfc8799>.
[RFC9055] Grossman, E., Ed., Mizrahi, T., and A. Hacker,
"Deterministic Networking (DetNet) Security
Considerations", RFC 9055, DOI 10.17487/RFC9055, June
2021, <https://www.rfc-editor.org/rfc/rfc9055>.
[RFC9098] Gont, F., Hilliard, N., Doering, G., Kumari, W., Huston,
G., and W. Liu, "Operational Implications of IPv6 Packets
with Extension Headers", RFC 9098, DOI 10.17487/RFC9098,
September 2021, <https://www.rfc-editor.org/rfc/rfc9098>.
[RFC9099] Vyncke, É., Chittimaneni, K., Kaeo, M., and E. Rey,
"Operational Security Considerations for IPv6 Networks",
RFC 9099, DOI 10.17487/RFC9099, August 2021,
<https://www.rfc-editor.org/rfc/rfc9099>.
[RFC9288] Gont, F. and W. Liu, "Recommendations on the Filtering of
IPv6 Packets Containing IPv6 Extension Headers at Transit
Routers", RFC 9288, DOI 10.17487/RFC9288, August 2022,
<https://www.rfc-editor.org/rfc/rfc9288>.
[RFC9416] Gont, F. and I. Arce, "Security Considerations for
Transient Numeric Identifiers Employed in Network
Protocols", BCP 72, RFC 9416, DOI 10.17487/RFC9416, July
2023, <https://www.rfc-editor.org/rfc/rfc9416>.
[STRIDE] "The STRIDE Threat Model", 2018,
<https://msdn.microsoft.com/en-us/library/
ee823878(v=cs.20).aspx>.
Acknowledgments
The authors would like to acknowledge the contributions from Andrew
Alston, Dale Carder, Bruno Decraene, Dhruv Dhody, Joel Halpern, Bruno
Hassanov, Alvaro Retana, Eric Vyncke, and Zafar Ali.
Authors' Addresses
Nick Buraglio
Energy Sciences Network
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Email: buraglio@forwardingplane.net
Tal Mizrahi
Huawei
Email: tal.mizrahi.phd@gmail.com
Tian Tong
China Unicom
Email: tongt5@chinaunicom.cn
Luis M. Contreras
Telefonica
Email: luismiguel.contrerasmurillo@telefonica.com
Fernando Gont
SI6 Networks
Email: fgont@si6networks.com
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