Security Considerations for SRv6 Networks
draft-li-spring-srv6-security-consideration-07
Spring C. Li
Internet-Draft Z. Li
Intended status: Informational Huawei
Expires: April 24, 2022 C. Xie
China Telecom
H. Tian
CAICT
J. Mao
Huawei
October 21, 2021
Security Considerations for SRv6 Networks
draft-li-spring-srv6-security-consideration-07
Abstract
SRv6 inherits potential security vulnerabilities from Source Routing
in general, and also from IPv6. This document describes various
threats and security concerns related to SRv6 networks and existing
approaches to solve these threats.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
3. Security Principles of SRv6 Networking . . . . . . . . . . . 4
4. Types of Vulnerabilities in SR Networks . . . . . . . . . . . 4
4.1. Eavesdropping Vulnerabilities in SRv6 Networks . . . . . 4
4.2. Packet Falsification in SRv6 Networks . . . . . . . . . . 5
4.3. Identity Spoofing in SRv6 Networks . . . . . . . . . . . 6
4.4. Packet Replay in SRv6 Networks . . . . . . . . . . . . . 7
4.5. DOS/DDOS in SRv6 Networks . . . . . . . . . . . . . . . . 7
4.6. Malicious Packet Data in SRv6 Networks . . . . . . . . . 8
5. Effects of the above on SRv6 Use Cases . . . . . . . . . . . 8
6. Security Policy Design . . . . . . . . . . . . . . . . . . . 8
6.1. Basic Security Design . . . . . . . . . . . . . . . . . . 9
6.1.1. ACL for External Interfaces . . . . . . . . . . . . . 9
6.1.2. ACL for Internal Interfaces . . . . . . . . . . . . . 9
6.1.3. SID Instantiation . . . . . . . . . . . . . . . . . . 9
6.2. Enhanced Security Design . . . . . . . . . . . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 10
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.1. Normative References . . . . . . . . . . . . . . . . . . 10
9.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
Segment Routing (SR) [RFC8402] is a source routing paradigm that
explicitly indicates the forwarding path for packets at the source
node by inserting an ordered list of instructions, called segments.
A segment can represent a topological or service-based instruction.
When segment routing is deployed on IPv6 [RFC8200] dataplane, called
SRv6 [RFC8754], a segment is a 128 bit value, and can the IPv6
address of a local interface but it does not have to. For supporting
SR, a new type of Routing Extension Header is defined and called the
Segment Routing Header (SRH). The SRH contains a list of SIDs and
other information such as Segments Left. The SRH is defined in
[RFC8754]. By using the SRH, an ingress router can steer SRv6
packets into an explicit forwarding path so that many use cases like
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Traffic Engineering, Service Function Chaining can be deployed easily
by SRv6.
However, SRv6 also brings some new security concerns. This document
describes various threats to networks deploying SRv6. SRv6 inherits
potential security vulnerabilities from source routing in general,
and also from IPv6.
o SRv6 makes use of the SRH which is a new type of Routing Extension
Header. Therefore, the security properties of the Routing
Extension Header are addressed by the SRH. See [RFC5095] and
[RFC8754] for details.
o SRv6 consists of using the SRH on the IPv6 dataplane which
security properties can be understood based on previous work
[RFC4301], [RFC4302], [RFC4303] and [RFC4942].
In this document, we will consider the dangers from the following
kinds of threats:
o Wiretapping/eavesdropping
o Packet Falsification
o Identity Spoofing
o Packet Replay
o DOS/DDOS
o Malicious Packet Data
The rest of this document describes the above security threats in
SRv6 networks and existing approaches to mitigate and avoid the
threats.
2. Terminology
This document uses the terminology defined in [RFC5095] and
[RFC8754].
2.1. 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. Security Principles of SRv6 Networking
As with other similar source-routing architectures, an attacker may
manipulate the traffic path by modifying the packet header. SPRING
architecture [RFC8402] allows clear trust domain boundaries so that
source-routing information is only usable within the trusted domain
and never exposed to the outside world. It is expected that, by
default, explicit routing is only used within the boundaries of the
administered domain. Therefore, the data plane does not expose any
source-routing information when a packet leaves the trusted domain.
Traffic is filtered at the domain boundaries [RFC8402].
Unless otherwise noted, the discussion in this document pertain to SR
networks which can be characterized as "trusted domains", i.e., the
SR routers in the domain are presumed to be operated by the same
administrative entity without malicious intent and also according to
specifications of the protocols that they use in the infrastructure.
This document assumes that the SR-capable routers and transit IPv6
routers within the SRv6 trusted domains are trustworthy. Hence, the
SRv6 packets are treated as normal IPv6 packets in transit nodes and
the SRH will not bring new security problem. The security
considerations of IPv6 networks are out of scope of this document.
4. Types of Vulnerabilities in SR Networks
This section outlines in details the different types of
vulnerabilities listed in Section 1. Then, for each type, an attempt
to determine whether or not the vulnerability exists in a trusted
domain is made.
4.1. Eavesdropping Vulnerabilities in SRv6 Networks
As with practically all kinds of networks, traffic in an SRv6 network
may be vulnerable to eavesdropping.
o Threats: Eavesdropping
o Solutions: Encapsulating Security Payload (ESP, [RFC4303]) can be
used in order to prevent Eavesdropping. The ESP header is either
inserted between the IP header and the next layer(transport)
protocol header, or before an encapsulated IP header (tunnel
mode). ESP can be used in order to provide confidentiality, data
origin authentication, connectionless integrity, an anti-replay
service (a form of partial sequence integrity), and (limited)
traffic flow confidentiality. The set of services provided
depends on the selected options at the time of the Security
Association (SA) establishment and on the location of the
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implementation in a network topology.(add reference to the
different points explained in this paragraph).
o Conclusion: In tunnel mode of ESP, packets are encrypted and can
not be eavesdropped in a trusted SRv6 domain. In transport mode
of ESP, the payload of packets are encrypted and cannot be
eavesdropped in a trusted SRv6 domain, even if the IPv6 and SRH
headers are not encrypted.
o Gaps: The IPv6 and SRH headers are not encrypted in transport mode
of ESP which may be eavesdropped by attackers.
+------------------------------------------------------------------+
|IPv6 Header| SRH | ESP| Payload |ESP Tail| ESP Auth data|
+------------------------------------------------------------------+
|----- Encryption Scope -----|
|------ Authentication Scope -----|
Figure 1: Transport Mode ESP for SRv6 packets
+----------------------------------------------------------------------+
|New IPv6 Header|SRH|ESP|IPv6 Header|SRH|Payload|ESP Tail|ESP Auth data|
+----------------------------------------------------------------------+
|------ Encryption Scope --------|
|------- Authentication Scope -------|
Figure 2: Tunnel Mode ESP for SRv6 packets
4.2. Packet Falsification in SRv6 Networks
As SRv6 domain is a trusted domain, there is no Packet Falsification
within the SRv6 domain.
As the packets from outside of SRv6 domain cannot be trusted, an
Integrity Verification policy is typically deployed at the external
interfaces of the ingress SRv6 routers in order to verify the
incoming packets (i.e., from outside of SRv6 domain [RFC8986]).
Also, the packets with SRH sent form hosts within the SRv6 domain
should be verified in order to prevent the falsification between the
host and the ingress router. [RFC8986].
o Threats: Packet Falsification
o Solutions: The packets from outside can not be trusted, so
Integrity Verification policy should be deployed at the external
interfaces by using , e.g., IPSec [RFC4301] (AH [RFC4302], ESP
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[RFC4303] ) or HMAC [RFC2104]. AH [RFC4302], ESP [RFC4303] and
HMAC [RFC2104] can provide Integrity Verification for packets,
while the ESP can encrypt the payload in order to provide higher
security. However, it has been noted that the AH and ESP are not
directly applicable in order to reduce the vulnerabilities of SRv6
due to the presence of mutable fields in the SRH. In order to
solve this problem, [RFC8754] defines a mechanism in order to
carry HMAC TLV in the SRH so to verify the integrity of packets
including the SRH fields. The HMAC TLV is usually processed based
on the local policy, only at the ingress router. Within the SRv6
domain, the packets are trusted, so HMAC TLV is typically ignored.
In other words, the segment list is mutable within the SRv6 domain
but cannot be changed before processing the HMAC TLV.
o Conclusions: There is no Packet Falsification within a trusted
SRv6 domain. Integrity Verification policy like HMAC processing
should be deployed at the external interfaces of the ingress SRv6
routers filtering SRH packets from outside the trusted domain and
SRH packets from hosts within the SRv6 domain.
o Gaps: IPsec cannot provide verification for SRH.
+-----------------------------------------------------------------+
|IPv6 Header | SRH | AH| Payload |
+-----------------------------------------------------------------+
|--Auth Scope--|HMAC |---------------Auth Scope-------------------|
Figure 3: Transport Mode AH and HMAC for SRv6 packets
+-----------------------------------------------------------------+
|New IPv6 Header|SRH | AH |IPv6 Header|SRH|Payload |
+-----------------------------------------------------------------+
|--Auth Scope---|HMAC|---------------Auth Scope-------------------|
Figure 4: Tunnel Mode AH and HMAC for SRv6 packets
4.3. Identity Spoofing in SRv6 Networks
The same as for Packet Falsification, there is no Identity Spoofing
possible within the boundaries of a SRv6 trusted domain where all
nodes are under control of the same administrative organization.
Authentication policy should be deployed at the external interfaces
of the ingress SRv6 routers in order to validate the packets from
outside of SRv6 domain [RFC8986]. Also, the packets with SRH sent
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form hosts inside the SRv6 domain should be validated in order to
prevent the Identity Spoofing [RFC8986].
o Threats: Identity Spoofing
o Solutions: IPSec [RFC4301] (AH [RFC4302], ESP [RFC4303] ) or HMAC
[RFC2104] can be used for Authentication. AH, ESP and HMAC can
provide Authentication of source node, while the ESP can encrypt
the payload in order to provide higher security. Same as section
3.2.
o Conclusion: There is no Identity Spoofing within a trusted SRv6
domain. Identity Spoofing policy should be deployed on the
external interfaces of the ingress SRv6 routers for the packets
from outside and the packets with SRH from hosts within the SRv6
domain.
o Gaps: TBA
4.4. Packet Replay in SRv6 Networks
There are no new Packet Replay threat brought by SRH. ESP can be
applied to SRv6 in order to prevent Packet replay attacks.
o Threats: Packet Replay
o Solutions: ESP [RFC4303] can be used to prevent Replay Attacks.
o Conclusion: There are no new Packet Replay threat brought by SRH.
ESP can be applied to SRv6 in order to prevent Packet replay
attacks.
o Gaps: TBD
4.5. DOS/DDOS in SRv6 Networks
The generation of ICMPv6 error messages may be used in order to
attempt DOS(Denial-Of-Service)/DDOS(Distributed Denial-Of-Service)
attacks by sending an error-causing destination address or SRH in
back-to-back packets [RFC8754]. An implementation that correctly
follows Section 2.4 of [RFC4443] would be protected by the ICMPv6
rate-limiting mechanism also in the case of packets with an SRH.
o Threats: DOS/DDOS
o Solutions: ICMPv6 rate-limiting mechanism as defined in [RFC4443]
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o Conclusions: There are no DOS/DDOS threats within SRv6 domain, the
threats come from outside of the domain, and can be prevented by
ICMPv6 rate-limiting mechanism.
o Gaps: TBD
4.6. Malicious Packet Data in SRv6 Networks
TBA
5. Effects of the above on SRv6 Use Cases
This section describes the effects of the above-mentioned
vulnerabilities in terms of applicability statement and the use cases
given in citation.
TBA.
6. Security Policy Design
The basic security for intra-domain deployment is described in
[RFC8986] and the enhanced security mechanism is defined in
[RFC8754].
In [RFC8986], additional basic security mechanisms are defined. For
easier understanding, a easy example is shown in Figure 5.
*************************** *****
* (3) h2 * * * SRv6 domain
* \ | * *****
h1-----A-----B-----C-----D-------E-------F
/ * (2) (2) (2) * \
(1,2,3) * * (1,2)
* *
***************************
Figure 5: SRv6 Security Policy Design
o A-E: SRv6 Routers inside the SRv6 domain, A and E are the edge
router, can be called Ingress router instead.
o F: Router F outside the SRv6 domain.
o h1: A host outside the SRv6 domain connects to router Router A.
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o h2: A host within SRv6 domain, which connects to the Router D.
o (1): Security policy 1: ACL for External Interface.
o (2): Security policy 2: ACL for Internal Interfaces.
o (3): Security policy 3: Policy for processing HMAC, should be
deployed at the ingress nodes.
6.1. Basic Security Design
6.1.1. ACL for External Interfaces
Typically, in any trusted domain, ingress routers are configured with
Access Control Lists (ACL) filtering out any packet externally
received with SA/DA having a domain internal address. An SRv6 router
typically comply with the same rule.
A provider would generally do this for its internal address space in
order to prevent access to internal addresses and in order to prevent
spoofing. The technique is extended to the local SID space.
However, in some use cases, Binding SID can be leaked outside of SRv6
domain. Detailed ACL should be then configured in order to consider
the externally advertised Binding SID.
6.1.2. ACL for Internal Interfaces
An SRv6 router MUST support an ACL with the following behavior:
1. IF (DA == LocalSID) && (SA != internal address or SID space) :
2. drop
This prevents access to locally instantiated SIDs from outside the
operator's infrastructure. Note that this ACL may not be enabled in
all cases. For example, specific SIDs can be used to provide
resources to devices that are outside of the operator's
infrastructure.
6.1.3. SID Instantiation
As per the End definition [RFC8986], an SRv6 router MUST only
implement the End behavior on a local IPv6 address if that address
has been explicitly enabled as an SRv6 SID.
Packets received with destination address representing a local
interface that has not been enabled as an SRv6 SID MUST be dropped.
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6.2. Enhanced Security Design
HMAC [RFC2104] is the enhanced security mechanism for SRv6 as defined
in [RFC8754]. HMAC is used for validating the packets with SRH sent
from hosts within SRv6 domain.
Since the SRH is mutable in computing the Integrity Check Value (ICV)
of AH [RFC8754], so AH can not be directly applicable to SRv6
packets. HMAC TLV in SRH is used for making sure that the SRH fields
like SIDs are not changed along the path. While the intra SRv6
domain is trustworthy, so HMAC will be processed at the ingress nodes
only, and could be ignore at the other nodes inside the trusted
domain.
7. Security Considerations
TBA
8. Acknowledgements
Manty thanks to Charles Perkins and Stefano Previdi's valuable
comments.
9. References
9.1. 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>.
[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/info/rfc5095>.
[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>.
[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/info/rfc8200>.
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[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/info/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/info/rfc8754>.
9.2. Informative References
[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
P. Mattes, "Segment Routing Policy Architecture", draft-
ietf-spring-segment-routing-policy-13 (work in progress),
May 2021.
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104,
DOI 10.17487/RFC2104, February 1997,
<https://www.rfc-editor.org/info/rfc2104>.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
December 2005, <https://www.rfc-editor.org/info/rfc4301>.
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302,
DOI 10.17487/RFC4302, December 2005,
<https://www.rfc-editor.org/info/rfc4302>.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, DOI 10.17487/RFC4303, December 2005,
<https://www.rfc-editor.org/info/rfc4303>.
[RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification", STD 89,
RFC 4443, DOI 10.17487/RFC4443, March 2006,
<https://www.rfc-editor.org/info/rfc4443>.
[RFC4942] Davies, E., Krishnan, S., and P. Savola, "IPv6 Transition/
Co-existence Security Considerations", RFC 4942,
DOI 10.17487/RFC4942, September 2007,
<https://www.rfc-editor.org/info/rfc4942>.
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[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/info/rfc7855>.
[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/info/rfc8986>.
Authors' Addresses
Cheng Li
Huawei
China
Email: c.l@huawei.com
Zhenbin Li
Huawei
China
Email: lizhenbin@huawei.com
Chongfeng Xie
China Telecom
China Telecom Information Science&Technology Innovation park, Beiqijia Town,Changping District
Beijing
China
Email: xiechf@chinatelecom.cn
Hui Tian
CAICT
Beijing
China
Email: tianhui@caict.ac.cn
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Jianwei Mao
Huawei
China
Email: MaoJianwei@huawei.com
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