Security Considerations for SRv6 Networks
draft-li-spring-srv6-security-consideration-04

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Spring                                                             C. Li
Internet-Draft                                                     Z. Li
Intended status: Informational                                    Huawei
Expires: November 10, 2020                                        C. Xie
                                                           China Telecom
                                                                 H. Tian
                                                                   CAICT
                                                                  J. Mao
                                                                  Huawei
                                                             May 9, 2020

               Security Considerations for SRv6 Networks
             draft-li-spring-srv6-security-consideration-04

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.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on November 10, 2020.

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   Copyright (c) 2020 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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   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents

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   carefully, as they describe your rights and restrictions with respect
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

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
   [I-D.ietf-spring-srv6-network-programming]).  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.  [I-D.ietf-spring-srv6-network-programming].

   o  Threats: Packet Falsification

   o  Solutions: The packets from outside can not be trusted, so
      Integrity Verification policy should be deployed at the external

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      interfaces by using , e.g., IPSec [RFC4301] (AH [RFC4302], ESP
      [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

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   outside of SRv6 domain [I-D.ietf-spring-srv6-network-programming].
   Also, the packets with SRH sent form hosts inside the SRv6 domain
   should be validated in order to prevent the Identity Spoofing
   [I-D.ietf-spring-srv6-network-programming].

   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
   [I-D.ietf-spring-srv6-network-programming] and the enhanced security
   mechanism is defined in [RFC8754].

   In [I-D.ietf-spring-srv6-network-programming], 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 [I-D.ietf-spring-srv6-network-programming],
   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., Sivabalan, S., Voyer, D., Bogdanov, A., and
              P. Mattes, "Segment Routing Policy Architecture", draft-
              ietf-spring-segment-routing-policy-07 (work in progress),
              May 2020.

   [I-D.ietf-spring-srv6-network-programming]
              Filsfils, C., Camarillo, P., Leddy, J., Voyer, D.,
              Matsushima, S., and Z. Li, "SRv6 Network Programming",
              draft-ietf-spring-srv6-network-programming-15 (work in
              progress), March 2020.

   [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>.

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   [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>.

   [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>.

Authors' Addresses

   Cheng Li
   Huawei
   China

   Email: ChengLi13@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.bri@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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