Trusted Domain SRv6
draft-raviolli-intarea-trusted-domain-srv6-03

Network Working Group                                          A. Alston
Internet-Draft                           Liquid Intelligent Technologies
Intended status: Standards Track                                 T. Hill
Expires: 11 October 2024                                 British Telecom
                                                           A. Przygienda
                                                                 Juniper
                                                                L. Jalil
                                                                 Verizon
                                                            9 April 2024

                          Trusted Domain SRv6
             draft-raviolli-intarea-trusted-domain-srv6-03

Abstract

   SRv6 as designed has evoked interest from various parties, though its
   deployment is being limited, amongst other things, by known security
   problems in its architecture.  This document specifies a standard way
   to create a solution that closes some of the major security concerns,
   while retaining the tenants of the SRv6 protocol.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

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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   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on 11 October 2024.

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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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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Description . . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Glossary  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  The SRv6 Security Problems  . . . . . . . . . . . . . . . . .   3
   4.  Characteristics of a Fail-Closed Domain . . . . . . . . . . .   4
   5.  SRv6 in the context of a trusted domain - an objective
           analysis  . . . . . . . . . . . . . . . . . . . . . . . .   4
   6.  Trusted-Domain Implementation . . . . . . . . . . . . . . . .   5
     6.1.  Boundary routers  . . . . . . . . . . . . . . . . . . . .   5
     6.2.  Transit and egress routers  . . . . . . . . . . . . . . .   6
     6.3.  Transit and egress routers not using TD-SRv6  . . . . . .   6
   7.  Registry Considerations . . . . . . . . . . . . . . . . . . .   6
     7.1.  IANA Considerations . . . . . . . . . . . . . . . . . . .   6
     7.2.  IEEE Considerations . . . . . . . . . . . . . . . . . . .   6
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   9.  Applicability Considerations  . . . . . . . . . . . . . . . .   6
   10. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   7
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     11.1.  Informative References . . . . . . . . . . . . . . . . .   7
     11.2.  Normative References . . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Description

   SRv6 as designed has evoked interest from various parties, though its
   deployment is being limited by known security problems in its
   architecture.  This document specifies a standard way to create a
   solution that closes some of the major security concerns, while
   retaining the basis of the SRv6 protocol.

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2.  Glossary

   Fail-Closed Domain:
      synonymous with a Trusted Domain.

   Trusted Domain (TD):
      A domain that prevents processing of a protocol without explicit
      configuration, defined in detail in Section 4.  This document is
      limited to treatment of deployment of SRv6 in the context of a
      trusted domain only.

   Fail-Closed Protocol (FCP):
      A protocol that can be deployed by establishing a fail-closed
      domain.

   TD-SRv6:
      SRv6 modified to become a FCP and with that allowing for easy
      deployment in a trusted domain.

3.  The SRv6 Security Problems

   SRv6 [RFC8402] relies on the concept of limited domain.  The
   application of this concept in the context of the draft however,
   suffers from a lack of security that is easily deployable in an
   economi and scalable fashion.

   Limited domains without very careful deployment will invariably leak
   beyond the domain and allow untrusted traffic to enter the domain and
   terminate on any arbitrary node.

   As per RFC 8402 [RFC8402]RFC8402 Section 8, SRv6 that leaks beyond
   the border of a trusted domain creates a security violation.

   An established and proven solution is to create a trusted domain that
   has a default fail-closed approach and a well-defined trusted/
   untrusted boundary.

   Examples of fail-closed protocols include:

   *  mpls

   *  clns

   *  bier

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4.  Characteristics of a Fail-Closed Domain

   A fail-closed domain is determined by following properties:

   Processing of the protocol packet on an interface requires explicit
   configuration.  Otherwise, due to lack of packet classification,
   further processing and forwarding cannot be achieved.  In practical
   terms the behavior used most often is a drop of the offending packet.

   In a fail-closed protocol, leaking beyond the boundary of the domain
   requires explicit config.

   Fail-closed protocols are easily identifiable by their top level
   (e.g. link layer) encoding early in the packet formats and often by
   fields at a fixed offset.  In another words either their encoding or
   encapsulation allows such packets to be easily distinguished from
   other traffic.

   Classification of the protocol packets is completely deterministic.

   Confining the protocol to the trusted domaim does not require complex
   processing in either hardware or software to allow for scalable and
   economical deployment.

   The boundary of a trusted domain consists of a set of interfaces that
   exhibit default behavior.

5.  SRv6 in the context of a trusted domain - an objective analysis

   It is impossible to differentiate SRv6 and IPv6 at the link-layer or
   easily at network layer by e.g. a reserved protocol number the way
   IPSec does since SRv6 and IPv6 share the same ethernet types and IP
   protocol numbers.

   Hence, in the event of a packet being sent into a trusted domain,
   either accidentally or by a malicious actor, it is possible to send
   the frame to a node binding the specific SID, and have the packet
   processed, irrespective of the content of the underlying
   (encapsulated) packet.

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   The security proposals in RFC8402 section 8.2 is based on the
   application of filters preventing ingress traffic at the boundary
   routers destined towards a SID within the domain.  Such filtering is
   prone to configuration errors and in addition, has significant impact
   on fast matching hardware utilization on devices that have large
   numbers of ingress points into the domain.  The matching itself, due
   to the complexity and numerous possibilities of expressing a set of
   SIDs will likely necessitate a complete semantic parsing of such list
   to guarantee fully precise matching including wildcarding in
   different forms.

   In the context of a trusted domain, anything outside of the operators
   control should not be considered trusted.  This means applying
   filters to prevent leakage into the domain at every customer port,
   every server, and every cloud stack.  The scale and complexity of
   maintaining such a "shorewall" is daunting and at large scale will
   not be likely to keep up with the timing necessary in case of attacks
   mounted and metamorphosing in short time intervals.  An attack
   avoiding the filter wall may evade discovery for a long time in the
   absence of sophisticated traffic analyis and analytics tools.

6.  Trusted-Domain Implementation

   To implement SRv6 in the context of a trusted domain, it is necessary
   to modify it to allow deployment in a fail-closed boundary
   efficiently.  This requires changes to the protocol encapsulation at
   both the boundary routers and the transit nodes.  This document
   introduces a distinct ethertype to be used for TD-SRv6 packets.

6.1.  Boundary routers

   Trusted Domain boundary routers form the point at which the new
   ethertype is imposed on interfaces configured to represent such
   boundary.  Imposition of the ethertype happens on packet ingress, at
   the same point as SRv6 header imposition is performed.

   Boundary interfaces will, by default behavior and unless configured
   otherwise, drop packets containing the TD-SRv6 ethertype already and
   MUST drop packets containing an SRH (or otherwise being classified
   clearly as SRv6 frame) if received on any ethertype except TD-SRv6.

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6.2.  Transit and egress routers

   In the case of a transit or egress router, should a frame not be
   marked with the TD-SRv6 ethertype, the frame will be treated as a
   standard IPv6 packet for the purposes of handling and forwarding.
   Even if an SRv6 packet is introduced into such domain with an
   ethertype different from TD-SRv6, the according SRv6 packet handling
   will not occur.  Hence the resulting handling of the packet is
   indistinguishable from standard IPv6 processing.

   A router configured to process TD-SRv6 MUST drop packets containing
   an SRH (or otherwise being classified clearly as SRv6 frame) if
   received on any ethertype except TD-SRv6 and MUST apply SRv6
   processing if and only if the frame is marked as TD-SRv6 ethertype.

6.3.  Transit and egress routers not using TD-SRv6

   It cannot be excluded that deployment of TD-SRv6 are using TD-SRv6 on
   only a subset of external interfaces and/or choose to revert to
   standard IPv6 ether type for SRv6 packets within some or all
   interfaces facing the internal domain.  The mechanisms required to
   realize such a deployment and risks incurred are outside the scope of
   this document.

7.  Registry Considerations

7.1.  IANA Considerations

   No IANA Considerations

7.2.  IEEE Considerations

   TD-SRv6 Ethertype: TBD0

8.  Security Considerations

   This draft enhances the security mechanisms required by section 8 of
   RFC8402, and does not impose any further security considerations of
   its own.

9.  Applicability Considerations

   TD-SRv6 is applicable in situations where the transport domain using
   SRv6 is not considered a fully trusted closed user group, i.e. not
   every participant can be trusted to not accept IPv6 frames from other
   domains or issue IPv6 frames within the domain using some mechanism.
   In the latter case the attack surface to craft malicious SRv6 frames
   looking potentially like innocuous IPv6 frames is open.  A good

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   example being servers.  On the other hand, a fully trusted user group
   can be assumed e.g. in overlay situation, i.e.  a transport provider
   offering VPN service where IPv6 framed are neither injected or
   accepted from the overlay.  In a sense, the VPN tunnel encapsulation
   acts as security mechanism preventing the closed user group from
   injecting IPv6 frames carried on the tunnel into the transport
   domain.

10.  Contributors

   Weiqiang Cheng

   chengweiqiang@chinamobile.com

   Anthony Somerset

   anthony.somerset@liquid.tech

11.  References

11.1.  Informative References

11.2.  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>.

   [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>.

Authors' Addresses

   Andrew Alston
   Liquid Intelligent Technologies
   Email: andrew-ietf@liquid.tech

   Tom Hill
   British Telecom
   Email: tom@ninjabadger.net

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   Tony Przygienda
   Juniper
   United States of America
   Email: prz@juniper.net

   Luay Jalil
   Verizon
   United States of America
   Email: luay.jalil@verizon.com

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