Internet DRAFT - draft-raviolli-intarea-trusted-domain-srv6
draft-raviolli-intarea-trusted-domain-srv6
Network Working Group A. Alston
Internet-Draft Liquid Intelligent Technologies
Intended status: Standards Track T. Hill
Expires: 4 October 2023 British Telecom
A. Przygienda
Juniper
L. Jalil
Verizon
2 April 2023
Trusted Domain SRv6
draft-raviolli-intarea-trusted-domain-srv6-01
Abstract
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.
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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Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on 4 October 2023.
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Copyright Notice
Copyright (c) 2023 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. Description . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. The SRv6 Security Problems . . . . . . . . . . . . . . . . . 3
4. Characteristics of a Fail-Closed Domain . . . . . . . . . . . 3
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 . . . . . . . . . . . . . . . 5
6.3. Transit and egress routers not using TD-SRv6 . . . . . . 5
7. Registry Considerations . . . . . . . . . . . . . . . . . . . 6
7.1. IANA Considerations . . . . . . . . . . . . . . . . . . . 6
7.2. IEEE Considerations . . . . . . . . . . . . . . . . . . . 6
8. Security Considerations . . . . . . . . . . . . . . . . . . . 6
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 6
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
10.1. Informative References . . . . . . . . . . . . . . . . . 6
10.2. Normative References . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
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.
2. Glossary
Fail-Closed Domain:
synonymous with a Trusted Domain.
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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
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.
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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.
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
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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. Imposition of the ethertype happens on packet
ingress, at the same point as SRv6 header imposition is performed.
Boundary interfaces will, by default behavior, drop packets already
containing the TD-SRv6 ethertype.
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.
Only frames marked with the TD-SRv6 ethertype will be processed as
SRv6 packets.
A router configured to process TD-SRv6 MUST drop packets containing
an SRH if received on any ethertype except TD-SRv6.
6.3. Transit and egress routers not using TD-SRv6
It cannot be excluded that deployment of TD-SRv6 are using TD-SRv6 on
external interfaces but choose to revert to standard IPv6 ether type
for SRv6 packets within the domain. The mechanisms required to
realize such a deployment and risks incurred are outside the scope of
this document.
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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. Contributors
Weiqiang Cheng
chengweiqiang@chinamobile.com
Anthony Somerset
anthony.somerset@liquid.tech
10. References
10.1. Informative References
10.2. 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
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Tom Hill
British Telecom
Email: tom@ninjabadger.net
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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