Internet DRAFT - draft-dekater-panrg-scion-overview
draft-dekater-panrg-scion-overview
PANRG C. de Kater
Internet-Draft N. Rustignoli
Intended status: Informational SCION Association
Expires: 8 September 2023 A. Perrig
ETH Zuerich
7 March 2023
SCION Overview
draft-dekater-panrg-scion-overview-03
Abstract
The Internet has been successful beyond even the most optimistic
expectations and is intertwined with many aspects of our society.
But although the world-wide communication system guarantees global
reachability, the Internet has not primarily been built with security
and high availability in mind. The next-generation inter-network
architecture SCION (Scalability, Control, and Isolation On Next-
generation networks) aims to address these issues. SCION was
explicitly designed from the outset to offer security and
availability by default. The architecture provides route control,
failure isolation, and trust information for end-to-end
communication. It also enables multi-path routing between hosts.
This document discusses the motivations behind the SCION architecture
and gives a high-level overview of its fundamental components,
including its authentication model and the setup of the control- and
data plane. A more detailed analysis of relationships and
dependencies between components is available in
[I-D.rustignoli-scion-components]. As SCION is already in production
use today, the document concludes with an overview of SCION
deployments.
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://scionassociation.github.io/scion-overview_I-D/draft-dekater-
panrg-scion-overview.html. Status information for this document may
be found at https://datatracker.ietf.org/doc/draft-dekater-panrg-
scion-overview/.
Discussion of this document takes place on the WG Working Group
mailing list (mailto:panrg@irtf.org), which is archived at
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https://www.ietf.org/mailman/listinfo/panrg/.
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Source for this draft and an issue tracker can be found at
https://github.com/scionassociation/scion-overview_I-D.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Why SCION - Motivation . . . . . . . . . . . . . . . . . 3
1.1.1. Scope of SCION . . . . . . . . . . . . . . . . . . . 5
1.1.2. Practical Considerations Based on Related RFCs . . . 5
1.1.3. Why Now? . . . . . . . . . . . . . . . . . . . . . . 7
1.2. SCION Overview . . . . . . . . . . . . . . . . . . . . . 7
1.2.1. Network Architecture and Naming . . . . . . . . . . . 7
1.2.2. Routing . . . . . . . . . . . . . . . . . . . . . . . 9
1.2.3. Infrastructure Components . . . . . . . . . . . . . . 10
1.2.4. Formal Verification . . . . . . . . . . . . . . . . . 11
1.3. Conventions and Definitions . . . . . . . . . . . . . . . 11
2. Key Concepts . . . . . . . . . . . . . . . . . . . . . . . . 11
2.1. Authentication . . . . . . . . . . . . . . . . . . . . . 12
2.1.1. The Control-Plane PKI (CP-PKI) . . . . . . . . . . . 12
2.1.2. TRC Update and Verification . . . . . . . . . . . . . 13
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2.1.3. Dissemination of TRC Updates . . . . . . . . . . . . 14
2.1.4. Grace Period . . . . . . . . . . . . . . . . . . . . 14
2.1.5. Revocation and Recovery from a Catastrophic Event . . 14
2.2. SCION Control Plane . . . . . . . . . . . . . . . . . . . 15
2.2.1. Path Exploration . . . . . . . . . . . . . . . . . . 15
2.2.2. Path Registration . . . . . . . . . . . . . . . . . . 18
2.2.3. Path Lookup . . . . . . . . . . . . . . . . . . . . . 19
2.2.4. Link Failures . . . . . . . . . . . . . . . . . . . . 20
2.3. SCION Data Plane . . . . . . . . . . . . . . . . . . . . 21
2.3.1. Path Construction via Segment Combination . . . . . . 21
2.3.2. Path Authorization . . . . . . . . . . . . . . . . . 24
2.3.3. Forwarding . . . . . . . . . . . . . . . . . . . . . 24
2.3.4. Intra-AS Communication . . . . . . . . . . . . . . . 24
3. Deployment . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.1. Autonomous System Deployment . . . . . . . . . . . . . . 25
3.2. Internet Exchange Points . . . . . . . . . . . . . . . . 26
3.3. Endpoints and Incremental Deployability . . . . . . . . . 26
3.3.1. Native Endpoints . . . . . . . . . . . . . . . . . . 27
3.3.2. SCION to IP Gateway (SIG) . . . . . . . . . . . . . . 27
3.4. Deployment Experiences . . . . . . . . . . . . . . . . . 27
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28
5. Security Considerations . . . . . . . . . . . . . . . . . . . 28
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 28
6.1. Normative References . . . . . . . . . . . . . . . . . . 28
6.2. Informative References . . . . . . . . . . . . . . . . . 29
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 33
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 33
1. Introduction
The Introduction section explores the motivation to develop SCION,
followed by a short description of SCION's main elements. The
sections after the Introduction provide further insight into SCION's
key concepts and deployment scenarios. The document concludes with
some concrete case studies where SCION has been successfully deployed
in production.
1.1. Why SCION - Motivation
Since its inception, the Internet has continued to expand,
encompassing new uses over time. The continuous expansion has
brought many issues to light, including a lack of control,
limitations in scalability, performance and security, occurrences of
severe outages, weak fault isolation, and energy consumption. With
the core focus on functionality and operation, the current Internet
offers little protection against attacks such as spoofing, IP-address
hijacking, denial-of-service, and combinations of these. For more
background information, see [SCHUCHARD2011], [LABOVITZ2000],
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[GRIFFIN1999], [SAHOO2009], and [RFC4264].
There have been numerous initiatives to address the above issues.
Although these initiatives have brought many improvements, concerns
regarding security and scalability still remain. For more details,
see, e.g., [RFC4033], [RFC6480], [RFC8205], and [RFC8446], as well as
[LYCHEV2013], [LI2014], [COOPER2013], [ROTHENBERGER2017],
[MORILLO2021], and [KING2022].
As a consequence, today's Internet fails to fulfil many users'
requirements. This especially pertains to the demands of enterprises
globally exchanging sensitive information, such as financial
institutions, healthcare providers, universities, multinationals,
governments, critical and transportation infrastructure operators.
These users require the Internet to be highly available at all times.
They expect reliable operation of the global network also in case of
failures. They need availability guarantees across multiple routing
domains, even in the presence of attacks. They further want to rely
on an Internet that can be multilaterally governed and is free from
global kill-switches.
SCION has been developed in order to meet the above-mentioned
requirements. SCION aims to reach the following goals:
* Provide high-availability architecture (also in the presence of
adversaries)
* Provide fast failover in the case of inter-domain link or router
failures
* Prevent from IP-address hijacking, DoS, and other attacks
* Enable path transparency as well as application-specific path
optimizations
* Improve the inter-domain control plane's scalability
* Prepare the Internet for tomorrow's applications, such as virtual
reality, Internet of Things (IoT), and all other applications
requiring high-performance connectivity.
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1.1.1. Scope of SCION
The above section describes SCION's aspiration to improve _inter_-AS
routing and to focus on providing end-to-end connectivity. However,
SCION does not solve _intra_-AS routing issues, nor does it provide
end-to-end payload encryption, and identity authentication. These
topics, which are equally important for the Internet to perform well,
lie outside the scope of SCION.
1.1.2. Practical Considerations Based on Related RFCs
The SCION inter-domain routing concept has initially been developed
by researchers of the ETH Zuerich [PERRIG2017], and could in the
meantime also gain attention and recognition in the international
academic world. However, for an IT architecture to be successful, it
must work well in practice, too. This section pays attention to the
implementation considerations of a conceptual framework such as SCION
in real life, on the basis of some RFCs exploring this topic. It
also verifies in how far SCION meets the requirements mentioned and
questions raised in these RFCs.
1.1.2.1. Avoiding Pitfalls
[RFC9049] describes why previous proposals to tackle some of the
Internet's fundamental issues did not manage to succeed. SCION seems
to avoid the pitfalls mentioned in that document. For example, SCION
does not have to be adopted by the entire Internet to be effective:
The routing architecture provides benefits already to early adapters.
Even if only a small part of the global network works with SCION,
adapters will still take advantage of using the SCION routing
technology. Moreover, not only users of SCION benefit from it, also
ISPs and operators benefit from deploying SCION: early deployments
showed that providers can charge the use of SCION as premium
connectivity, with users who are willing to pay for it. Furthermore,
SCION can be installed on top of and function alongside the existing
routing infrastructure and protocols--there is no need for high-
impact changes in an operational network.
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Another RFC that must be mentioned in this context is [RFC5218],
"What Makes for a Successful Protocol?". SCION seems to fulfil most
factors that contribute to the success of a protocol, as described in
section 2.1 of the RFC. This includes such factors as offering a
positive net value (i.e., the benefits of deploying SCION outweigh
the costs), incremental deployability, and open source code
availability. More importantly, SCION averts the failure criteria
mentioned in section 1.4 of the RFC: SCION is already deployed and in
use by many actors of the Swiss financial and academic ecosystems,
and allows for multiple implementations, both open and closed source.
As existing SCION implementations are easily portable, adoption in
mainstream platforms is also possible.
1.1.2.2. Answering Questions
SCION can be considered a _path-aware internetworking_ architecture,
as described in [RFC9217]. This RFC poses (open) questions that must
be answered in order to realize such a path-aware networking system.
It was originally written to frame discussions in the Path Aware
Networking Research Group (PANRG), and has been published to snapshot
current thinking in this space.
SCION intends to answer the questions raised in this RFC. This
especially pertains to the second, third, seventh, and eighth
question:
* How do endpoints and applications get access to accurate, useful,
and trustworthy path properties?
* How can endpoints select paths to use for traffic in a way that
can be trusted by the network, the endpoints, and the applications
using them?
* How can a path-aware network in a path-aware internetwork be
effectively operated, given control inputs from network
administrators, application designers, and end users?
* How can the incentives of network operators and end users be
aligned to realize the vision of path-aware networking, and how
can the transition from current ("path-oblivious") to path-aware
networking be managed?
SCION's answers to these questions can be found in Key Concepts
(Section 2) and Deployments (Section 3.4), respectively.
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1.1.3. Why Now?
The emergence of multiple SCION implementations and early deployments
highlights the need for standardization. The time seems therefore
ripe to take SCION to the IETF, also in order to contribute to the
important discussion regarding path-aware networking.
1.2. SCION Overview
SCION has been designed to address the fundamental issues of today's
Internet depicted in Why SCION - Motivation (Section 1.1). The
following section gives a high-level overview of SCION's main
elements, providing a basic understanding of this next-generation
inter-network architecture.
1.2.1. Network Architecture and Naming
SCION's main goal is to offer highly available and efficient inter-
domain packet delivery—even in the presence of actively malicious
entities. To achieve scalability and sovereignty, SCION organizes
existing ASes into groups of independent routing planes, called
*Isolation Domains (ISD)*. An AS can be a member of multiple ISDs.
All ASes in an ISD agree on a set of trust roots, called the *Trust
Root Configuration (TRC)*. The ISD is governed by a set of *core
ASes*, which provide connectivity to other ISDs and manage the trust
roots. Typically, a few distinguished ASes within an ISD form the
ISD’s core.
Isolation domains serve the following purposes:
* They allow SCION to support trust heterogeneity, as each ISD can
independently define its roots of trust;
* They provide transparency for trust relationships;
* They isolate the routing process within an ISD from external
influences such as attacks and misconfigurations; and
* They improve the scalability of the routing protocol by separating
it into a process within and one between ISDs.
ISDs provide natural isolation of routing failures and
misconfigurations, provide meaningful and enforceable trust, enable
endpoints to optionally restrict traffic forwarding to trusted parts
of the Internet infrastructure only, and enable scalable routing
updates with high path-freshness.
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1.2.1.1. Links
There are three types of links in SCION: core links, parent-child
links, and peering links.
* A *core link* can only exist between two core ASes.
* A *parent-child link* requires that at least one of the two
connected ASes is a non-core AS. ASes with a parent-child link
usually belong to the same entity or have a provider-customer
relationship.
* A *peering link* also includes at least one non-core AS.
See Figure 1 for a high-level overview of the SCION network
structure.
...............................
: :
: [TRC] :
: (::::::::::::::) : ......................
: (::::: ISD core :::::) : : :
: (:: +---+ ::::::::: +---+ ::) : : [TRC] :
: (::::: |CAS|===+---+ : |CAS| :::::) : : (: ISD core :) :
: (:: +---+ : |CAS|===+---+====)===:==:=====(=+---+ :: +---+ :) :
: /(:::::: +---+ ::::::) \ : : (: |CAS| == |CAS| :) :
: / (::::::: | :::::::) \ : : ( +---+ :: +---+ ) :
: / | o : : /(::::::::::::) :
: o | +---+ : : / \ :
: +---+ | /|ASb| : : / \ :
: |ASa| | / +---+ : : o o :
: +---+ | / | : : +---+ +---+ :
: | | / | : : |ASx| ---------|ASy| :
: | | / o : : +---+ +---+ :
: o o / +---+ : : | :
: +---+ +---+ / |ASe| : : o :
: |ASc|---------|ASd| o +---+ -:--:--+---+ :
: +---+ +---+ : : |ASz| ISD 2 :
: : : +---+ :
: ISD 1 : ........................
.................................
Legend:
|
|
Parent AS - child AS: o
Peering link: ----
Core link: ===
Core AS: CAS
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Figure 1: SCION network structure
1.2.2. Routing
SCION operates on two routing levels: intra-ISD and inter-ISD. Both
levels use *path-segment construction beacons (PCBs)* to explore
network paths. A PCB is initiated by a core AS and then disseminated
either within an ISD (to explore intra-ISD paths) or among core ASes
(to explore core paths across different ISDs). The PCBs accumulate
cryptographically protected path and forwarding information on AS-
level, and store this information in the form of *hop fields (HFs)*.
Endpoints use information from these hop fields to create end-to-end
forwarding paths for data packets, who carry this information in
their packet headers. This concept is called *packet-carried
forwarding state (PCFS)*. The concept also supports multi-path
communication among endpoints.
The process of creating an end-to-end forwarding path consists of the
following steps:
1. First, an AS discovers paths to other ASes, during the _path
exploration_ (or beaconing) phase.
2. The AS then selects a few PCBs according to defined policies,
transforms the selected PCBs into path segments, and registers
these segments with its path infrastructure, thus making them
available to other ASes. This happens during the _path
registration_ phase.
3. During the _path resolution_ phase, the actual creation of an
end-to-end forwarding path to the destination takes place. For
this, an endpoint performs (a) a _path lookup_ step, to obtain
path segments, and (b) a _path combination_ step, to combine the
forwarding path from the segments.
Figure 2 below shows the SCION routing process in a nutshell.
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+------------------+ +------------------+
| Path Exploration | | |
| (Beaconing) |------------>|Path Registration |
| | | |
+------------------+ +--------+---------+
|
+-----------------+
|
+------------------v-----------------------+
| Path Resolution |
|+--------------+ +-------------------+|
|| Path Lookup |---->| Path Combination ||
|+--------------+ +-------------------+|
+------------------------------------------+
Figure 2: SCION routing in a nutshell
1.2.2.1. ISD and AS numbering
SCION decouples endpoint addressing from inter-domain routing.
Routing is based on the <ISD, AS> tuple, agnostic of endpoint
addressing. Existing AS numbers are inherited from the current
Internet, but a 48-bit namespace allows for additional SCION AS
numbers beyond the 32-bit space in use today. The endpoint local
address is not used for inter-domain routing or forwarding, does not
need to be globally unique, and can thus be an IPv4, IPv6, or MAC
address, for example. A SCION address is therefore composed of the
<ISD, AS, local address> 3-tuple.
1.2.3. Infrastructure Components
The *beacon service*, the *path service*, and the *certificate
service* are the main control-plane infrastructure components within
a SCION AS. Each service can be deployed redundantly, depending on
the AS's size and type. Existing Internal routers are used to
forward packets inside the AS, while _SCION border routers_ provide
interconnectivity between ASes.
* The _beacon service_ discovers path information. It is
responsible for generating, receiving, and propagating PCBs.
Periodically, the beacon service generates a set of PCBs, which
are forwarded to its child ASes or neighboring core ASes. The
PCBs are flooded over policy-compliant paths to discover multiple
paths between any pair of core ASes.
* The _path service_ stores mappings from AS identifiers to sets of
announced path segments. The path service is organized as a
hierarchical caching system similar to that of DNS. Through the
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beacon service, ASes select the set of path segments through which
they want to be reached, and they register them to the path
service in the ISD core.
* The _certificate service_ keeps cached copies of certificates and
manages keys and certificates for securing inter-AS communication.
The certificate service is queried by the beacon service when
validating the authenticity of PCBs (i.e., when the beacon service
lacks a certificate).
_Border routers_ are deployed at the edge of SCION ASes. The main
task of border routers is to forward packets to a neighbor border
router or to the destination host within the AS. While SCION takes
care of inter-domain routing, it relies on existing routing protocols
(e.g., IS-IS, OSPF, SR) and communication fabric (e.g., IP, MPLS) for
intra-domain forwarding. _Internal routers_, therefore, do not need
to be changed to support SCION.
1.2.4. Formal Verification
An additional feature of SCION is its formal verification. The SCION
network system consists of a variety of components such as routers,
servers, and edge devices. Such a complex system eludes the mental
capacities of human beings for considering all possible states and
interactions. That is why SCION includes a formal verification
framework developed by the Department of Computer Science of the ETH
Zurich [KLENZE2021]. This guarantees that packet forwarding as well
as SCION's authentication mechanisms and implementations are correct
and consistent.
1.3. Conventions and Definitions
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.
2. Key Concepts
This section explains the SCION key concepts, including
authentication, control- and data plane.
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2.1. Authentication
SCION's control plane relies on a public-key infrastructure called
the *control-plane PKI (CP-PKI)*, which is organized on ISD-level.
Each ISD can independently build its own roots of trust, defined in a
file called *trust root configuration (TRC)*.
*Note*: This section describes the SCION authentication concept on a
very high level. A much more detailed description of SCION's
authentication is available in [I-D.dekater-scion-pki].
2.1.1. The Control-Plane PKI (CP-PKI)
Trust within each isolation domain is anchored in the trust root
configuration (TRC) file. Each TRC contains a collection of signed
root certificates, which are used to sign CA certificates, which are
in turn used to sign AS certificates. The TRC also includes ISD-
policies that specify, for example, the TRC's usage, validity, and
future updates. A TRC is a fundamental component of an CP-PKI.
The initial TRC in an ISD is called the *base TRC*. This base TRC
constitutes the ISD's trust anchor. It is signed during a signing
ceremony and then distributed throughout the ISD. All entities
within the ISD obtain the initial TRC with an offline mechanism such
as a USB flash drive provided by a trusted AS, like the relevant ISP,
or with an online mechanism that relies on a trust-on-first-use
(TOFU) approach. However, all updates to the base TRCs are performed
in a straightforward process that does not require any manual or out-
of-band action (such as a software update), see TRC Update and
Verification (Section 2.1.2).
Figure 3 shows the TRC trust chain and associated certificates. TRC
1 is the base TRC, and TRC 2 and 3 constitute updates to this base
TRC. TRC 2 must be verified using the voting certificates in TRC 1.
Control-plane (CP) root certificates are used to verify other CP
certificates (which are in turn used to verify path-segment
construction beacons PCBs).
Each SCION AS must hold a private key (to sign PCBs) and a
certificate attesting that it is the rightful owner of the
corresponding public key. One of the main roles of the TRC is thus
enabling the verification of *AS certificates* and PCBs.
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TRC 2
+--------------------------------------+
|+------------------------------------+|
||- Version - Core ASes ||
+--------+ ||- ID - Description || +--------+
| TRC 1 | ||- Validity - No Trust Reset || | TRC 3 |
| (Base |---->||- Grace Period - Voting Quorum ||--->| |
| TRC) | ||- ... || | |
+--------+ |+------------------------------------+| +--------+
|+----------------+ +----------------+|
|| Regular Voting | |Sensitive Voting||
|| Certificate | | Certificate ||
|+----------------+ +----------------+|
|+----------------+ +----------------+|
|| Votes | | Signatures ||
|+----------------+ +----------------+|
|+------------------------------------+|
|| CP Root Certificates ||
|+----------+-------------+-----------+|
| | | |
+-----------+-------------+------------+
| |
| |
v v
+-----------+ +-----------+
| CP CA | | CP CA |
|Certificate| |Certificate|
+-+-------+-+ +-----+-----+
| | |
| | |
v v v
+-----------+ +-----------+ +-----------+
| CP AS | | CP AS | | CP AS |
|Certificate| |Certificate| |Certificate|
+-----------+ +-----------+ +-----------+
Figure 3: TRC contents and trust chain
2.1.2. TRC Update and Verification
With a base TRC as trust anchor, TRCs can be updated in a verifiable
manner. There are two kinds of TRC updates: regular and sensitive
updates. A _regular_ TRC update happens when the TRC's validity
period expires. This period is defined by the _validity_ parameter
in the TRC. The default is one year. A TRC update is _sensitive_ if
and only if critical sections of the TRC are affected (for example,
if the set of core ASes is modified). For both regular and sensitive
TRC updates, a number of votes (in the form of signatures) must be
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cast to approve the update. This number of votes is dictated by the
voting quorum and set in each TRC with the _voting quorum_ parameter.
2.1.3. Dissemination of TRC Updates
Information about a TRC update is disseminated via the SCION’s
beaconing process, through the path-segment constructions beacons.
Each PCB contains the version number of the currently active TRC. If
an AS receives a PCB with a TRC version number higher than the
locally stored TRC, it requests the PCB-sending AS for the new TRC.
The new TRC is verified on the basis of the current one, and is
accepted if it contains at least the required quorum of correct
signatures by trust roots defined in the current TRC. This simple
dissemination mechanism has two advantages: It is very efficient (as
fresh PCBs rapidly reach all ASes), and it avoids circular
dependencies with regard to the verification of PCBs and the
beaconing process itself (as no server needs to be contacted over
unknown paths in order to fetch the updated TRC).
2.1.4. Grace Period
At most two TRCs per ISD can be active at the same time. The TRC
parameter _grace period_ indicates for how long the currently active
TRC can still be active after a new TRC is disseminated. This so-
called *grace period* starts at the beginning of the validity period
of the new TRC. An older TRC can only be active until either (1) the
grace period has passed, or (2) yet a newer TRC is announced. AS
certificates are validated by following the chain of trust up to an
active TRC.
2.1.5. Revocation and Recovery from a Catastrophic Event
The TRC dissemination mechanism also enables rapid revocation of
trust roots. When a trust root is compromised, the other trust roots
can remove it from the TRC and disseminate a new TRC alongside a PCB
with a new version number.
In case of a catastrophic event—such as several private root keys
being disclosed due to a critical vulnerability in a cryptographic
library—SCION is equipped with a recovery procedure called *trust
reset*. This procedure consists of creating a new TRC with fresh,
trustworthy keys (and potentially new algorithms), and redistributing
this TRC out-of-band. A trust reset effectively establishes a new
base TRC for the ISD. It is possible for ISDs to disable trust
resets by setting the _no trust reset_ Boolean parameter to "true" in
their TRC, with the effect that the entire ISD would have to be
abandoned in the event of such a catastrophic compromise (this
abandonment would also have to be announced out-of-band).
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The partition of the SCION network into ISDs guarantees that no
single entity can take down the entire network. Even if several
entities formed a coalition to carry out an attack, the effects of
that attack would be limited to one or a few ISDs.
2.2. SCION Control Plane
The SCION control plane is responsible for discovering path segments
and making them available to endpoints. This process includes path
exploration, registration, and lookup; it involves the path service,
beacon service, and certificate service, both in core ASes and non-
core ASes.
*Note*: This section describes the SCION control plane on a very high
level. A much more detailed description of SCION's control plane
will follow in a separate internet draft.
2.2.1. Path Exploration
In SCION, the path segment construction process is referred to as
*beaconing*. The _beacon service_ of each AS is responsible for the
beaconing process. The beacon service generates, receives, and
propagates the *path-segment construction beacons (PCBs)* on a
regular basis, to iteratively construct path segments.
There are three types of path segments (note that all path segments
can be used to send data traffic in both directions):
* A path segment from a non-core AS to a core AS is an _up-path
segment_.
* A path segment from a core AS to a non-core AS is a _down-path
segment_.
* A path segment between core ASes is a _core-path segment_.
All path segments are invertible: A core-path segment can be used
bidirectional, and an up-path segment can be converted into a down-
path segment, or vice versa, depending on the direction of the end-
to-end path.
Path segment construction is conducted hierarchically on two levels:
* _Core beaconing_ is the process of constructing path segments
between core ASes. During core beaconing, the beacon service of a
core AS either initiates PCBs or propagates PCBs received from
neighboring core ASes to all other neighboring core ASes. Core
beaconing in SCION is similar to BGP's route-advertising process,
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although in SCION the process is periodic and PCBs are flooded
over policy-compliant paths to discover multiple paths between any
pair of core ASes.
* _Intra-ISD beaconing_ creates path segments from core ASes to non-
core ASes. For this, the beacon service of a core AS creates PCBs
and sends them to the non-core child ASes (typically customer
ASes). The beacon service of a non-core child AS receives these
PCBs and forwards them to its child ASes, and so on. This
procedure continues until the PCB reaches an AS without any
customer (leaf AS). As a result, all ASes receive path segments
to reach the core ASes of their ISD.
On its way down, a PCB accumulates cryptographically protected path-
and forwarding information per traversed AS. At every AS, metadata
as well as information about the AS's ingress and egress interfaces
(i.e., link identifiers) is added to the PCB. The ingress and egress
interface IDs identify connections to neighboring ASes. These IDs
only need to be unique within each AS. Therefore, they can be chosen
and encoded by each AS independently and without any need for
coordination.
SCION also supports shortcuts and peering links. In a _shortcut_, a
path only contains an up-path and a down-path segment, which can
cross over at a non-core AS that is common to both paths. _Peering
links_ can be added to up- or down-path segments, resulting in an
operation similar to today’s Internet.
To reduce beaconing overhead and prevent possible forwarding loops,
PCBs do not traverse peering links. Instead, peering links are
announced along with a regular path in a PCB. If the path segments
of both ASes at the end of a peering link contain this peering link,
then it is possible to use the peering link to shortcut the end-to-
end path (i.e., without going through the core). SCION also supports
peering links that cross ISD boundaries, according to SCION’s path
transparency property.
Figure 4 shows how intra-ISD PCB propagation works, from the ISD's
core AS down to child ASes. For the sake of illustration, the
interfaces of each AS are numbered with integer values. In practice,
each AS can choose any encoding for its interfaces; in fact, only the
AS itself needs to understand its encoding. Here, AS F receives two
different PCBs via two different links from core AS X. Moreover, AS
F uses two different links to send two different PCBs to AS G, each
containing the respective egress interfaces. AS G extends the two
PCBs and forwards both of them over a single link to a child AS.
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.-----.
; Core :
+-----+ : AS X ;
|PCB | \ 2 1 / +-----+
|Core | `+-+' |pcb |
|Out:2| | | |core |
+--+--+ +-+ | |out:1|
| | | +--+--+
v | | |
.-+---+. v
.---. / 2 3 \ .---.
( J )- - -; 1 4 :- - - - - -( H )
`---' : AS F ; `---'
+--\7 /
+----------+ +----------+ <-+ 6 5
|PCB | |pcb | `+--+'
|Core | |core | | |
|Out:2 | |out:1 | | |
|----------| |----------| | |
|AS F | |as f | | |
|In:2 Out:7| |in:3 out:7| | |
|Peer J:1 | |peer j:1 | | | +----------+ +----------+
|Peer H:4 | |peer h:4 | | | |PCB | |pcb |
| | | | | | |Core | |core |
+--+-------+ +--+-------+ | | |Out:2 | |out:1 |
| | | | |----------| |----------|
<+ <+ | | |AS F | |as f |
| | |In:2 Out:5| |in:3 out:5|
+----------+ +----------+| | |Peer J:1 | |peer j:1 |
|PCB | |pcb || | |Peer H:4 | |peer h:4 |
|Core | |core || | | | | |
|Out:2 | |out:1 || | +----+-----+ +----+-----+
|----------| |----------|| | | |
|AS F | |as f || | v v
|In:2 Out:6| |in:3 out:6|| |
|Peer J:1 | |peer j:1 || |
|Peer H:4 | |peer h:4 || |
| | | || |
+----+-----+ +----+-----+| |
| | .+--+-.
v v ,' 5 1 `.
; :
: AS G ;
\ /
+---` 4 3 ,'
<-+ `--+'
| +----------+ +----------+
| |PCB | |pcb |
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| |Core | |core |
| |Out:2 | |out:1 |
+----------+ +----------+ | |----------| |----------|
|PCB | |pcb | | |AS F | |as f |
|Core | |core | | |In:2 Out:5| |in:3 out:5|
|Out:2 | |out:1 | | |Peer J:1 | |peer j:1 |
|----------| |----------| | |Peer H:4 | |peer h:4 |
|AS F | |as f | | |----------| |----------|
|In:2 Out:6| |in:3 out:6| | |AS G | |as g |
|Peer J:1 | |peer j:1 | | |In:1 Out:3| |in:1 out:3|
|Peer H:4 | |peer h:4 | | | | | |
|----------| |----------| | +----+-----+ +----+-----+
|AS G | |as g | | | |
|In:5 Out:3| |in:5 out:3| v v v
| | | |
+----+-----+ +----+-----+
| |
v v
Figure 4: Intra-ISD PCB propagation from the ISD core down to
child ASes
2.2.1.1. Security
Each PCB contains signatures of all on-path ASes. Every time a
beacon service receives a PCB, it validates the PCB's authenticity.
During this process, the beacon service can query the certificate
service, for example, when it lacks an intermediate certificate.
2.2.1.2. Policies
Each AS can independently set policies dictating which PCBs are sent
in which time intervals, and to which neighbors. In particular, PCBs
do not need to be propagated immediately upon arrival. However,
during bootstrapping and if the AS obtains a PCB containing a
previously unknown path, the AS should forward the PCB immediately,
to ensure quick connectivity establishment.
2.2.2. Path Registration
Both the beacon service and the path service are involved in the path
registration process. A non-core AS typically receives several PCBs
representing several path segments to various core ASes. Out of
these PCBs, the non-core AS must select those down-path segments
through which it wants to be reached. It is the task of the AS's
beacon service to make this selection, according to the criteria
described in Path-Segment Selection (Section 2.2.2.1). The beacon
service then registers these path segments both at the local path
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service and at the path service of all core ASes. When links fail,
segments expire, or better segments become available, the beacon
service updates the down-path segments registered for its AS.
As a result, a core AS’s path service contains all intra-ISD path
segments registered by the leaf ASes of its ISD. In addition, a core
AS path service also stores the preferred core-path segments to other
core ASes.
2.2.2.1. Path-Segment Selection
Among the received PCBs, the beacon service of an AS must choose (1)
a set of PCBs to propagate further, and (2) a set of path segments to
register. The selection of these PCBs and path segments is based on
a path quality metric. This metric aims at identifying consistent,
diverse, efficient, and policy-compliant paths:
* _Consistency_ implies that at least one property along the path is
uniform, such as an AS capability (e.g., high bandwidth).
* _Diversity_ means that the set of paths announced over time are as
path-disjoint as possible, in order to provide high-quality
multipath options.
* _Efficiency_ refers to the length, bandwidth, latency,
utilization, and availability of a path, where more efficient
paths are naturally preferred.
* _Policy compliance_ implies that the path adheres to the AS's
routing policy.
Based on past PCBs, the AS beacon service assigns scores to the
current set of candidate path segments, and sends the best segments
in the next beaconing interval.
Core beaconing operates similarly to intra-ISD beaconing, except that
core PCBs only traverse core ASes. The same path selection metrics
apply, where a core AS attempts to forward the set of most desirable
paths to its neighbors.
2.2.3. Path Lookup
A host (source) who wants to start communication with another host
(destination), requires up to three path segments: An up-path segment
to reach the ISD core, a core-path segment to reach the destination
ISD, and a down-path segment to reach the destination AS. The source
host queries the path service in its AS for such segments. The path
service has up-path segments stored in its database and furthermore
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checks if it has appropriate core- and down-path segments in its
cache; in this case it returns them immediately.
If not, the path service in the source AS queries core path services
(using locally stored up-path segments) in the source ISD for core-
path segments to the destination ISD. Then, it combines up-path
segments with the newly retrieved core-path segments, and queries
core path services in the remote ISD to fetch remote down-path
segments. To improve overall efficiency, the local path service
caches the returned path segments and uses parallelism when
requesting path segments from core path services. Finally, the local
path service returns all path segments to the source host.
This recursive lookup significantly simplifies the process for
endpoints (which only have to send a single query, similar to stub
DNS resolvers). The caching strategy ensures that path lookups are
fast for frequently used destinations (similar to caching in
recursive DNS resolvers).
2.2.4. Link Failures
Unlike in the current Internet, link failures are not automatically
resolved by the network, but require active handling by endpoints.
Since SCION forwarding paths are static, they break when one of the
links fails. Link failures are handled by a two-pronged approach
that typically masks link failures without any outage to the
application and rapidly re-establishes fresh working paths:
* The SCION Control Message Protocol (SCMP) (the SCION equivalent of
ICMP) is used for signaling connectivity problems. Instead of
relying on application- or transport-layer timeouts, endpoints get
immediate feedback from the network if a path stops working, and
can quickly switch to an alternative path.
* SCION endpoints are encouraged to use multipath communication by
default, thus masking a link failure with another working path.
As multipath communication can increase availability (even in
environments with very limited path choices), SCION beacon
services attempt to create disjoint paths, SCION path services
attempt to select and announce disjoint paths, and endpoints
compose path segments to achieve maximum resilience to path
failure. Consequently, most link failures in SCION remain
unnoticed by the application, unlike the frequent (albeit mostly
brief) outages in the current Internet. See also [ANDERSEN2001],
[KATZ2012], [KUSHMAN2007], and [HITZ2021].
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2.3. SCION Data Plane
While the control plane is responsible for providing end-to-end
paths, the data plane ensures that packets are forwarded on the
selected path. SCION border routers forward packets to the next AS
based on the AS-level path in the packet header (which is extended
with ingress and egress interface identifiers for each AS), without
inspecting the destination address and also without consulting an
inter-domain forwarding table. Only the border router at the
destination AS needs to inspect the destination address to forward it
to the appropriate local endpoint.
Because SCION splits the information about the locator (the path
towards the destination AS) and the identifier (the destination
address), the identifier can have any format that the destination AS
can interpret--only the destination needs to consider that local
identifier (see also [RFC6830]). In other words, an AS can select an
arbitrary addressing format for its hosts, e.g., a 4-byte IPv4,
6-byte media access control (MAC) address, 16-byte IPv6, or any other
up to 16-byte addressing scheme. A valuable consequence is that
hosts with different address types can directly communicate.
The next two sections describe how an endpoint combines path segments
into an end-to-end forwarding path, and how border routers forward
packets efficiently.
*Note*: This section describes the SCION data plane on a very high
level. A much more detailed description of SCION's data plane will
follow in a separate internet draft.
2.3.1. Path Construction via Segment Combination
Through the path lookup, the endpoint obtains path segments that must
be combined into an end-to-end path. A valid SCION *forwarding path*
can be created by combining up to three path segments, in the
following ways:
* *Immediate combination of path segments*: The last AS on the up-
path segment is also the first AS on the down-path segment. In
this case, the simple combination of an up-path segment and a
down-path segment creates a valid forwarding path.
* *AS shortcut*: The up-path segment and down-path segment intersect
at a non-core AS. In this case, a shorter forwarding path can be
created by removing the extraneous part of the path.
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* *Peering shortcut*: A peering link exists between the two
segments, so a shortcut via the peering link is possible. As in
the AS shortcut case, the extraneous path segment is cut off. The
peering link could be traversing to a different ISD.
* *Combination with a core-path segment*: The last AS on the up-path
segment is different from the first AS on the down-path segment.
This case requires an additional core-path segment to connect the
up- and down-path segment. If the communication remains within
the same ISD, a local ISD core-path segment is needed; otherwise,
an inter-ISD core-path segment is required.
* *On-path*: The destination AS is part of the up-path segment or
the source AS is part of the down-path segment; in this case, a
single up- or down-path segment, respectively, is sufficient to
create a forwarding path.
Once a forwarding path is chosen, it is encoded in the SCION packet
header. This makes inter-domain routing tables unnecessary for
border routers: Both the ingress and the egress interface of each AS
on the path are encoded as *packet-carried forwarding state (PCFS)*
in the packet header. The destination can respond to the source by
reversing the end-to-end path from the packet header, or it can
perform its own path lookup and combination.
The SCION packet header contains of a sequence of *hop fields (HFs)*,
one HF for each AS that is traversed on the end-to-end path. Each
hop field contains the encoded numbers of the ingress and egress
links, and thus defines which interfaces may be used to enter and
leave an AS. In addition to the hop fields, each path segment
contains an *info field (INF)* with basic information about the
segment. A host can create an end-to-end forwarding path by
extracting info fields and hop fields from path segments, as depicted
in Figure 5. The additional meta header (META) contains pointers to
the currently active INF and HF.
up-path segment core-path segment down-path segment
+-------+ +-------+ +-------+
|+-----+| |+-----+| |+-----+|
|+ INF ||----------+ |+ INF ||---+ |+ INF ||-+
|+-----+| | |+-----+| | |+-----+| |
|+-----+| | |+-----+| | |+-----+| |
|| hf ||--------+ | || hf ||---+--+ || hf ||-+--+
|+-----+| | | |+-----+| | | |+-----+| | |
|+-----+| | | |+-----+| | | |+-----+| | |
|| hf ||-----+ | | || hf ||---+--+--+ || hf ||-+--+--+
|+-----+| | | | |+-----+| | | | |+-----+| | | |
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|+-----+| | | | +-------+ | | | +-------+ | | |
|| hf ||--+ | | | | | | | | |
|+-----+| | | | | +--------+ | | | | | |
+-------+ | | | | |++-----+| | | | | | |
| | | | |++ Meta|| | | | | | |
| | | | |++-----+| | | | | | |
| | | | |+-----+ | | | | | | |
| | | +-->|+ INF | | | | | | | |
| | | |+-----+ | | | | | | |
| | | |+-----+ | | | | | | |
| | | |+ INF | |<-+ | | | | |
| | | |+-----+ | | | | | |
| | | |+-----+ | | | | | |
| | | |+ INF | |<----+--+----------------+ | |
| | | |+-----+ | | | | |
| | | |+-----+ | | | | |
| | +---->|| hf | | | | | |
| | |+-----+ | | | | |
| | |+-----+ | | | | |
| +------->|| hf | | | | | |
| |+-----+ | | | | |
| |+-----+ | | | | |
+---------->|| hf | | | | | |
|+-----+ | | | | |
|+-----+ | | | | |
|| hf | |<----+ | | |
|+-----+ | | | |
|+-----+ | | | |
|| hf | |<-------+ | |
|+-----+ | | |
|+-----+ | | |
|| hf | |<---------------------------+ |
|+-----+ | |
|+-----+ | |
|| hf | |<------------------------------+
|+-----+ |
+--------+
forwarding path
Figure 5: Combining three path segments into a forwarding path
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2.3.2. Path Authorization
It is crucial for the data plane that endpoints only use paths
constructed and authorized by ASes in the control plane. In
particular, endpoints should not be able to craft HFs themselves,
modify HFs in authorized path segments, or combine HFs of different
path segments (path splicing). This property is called *path
authorization* (see [KLENZE2021] and [LEGNER2020]).
SCION achieves path authorization by creating message-authentication
codes (MACs) during the beaconing process. Each AS calculates these
MACs using a local secret key (that is only shared between SCION
infrastructure elements within the AS) and chains them to the
previous HFs. The MACs are then included in the forwarding path as
part of the respective HFs.
2.3.3. Forwarding
Routers can efficiently forward packets in the SCION architecture.
In particular, the absence of inter-domain routing tables and of
complex longest-IP-prefix matching performed by current routers
enables the construction of more efficient routers.
During packet forwarding, a SCION border router at the ingress point
of the AS verifies that:
* the packet entered through the correct ingress interface
corresponding to the information in the HF,
* the HF is still valid, and
* the MAC in the HF is correct.
If the packet has not yet reached the destination AS, the egress
interface number in the HF of the non-destination AS refers to the
egress SCION border router of this AS. In this case, the packet can
be sent from the ingress SCION border router to the egress SCION
border router via native intra-domain forwarding (e.g., IP or MPLS).
In case the packet has arrived at the destination AS, the destination
AS's border router inspects the destination address and sends the
packet to the corresponding host.
2.3.4. Intra-AS Communication
SCION routers use IP to communicate within an AS, therefore they rely
on existing intra-domain routing protocols, such as Multiprotocol
Label Switching (MPLS) or others.
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3. Deployment
Adoption of a next-generation architecture is a challenging task, as
it needs to be integrated with, and operate alongside existing
infrastructure. SCION is designed to coexist with existing intra-
domain routing infrastructure, and comprises coexistence and
transition mechanisms that facilitate adoption, in accordance to
principles defined in [RFC8170]. The following section discusses
practical considerations for deploying SCION and briefly touches on
some of the transition mechanisms, with focus on:
* Autonomous Systems (Section 3.1),
* Internet Exchange Points (Section 3.2), and
* endpoints (Section 3.3), covering both native SCION hosts and
SCION to IP encapsulation.
We then describe some of the early adopters deployment experiences.
A more detailed adoption plan is to be outlined in dedicated
documents.
3.1. Autonomous System Deployment
A SCION AS needs to deploy the SCION infrastructure components
(Section 1.2.3) and border routers. Within an AS, SCION is often
deployed as an IP overlay on top of the existing network. This way
SCION allows to reuse the existing intra-domain network and equipment
(e.g., IP, MPLS). Customer-side SCION border routers directly
connect to the provider-side border routers using last-mile
connections. The SCION design assumes that AS’s internal entities
are considered to be trustworthy, therefore the IP overlay or the
first-hop routing does not compromise or degrade any security
properties SCION delivers. When it comes to inter-domain
communication, an overlay deployment on top of today’s Internet is
not desirable, as SCION would inherit issues from its weak underlay.
Thus, inter-AS SCION links are usually deployed in parallel to
existing links, in order to preserve its security properties. That
is, two SCION border routers from neighbour ASes are directly
connected via a layer-2 cross-connection at a common point-of-
presence.
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All SCION AS components can be deployed on standard x86 commercial
off-the-shelf servers or virtual machines. In fact, SCION border
routers do not rely on forwarding tables, therefore they do not
require specialized hardware. Practice shows that off-the-shelf
hardware can handle up to 100 Gbps links, while a prototype P4
implementation [DERUITER2021] showed that it is possible to forward
SCION traffic even at terabit speeds.
Overall, an AS can be connected to SCION without high-impact changes
to its network. In addition, use of commodity hardware for both
control and data-plane components reduces initial deployment costs.
3.2. Internet Exchange Points
Internet Exchange Points (IXP) play as important a role for SCION as
they do in today's Internet. SCION can be deployed at existing IXPs
following a "big switch" model, where the IXP provides a large L2
switch between multiple SCION ASes. SCION has been deployed
following this model at the Swiss Internet Exchange (SwissIX),
currently interconnecting major SCION Swiss ISPs and enterprises
through bi-lateral peering over dedicated SCION ports.
Additionally, thanks to its path-awareness, SCION offers the option
of an enhanced deployment model, i.e., to expose the internal
topology of an IXP within the SCION control plane. This enables IXP
customers to use SCION’s multipath and fast failover capabilities to
leverage the IXP’s internal links (including backup links) and to
select paths depending on the application’s needs. IXPs have
therefore an incentive to expose their rich internal connectivity, as
the benefits from SCION’s multipath capabilities would increase their
value for customers and provide them with a competitive advantage.
3.3. Endpoints and Incremental Deployability
End users can leverage SCION in two different ways: (1) using SCION-
aware applications on a SCION native endpoint (Section 3.3.1), or (2)
using transparent IP-to-SCION conversion (Section 3.3.2). The
benefit of using SCION natively is that the full range of advantages
becomes available to applications, at the cost of installing the
SCION endpoint stack and making the application SCION-aware. In
early deployments, the second approach is often preferred, so that no
changes are needed within applications or endpoints.
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3.3.1. Native Endpoints
A SCION native endpoint's stack consists of a dispatcher, which
handles all incoming and outgoing SCION packets, and of a SCION
daemon, which handles control-plane messages. The latter fetches
paths to remote ASes and provides an API for applications and
libraries to interact with the SCION control plane (i.e., for path
lookup, SCION extensions). The current SCION implementation uses an
UDP/IP underlay for communication between endpoints and SCION
routers. This allows reuse of existing intra-domain networking
infrastructure. SCION endpoints can optionally use automated
bootstrapping mechanisms to retrieve configuration from the network
and establish SCION connectivity. This way, clients require no pre-
existing network-specific configurations.
3.3.2. SCION to IP Gateway (SIG)
A SCION-IP-Gateway (SIG) encapsulates regular IP packets into SCION
packets with a corresponding SIG at the destination that performs the
decapsulation. A SIG can be deployed close to the end user (i.e., at
branches of an enterprise, on a CPE), or within an ISP's network. In
the latter case, the SIG is called carrier-grade SIG, as it serves
multiple customers within the AS where it is deployed. This approach
has the advantage that it does not require any changes at the
customer's premises. In order to allow incremental deployability and
to ease transition from legacy IP-based Internet to SCION, SIGs can
be augmented with mechanisms allowing them to coordinate and
automatically exchange IP prefix information. A more detailed
description of the SIG and its coordination mechanisms is to be
presented in dedicated documents.
3.4. Deployment Experiences
SCION has been deployed in production by multiple entities, growing
its acceptance among industry. While early deployments started on
academic and research networks, SCION has expanded to serve the
financial industry, government, and it is being evaluated for the
healthcare sector.
In 2017, SCION was evaluated for production use by a central bank,
with the goal of modernising the network interconnecting banks and
their branches. SCION was chosen, as it allows moving away from a
dedicated private network to a reliable Internet-based solution.
SCION connectivity was later extended to support system-critical
applications, like the national real-time gross settlement (RTGS)
system, connecting all country's banks to exchange real-time payment
information. The network, called Secure Swiss Finance Network or
SSFN (https://perma.cc/PU5L-ALPM), is implemented as a SCION ISD,
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where a federation of three ISPs forms the ISD core. Financial
institutions are themselves SCION ASes and directly connect to one or
more of the core ASes. Institutions deploy SCION–IP gateways (SIGs),
transparently enabling their traditional IP-based applications to use
the SCION network. The concept of the SCION ISD also provides a
mechanism to implement strict governance and access control (through
the issuance of AS certificates).
Besides the SSFN, SCION connectivity has also been adopted by
government entities for their international communications. In
addition, Swiss higher education institutions are connected thanks to
the SCI-ED (http://scied.scion-architecture.net/) network.
In addition to productive deployments, SCION also comprises a global
SCION research testbed called SCIONLab (https://www.scionlab.org).
It is composed of dozens of globally distributed infrastructure ASes,
mostly run by academic institutions. The testbed is open to any user
who can easily set up their own AS with the aid of a web-based UI,
connect to the network, and run experiments. The setup has been the
earliest global deployment of SCION and it has been supporting
research and development of path-aware networking and SCION.
4. IANA Considerations
Currently, this document has no request for action to IANA. However,
when full specification of SCION is available, requests for IANA
actions are expected regarding the registration of optional packet
header fields as well as the coordination of SCION ISD and AS number
assignments.
5. Security Considerations
SCION has been designed from the outset to offer security by default,
and thus there are manifold security considerations. As a matter of
fact, SCION's protocol design has been formally verified and the open
source router implementation is undergoing formal verification (see
also [KLENZE2021]). Describing all security considerations here,
therefore, would go beyond the scope of this document. A separate
document including all security implications and considerations will
follow later.
6. References
6.1. 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>.
6.2. Informative References
[ANDERSEN2001]
Andersen, D., Balakrishnan, H., Kaashoek, F., and R.
Morris, "Resilient overlay networks", Proceedings of the
eighteenth ACM symposium on Operating systems principles,
DOI 10.1145/502034.502048, October 2001,
<https://doi.org/10.1145/502034.502048>.
[CHUAT22] Chuat, L., Legner, M., Basin, D., Hausheer, D., Hitz, S.,
Mueller, P., and A. Perrig, "The Complete Guide to SCION",
ISBN 978-3-031-05287-3, 2022,
<https://doi.org/10.1007/978-3-031-05288-0>.
[COOPER2013]
Cooper, D., Heilman, E., Brogle, K., Reyzin, L., and S.
Goldberg, "On the risk of misbehaving RPKI authorities",
Proceedings of the Twelfth ACM Workshop on Hot Topics
in Networks, DOI 10.1145/2535771.2535787, November 2013,
<https://doi.org/10.1145/2535771.2535787>.
[DERUITER2021]
de Ruiter, J. and C. Schutijser, "Next-generation internet
at terabit speed: SCION in P4", Proceedings of the 17th
International Conference on emerging Networking
EXperiments and Technologies, DOI 10.1145/3485983.3494839,
December 2021, <https://doi.org/10.1145/3485983.3494839>.
[GRIFFIN1999]
Griffin, T. and G. Wilfong, "An analysis of BGP
convergence properties", ACM SIGCOMM Computer
Communication Review vol. 29, no. 4, pp. 277-288,
DOI 10.1145/316194.316231, August 1999,
<https://doi.org/10.1145/316194.316231>.
[HITZ2021] Hitz, S., "Demonstrating the reliability and resilience of
Secure Swiss Finance Network", 2021,
<https://perma.cc/4H3Q-WZNG>.
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[I-D.dekater-scion-pki]
de Kater, C. and N. Rustignoli, "SCION Control-Plane PKI",
2023, <https://datatracker.ietf.org/doc/draft-dekater-
scion-pki/>.
[I-D.rustignoli-scion-components]
de Kater, C. and N. Rustignoli, "SCION Components
Analysis", 2023, <https://datatracker.ietf.org/doc/draft-
rustignoli-panrg-scion-components/>.
[KATZ2012] Katz-Bassett, E., Scott, C., Choffnes, D., Cunha, Í.,
Valancius, V., Feamster, N., Madhyastha, H., Anderson, T.,
and A. Krishnamurthy, "LIFEGUARD: practical repair of
persistent route failures", ACM SIGCOMM Computer
Communication Review vol. 42, no. 4, pp. 395-406,
DOI 10.1145/2377677.2377756, August 2012,
<https://doi.org/10.1145/2377677.2377756>.
[KING2022] King, D., Farrel, A., and C. Jacquenet, "Challenges for
the Internet Routing Systems Introduced by Semantic
Routing", 2022, <https://datatracker.ietf.org/doc/draft-
king-irtf-challenges-in-routing/>.
[KLENZE2021]
Klenze, T., Sprenger, C., and D. Basin, "Formal
Verification of Secure Forwarding Protocols", 2021 IEEE
34th Computer Security Foundations Symposium (CSF),
DOI 10.1109/csf51468.2021.00018, June 2021,
<https://doi.org/10.1109/csf51468.2021.00018>.
[KUSHMAN2007]
Kushman, N., Kandula, S., and D. Katabi, "Can you hear me
now?!: it must be BGP", ACM SIGCOMM Computer Communication
Review vol. 37, no. 2, pp. 75-84,
DOI 10.1145/1232919.1232927, March 2007,
<https://doi.org/10.1145/1232919.1232927>.
[LABOVITZ2000]
Labovitz, C., Ahuja, A., Bose, A., and F. Jahanian,
"Delayed Internet routing convergence", Proceedings of the
conference on Applications, Technologies, Architectures,
and Protocols for Computer Communication,
DOI 10.1145/347059.347428, August 2000,
<https://doi.org/10.1145/347059.347428>.
[LEGNER2020]
Legner, M., Klenze, T., Wyss, M., Sprenger, C., and A.
Perrig, "EPIC: Every Packet Is Checked in the Data Plane
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of a Path-Aware Internet", 2020,
<https://www.usenix.org/conference/usenixsecurity20/
presentation/legner>.
[LI2014] Li, Q., Hu, Y., and X. Zhang, "Even Rockets Cannot Make
Pigs Fly Sustainably: Can BGP be Secured with BGPsec?",
Proceedings 2014 Workshop on Security of Emerging
Networking Technologies, DOI 10.14722/sent.2014.23001,
2014, <https://doi.org/10.14722/sent.2014.23001>.
[LYCHEV2013]
Lychev, R., Goldberg, S., and M. Schapira, "BGP security
in partial deployment: is the juice worth the squeeze?",
ACM SIGCOMM Computer Communication Review vol. 43, no. 4,
pp. 171-182, DOI 10.1145/2534169.2486010, August 2013,
<https://doi.org/10.1145/2534169.2486010>.
[MORILLO2021]
Morillo, R., Furuness, J., Morris, C., Breslin, J.,
Herzberg, A., and B. Wang, "ROV++: Improved Deployable
Defense against BGP Hijacking", Proceedings 2021 Network
and Distributed System Security Symposium,
DOI 10.14722/ndss.2021.24438, 2021,
<https://doi.org/10.14722/ndss.2021.24438>.
[PERRIG2017]
Perrig, A., Szalachowski, P., Reischuk, R., and L. Chuat,
"SCION: A Secure Internet Architecture",
ISBN 978-3-319-67079-9, 2017,
<https://doi.org/10.1007/978-3-319-67080-5>.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements",
RFC 4033, DOI 10.17487/RFC4033, March 2005,
<https://www.rfc-editor.org/rfc/rfc4033>.
[RFC4264] Griffin, T. and G. Huston, "BGP Wedgies", RFC 4264,
DOI 10.17487/RFC4264, November 2005,
<https://www.rfc-editor.org/rfc/rfc4264>.
[RFC5218] Thaler, D. and B. Aboba, "What Makes for a Successful
Protocol?", RFC 5218, DOI 10.17487/RFC5218, July 2008,
<https://www.rfc-editor.org/rfc/rfc5218>.
[RFC6480] Lepinski, M. and S. Kent, "An Infrastructure to Support
Secure Internet Routing", RFC 6480, DOI 10.17487/RFC6480,
February 2012, <https://www.rfc-editor.org/rfc/rfc6480>.
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[RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The
Locator/ID Separation Protocol (LISP)", RFC 6830,
DOI 10.17487/RFC6830, January 2013,
<https://www.rfc-editor.org/rfc/rfc6830>.
[RFC8170] Thaler, D., Ed., "Planning for Protocol Adoption and
Subsequent Transitions", RFC 8170, DOI 10.17487/RFC8170,
May 2017, <https://www.rfc-editor.org/rfc/rfc8170>.
[RFC8205] Lepinski, M., Ed. and K. Sriram, Ed., "BGPsec Protocol
Specification", RFC 8205, DOI 10.17487/RFC8205, September
2017, <https://www.rfc-editor.org/rfc/rfc8205>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/rfc/rfc8446>.
[RFC9049] Dawkins, S., Ed., "Path Aware Networking: Obstacles to
Deployment (A Bestiary of Roads Not Taken)", RFC 9049,
DOI 10.17487/RFC9049, June 2021,
<https://www.rfc-editor.org/rfc/rfc9049>.
[RFC9217] Trammell, B., "Current Open Questions in Path-Aware
Networking", RFC 9217, DOI 10.17487/RFC9217, March 2022,
<https://www.rfc-editor.org/rfc/rfc9217>.
[ROTHENBERGER2017]
Rothenberger, B., Asoni, D., Barrera, D., and A. Perrig,
"Internet Kill Switches Demystified", Proceedings of the
10th European Workshop on Systems Security,
DOI 10.1145/3065913.3065922, April 2017,
<https://doi.org/10.1145/3065913.3065922>.
[SAHOO2009]
Sahoo, A., Kant, K., and P. Mohapatra, "BGP convergence
delay after multiple simultaneous router failures:
Characterization and solutions", Computer
Communications vol. 32, no. 7-10, pp. 1207-1218,
DOI 10.1016/j.comcom.2009.03.009, May 2009,
<https://doi.org/10.1016/j.comcom.2009.03.009>.
[SCHUCHARD2011]
Schuchard, M., Mohaisen, A., Foo Kune, D., Hopper, N.,
Kim, Y., and E. Vasserman, "Losing control of the
internet: using the data plane to attack the control
plane", Proceedings of the 17th ACM conference on Computer
and communications security, DOI 10.1145/1866307.1866411,
October 2010, <https://doi.org/10.1145/1866307.1866411>.
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Acknowledgments
Many thanks go to Cyrill Krähenbühl and Juan A. Garcia-Pardo for
reviewing this document. We are also indebted to Laurent Chuat,
Markus Legner, David Basin, David Hausheer, Samuel Hitz, and Peter
Müller, for writing the book "The Complete Guide to SCION" (see
[CHUAT22]), which provides the background information needed to write
this informational draft.
Authors' Addresses
Corine de Kater
SCION Association
Email: cdk@scion.org
Nicola Rustignoli
SCION Association
Email: nic@scion.org
Adrian Perrig
ETH Zuerich
Email: adrian.perrig@inf.ethz.ch
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