RPKI Autonomous Systems Cones: A Profile To Define Sets of Autonomous Systems Numbers To Facilitate BGP Filtering
draft-ss-grow-rpki-as-cones-00

Abstract

This document describes a way to define groups of Autonomous System numbers in RPKI [RFC6480]. We call them AS-Cones. AS-Cones provide a mechanism to be used by operators for filtering BGP-4 [RFC4271] announcements.

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.

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 Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.

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This Internet-Draft will expire on November 2, 2018.

Copyright Notice

Copyright (c) 2018 IETF Trust and the persons identified as the document authors. All rights reserved.

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Table of Contents

• 1. Introduction
• 2. Format of AS-Cone objects
• 2.1. Policy definition object
• 2.1.1. Naming convention for Policy definition objects
• 2.1.2. ASN.1 format of a Policy Definition object
• 2.1.3. Naming convention for neighbour relationships
• 2.2. AS-Cone definition object
• 2.2.1. Naming convention for AS-Cone objects
• 2.2.2. ASN.1 format of an AS-Cone
• 3. Validating an AS-Cone
• 4. Recommendations for use of AS-Cones at Internet Exchange points
• 5. Publication of AS-Cones as IRR objects
• 6. Security Considerations
• 7. IANA Considerations
• 8. Contributors
• 9. Acknowledgments
• 10. References
• 10.1. Normative References
• 10.2. Informative References
• Authors' Addresses

1. Introduction

The main goal of the Resource Public Key Infrastructure (RPKI) system [RFC6480] is to support improved security for the global routing system. This is achieved through the use of information stored in a distributed repository system comprised of signed objects. A commonly used object type is the Route Object Authorisation (ROAs), which describe the prefixes originated by ASNs.

There is however no way for an operator to assert the routes for its customer networks, making it difficult to use the information carried by RPKI to create meaningful BGP-4 filters without relying on RPSL [RFC2622] as-sets.

This memo introduces a new attestation object, called an AS-Cone. An AS-Cone is a digitally signed object with the goal to enable operators to define a set of customers that can be found as "right adjacencies", or transit customer networks, facilitating the construction of prefix filters for a given ASN, thus making routing more secure.

2. Format of AS-Cone objects

AS-Cones are composed of two types of distinct objects:

• Policy definitions; and
• The AS-Cones themselves.

These objects are stored in ASN.1 format and are digitally signed according to the same rules and conventions applied for RPKI ROA Objects ([RFC6482]).

2.1. Policy definition object

A policy definition contains a list the upstream and peering relationships for a given Autonomous System that need an AS-Cone to be used for filtering. For each relationship, an AS-Cone is referenced to indicate which BGP networks will be announced to the other end of the relationship.

The default behaviour for a neighbour, if the relationship is not explicitly described in the policy, is to only accept the networks originated by the ASN. This means that a stub ASN does not have to set up any AS-Cone nor any description or policy.

Only one AS-Cone can be supplied for a given relationship. If more than one AS-Cone needs to be announced in the relationship, then it is mandatory to create a third AS-Cone that includes those two.

2.1.1. Naming convention for Policy definition objects

A Policy object is referenced using the Autonomous System number it refers to, preceded by the string "AS".

2.1.2. ASN.1 format of a Policy Definition object

ASNPolicy DEFINITIONS ::=
BEGIN
Neighbours ::= SEQUENCE OF Neighbour

Neighbour ::= SEQUENCE 
{
    ASN INTEGER (1..4294967296),
    ASCone  VisibleString
}

Version ::= INTEGER
LastModified ::= GeneralizedTime
Created ::= GeneralizedTime
END
                            
                        

ASN.1 format of a Policy definition object

2.1.3. Naming convention for neighbour relationships

When referring to a neighbour relationship contained in a Policy definition object the following convention should be used:

ASX:ASY

Where X is the number of the AS holder and Y is the number of the ASN intended to use the AS-Cone object to generate a filter.

2.2. AS-Cone definition object

An AS-Cone contains a list of the downstream customers and AS-Cones of a given ASN. The list is used to create filter lists by the networks providing transit or a peering relationship with the ASN.

An AS-Cone can reference another AS-Cone if a customer of the operator also has defined an AS-Cone to be announced upstream.

2.2.1. Naming convention for AS-Cone objects

AS-Cones MUST have a unique name for the ASN they belong to. Names are composed of ASCII strings up to 255 characters long and cannot contain spaces.

In order for AS-Cones to be unique in the global routing system, their string name is preceded by the AS number of the ASN they are part of, followed by ":". For example, AS-Cone "EuropeanCustomers" for ASN 65530 is represented as "AS65530:EuropeanCustomers" when referenced from a third party.

2.2.2. ASN.1 format of an AS-Cone

ASCone DEFINITIONS ::=
BEGIN
Entities ::= SEQUENCE OF Entity

Entity CHOICE
{
    ASN INTEGER (1..4294967296),
    OtherASCone VisibleString
}

Version ::= INTEGER
LastModified ::= GeneralizedTime
Created ::= GeneralizedTime
END
                            
                        

ASN.1 format of an AS-Cone

3. Validating an AS-Cone

The goal of AS-Cones is to be able to recursively define all the originating ASNs that define the customer base of a given ASN, including all the transit relationships. This means that through AS-Cones, it is possible to create a graph of all the neighbour relationships for the customers of a given ASN.

In order to validate a full AS-Cone, we have to assume that a network operator already runs an RPKI validator software. The software provides access to a validated cache containing all the Policy definitions and AS-Cone objects. Validation occurs following the description in: [RFC6488].

In order to validate a full AS-Cone, an operator should perform the following steps:

1. For Every downstream ASN, the operator takes its policy definition file and collects a list of ASNs for the cone by looking at the following data, in exact order:
   1. A policy for the specific relationship, in the form of ASX:ASY, where ASX is the downstream ASN, and ASY is the ASN of the operator validating the AS-Cone;
   2. If there is no specific definition for the relationship, the ASX:Default policy;

   If none of the two objects above exists, then the operator should only consider the ASN of its downstream to be added to the list.

2. These objects can either point to:
   1. An AS-Cone; or
   2. An ASN

3. If the definition points to an AS-Cone, the operator looks for the object referenced, which should be contained in the validated cache;
4. If the validated cache does not contain the referenced object, then the validation moves on to the next downstream network;
5. If the validated cache contains the referenced object, the validation process evaluates every entry in the AS-Cone. For each entry:
   1. If there is a reference to an ASN, then the operator adds the ASN to the list for the given AS-Cone;
   2. If there is a reference to another AS-Cone, the validating process should recursively process all the entries in that AS-Cone first, with the same principles contained in this list.

   Since the goal is to build a list of ASNs announcing routes in the AS-Cone, then if an ASN or an AS-Cone are referenced more than once in the process, their contents should only be added once to the list. This is intended to avoid endless loops, and in order to avoid cross-reference of AS-Cones

6. When all the AS-Cones referenced in the policies have been recursively iterated, and all the originating ASNs have been taken into account, the operator can then build a full prefix-list with all the prefixes originated in its AS-Cone. This can be done by querying the RPKI validator software for all the networks originated by every ASN referenced in the AS-Cone.

4. Recommendations for use of AS-Cones at Internet Exchange points

When an operator is a member of an internet exchange point, it is recommended for it to create at least a Default policy.

In case of a peering session with a route server, the operator could publish a policy pointing to the ASN of the route server. A route server operator, then, could build strict prefix filtering rules for all the participants, and offer it as a service to its members.

5. Publication of AS-Cones as IRR objects

AS-Cones are very similar to AS-Set RPSL Objects, so they could also be published in IRR Databases as AS-Set objects. Every ASN contained in an AS-Cone, and all the AS-Cones referenced should be considered as member: attributes. The naming convention for AS-Cones (ASX:AS-Cone) should be maintained, in order to keep consistency between the two databases.

6. Security Considerations

TBW

7. IANA Considerations

This memo includes no request to IANA.

8. Contributors

The following people contributed significantly to the content of the document:

9. Acknowledgments

The authors would like to thank ...

10. References

10.1. Normative References

10.2. Informative References

Authors' Addresses