--- 1/draft-ietf-idr-bgp-open-policy-08.txt 2020-04-19 15:13:04.604836245 -0700 +++ 2/draft-ietf-idr-bgp-open-policy-09.txt 2020-04-19 15:13:04.628836851 -0700 @@ -1,24 +1,24 @@ Network Working Group A. Azimov Internet-Draft E. Bogomazov Intended status: Standards Track Qrator Labs -Expires: September 10, 2020 R. Bush +Expires: October 21, 2020 R. Bush Internet Initiative Japan & Arrcus K. Patel Arrcus, Inc. K. Sriram US NIST - March 9, 2020 + April 19, 2020 Route Leak Prevention using Roles in Update and Open messages - draft-ietf-idr-bgp-open-policy-08 + draft-ietf-idr-bgp-open-policy-09 Abstract Route leaks are the propagation of BGP prefixes which violate assumptions of BGP topology relationships; e.g. passing a route learned from one peer to another peer or to a transit provider, passing a route learned from one transit provider to another transit provider or to a peer. Today, approaches to leak prevention rely on marking routes by operator configuration, with no check that the configuration corresponds to that of the BGP neighbor, or enforcement @@ -46,21 +46,21 @@ 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/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on September 10, 2020. + This Internet-Draft will expire on October 21, 2020. Copyright Notice Copyright (c) 2020 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents @@ -124,26 +124,26 @@ [Gao]. The following is a list of various roles in BGP peering and the corresponding rules for route propagation: Provider: MAY send to a customer all available prefixes. Customer: MAY send to a provider their own prefixes and prefixes learned from any of their customers. A customer MUST NOT send to a provider prefixes learned from its peers, from other providers, or from Route Servers. - Route Server (RS): MAY send to an RS Client all available prefixes. + Route Server (RS): MAY send to an Route Server client (RS-client) + all available prefixes. - Route Server Client (RS-client): MAY send to an RS its own prefixes - and prefixes learned from its customers. An RS-client MUST NOT - send to an RS prefixes learned from its peers or providers, or - from another RS. + RS-client: MAY send to an RS its own prefixes and prefixes learned + from its customers. An RS-client MUST NOT send to an RS prefixes + learned from its peers or providers, or from another RS. Peer: MAY send to a peer its own prefixes and prefixes learned from its customers. A peer MUST NOT send to a peer prefixes learned from other peers, from its providers, or from RS(s). Of course, any BGP speaker may apply policy to reduce what is announced, and a recipient may apply policy to reduce the set of routes they accept. Violation of the above rules may result in route leaks and MUST not be allowed. Automatic enforcement of these rules should significantly reduce route leaks that may otherwise occur due @@ -160,21 +160,21 @@ Allowed Role values for eBGP sessions are: o Provider - sender is a transit provider to neighbor; o Customer - sender is a transit customer of neighbor; o RS - sender is a Route Server, usually at an Internet exchange point (IX); - o RS-Client - sender is client of an RS; + o RS-client - sender is client of an RS; o Peer - sender and neighbor are peers. Since BGP Role reflects the relationship between two BGP speakers, it could also be used for other purposes besides route leak mitigation. 4. BGP Role Capability The TLV (type, length, value) of the BGP Role capability are: @@ -182,113 +182,115 @@ o Length - 1 (octet); o Value - integer corresponding to speaker's BGP Role. +-------+---------------------+ | Value | Role name | +-------+---------------------+ | 0 | Sender is Provider | | 1 | Sender is RS | - | 2 | Sender is RS-Client | + | 2 | Sender is RS-client | | 3 | Sender is Customer | | 4 | Sender is Peer | +-------+---------------------+ Table 1: Predefined BGP Role Values 5. Role correctness Section 3 described how BGP Role encodes the relationship between two BGP speakers. But the mere presence of BGP Role doesn't automatically guarantee role agreement between two BGP peers. To enforce correctness, the BGP Role check is applied with a set of constraints on how speakers' BGP Roles MUST correspond. Of course, each speaker MUST announce and accept the BGP Role capability in the BGP OPEN message exchange. If a speaker receives a BGP Role capability, it MUST check the value - of the received capability with its own BGP Role (if it is set). The - allowed pairings are (first a sender's Role, second the receiver's - Role): + of the received capability (i.e., the sender's role) with its own BGP + Role. The allowed pairings are as follow: - +-------------+---------------+ - | Sender Role | Receiver Role | - +-------------+---------------+ + +---------------+-----------------+ + | Sender's Role | Receiver's Role | + +---------------+-----------------+ | Provider | Customer | | Customer | Provider | - | RS | RS-Client | - | RS-Client | RS | + | RS | RS-client | + | RS-client | RS | | Peer | Peer | - +-------------+---------------+ + +---------------+-----------------+ - Table 2: Allowed Role Capabilities + Table 2: Allowed Pairs of Role Capabilities If the observed Role pair is not in the above table, then the - receiving speaker MUST send a Role Mismatch Notification (code 2, - subcode ) and reset the BGP session. + receiving speaker MUST reject the BGP connection, send a Role + Mismatch Notification (code 2, subcode ), and also send a + Connection Rejected Notification [RFC4486] (Notification with error + code 6, subcode 5). 5.1. Strict mode A new BGP configuration option "strict mode" is defined with values of true or false. If set to true, then the speaker MUST refuse to establish a BGP session with a neighbor which does not announce the BGP Role capability in the OPEN message. If a speaker rejects a connection, it MUST send a Connection Rejected Notification [RFC4486] (Notification with error code 6, subcode 5). By default, strict mode SHOULD be set to false for backward compatibility with BGP speakers that do not yet support this mechanism. 6. BGP Only to Customer (OTC) Attribute - Newly defined here, the Only to Customer (OTC) is an optional, 4 byte - long, transitive BGP Path attribute with the Type Code . The - purpose of this attribute is to guarantee that once route is sent to - customer, peer or RS-client it will go only to customers. The - semantics and usage of the OTC attribute are made clear by the - ingress and egress policies described below. + Newly defined here, the Only to Customer (OTC) is an optional, 4 + bytes long, transitive BGP Path attribute with the Type Code . + The purpose of this attribute is to guarantee that once route is sent + to customer, peer, or RS-client, it will subsequently go only to + customers. The value of OTC is an AS number determined by policy as + described below. The semantics and usage of the OTC attribute are + made clear by the ingress and egress policies described below. The following ingress policy applies to the OTC attribute: 1. If a route with OTC attribute is received from a Customer or RS- client, then it is a route leak and MUST be rejected. 2. If a route with OTC attribute is received from a Peer and its - value is not equal to the neighbor's ASN, then it is a route leak - and MUST be rejected. + value is not equal to the sending neighbor's Autonomous System + (AS) number, then it is a route leak and MUST be rejected. - 3. If a route is received from a Provider, Peer or RS and the OTC + 3. If a route is received from a Provider, Peer, or RS and the OTC attribute is not present, then it MUST be added with value equal - to the neighbor's AS number. + to the sending neighbor's AS number. The egress policy MUST be: - 1. A route with the OTC attribute set MUST NOT be sent to providers, - peers, or RS(s). + 1. A route with the OTC attribute set MUST NOT be sent to Providers, + Peers, or RS(s). - 2. If route is sent to a customer or peer, or an RS-Client and the - OTC attribute is not present, then it MUST be added with value - equal to AS number of the sender. + 2. If route is sent to a Customer or Peer, or an RS-client (when the + sender is an RS) and the OTC attribute is not present, then it + MUST be added with value equal to AS number of the sender. Once the OTC attribute has been set, it MUST be preserved unchanged. 7. Enforcement Having the relationship unequivocally agreed between the two peers in BGP OPEN is critical; BGP implementations MUST enforce the relationship/role establishment rules (see Section 5) in order to - overcome operator policy configuration errors (if any). + ameliorate operator policy configuration errors (if any). Similarly, the application of that relationship on prefix propagation using OTC MUST BE enforced by the BGP implementations, and not - exposed to user mis-configuration. + exposed to user misconfiguration. As opposed to communities, BGP attributes may not be generally modified or filtered by the operator; BGP router implementations enforce such treatment. This is the desired property for the OTC marking. Hence, this document specifies OTC as an attribute. 8. Additional Considerations There are peering relationships that are 'complex', i.e., both parties are intentionally sending prefixes received from each other @@ -297,35 +299,35 @@ complex peering roles can be segregated into different normal BGP sessions, and BGP Roles MUST be used on each of the resulting normal (non-complex) BGP sessions. No Roles SHOULD be configured on a 'complex' BGP session (assuming it is not segregated) and in that case, OTC MUST be set by configuration on a per-prefix basis. However, there are no built-in measures to check correctness of OTC use if BGP Role is not configured. As the BGP Role reflects the peering relationship between neighbors, - it might have other uses beyond the route leaks solution discussed so + it might have other uses beyond the route leak solution discussed so far. For example, BGP Role might affect route priority, or be used to distinguish borders of a network if a network consists of multiple ASs. Though such uses may be worthwhile, they are not the goal of this document. Note that such uses would require local policy control. As BGP role configuration results in automatic creation of inbound/ outbound filters, existence of roles should be treated as existence of Import and Export policy [RFC8212]. 9. IANA Considerations This document defines a new Capability Codes option [to be removed - upon publication: http://www.iana.org/assignments/capability-codes/ + upon publication: https://www.iana.org/assignments/capability-codes/ capability-codes.xhtml] [RFC5492], named "BGP Role" with an assigned value . The length of this capability is 1. The BGP Role capability includes a Value field, for which IANA is requested to create and maintain a new sub-registry called "BGP Role Value". Assignments consist of Value and corresponding Role name. Initially this registry is to be populated with the data in Table 1. Future assignments may be made by a standard action procedure [RFC5226]. @@ -336,21 +338,21 @@ This document defines a new optional, transitive BGP Path Attributes option, named "Only to Customer (OTC)" with an assigned value [To be removed upon publication: http://www.iana.org/assignments/bgp- parameters/bgp-parameters.xhtml#bgp-parameters-2] [RFC4271]. The length of this attribute is four bytes. 10. Security Considerations This document proposes a mechanism for prevention of route leaks that - are the result of BGP policy mis-configuration. + are the result of BGP policy misconfiguration. A misconfiguration in OTC setup may affect prefix propagation. But the automation that is provided by BGP roles should make such misconfiguration unlikely. 11. Acknowledgments The authors wish to thank Douglas Montgomery, Brian Dickson, Andrei Robachevsky, and Daniel Ginsburg for their contributions to a variant of this work.