Prefix Limit Based ORF for BGP-4
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|Authors||Keyur Patel , John Scudder , Marco Marzetti , Jakob Heitz|
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IDR K. Patel Internet-Draft Arrcus, Inc Intended status: Standards Track J. Scudder Expires: May 4, 2017 Juniper Networks M. Marzetti PCCW Global J. Heitz Cisco October 31, 2016 Prefix Limit Based ORF for BGP-4 draft-keyur-idr-bgp-prefix-limit-orf-00.txt Abstract The BGP specification allows for "the ability to impose an (locally configured) upper bound on the number of address prefixes the speaker is willing to accept from a neighbor". In this specification, we define a new Outbound Route Filter type for BGP, termed "Prefix Limit Outbound Route Filter", which the speaker can use to communicate that upper bound to its peer. The peer is then required to abide by the limit. This is expected to have benefits in terms of resource consumption and more importantly, transparency of operation. 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 http://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 May 4, 2017. Copyright Notice Copyright (c) 2016 IETF Trust and the persons identified as the document authors. All rights reserved. Patel, et al. Expires May 4, 2017 [Page 1] Internet-Draft Prefix Limit Based ORF for BGP-4 October 2016 This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Prefix Limit ORF-Type . . . . . . . . . . . . . . . . . . . . 2 3. Prefix Limit ORF encoding . . . . . . . . . . . . . . . . . . 3 4. Capability Specification for Cooperative route filtering with Prefix Limit . . . . . . . . . . . . . . . . . . . . . . . . 3 5. Rules for Prefix Limit ORF . . . . . . . . . . . . . . . . . 3 5.1. Rules for Sending Speaker . . . . . . . . . . . . . . . . 4 5.1.1. Enforcing the Prefix Limit . . . . . . . . . . . . . 4 5.2. Rules for Receiving Speaker . . . . . . . . . . . . . . . 5 6. Error handling . . . . . . . . . . . . . . . . . . . . . . . 6 7. Security Considerations . . . . . . . . . . . . . . . . . . . 6 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 10. Normative References . . . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 1. Introduction The Cooperative Outbound Route Filtering Capability defined in [RFC5291] provides a mechanism for a BGP speaker to send to its BGP neighbor a set of Outbound Route Filters (ORFs) that can be used by its neighbor to filter its outbound routing updates to the speaker. This documents defines a new ORF-type for BGP, termed "Prefix Limit Outbound Route Filter (PrefixLimit ORF)", that can be used to perform Prefix Limit based route filtering. This filtering mechanism imposes a limit on a the number of unique prefixes that the BGP speaker can advertise to its neighbor. 2. Prefix Limit ORF-Type The Prefix Limit ORF-Type allows a BGP speaker to inform its neighbor of its prefix limits. That is, it provides a mechanism through which a BGP speaker can request its neighbor to limit the number of unique prefixes that neighbor will advertise to the BGP speaker. Patel, et al. Expires May 4, 2017 [Page 2] Internet-Draft Prefix Limit Based ORF for BGP-4 October 2016 Conceptually a Prefix Limit ORF entry consists of the fields "Action, Match, Reserved, Prefix-Limit". Action is a two-bit field. The definition and use of the Action field is described in [RFC5291]. Match is a one-bit field. The value of this field is 0 for PERMIT and 1 for DENY. In the context of the Prefix Limit ORF-Type, DENY indicates that the BGP speaker sending the ORF will terminate the connection in the event that the Prefix Limit is exceeded. Reserved is a 5-bit field. The definition and use of the Reserved field is described in [RFC5291]. The "Prefix-Limit" is a four byte unsigned integer. It states the maximum number of unique prefixes that the ORF sending BGP speaker is willing to accept from the ORF receiving BGP spea 3. Prefix Limit ORF encoding The value of the ORF-Type for the Prefix Limit ORF-Type is [TBD]. A Prefix Limit ORF entry is encoded as follows. The "Action", "Match", and the "Reserved" field of the entry is encoded in the common part [RFC5291], and the remaining field of the entry is encoded in the "Type specific part" as follows. +--------------------------------------------------+ | Prefix-Limit (4 octets) | +--------------------------------------------------+ 4. Capability Specification for Cooperative route filtering with Prefix Limit A BGP speaker signals its compliance with this specification by listing the PrefixLimit ORF type in the Cooperative Route Filtering Capability as defined in [RFC5291]. 5. Rules for Prefix Limit ORF We describe the rules for PrefixLimit primarily in terms of the rules for the router which sends a PrefixLimit ORF to its peer, which we term the "sending speaker", and for the router which receives a PrefixLimit ORF from its peer, which we term the "receiving speaker". Note that a given router may be either a sending or receiving speaker, or both, with respect to any given peering session. Patel, et al. Expires May 4, 2017 [Page 3] Internet-Draft Prefix Limit Based ORF for BGP-4 October 2016 A router which supports PrefixLimit ORF MUST keep track of the number of prefixes it has advertised to its peer -- when a new prefix is advertised, the count is incremented, and when a prefix is withdrawn, the count is decremented. A modification to the route for an already-advertised prefix does not change the count. We refer to this count as the "advertised prefix count" for the session. In effect, the advertised prefix count is equivalent to the size of the Adj-RIB-Out for the session. A router which supports PrefixLimit ORF MAY maintain a received prefix count for its peer, which tracks the number of prefixes it has accepted from the peer. In effect, the received route count is equivalent to the size of the Adj-RIB-In for the session. The use of such a count is elaborated in the following section. 5.1. Rules for Sending Speaker If a BGP speaker (the sending speaker) is configured to bound the number of prefixes it is willing to accept from its neighbor, it MAY advertise the value of that upper bound to that neighbor using PrefixLimit ORF. In this section and its subsection, when we refer to "the PrefixLimit" we are referring to the PrefixLimit value most recently advertised by the sending speaker to the receiving speaker. If the sending speaker does not maintain a received prefix count, it is implicitly relying on its peer to correctly abide by this specification and no further action is required. If the sending speaker does maintain a received prefix count, it MAY locally enforce the PrefixLimit, according to the following rules. 5.1.1. Enforcing the Prefix Limit When the sending speaker sends a PrefixLimit ORF which is less than its current received prefix count, it SHOULD wait for some interval before enforcing the new PrefixLimit. The interval to be used is a matter of local policy. Also, even if the PrefixLimit ORF is greater than or equal to the current received prefix count, the router may wish to wait for some interval before enforcing the new limit in order to allow for UPDATEs which may have been in flight prior to the receipt of the PrefixLimit ORF by the peer. Subsequent to any such waiting period, the remaining rules in this section SHALL apply. If the PrefixLimit is exceeded (either because of a route announced by the peer or because the peer failed to timely withdraw routes after the PrefixLimit is revised downward), the peer is in violation, and the sending speaker MAY take corrective action. The router MAY also allow the received prefix count to exceed the PrefixLimit by some amount as a matter of local policy. Patel, et al. Expires May 4, 2017 [Page 4] Internet-Draft Prefix Limit Based ORF for BGP-4 October 2016 Corrective actions MAY include dropping the BGP session or refusing to accept new prefixes in excess of the PrefixLimit. If the former option -- dropping the BGP session -- is chosen, the router MUST indicate this in advance by advertising its PrefixLimit ORF with the Match flag set to DENY. Also, by default it SHOULD NOT automatically reestablish the session. If the latter option -- refusing to accept new prefixes -- is chosen, the router MUST accept modifications to already-accepted prefixes, and it MUST accept withdrawals of already-accepted prefixes. If prefixes are withdrawn, the received prefix count will drop below the announced PrefixLimit and new prefixes SHOULD be accepted, again up to but not exceeding the limit. Prefixes which are refused SHOULD NOT contribute to the received prefix count. We note that the option of refusing to accept new prefixes will likely lead to desynchronization of the BGP session and is a flawed solution at best; operator intervention will be required in order to restore synchronization (for example, through correction of routing policies and a subsequent route-refresh). 5.2. Rules for Receiving Speaker When a PrefixLimit ORF is received, the new Prefix Limit value in the ORF is considered to be the new maximum Prefix Limit for the neighbor. In this section, when we refer to "the PrefixLimit" we are referring to the PrefixLimit value most recently received from the sending speaker by the receiving speaker. The receiving speaker MUST NOT advertise a prefix to its peer if doing so would cause its advertised prefix count to exceed the PrefixLimit. The receiving speaker MAY take local action when its advertised prefix count approaches the PrefixLimit. The nature of the action (logging, etc) is a matter of local policy, as is the threshold at which the action occurs. When the receiving speaker receives a PrefixLimit ORF with When-to- Refresh set to DEFER, it need not take any additional action unless its current advertised prefix count exceeds the new PrefixLimit. In that case, it MUST take immediate steps to correct the violation. Such steps MAY include withdrawing already-advertised prefixes so as to reduce the advertised prefix count to be less than or equal to the PrefixLimit. The selection of which prefixes to withdraw is a matter of local policy. Another option to correct the violation would be to Patel, et al. Expires May 4, 2017 [Page 5] Internet-Draft Prefix Limit Based ORF for BGP-4 October 2016 drop the session; in this case the session SHOULD NOT be automatically reestablished. When the receiving speaker receives a PrefixLimit ORF with When-to- Refresh set to IMMEDIATE, it behaves as given for DEFER but in addition advertises its Adj-RIB-Out as specified in [RFC5291]. 6. Error handling ORFs provide information that guides future sending, but any malformed ORF is simply missed filtering information. If Prefix Limit ORF is malformed, then the Refresh messages shall simply be discarded. 7. Security Considerations This extension to BGP does not change the underlying security issues. However, it does suggest a mechanism by which certain denial of service risks may be reduced. 8. Acknowledgements The authors would like to thank ... for their valuable comments. 9. IANA Considerations This specification requests a new Cooperative Route Filter [RFC5291] type code. 10. 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, <http://www.rfc-editor.org/info/rfc2119>. [RFC3392] Chandra, R. and J. Scudder, "Capabilities Advertisement with BGP-4", RFC 3392, DOI 10.17487/RFC3392, November 2002, <http://www.rfc-editor.org/info/rfc3392>. [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, DOI 10.17487/RFC4271, January 2006, <http://www.rfc-editor.org/info/rfc4271>. [RFC5291] Chen, E. and Y. Rekhter, "Outbound Route Filtering Capability for BGP-4", RFC 5291, DOI 10.17487/RFC5291, August 2008, <http://www.rfc-editor.org/info/rfc5291>. Patel, et al. Expires May 4, 2017 [Page 6] Internet-Draft Prefix Limit Based ORF for BGP-4 October 2016 [RFC5292] Chen, E. and S. Sangli, "Address-Prefix-Based Outbound Route Filter for BGP-4", RFC 5292, DOI 10.17487/RFC5292, August 2008, <http://www.rfc-editor.org/info/rfc5292>. Authors' Addresses Keyur Patel Arrcus, Inc Email: firstname.lastname@example.org John Scudder Juniper Networks Email: email@example.com Marco Marzetti PCCW Global 450 Spring Park Place, Suite 100 Herndon , VA 20170 Email: firstname.lastname@example.org Jakob Heitz Cisco 170 W. Tasman Drive San Jose, CA 95124 Email: email@example.com Patel, et al. Expires May 4, 2017 [Page 7]