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rfc:rfc4384

Network Working Group D. Meyer Request for Comments: 4384 February 2006 BCP: 114 Category: Best Current Practice

                BGP Communities for Data Collection

Status of This Memo

 This document specifies an Internet Best Current Practices for the
 Internet Community, and requests discussion and suggestions for
 improvements.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2006).

Abstract

 BGP communities (RFC 1997) are used by service providers for many
 purposes, including tagging of customer, peer, and geographically
 originated routes.  Such tagging is typically used to control the
 scope of redistribution of routes within a provider's network and to
 its peers and customers.  With the advent of large-scale BGP data
 collection (and associated research), it has become clear that the
 information carried in such communities is essential for a deeper
 understanding of the global routing system.  This memo defines
 standard (outbound) communities and their encodings for export to BGP
 route collectors.

Meyer Best Current Practice [Page 1] RFC 4384 BGP Communities for Data Collection February 2006

Table of Contents

 1. Introduction ....................................................2
 2. Definitions .....................................................3
    2.1. Peers and Peering ..........................................3
    2.2. Customer Routes ............................................3
    2.3. Peer Routes ................................................3
    2.4. Internal Routes ............................................4
    2.5. Internal More Specific Routes ..............................4
    2.6. Special Purpose Routes .....................................4
    2.7. Upstream Routes ............................................4
    2.8. National Routes ............................................4
    2.9. Regional Routes ............................................4
 3. RFC 1997 Community Encoding and Values ..........................5
 4. Community Values for BGP Data Collection ........................5
    4.1. Extended Communities .......................................7
    4.2. Four-Octet AS Specific Extended Communities ................9
 5. Note on BGP UPDATE Packing ......................................9
 6. Acknowledgements ................................................9
 7. Security Considerations ........................................10
    7.1. Total Path Attribute Length ...............................10
 8. IANA Considerations ............................................10
 9. References .....................................................11
    9.1. Normative References ......................................11
    9.2. Informative References ....................................11

1. Introduction

 BGP communities [RFC1997] are used by service providers for many
 purposes, including tagging of customer, peer, and geographically
 originated routes.  Such tagging is typically used to control the
 scope of redistribution of routes within a provider's network and to
 its customers and peers.  Communities are also used for a wide
 variety of other applications, such as allowing customers to set
 attributes such as LOCAL_PREF [RFC1771] by sending appropriate
 communities to their service provider.  Other applications include
 signaling various types of Virtual Private Networks (VPNs) (e.g.,
 Virtual Private LAN Service (VPLS) [VPLS]), and carrying link
 bandwidth for traffic engineering applications [RFC4360].
 With the advent of large-scale BGP data collection [RV] [RIS] (and
 associated research), it has become clear that the geographical and
 topological information, as well as the relationship the provider has
 to the source of a route (e.g., transit, peer, or customer), carried
 in such communities is essential for a deeper understanding of the
 global routing system.  This memo defines standard communities for
 export to BGP route collectors.  These communities represent a
 significant part of information carried by service providers as of

Meyer Best Current Practice [Page 2] RFC 4384 BGP Communities for Data Collection February 2006

 this writing, and as such could be useful for internal use by service
 providers.  However, such use is beyond the scope of this memo.
 Finally, those involved in BGP data analysis are encouraged to verify
 with their data sources as to which peers implement this scheme (as
 there is a large amount of existing data as well as many legacy
 peerings).
 The remainder of this memo is organized as follows.  Section 2
 provides the definition of terms used as well as the semantics of the
 communities used for BGP data collection, and Section 3 defines the
 corresponding encodings for RFC 1997 [RFC1997] communities.  Finally,
 Section 4 defines the encodings for use with extended communities
 [RFC4360].

2. Definitions

 In this section, we define the terms used and the categories of
 routes that may be tagged with communities.  This tagging is often
 referred to as coloring, and we refer to a route's "color" as its
 community value.  The categories defined here are loosely modeled on
 those described in [WANG] and [HUSTON].

2.1. Peers and Peering

 Consider two network service providers, A and B.  Service providers A
 and B are defined to be peers when (i) A and B exchange routes via
 BGP, and (ii) traffic exchange between A and B is settlement-free.
 This arrangement is also typically known as "peering".  Peers
 typically exchange only their respective customer routes (see
 "Customer Routes" below), and hence exchange only their respective
 customer traffic.  See [HUSTON] for a more in-depth discussion of the
 business models surrounding peers and peering.

2.2. Customer Routes

 Customer routes are those routes that are heard from a customer via
 BGP and are propagated to peers and other customers.  Note that a
 customer can be an enterprise or another network service provider.
 These routes are sometimes called client routes [HUSTON].

2.3. Peer Routes

 Peer routes are those routes heard from peers via BGP, and not
 propagated to other peers.  In particular, these routes are only
 propagated to the service provider's customers.

Meyer Best Current Practice [Page 3] RFC 4384 BGP Communities for Data Collection February 2006

2.4. Internal Routes

 Internal routes are those routes that a service provider originates
 and passes to its peers and customers.  These routes are frequently
 taken out of the address space allocated to a provider.

2.5. Internal More Specific Routes

 Internal more specific routes are those routes that are frequently
 used for circuit load balancing purposes and Interior Gateway
 Protocol (IGP) route reduction.  They also may correspond to customer
 services that are not visible outside the service provider's network.
 Internal more specific routes are not exported to any external peer.

2.6. Special Purpose Routes

 Special purpose routes are those routes that do not fall into any of
 the other classes described here.  In those cases in which such
 routes need to be distinguished, a service provider may color such
 routes with a unique value.  Examples of special purpose routes
 include anycast routes and routes for overlay networks.

2.7. Upstream Routes

 Upstream routes are typically learned from an upstream service
 provider as part of a transit service contract executed with the
 upstream provider.

2.8. National Routes

 These are route sets that are sourced from and/or received within a
 particular country.

2.9. Regional Routes

 Several global backbones implement regional policy based on their
 deployed footprint and on strategic and business imperatives.
 Service providers often have settlement-free interconnections with an
 Autonomous System (AS) in one region, and that same AS is a customer
 in another region.  This mandates use of regional routing, including
 community attributes set by the network in question to allow easy
 discrimination among regional routes.  For example, service providers
 may treat a route set received from another service provider in
 Europe differently than the same route set received in North America,
 as it is common practice to sell transit in one region while peering
 in the other.

Meyer Best Current Practice [Page 4] RFC 4384 BGP Communities for Data Collection February 2006

3. RFC 1997 Community Encoding and Values

 In this section, we provide RFC 1997 [RFC1997] community values for
 the categories described above.  RFC 1997 communities are encoded as
 BGP Type Code 8, and are treated as 32-bit values ranging from
 0x0000000 through 0xFFFFFFF.  The values 0x0000000 through 0x0000FFFF
 and 0xFFFF0000 through 0xFFFFFFFF are reserved.
 The best current practice among service providers is to use the
 high-order two octets to represent the provider's AS number, and the
 low-order two octets to represent the classification of the route, as
 depicted below:
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            <AS>               |         <Value>               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 where <AS> is the 16-bit AS number.  For example, the encoding
 0x2A7C029A would represent the AS 10876 with value 666.

4. Community Values for BGP Data Collection

 In this section, we define the RFC 1997 community encoding for the
 route types described above for use in BGP data collection.  It is
 anticipated that a service provider's internal community values will
 be converted to these standard values for output to a route
 collector.
 This memo follows the best current practice of using the basic format
 <AS>:<Value>.  The values for the route categories are described in
 the following table:

Meyer Best Current Practice [Page 5] RFC 4384 BGP Communities for Data Collection February 2006

     Category                                 Value
   ===============================================================
   Reserved                                 <AS>:0000000000000000
   Customer Routes                          <AS>:0000000000000001
   Peer Routes                              <AS>:0000000000000010
   Internal Routes                          <AS>:0000000000000011
   Internal More Specific Routes            <AS>:0000000000000100
   Special Purpose Routes                   <AS>:0000000000000101
   Upstream Routes                          <AS>:0000000000000110
   Reserved                                 <AS>:0000000000000111-
                                            <AS>:0000011111111111
   National and Regional Routes             <AS>:0000100000000000-
                                            <AS>:1111111111111111
    Encoded as                               <AS>:<R><X><CC>
    Reserved National and Regional values    <AS>:0100000000000000-
                                             <AS>:1111111111111111
 Where
  <AS> is the 16-bit AS
  <R>  is the 5-bit Region Identifier
  <X>  is the 1-bit satellite link indication
       X = 1 for satellite links, 0 otherwise
  <CC> is the 10-bit ISO-3166-2 country code [ISO3166]
 and <R> takes the values:
  Africa (AF)                            00001
  Oceania (OC)                           00010
  Asia (AS)                              00011
  Antarctica (AQ)                        00100
  Europe (EU)                            00101
  Latin America/Caribbean Islands (LAC)  00110
  North America (NA)                     00111
  Reserved                               01000-11111

Meyer Best Current Practice [Page 6] RFC 4384 BGP Communities for Data Collection February 2006

 That is:
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            <AS>               |   <R>   |X|        <CC>       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 For example, the encoding for a national route over a terrestrial
 link in AS 10876 from the Fiji Islands would be:
  <AS>  = 10876 = 0x2A7C
  <R>   = 00010
  <X>   = 0
  <CC>  = Fiji Islands Country Code = 242 = 0011110010
 In this case, the low-order 16 bits are 0001000011110010 = 0x10F2.
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           0x2A7C              |           0x10F2              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Note that a configuration language might allow the specification of
 this community as 10876:4338 (0x10F2 == 4338 decimal).
 Finally, note that these categories are not intended to be mutually
 exclusive, and multiple communities can be attached where
 appropriate.

4.1. Extended Communities

 In some cases, the values and their encoding described in Section 4
 may clash with a service provider's existing community assignments.
 Extended communities [RFC4360] provide a convenient mechanism that
 can be used to avoid such clashes.
 The Extended Communities attribute is a transitive optional BGP
 attribute with the Type Code 16 and consists of a set of extended
 communities of the following format:

Meyer Best Current Practice [Page 7] RFC 4384 BGP Communities for Data Collection February 2006

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Type high    |  Type low(*)  |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+          Value                |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 For purposes of BGP data collection, we encode the communities
 described in Section 4 using the two-octet AS specific extended
 community type, which has the following format:
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      0x00     |   Sub-Type    |    Global Administrator       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Local Administrator                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 The two-octet AS specific extended community attribute encodes the
 service provider's two-octet Autonomous System number (as assigned by
 a Regional Internet Registry, or RIR) in the Global Administrator
 field, and the Local Administrator field may encode any information.
 This memo assigns Sub-Type 0x0008 for BGP data collection, and
 specifies that the <Value> field, as defined in Section 3.1, is
 carried in the low-order octets of the Local Administrator field.
 The two high-order octets of the Local Administrator field are
 reserved, and are set to 0x00 when sending and ignored upon receipt.
 For example, the extended community encoding for 10876:4338
 (representing a terrestrial national route in AS 10876 from the Fiji
 Islands) would be:
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      0x00     |      0x0008   |           0x2A7C              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      0x00     |      0x00     |           0x10F2              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Meyer Best Current Practice [Page 8] RFC 4384 BGP Communities for Data Collection February 2006

4.2. Four-Octet AS Specific Extended Communities

 The four-octet AS specific extended community is encoded as follows:
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      0x02     |    0x0008     |    Global Administrator       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Global Administrator (cont.)  |           0x10F2              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 In this case, the four-octet Global Administrator sub-field contains
 a four-octet Autonomous System number assigned by the IANA.

5. Note on BGP UPDATE Packing

 Note that data collection communities have the potential of making
 the attribute set of a specific route more unique than it would be
 otherwise (since each route collects data that is specific to its
 path inside one or more ASes).  This, in turn, can affect whether
 multiple routes can be grouped in the same BGP update message, and it
 may lead to increased use of bandwidth, router CPU cycles, and
 memory.

6. Acknowledgements

 The community encoding described in this memo germinated from an
 interesting suggestion from Akira Kato at WIDE.  In particular, the
 idea would be to use the collection community values to select paths
 that would result in (hopefully) more efficient access to various
 services.  For example, in the case of RFC 3258 [RFC3258] based DNS
 anycast service, BGP routers may see multiple paths to the same
 prefix, and others might be coming from the same origin with
 different paths, but others might be from different region/country
 (with the same origin AS).
 Joe Abley, Randy Bush, Sean Donelan, Xenofontas Dimitropoulos, Vijay
 Gill, John Heasley, Geoff Huston, Steve Huter, Michael Patton,
 Olivier Marce, Ryan McDowell, Rob Rockell, Rob Thomas, Pekka Savola,
 Patrick Verkaik, and Alex Zinin all made many insightful comments on
 early versions of this document.  Henk Uijterwaal suggested the use
 of the ISO-3166-2 country codes.

Meyer Best Current Practice [Page 9] RFC 4384 BGP Communities for Data Collection February 2006

7. Security Considerations

 While this memo introduces no additional security considerations into
 the BGP protocol, the information contained in the communities
 defined in this memo may in some cases reveal network structure that
 was not previously visible outside the provider's network.  As a
 result, care should be taken when exporting such communities to route
 collectors.  Finally, routes exported to a route collector should
 also be tagged with the NO_EXPORT community (0xFFFFFF01).

7.1. Total Path Attribute Length

 The communities described in this memo are intended for use on egress
 to a route collector.  Hence an operator may choose to overwrite its
 internal communities with the values specified in this memo when
 exporting routes to a route collector.  However, operators should in
 general ensure that the behavior of their BGP implementation is
 well-defined when the addition of an attribute causes a PDU to exceed
 4096 octets.  For example, since it is common practice to use
 community attributes to implement policy (among other functionality
 such as allowing customers to set attributes such as LOCAL_PREF), the
 behavior of an implementation when the attribute space overflows is
 crucial.  Among other behaviors, an implementation might usurp the
 intended attribute data or otherwise cause indeterminate failures.
 These behaviors can result in unanticipated community attribute sets,
 and hence result in unintended policy implications.

8. IANA Considerations

 This memo assigns a new Sub-Type for the AS specific extended
 community type in the First Come First Served extended transitive
 category.  The IANA has assigned Sub-Type 0x0008 as defined in
 Section 4.1.
 In addition, the IANA has created two registries for BGP Data
 Collection Communities, one for standard communities and one for
 extended communities.  Both of these registries will initially be
 populated by the values described in Section 4.  IETF Consensus, as
 described in [RFC2434], usually through the Global Routing Operations
 Working Group (grow), is required for the assignment of new values in
 these registries (in particular, for <Value> or <R> in the table of
 values for the route categories in Section 4).

Meyer Best Current Practice [Page 10] RFC 4384 BGP Communities for Data Collection February 2006

9. References

9.1. Normative References

 [ISO3166]       "ISO 3166 Maintenance agency (ISO 3166/MA)", Web
                 Page:  http://www.iso.org/iso/en/prods-services/
                 iso3166ma/index.html, 2004.
 [RFC1771]       Rekhter, Y. and T. Li (Editors), "A Border Gateway
                 Protocol (BGP-4)", RFC 1771, March 1995.
 [RFC1997]       Chandra, R. and P. Traina, "BGP Communities
                 Attribute", RFC 1997, August 1996.
 [RFC4360]       Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
                 Communities Attribute", RFC 4360, January 2006.

9.2. Informative References

 [HUSTON]        Huston, G., "Interconnection, Peering, and
                 Settlements",
                 http://www.isoc.org/inet99/proceedings/1e/1e_1.htm
 [RFC2434]       Narten, T., and H. Alvestrand, "Guidelines for
                 Writing an IANA Considerations Section in RFCs", BCP
                 26, RFC 2434, October 1998.
 [RFC3258]       Hardie, T., "Distributing Authoritative Name Servers
                 via Shared Unicast Addresses", RFC 3258, April 2002.
 [RIS]           "The RIPE Routing Information Service", Web Page:
                 http://www.ripe.net/ris, 2004.
 [RV]            Meyer, D., "The Routeviews Project", Web Page:
                 http://www.routeviews.org, 2002.
 [VPLS]          Kompella, K., et al., "Virtual Private LAN Service",
                 Work in Progress, April 2005.
 [WANG]          Wang, F. and L. Gao, "Inferring and Characterizing
                 Internet Routing Policies", ACM SIGCOMM Internet
                 Measurement Conference 2003.

Author's Address

 David Meyer
 EMail: dmm@1-4-5.net

Meyer Best Current Practice [Page 11] RFC 4384 BGP Communities for Data Collection February 2006

Full Copyright Statement

 Copyright (C) The Internet Society (2006).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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Acknowledgement

 Funding for the RFC Editor function is provided by the IETF
 Administrative Support Activity (IASA).

Meyer Best Current Practice [Page 12]

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