Network Working Group J. Snijders
Internet-Draft Atrato IP Networks
Intended status: Informational August 09, 2013
Expires: February 10, 2014

The "import-via" and "export-via" attributes in RPSL Policy Specifications


This document defines two attributes in the aut-num Class which can be used in RPSL policy specifications to publish desired routing policy regarding non-adjacent networks.

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Table of Contents

1. Introduction

The Routing Policy Specification Language [RFC4012] allows operators to specify routing policies regarding directly adjacent networks through various import and export attributes. These attributes only apply to directly adjacent networks.

This document proposes to extend RPSL according to the following goals and requirements:

The addition of the "import-via" and "export-via" attributes in the aut-num Class will especially help participants of Multi-Lateral Peering services to inform the intermediate autonomous system what routing policy should be applied towards other participants.

2. Notational Conventions

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 [RFC2119].

3. Background

The via keyword specifically benefits operators whom were assigned a 32 bit AS Number and transit providers when participating in Multi-Lateral Peering Agreements facilitated by a Route Server.

Often Route Server operators overload BGP Communities [RFC1997]) to facilitate signalling of desired routing policy between the participants and the Route Server. Because BGP Communities have a length of 32 bit, it is not possible to signal a 32 bit AS Number coupled with an action. In practise this means Route Server participants whom use a 32 bit AS Number cannot specifically be included or excluded during path distribution calculations on the Route Server unless a mapping system is applied.

Transit providers often have a routing policy which states that the transit provider does not want to exchange paths with its downstream customers through Route Servers via public Internet Exchanges. The import-via and export-via attributes allow transit providers to participate in Multi-Lateral Peering services while instructing Route Server operators through a simple routing policy specification that paths should not be distributed to downstream customers and reducing the likelihood of Path Hiding on the Route Server.

4. Import and Export Via Syntax and Semantics

The two attributes can be used within the aut-num class.

The syntax for these attributes is as follows:

Attribute  Value                                         Type
import-via [protocol <protocol-1>] [into <protocol-2>]   optional,
           [afi <afi-list>]                              multi-valued
           from <mp-peering-2> [action <action-1>; ... <action-N>;]
           . . .
           from <mp-peering-M> [action <action-1>; ... <action-N>;]
           accept <mp-filter> [;]

export-via [protocol <protocol-1>] [into <protocol-2>]   optional,
           [afi <afi-list>]                              multi-valued
           to <mp-peering-2> [action <action-1>; ... <action-N>;]
           . . .
           to <mp-peering-M> [action <action-1>; ... <action-N>;]
           announce <mp-filter> [;]


Figure 1

The import-via and export-via attributes are optional, and should be ignored by implementations which do not support interpretation of those attributes. The syntax closely mimicks the mp-import and mp-export attributes described in Section 2.5 of [RFC4012], with the exception that before the "from" and "to" keywords an <mp-peering> is defined to indicate the common AS between two non-adjacent networks.

In the above example <peering-1> and <peering-3> are directly adjacent networks, for instance a Multi-Lateral Peering service. <peering-2> is a non-adjacent network.

5. Example Usage

Putting it all together:

   aut-num: AS5580
   import-via: AS6777
                from AS15562
                action pref = 2;
                accept AS-SNIJDERS
   export-via: AS6777
                to AS15562 action community.={5580:40};
                announce AS-ATRATO
   import-via: AS5580:AS-ROUTESERVERS
                from AS5580:AS-CUSTOMERS
                accept NOT ANY
   export-via: AS5580:AS-ROUTESERVERS
                to AS5580:AS-CUSTOMERS announce NOT ANY
   import-via: AS6777
                from AS4247483647
                accept AS4247483647
   export-via: AS6777
                to AS4247483647 action community.={5580:40};
                announce AS-ATRATO

Figure 2

In the above examples AS5580 and AS15562 are Route Server participants. AS4247483647 is a participant whom has been assigned a 32 bit AS Number. AS6777 functions as a Route Server [I-D.ietf-idr-ix-bgp-route-server] and AS-SET AS5580:AS-ROUTESERVERS contains a list of Route Server AS Numbers. AS-SET AS5580:AS-CUSTOMERS contains a list of downstream transit customers from AS5580.

The intention of the above policy would be to enable the exchange of NLRI's through AS6777 with two parties: AS15562 and AS4247483647, yet prevent the Route Server from distributing NLRI's announced by AS5580 towards customers of said network. Publishing the policy that AS5580 will not accept customer routes through the Route Server can help counteract the "path hiding" phenomenon as described in Section 2.3.1 of [I-D.ietf-idr-ix-bgp-route-server], as the Route Server now is informed which NLRI's should not be considered in the best path selection process.

6. Ambiguity Resolution

The same peering can be covered by more than one "via" policy attribute or by a combination of multi-protocol policy attributes, or multi-protocol policy attributes (when specifying IPv4 unicast policy) and the previously defined IPv4 unicast policy attributes. In these cases, implementations should follow the specification-order rule as defined in Section 6.4 of RFC 2622 [1]. Operators should take note that in order to break ambiguity, the action corresponding to the first peering specification is used.

 aut-num: AS5580
 export:     to AS6777 to announce AS5580
 export-via: AS6777 to AS-AMS-IX-RS announce AS-ATRATO

Figure 3

 aut-num: AS5580
 export-via: AS6777 to AS-AMS-IX-RS announce AS-ATRATO
 export:     to AS6777 to announce AS5580

Figure 4

Consider the following example regarding ambiguity resolution.

7. Security Considerations

There are no security considerations for this specification.

8. IANA Considerations

This document has no IANA actions.

9. Acknowledgments

The authors would like to thank Remko van Mook for confirming that "via" is a better keyword than 'through' or 'thru', Nick Hilliard for his unparalleled support, Jeffrey Haas for providing historic perspective and David Croft for nitpicking.

10. References

10.1. Normative References

[RFC1997] Chandrasekeran, R., Traina, P. and T. Li, "BGP Communities Attribute", RFC 1997, August 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2622] Alaettinoglu, C., Villamizar, C., Gerich, E., Kessens, D., Meyer, D., Bates, T., Karrenberg, D. and M. Terpstra, "Routing Policy Specification Language (RPSL)", RFC 2622, June 1999.
[RFC4012] Blunk, L., Damas, J., Parent, F. and A. Robachevsky, "Routing Policy Specification Language next generation (RPSLng)", RFC 4012, March 2005.

10.2. Informative References

[I-D.ietf-idr-ix-bgp-route-server] Jasinska, E., Hilliard, N., Raszuk, R. and N. Bakker, "Internet Exchange Route Server", Internet-Draft draft-ietf-idr-ix-bgp-route-server-01, July 2012.

Appendix A. Grammar Rules

Note that only relevant grammer rules have been listed. An example implementation based on IRRd 2.3.10 is available at <>, and an updated version of the RIPE Database whois code is available at: <>.

%type <string> line_autnum
%type <string> attr_autnum
%type <string> attr_import_via
%type <string> attr_export_via

%token T_IV_KEY //*** import-via: ***
%token T_EV_KEY //*** export-via: ***

line_autnum: attr_autnum 
    | attr_import_via
    | attr_export_via

attr_import_via: T_IV_KEY attr_import_syntax

attr_import_syntax: opt_protocol_from opt_protocol_into import_simple
    | opt_protocol_from opt_protocol_into afi_import_exp

attr_export_via: T_EV_KEY attr_export_syntax 

attr_export_syntax: opt_protocol_from opt_protocol_into export_simple
    | opt_protocol_from opt_protocol_into afi_export_exp

    | T_AFI afi_list 

afi_list: afi_token 
    | afi_list ',' afi_token

afi_token: afi_name 



import_simple: opt_afi_specification import_factor

export_simple: opt_afi_specification export_factor

afi_import_exp: opt_afi_specification import_exp

afi_export_exp: opt_afi_specification export_exp

import_exp: import_term
    | import_term T_EXCEPT afi_import_exp
    | import_term T_REFINE afi_import_exp

import_factor_list: import_factor ';'
    | import_factor_list import_factor ';'

import_term: import_factor ';'
    | '{' import_factor_list '}'

export_exp: export_term
    | export_term T_EXCEPT afi_export_exp
    | export_term T_REFINE afi_export_exp

export_factor_list: export_factor ';'
    | export_factor_list export_factor ';'

export_term: export_factor ';'
    | '{' export_factor_list '}'

import_factor: import_peering_action_list T_ACCEPT filter

export_factor: export_peering_action_list T_ANNOUNCE filter

peering: as_expression opt_router_expression \

// Below are two grammer rules that actually differ
// from mp-import: + mp-export:

import_peering_action_list: peering T_FROM peering opt_action
    | import_peering_action_list peering T_FROM peering opt_action

export_peering_action_list: peering T_TO peering opt_action
    | export_peering_action_list peering T_TO peering opt_action

Figure 5

Appendix B. Document Change Log

(RFC Editor - this Appendix can be removed upon publication as RFC)

  1. Initial document.
  2. Changes to draft-snijders-rpsl-via-01.txt
    1. Moved from adding a new RPSL keyword to a new RPSL attribute to improve backwards compatibility.

  3. Changes to draft-snijders-rpsl-via-02.txt
    1. Added grammer appendix.
    2. Added section about Ambiguity Resolution.

Author's Address

Job Snijders Atrato IP Networks Tupolevlaan 103a Schiphol-Rijk, 1119 PA NL EMail: