BGP AS_PATH Validation State Extended Community

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Table of Contents

1. Introduction

This document defines a new BGP opaque extended community to carry the AS_PATH validation state based on Autonomous System Provider Authorization (ASPA) inside an autonomous system. Internal IBGP speakers that receive this validation state can configure local policies that allow it to influence their decision process.¶

2. Origin Validation State Extended Community

The origin validation state extended community is an opaque extended community [RFC4360] with the following encoding:¶

   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
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |       0x43    |      0x03     |             Reserved          |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                    Reserved                   |validationstate|
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The value of the high-order octet of the extended Type field is 0x43, which indicates it is non-transitive and opaque [RFC7153]. The value of the low-order octet of the extended Type field is 0x03 which is an unassigned sub-type of non-transitive opaque extended communities. The Reserved field MUST be set to 0 and ignored upon the receipt of this community. The last octet of the extended community is an unsigned integer that gives the AS_PATH's validation state [I-D.ietf-sidrops-aspa-verification]. It can assume the following values:¶

  +-------+-----------------------------+
  | Value | Meaning                     |
  +-------+-----------------------------+
  |   0   | Lookup result = "Valid"     |
  |   1   | Lookup result = "Unknown"   |
  |   2   | Lookup result = "Invalid"   |
  +-------+-----------------------------+

If the router is configured to support the extensions defined in this document, it SHOULD attach the AS-PATH validation state extended community to BGP UPDATE messages sent to IBGP peers by mapping the computed validation state in the last octet of the extended community. Similarly, a receiving BGP speaker, in the absence of validation state set based on local data, SHOULD derive a validation state from the last octet of the extended community, if present.¶

An implementation SHOULD NOT send more than one instance of the AS-PATH validation state extended community. However, if more than one instance is received, an implementation MUST disregard all instances other than the one with the numerically greatest validation state value. If the value received is greater than the largest specified value (2), the implementation MUST apply a strategy similar to attribute discard [RFC7606] by discarding the erroneous community and logging the error for further analysis.¶

By default, implementations MUST drop the AS-PATH validation state extended community if received from an External BGP (EBGP) peer, without processing it further. Similarly, by default, an implementation SHOULD NOT send the community to EBGP peers. However, it SHOULD be possible to configure an implementation to send or accept the community when warranted. An example of a case where the community would reasonably be received from, or sent to, an EBGP peer is when two adjacent ASes are under control of the same administration.¶

3. Deployment Considerations

In deployment scenarios in which not all the speakers in an autonomous system are upgraded to support the extensions defined in this document, it is necessary to define policies that match on the AS-PATH validation extended community and set another BGP attribute that influences selection of the best path in the same way that an implementation of this extension would.¶

4. IANA Considerations

The value 0x03 in the "Non-Transitive Opaque Extended Community Sub-Types" registry is unassigned by IANA. This value can be used as "BGP AS-PATH Validation State Extended Community".¶

5. Security Considerations

Security considerations such as those described in [RFC4272] continue to apply. Since this document introduces an extended community that will generally be used to affect route selection, the analysis in Section 4.5 ("Falsification") of [RFC4593] is relevant. These issues are neither new, nor unique to the origin validation extended community.¶

This document describes a scheme where router A outsources validation to some router B. If this scheme is used, the participating routers should have the appropriate trust relationship -- B should trust A either because they are under the same administrative control. The security properties of the propagation path between the two routers should also be considered. See [RFC7454] Section 5.1 for advice regarding protection of the propagation path.¶

Authors' Addresses