Deprecation of BGP Entropy Label Capability Attribute

This RFC 7447 was published in 2015.

Abstract

The BGP Entropy Label Capability attribute is defined in RFC 6790.
Regrettably, it has a bug: although RFC 6790 mandates that routers incapable of processing Entropy Labels must remove the attribute, fulfillment of this requirement cannot be guaranteed in practice.
This specification deprecates the attribute.
A forthcoming document will propose a replacement.

RFC 7447 introduction

[RFC6790] defines the Entropy Label Capability attribute (ELCA), an optional, transitive BGP path attribute.
For correct operation, an intermediate node modifying the next hop of a route must remove the ELCA unless the node doing so is able to process entropy labels.
Sadly, this requirement cannot be fulfilled with the ELCA as specified, because it is an optional, transitive attribute.
By definition, a node that does not support the ELCA will propagate the attribute (this is a general property of optional, transitive attributes; see [RFC4271]).
But such an ELCA-oblivious node is likely to be incapable of processing entropy labels and is exactly the node that we desire to remove the attribute!

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