Deprecation of BGP Entropy Label Capability Attribute
updates
- rfc-6790 — The Use of Entropy Labels in MPLS Forwarding
Extracted elements (7)
The ELCA was deprecated because it is an optional, transitive BGP path attribute: nodes that do not support it will propagate it by definition (per RFC 4271), yet those same nodes are precisely the ones that must remove it when modifying the next hop. This fundamental contradiction makes correct operation unenforceable.
An ELCA-oblivious intermediate node that modifies a route's next hop will propagate the ELCA attribute rather than removing it (as required by RFC 6790), because propagation of unrecognized optional, transitive attributes is the default BGP behavior per RFC 4271. This interoperability constraint is the core motivation for deprecation.
If the deprecated ELCA attribute is received, it MUST be treated as any other unrecognized optional, transitive attribute per RFC 4271, until and unless the code point is reused by a new specification.
Implementations MUST NOT generate the ELCA (Entropy Label Capability Attribute) path attribute, as it is deprecated by this specification.
The Entropy Label Capability Attribute (ELCA) is an optional, transitive BGP path attribute defined in RFC 6790 Section 5.2. It was intended to signal that a router is capable of processing MPLS entropy labels. This document deprecates it.
IANA has marked attribute 28 'BGP Entropy Label Capability Attribute' in the 'BGP Path Attributes' registry as 'deprecated' and added a reference to RFC 7447.
The ELCA's optional, transitive nature causes it to be tunneled through routers that don't implement it; implementations receiving such tunneled attributes could improperly rely on them, potentially creating a black hole in the forwarding path for affected routes. Deprecating the ELCA eliminates this risk.