RFC 4271, "A Border Gateway Protocol 4 (BGP-4)", January 2006Source of RFC: idr (rtg)
Errata ID: 6498
Status: Held for Document Update
Publication Format(s) : TEXT
Reported By: Graham Paasch
Date Reported: 2021-03-27
Held for Document Update by: Alvaro Retana
Date Held: 2021-03-29
Section 5.1.5 says:
LOCAL_PREF is a well-known attribute that SHALL be included in all UPDATE messages that a given BGP speaker sends to other internal peers.
It should say:
LOCAL_PREF is a well-known discretionary attribute that SHALL be included in all UPDATE messages that a given BGP speaker sends to other internal peers.
It is unclear from the text to which of the four path attribute categories LOCAL_PREF belongs. There was even submitted an errata to create a fifth category for this attribute, but it is clear from the definition of the categories, that this attribute is well known discretionary. All routers must be capable of sending or receiving the LOCAL_PREF attribute, however it is up to a routers discretion whether to include that attribute in an UPDATE message.
This is a valid report. The terminology in rfc4271 is not ideal, so using "discretionary" with a required action can cause significant confusion, even if that is the correct term for this attribute. A future version of this RFC should consider updating/cleaning up the terminology.