5. Essential Correction to RFC 2205

This section provides an essential correction to RFC 2205 (RSVP) regarding the use of the IPv6 Flow Label field.

Background

RFC 2205 defines the Resource Reservation Protocol (RSVP), which includes provisions for using the IPv6 Flow Label field. However, the original specification in RFC 2205 contained requirements that are incompatible with the current Flow Label specification.

Correction

Section 3.1.8 of RFC 2205 states that RSVP can use the Flow Label field to identify flows. However, the text implies that RSVP may modify the Flow Label field, which conflicts with the requirement that the Flow Label MUST be set by the source node and MUST NOT be changed by intermediate nodes.

This document clarifies that:

1. RSVP Flow Label Usage: RSVP MAY use the Flow Label field as part of the flow identification mechanism, in combination with the source and destination addresses and other relevant fields.

2. No Modification: RSVP nodes MUST NOT modify the Flow Label field. The Flow Label value MUST be set by the source node and MUST be delivered unchanged to the destination.

3. Signaling: RSVP MAY signal the Flow Label value to be used for a flow, but this signaling is used to inform the source node of the value to use, not to modify the Flow Label in transit.

Impact on RSVP Implementation

Implementations of RSVP that use the IPv6 Flow Label MUST be updated to comply with this correction. Specifically:

• RSVP routers MUST NOT modify the Flow Label field in IPv6 packets.

• RSVP PATH and RESV messages MAY include information about the Flow Label value, but this is for informational purposes only.

• The source node is responsible for setting the Flow Label value, even when RSVP is used.

Compatibility

This correction does not affect the core functionality of RSVP. It only clarifies the proper use of the Flow Label field in an RSVP context. Existing RSVP implementations that do not modify the Flow Label field are already compliant with this correction.