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Browse Prior Art Database

Using the Flow Label Field in IPv6 (RFC1809)

IP.com Disclosure Number: IPCOM000004065D
Original Publication Date: 1995-Jun-01
Included in the Prior Art Database: 2000-Sep-13
Document File: 5 page(s) / 13K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

C. Partridge: AUTHOR

Abstract

The purpose of this memo is to distill various opinions and suggestions of the End-to-End Research Group regarding the handling of Flow Labels into a set of suggestions for IPv6. This memo is for information purposes only and is not one of the IPv6 specifications. Distribution of this memo is unlimited.

This text was extracted from a ASCII Text document.
This is the abbreviated version, containing approximately 23% of the total text.

Network Working Group C. Partridge

Request for Comments: 1809 BBN Systems and Technologies

Category: Informational June 1995

Using the Flow Label Field in IPv6

Status of this Memo

This memo provides information for the Internet community. This memo

does not specify an Internet standard of any kind. Distribution of

this memo is unlimited.

Abstract

The purpose of this memo is to distill various opinions and

suggestions of the End-to-End Research Group regarding the handling

of Flow Labels into a set of suggestions for IPv6. This memo is for

information purposes only and is not one of the IPv6 specifications.

Distribution of this memo is unlimited.

Introduction

This memo originated as the report of a discussion at an End-to-End

Research Group meeting in November 1994. At that meeting the group

discussed several issues regarding how to manage flow identifiers in

IPv6. A report of the meeting was then circulated to the IPv6

community. Feedback from that community resulted in changes to this

memo and in changes to the IPv6 specification to fix some minor

problems the End-to-End Group had raised.

While many of the ideas in this memo have found their way into the

IPv6 specification, the explanation of why various design decisions

were made have not. This memo is intended to provide some additional

context for interested parties.

Brief Description of the Flow Label

The current draft of the IPv6 specification states that every IPv6

header contains a 24-bit Flow Label. (Originally the specification

called for a 28-bit Flow ID field, which included the flow label and

a 4-bit priority field. The priority field is now distinct, for

reasons discussed at the end of this memo).

The Flow Label is a pseudo-random number between 1 and FFFFFF (hex)

that is unique when combined with the source address. The zero Flow

Label is reserved to say that no Flow Label is being used. The

specification requires that a source must not reuse a Flow Label

value until all state information for the previous use of the Flow

Label has been flushed from all routers in the internet.

The specification further requires that all datagrams with the same

(non-zero) Flow Label must have the same Destination Address, Hop-

by-Hop Options header, Routing Header and Source Address contents.

The notion is that by simply looking up the Flow Label in a table,

the router can decide how to route and forward the datagram without

examining the rest of the header.

Flow Label Issues

The IPv6 specification originally left open a number of questions, of

which these three were among the most important:

1. What should a router do if a datagram with a (non-zero)

Flow Label arrives and the router has no state for that

Flow Label?

2. How does an internet flush old Flow Labels?

...