Prenegotiated options for IP, ICMP and TCP headers
draft-rosenau-prenegotiated-options-00

Abstract

In many cases (example: PPTP) a data transfer between two hosts is initiated by using "generic" protocols (in the case of PPTP this is UDP) and later on "special" protocols (in the case of PPTP this is GRE) are used.

The drawback in this case is that the IANA has to assign protcol numbers (in the case of GRE this is 47)

The same is true for TCP header "options" and ICMP packet "types".

To avoid assigning numbers by the IANA this document proposes to reserve a range of protocol numbers for "negotiation" instead. During the phase using "generic" protocols the two hosts negotiate a protocol number in that range.

Status of This Memo

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This Internet-Draft will expire on June 25, 2018.

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1. Introduction

Currently about 140 different layer 4 protocol numbers are assigned by the IANA to be used in the "next header" field (IPv6; IPv4: "protocol" field). Only 250 different protocol numbers are supported.

Because of the development of new protocols the number of possible values might be exceeded soon.

Furthermore the IANA has the work to assign a protocol number, TCP option or ICMP packet type.

This document proposes to assign a range of numbers for "negotiation".

This means that in a data transfer between two hosts first negotiate to use a certain number from the range reserved from "negotiation" instead of using a pre-defined protocol number.

2. Current situation

Currently the IANA is assigning protocol numbers, TCP options and ICMP packet types of all "non-experimental" protocols.

However in many situations a data transfer is initiated not using pre-assigned numbers. The following example shows a PPTP session:

       Host A                    Host B
         |                         |
         +---------- UDP --------->|
         |                         |
         |<-------- UDP -----------+
         |                         |
         +--------- GRE ---------->|
         |   (Packet type = 47)    |
         |                         |
         |<-------- GRE -----------+
         |   (Packet type = 47)    |
         |           ...           |
      

Figure 1: Sequence: PPTP

3. Proposed future behaviour

If no assigned number is necessary for the first data packets both hosts should first negotiate a protocol number from a certain range to be assigned by the IANA.

It is not necessary that both hosts negotiate one value; instead it is also possible that both hosts tell each other which value to be used. For each packet the value desired by the destination host is used.

The following example shows some EXample Protocol (EXP) using this approach:

       Host A                    Host B
         |                           |
         +---------- UDP ----------->|
         |   (Desired value = 240)   |
         |                           |
         |<--------- UDP ------------+
         |   (Desired value = 241)   |
         |                           |
         +---------- EXP ----------->|
         |    (Packet type = 241)    |
         |                           |
         |<--------- EXP ------------+
         |    (Packet type = 240)    |
         |            ...            |
      

Figure 2: Sequence: Future protocol

4. Proposed ranges

4.1. Most use cases

RFC 4727 specifies values 253 and 254 to be used for "experimental" purposes in the following fields:

o IPv4 "protocol" field
o IPv6 "next header" field
o ICMPv4 "type" field
o TCP "option" type

Because the range immediately before the number 253 is unassigned for all of these fields this document proposes the range from 240 to 252 for use with negotiation.

4.2. ICMPv6 types

RFC 4727 specifies values 100 and 101 to be used for "experimental" error codes in the ICMPv6 "type" field.

Because the range before the number 100 is unassigned this document proposes the range from 90 to 99 to be used for "negotiated" error codes.

RFC 4727 specifies values 200 and 201 to be used for "experimental" non-error packet types in the ICMPv6 "type" field.

Because the range before the number 200 is unassigned this document proposes the range from 190 to 199 to be used for "negotiated" non-error packets.

4.3. IPv6 destination options

Currently this document does not propose the use of negotiated IPv6 destination options.

4.4. When not to use negotiated values

Because these options must be negotiated between two hosts these options MUST NOT be used whenever more than two hosts must understand these options.

Examples for this situation are:

o IPv4 header options
o IPv6 hop-by-hop options
o Fields in non-unicast packets (anycast, multicast, broadcast)

5. References

5.1. Normative References

5.2. Informational References

Author's Address

Table of Contents

• 1. Introduction
• 2. Current situation
• 3. Proposed future behaviour
• 4. Proposed ranges
• 4.1. Most use cases
• 4.2. ICMPv6 types
• 4.3. IPv6 destination options
• 4.4. When not to use negotiated values
• 5. References
• 5.1. Normative References
• 5.2. Informational References
• Author's Address