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Internet Engineering Task Force M. Sustrik, Ed.
Intended status: Informational March 2014
Expires: September 2, 2014
UDP Mapping for Scalability Protocols
This document defines the UDP mapping for scalability protocols.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
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This Internet-Draft will expire on September 2, 2014.
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1. Underlying protocol
This mapping should be layered directly on the top of UDP.
There's no fixed UDP port to use for the communication. Instead,
port numbers are assigned to individual services by the user.
2. Message delimitation
Each UDP packet maps to exactly one SP message.
There is no way to split one SP message into multiple UDP packets and
therefore SP messages larger than existing path MTU will be dropped
There is also no way to pack multiple SP messages into a single UDP
3. Packet layout
Each packet consists of an 8-byte header followed by the opaque
message payload:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
| 0x00 | 0x53 | 0x50 | version |
| type | reserved |
| payload ...
First four bytes of the protocol header are used to make sure that
the peer's protocol is compatible with the protocol used by the local
endpoint. Keep in mind that this protocol is designed to run on an
arbitrary UDP port, thus the standard compatibility check -- if it
runs on port X and protocol Y is assigned to X by IANA, it speaks
protocol Y -- does not apply. We have to use an alternative
First four bytes of the protocol header MUST be set to 0x00, 0x53,
0x50 and 0x00 respectively. If the protocol header received from the
peer differs, the UDP packets MUST be ignored.
The fact that the first byte of the protocol header is binary zero
eliminates any text-based protocols that were accidentally sending to
the endpoint. Subsequent two bytes make the check even more
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rigorous. At the same time they can be used as a debugging hint to
indicate that the connection is supposed to use one of the
scalability protocols -- ASCII representation of these bytes is 'SP'
that can be easily spotted in when capturing the network traffic.
Finally, the fourth byte rules out any incompatible versions of this
Fifth and sixth bytes of the header form a 16-bit unsigned integer in
network byte order representing the type of SP endpoint on the layer
above. The value SHOULD NOT be interpreted by the mapping, rather
the interpretation should be delegated to the scalability protocol
above the mapping. For informational purposes, it should be noted
that the field encodes information such as SP protocol ID, protocol
version and the role of endpoint within the protocol. Individual
values are assigned by IANA.
Finally, the last two bytes of the protocol header are reserved for
future use and must be set to binary zeroes. If the protocol header
from the peer contains anything else than zeroes in this field, the
implementation MUST ignore the UDP packet.
Packet header is followed by opaque message payload which spans all
the way to the end of the packet.
4. IANA Considerations
This memo includes no request to IANA.
5. Security Considerations
The mapping isn't intended to provide any additional security in
addition to what UDP does.
Author's Address
Martin Sustrik (editor)
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