Network Working Group Q. Xie
Internet-Draft Motorola
Intended status: Experimental R. Stewart
Expires: May 13, 2007 Cisco Systems, Inc.
M. Stillman
Nokia
M. Tuexen
Muenster Univ. of Applied Sciences
A. Silverton
Motorola, Inc.
November 9, 2006
Endpoint Handlespace Redundancy Protocol (ENRP)
draft-ietf-rserpool-enrp-14.txt
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Copyright Notice
Copyright (C) The Internet Society (2006).
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Abstract
Endpoint Handlespace Redundancy Protocol (ENRP) is designed to work
in conjunction with the Aggregate Server Access Protocol (ASAP) to
accomplish the functionality of the Reliable Server Pooling
(Rserpool) requirements and architecture. Within the operational
scope of Rserpool, ENRP defines the procedures and message formats of
a distributed, fault-tolerant registry service for storing,
bookkeeping, retrieving, and distributing pool operation and
membership information.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Conventions . . . . . . . . . . . . . . . . . . . . . . . 5
2. ENRP Message Definitions . . . . . . . . . . . . . . . . . . . 6
2.1. ENRP_PRESENCE message . . . . . . . . . . . . . . . . . . 6
2.2. ENRP_HANDLE_TABLE_REQUEST message . . . . . . . . . . . . 8
2.3. ENRP_HANDLE_TABLE_RESPONSE message . . . . . . . . . . . . 8
2.4. ENRP_HANDLE_UPDATE message . . . . . . . . . . . . . . . . 10
2.5. ENRP_LIST_REQUEST message . . . . . . . . . . . . . . . . 11
2.6. ENRP_LIST_RESPONSE message . . . . . . . . . . . . . . . . 12
2.7. ENRP_INIT_TAKEOVER message . . . . . . . . . . . . . . . . 13
2.8. ENRP_INIT_TAKEOVER_ACK message . . . . . . . . . . . . . . 14
2.9. ENRP_TAKEOVER_SERVER message . . . . . . . . . . . . . . . 14
2.10. ENRP_ERROR message . . . . . . . . . . . . . . . . . . . . 15
3. ENRP Operation Procedures . . . . . . . . . . . . . . . . . . 17
3.1. Methods for Communicating amongst ENRP Servers . . . . . . 17
3.2. ENRP Server Initialization . . . . . . . . . . . . . . . . 18
3.2.1. Generate a Server Identifier . . . . . . . . . . . . . 19
3.2.2. Acquire Peer Server List . . . . . . . . . . . . . . . 19
3.2.3. Download ENRP Handlespace Data from Mentor Peer . . . 21
3.3. Handle PE Registration . . . . . . . . . . . . . . . . . . 23
3.3.1. Rules on PE Re-registration . . . . . . . . . . . . . 25
3.4. Handle PE De-registration . . . . . . . . . . . . . . . . 25
3.5. Pool Handle Translation . . . . . . . . . . . . . . . . . 26
3.6. Server Handlespace Update . . . . . . . . . . . . . . . . 27
3.6.1. Announcing Addition or Update of PE . . . . . . . . . 27
3.6.2. Announcing Removal of PE . . . . . . . . . . . . . . . 28
3.7. Detecting and Removing Unreachable PE . . . . . . . . . . 28
3.8. Helping PE and PU to Discover Home ENRP Server . . . . . . 29
3.9. Maintaining Peer List and Monitoring Peer Status . . . . . 30
3.9.1. Discovering New Peer . . . . . . . . . . . . . . . . . 30
3.9.2. Server Sending Heartbeat . . . . . . . . . . . . . . . 30
3.9.3. Detecting Peer Server Failure . . . . . . . . . . . . 30
3.10. Taking-over a Failed Peer Server . . . . . . . . . . . . . 31
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3.10.1. Initiate Server Take-over Arbitration . . . . . . . . 31
3.10.2. Take-over Target Peer Server . . . . . . . . . . . . . 32
3.11. Handlespace Data Auditing and Re-synchronization . . . . . 33
3.11.1. Auditing Procedures . . . . . . . . . . . . . . . . . 33
3.11.2. PE Checksum Calculation Algorithm . . . . . . . . . . 34
3.11.3. Re-synchronization Procedures . . . . . . . . . . . . 34
3.12. Handling Unrecognized Message or Unrecognized Parameter . 35
4. Variables and Thresholds . . . . . . . . . . . . . . . . . . . 36
4.1. Variables . . . . . . . . . . . . . . . . . . . . . . . . 36
4.2. Thresholds . . . . . . . . . . . . . . . . . . . . . . . . 36
5. Security Considerations . . . . . . . . . . . . . . . . . . . 37
5.1. Implementing Security Mechanisms . . . . . . . . . . . . . 38
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 40
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 41
7.1. Normative References . . . . . . . . . . . . . . . . . . . 41
7.2. Informative References . . . . . . . . . . . . . . . . . . 42
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 43
Intellectual Property and Copyright Statements . . . . . . . . . . 45
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1. Introduction
ENRP is designed to work in conjunction with ASAP [1] to accomplish
the functionality of Rserpool as defined by its requirements [2] and
architecture [3].
Within the operational scope of Rserpool, ENRP defines the procedures
and message formats of a distributed fault-tolerant registry service
for storing, bookkeeping, retrieving, and distributing pool operation
and membership information.
Whenever appropriate, in the rest of this document we will refer to
this Rserpool registry service as ENRP handlespace, or simply
handlespace.
1.1. Definitions
This document uses the following terms:
Operational scope: See [3];
Pool (or server pool): See [3];
Pool handle: See [3];
Pool element (PE): See [3];
Pool user (PU): See [3];
Pool element handle: See [3];
ENRP handlespace (or handlespace): See [3];
ENRP client channel: The communication channel through which an ASAP
User (either a PE or PU) requests ENRP handlespace service. The
client channel is usually defined by the transport address of the
home server and a well known port number. The channel MAY make
use of multi-cast or a named list of ENRP servers.
ENRP server channel: Defined by a well known multicast IP address
and a well known port number. All ENRP servers in an operational
scope can send multicast messages to other servers through this
channel. PEs are also allowed to multicast on this channel
occasionally;
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Home ENRP server: The ENRP server to which a PE or PU currently
belongs. A PE MUST only have one home ENRP server at any given
time and both the PE and its home ENRP server MUST keep track of
this master/slave relationship between them. A PU SHOULD select
one of the available ENRP servers as its home ENRP server, but the
ENRP server does not need to know, nor does it need to keep track
of this relationship.
1.2. Conventions
The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and OPTIONAL, when
they appear in this document, are to be interpreted as described in
[6].
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2. ENRP Message Definitions
In this section, we defines the format of all ENRP messages. These
are messages sent and received amongst ENRP servers in an operational
scope. Messages sent and received between a PE/PU and an ENRP server
are part of ASAP and are defined in [1]. A common format, defined in
[11], is used for all ENRP and ASAP messages.
Most ENRP messages contains a combination of fixed fields and TLV
parameters. The TLV parameters are also defined in [11].
All messages, as well as their fields/parameters described below,
MUST be transmitted in network byte order (a.k.a. Big Endian, i.e.,
the most significant byte first).
For ENRP, the following message types are defined:
Type Message Name
----- -------------------------
0x00 - (reserved by IETF)
0x01 - ENRP_PRESENCE
0x02 - ENRP_HANDLE_TABLE_REQUEST
0x03 - ENRP_HANDLE_TABLE_RESPONSE
0x04 - ENRP_HANDLE_UPDATE
0x05 - ENRP_LIST_REQUEST
0x06 - ENRP_LIST_RESPONSE
0x07 - ENRP_INIT_TAKEOVER
0x08 - ENRP_INIT_TAKEOVER_ACK
0x09 - ENRP_TAKEOVER_SERVER
0x0a - ENRP_ERROR
0x0b-0xff - (reserved by IETF)
2.1. ENRP_PRESENCE message
This ENRP message is used to announce (periodically) the presence of
an ENRP server, or to probe the status of a peer ENRP sever.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 0x01 |0|0|0|0|0|0|0|R| Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Server's ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receiver Server's ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: PE Checksum Param :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Server Information Param (optional) :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
R (reply_required) flag: 1 bit
Set to '1' if the sender requires a response to this message,
otherwise set to '0'.
Sender Server's ID: 32 bit (unsigned integer)
This is the ID of the ENRP server which sends the message.
Receiver Server's ID: 32 bit (unsigned integer)
This is the ID of the ENRP server to which the message is
intended. If the message is not intended to an individual
server (e.g., the message is multicasted to a group of
servers), this field MUST be set with all 0's.
PE Checksum Parameter:
This is a TLV that contains the latest PE checksum of the ENRP
server who sends the ENRP_PRESENCE. This parameter SHOULD be
included for handlespace consistency auditing. See
Section 3.11.1 for details.
Server Information Parameter:
If present, contains the server information of the sender of
this message (Server Information Parameter is defined in [11]).
This parameter is optional. However, if this message is sent
in response to a received "reply required" ENRP_PRESENCE from a
peer, the sender then MUST include its server information.
Note, at startup an ENRP server MUST pick a randomly generated, non-
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zero 32-bit unsigned integer as its ID and MUST use this same ID for
its entire life.
2.2. ENRP_HANDLE_TABLE_REQUEST message
An ENRP server sends this message to one of its peers to request a
copy of the handlespace data. This message is normally used during
server initialization or handlespace re-synchronization.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 0x02 |0|0|0|0|0|0|0|W| Message Length = 0xC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Server's ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receiver Server's ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
W (oWn-children-only) flag: 1 bit
Set to '1' if the sender of this message is only requesting
information about the PEs owned by the message receiver.
Otherwise, set to '0'.
Sender Server's ID:
See Section 2.1.
Receiver Server's ID:
See Section 2.1.
2.3. ENRP_HANDLE_TABLE_RESPONSE message
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 0x03 |0|0|0|0|0|0|M|R| Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Server's ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receiver Server's ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: Pool entry #1 (see below) :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: ... :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: Pool entry #n (see below) :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
M (More_to_send) flag: 1 bit
Set to '1' if the sender has more pool entries to sent in
subsequent ENRP_HANDLE_TABLE_RESPONSE messages, otherwise, set
to '0'.
R (Reject) flag: 1 bit
MUST be set to '1' if the sender of this message is rejecting a
handlespace request. In such a case, this message MUST be sent
with no pool entries included.
Message Length: 16 bits (unsigned integer)
Indicates the entire length of the message in number of octets.
Note, the value in Message Length field will NOT cover any
padding at the end of this message.
Sender Server's ID:
See Section 2.1.
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Receiver Server's ID:
See Section 2.1.
Pool entry #1-#n:
If R flag is '0', at least one pool entry SHOULD be present in
the message. Each pool entry MUST start with a pool handle
parameter as defined in section 3.1.7, followed by one or more
pool element parameters, i.e.:
+---------------------------+
: Pool handle :
+---------------------------+
: PE #1 :
+---------------------------+
: PE #2 :
+---------------------------+
: ... :
+---------------------------+
: PE #n :
+---------------------------+
2.4. ENRP_HANDLE_UPDATE message
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 0x04 |0|0|0|0|0|0|0|0| Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Server's ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receiver Server's ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Update Action | (reserved) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Pool handle :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Pool Element :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message Length: 16 bits (unsigned integer)
Indicates the entire length of the message in number of octets.
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Note, the value in Message Length field will NOT cover any
padding at the end of this message.
Update Action: 16 bits (unsigned integer)
This field indicates what act is requested to the specified PE.
It MUST take one of the following values:
0x0 - ADD_PE: add or update the specified PE in the ENRP
handlespace
0x1 - DEL_PE: delete the specified PE from the ENRP
handlespace.
Other values are reserved by IETF and MUST not be used.
Reserved: 16 bits
MUST be set to 0's by sender and ignored by the receiver.
Sender Server's ID:
See Section 2.1.
Receiver Server's ID:
See Section 2.1.
Pool handle:
Specifies to which the PE belongs.
Pool Element:
Specifies the PE.
2.5. ENRP_LIST_REQUEST message
This ENRP message is used to request a copy of the current known ENRP
peer server list. This message is normally sent from a newly started
ENRP server to an existing ENRP server as part of the initialization
process of the new server.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 0x05 |0|0|0|0|0|0|0|0| Message Length = 0xC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Server's ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receiver Server's ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Sender Server's ID:
See Section 2.1.
Receiver Server's ID:
See Section 2.1.
2.6. ENRP_LIST_RESPONSE message
This message is used to respond an ENRP_LIST_REQUEST.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 0x06 |0|0|0|0|0|0|0|R| Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Server's ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receiver Server's ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Server Info Param of Peer #1 :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: ... :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Server Info Param of Peer #n :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
R (Reject) flag: 1 bit
MUST be set to '1' if the sender of this message is rejecting a
peer list request. In such a case, this message MUST be sent
with no peer server ID included.
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Message Length: 16 bits (unsigned integer)
Indicates the entire length of the message in number of octets.
Note, the value in Message Length field will NOT cover any
padding at the end of this message.
Sender Server's ID:
See Section 2.1.
Receiver Server's ID:
See Section 2.1.
Server Information Parameter of Peer #1-#n:
Each contains a Server Information Parameter of a peer known to
the sender. The Server Information Parameter is defined in
[11].
2.7. ENRP_INIT_TAKEOVER message
This message is used by an ENRP server (the takeover initiator) to
declare its intention of taking over a specific peer ENRP server.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 0x07 |0|0|0|0|0|0|0|0| Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Server's ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receiver Server's ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Target Server's ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Sender Server's ID:
See Section 2.1.
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Receiver Server's ID:
See Section 2.1.
Target Server's ID:
Contains the 32-bit server ID of the peer ENRP that is the
target of this takeover attempt.
2.8. ENRP_INIT_TAKEOVER_ACK message
This message is used to acknowledge the takeover initiator that the
sender of this message received the ENRP_INIT_TAKEOVER message and
that it does not object to the takeover.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 0x08 |0|0|0|0|0|0|0|0| Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Server's ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receiver Server's ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Target Server's ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Sender Server's ID:
See Section 2.1.
Receiver Server's ID:
See Section 2.1.
Target Server's ID:
Contains the 32-bit server ID of the peer ENRP that is the
target of this takeover attempt.
2.9. ENRP_TAKEOVER_SERVER message
This message is used by the takeover initiator to declare that a
takeover is underway.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 0x09 |0|0|0|0|0|0|0|0| Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Server's ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receiver Server's ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Target Server's ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Sender Server's ID:
See Section 2.1.
Receiver Server's ID:
See Section 2.1.
Target Server's ID:
Contains the 32-bit server ID of the peer ENRP that is the
target of this takeover operation.
2.10. ENRP_ERROR message
This message is used by an ENRP server to report an operational error
to one of its peers.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 0x0a |0|0|0|0|0|0|0|0| Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Server's ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receiver Server's ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Operational Error Parameter :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Sender Server's ID:
See Section 2.1.
Receiver Server's ID:
See Section 2.1.
Operational Error Parameter:
This parameter, defined in [11], indicates the type of error(s)
being reported.
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3. ENRP Operation Procedures
In this section, we discuss the operation procedures defined by ENRP.
An ENRP server MUST following these procedures when sending,
receiving, or processing ENRP messages.
Many of the Rserpool events call for both server-to-server and PU/
PE-to-server message exchanges. Only the message exchanges and
activities between an ENRP server and its peer(s) are considered
within the ENRP scope and are defined in this document.
Procedures for exchanging messages between a PE/PU and ENRP servers
are defined in [1].
3.1. Methods for Communicating amongst ENRP Servers
Within an Rserpool operational scope, ENRP servers need to
communicate with each other in order to exchange information such as
the pool membership changes, handlespace data synchronization, etc.
Two types of communications are used amongst ENRP servers:
o point-to-point message exchange from one ENPR server to a specific
peer server, and
o announcements from one server to all its peer servers in the
operational scope.
Point-to-point communication is always carried out over an SCTP
association between the sending server and the receiving server.
Announcements are communicated out with one of the following two
approaches:
1. The sending server sends the announcement message to a well-known
RSERPOOL IP multicast channel that its peer servers subscribe to.
Note: Because IP multicast is not reliable, this approach does
not guarantee that all the peers will receive the announcement
message. Moreover, since IP multicast is not secure, this
approach cannot provide any security to the communication.
2. The sending server sends multiple copies of the announcement, one
to each of its peer servers, over a set of point-to-point SCTP
associations between the sending server and the peers.
This approach guarantees the reliable reception of the message.
When needed, data security can be achieved by using IP security
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mechanisms such as IPsec [10] or TLS [9].
In order to maximize inter-operability of ENRP servers, the following
rules MUST be followed:
1. At the startup time, a new ENRP server SHOULD make a decision on
whether it will enable IP multicast for ENRP announcements. This
decision should be based on factors such as the availability of
IP multicast and the security requirements from the user of
Rserpool.
2. If an ENRP server disables multicast, it then:
A. MUST NOT subscribe to the well-known server multicast
channel, i.e., it only receives peer announcements over SCTP
associations, and
B. MUST transmit all its out-going announcements over point-to-
point SCTP associations with its peers.
3. If an ENRP server enables itself to use multicast, it then:
A. MUST subscribe to the well-known server multicast channel to
ready itself for receiving peers' multicast announcements,
B. MUST also be prepared to receive peer announcements over
point-to-point SCTP associations from peers.
C. MUST track internally which peers are multicast-enabled and
which are not. Note: A peer is always assumed to be
multicast-disabled until/unless an ENRP message of any type
is received from that peer over the well-known server
multicast channel.
D. when sending out an announcement, MUST send a copy to the
well-known server multicast channel AND a copy to each of the
peers that are marked as multicast-disabled over a point-to-
point SCTP association.
3.2. ENRP Server Initialization
This section describes the steps a new ENRP server needs to take in
order to join the other existing ENRP servers, or to initiate the
handlespace service if it is the first ENRP server started in the
operational scope.
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3.2.1. Generate a Server Identifier
A new ENRP server MUST generate a non-zero, 32-bit server Id that is
as unique as possible in the operational scope and this server Id
MUST remain unchanged for the lifetime of the server. Normally, a
good 32-bit random number will be good enough as the server Id ([13]
provides some information on randomness guidelines).
Note, there is a very remote chance (about 1 in 4 billion) that two
ENRP servers in an operational scope will generate the same server Id
and hence cause a server Id conflict in the pool. However, no severe
consequence of such a conflict has been identified.
3.2.2. Acquire Peer Server List
At startup, the ENRP server (initiating server) will first attempt to
learn all existing peer ENRP servers in the same operational scope,
or to determine that it is along in the scope.
The initiating server uses an existing peer server to bootstrap
itself into service. We call this peer server the mentor server.
3.2.2.1. Find the mentor server
If the initiating server is told about an existing peer server
through some administrative means (such as DNS query, configuration
database, startup scripts, etc), the initiating server SHOULD then
use this peer server as its mentor server and SHOULD skip the
remaining steps in this subsection.
If multiple existing peer servers are specified, the initiating
server SHOULD pick one of them as its mentor peer server, keep the
others as its backup mentor peers, and skip the remaining steps in
this subsection.
If no existing peer server is specified to the initiating server AND
if multicast is available in the operational scope, the following
mentor peer discovery procedures SHOULD be followed:
1. The initiating server SHOULD first join the well-known ENRP
server multicast channel.
2. Then the initiating server SHOULD send an ENRP_PRESENCE message,
with the 'Reply_required' flag set, over the multicast channel.
Upon the reception of this ENRP_PRESENCE message, a peer server
MUST send an ENRP_PRESENCE, without the 'Reply_required' flag,
back to the initiating server.
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3. When the first response to its original ENRP_PRESENCE arrives,
the initiating server SHOULD take the sender of this received
response as its mentor peer server. This completes the discovery
of the mentor peer server.
If responses are also received from other peers (a likely event
when multiple peers exist in the operational scope at the time
the new server started), the initiating server SHOULD keep a list
of those responded as its backup mentor peers (see below).
4. If no response to its ENRP_PRESENCE message are received after
TIMEOUT-SERVER-HUNT seconds, the initiating server SHOULD repeat
steps 2) and 3) for up to MAX-NUMBER-SERVER-HUNT times. After
that, if there is still no response, the initiating server MUST
assume that it is alone in the operational scope.
5. If the initiating server determined that it is alone in the
scope, it MUST skip the procedures in Section 3.2.2.2 and
Section 3.2.3 and MUST consider its initialization completed and
start offering ENRP services.
Note, if multicast is not available (or not allowed for reasons such
as security concerns) in the operational scope, at least one peer
server MUST be specified to the initiating server through
administrative means, unless the initiation server is the first
server to start in the operational scope.
Note, if the administratively specified mentor peer(s) fails, the
initiating server SHOULD use the auto-discover procedure defined in
steps 1-5 above.
3.2.2.2. Request complete server list from mentor peer
Once the initiating server finds its mentor peer server (by either
discovery or administrative means), the initiating server MUST send
an ENRP_LIST_REQUEST message to the mentor peer server to request a
copy of the complete server list maintained by the mentor peer (see
Section 3.9 for maintaining server list).
The initiating server SHOULD start a timer every time it finishes
sending an ENRP_LIST_REQUEST message. If the timer expires before
receiving a response from the mentor peer, the initiating server
SHOULD abort and send a new server list request to a backup mentor
peer, if one is available.
Upon the reception of this request, the mentor peer server SHOULD
reply with an ENRP_LIST_RESPONSE message and include in the message
body all existing ENRP servers known by the mentor peer.
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Upon the reception of the ENRP_LIST_RESPONSE message from the mentor
peer, the initiating server MUST use the server information carried
in the message to initialize its own peer list.
However, if the mentor itself is in the process of startup and not
ready to provide a peer server list (for example, the mentor peer is
waiting for a response to its own ENRP_LIST_REQUEST to another
server), it MUST reject the request by the initiating server and
respond with an ENRP_LIST_RESPONSE message with the R flag set to
'1', and with no server information included in the response.
In the case where its ENRP_LIST_REQUEST is rejected by the mentor
peer, the initiating server SHOULD either wait for a few seconds and
re-send the ENRP_LIST_REQUEST to the mentor server, or if there is a
backup mentor peer available, select another mentor peer server and
send the ENRP_LIST_REQUEST to the new mentor server.
3.2.3. Download ENRP Handlespace Data from Mentor Peer
After a peer list download is completed, the initiating server MUST
request a copy of the current handlespace data from its mentor peer
server, by taking the following steps:
1. The initiating server MUST first send a ENRP_HANDLE_TABLE_REQUEST
message to the mentor peer, with W flag set to '0', indicating
that the entire handlespace is requested.
2. Upon the reception of this message, the mentor peer MUST start a
download session in which a copy of the current handlespace data
maintained by the mentor peer is sent to the initiating server in
one or more ENRP_HANDLE_TABLE_RESPONSE messages (Note, the mentor
server may find it particularly desirable to use multiple
ENRP_HANDLE_TABLE_RESPONSE messages to send the handlespace when
the handlespace is large, especially when forming and sending out
a single response containing a large handlespace may interrupt
its other services).
If more than one ENRP_HANDLE_TABLE_RESPONSE message are used
during the download, the mentor peer MUST use the M flag in each
ENRP_HANDLE_TABLE_RESPONSE message to indicate whether this
message is the last one for the download session. In particular,
the mentor peer MUST set the M flag to '1' in the outbound
ENRP_HANDLE_TABLE_RESPONSE if there is more data to be
transferred and MUST keep track of the progress of the current
download session. The mentor peer MUST set the M flag to '0' in
the last ENRP_HANDLE_TABLE_RESPONSE for the download session and
close the download session (i.e., removing any internal record of
the session) after sending out the last message.
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3. During the downloading, every time the initiating server receives
an ENRP_HANDLE_TABLE_RESPONSE message, it MUST transfer the data
entries carried in the message into its local handlespace
database, and then check whether or not this message is the last
one for the download session.
If the M flag is set to '1' in the just processed
ENRP_HANDLE_TABLE_RESPONSE message, the initiating server MUST
send another ENRP_HANDLE_TABLE_REQUEST message to the mentor peer
to request for the next ENRP_HANDLE_TABLE_RESPONSE message.
4. When unpacking the data entries from a ENRP_HANDLE_TABLE_RESPONSE
message into its local handlespace database, the initiating
server MUST handle each pool entry carried in the message using
the following rules:
A. If the pool does not exist in the local handlespace, the
initiating server MUST creates the pool in the local
handlespace and add the PE(s) in the pool entry to the pool.
When creating the pool, the initiation server MUST set the
overall member selection policy type of the pool to the
policy type indicated in the first PE.
B. If the pool already exists in the local handlespace, but the
PE(s) in the pool entry is not currently a member of the
pool, the initiating server MUST add the PE(s) to the pool.
C. If the pool already exists in the local handlespace AND the
PE(s) in the Pool entry is already a member of the pool, the
initiating server SHOULD replace the attributes of the
existing PE(s) with the new information.
5. When the last ENRP_HANDLE_TABLE_RESPONSE message is received from
the mentor peer and unpacked into the local handlespace, the
initialization process is completed and the initiating server
SHOULD start to provide ENRP services.
Under certain circumstances, the mentor peer itself may not be able
to provide a handlespace download to the initiating server. For
example, the mentor peer is in the middle of initializing its own
handlespace database, or it has currently too many download sessions
open to other servers.
In such a case, the mentor peer MUST reject the request by the
initiating server and respond with an ENRP_HANDLE_TABLE_RESPONSE
message with the R flag set to '1', and with no pool entries included
in the response.
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In the case where its ENRP_HANDLE_TABLE_REQUEST is rejected by the
mentor peer, the initiating server SHOULD either wait for a few
seconds and re-send the ENRP_HANDLE_TABLE_REQUEST to the mentor
server, or if there is a backup mentor peer available, select another
mentor peer server and send the ENRP_HANDLE_TABLE_REQUEST to the new
mentor server.
A started handlespace download session may get interrupted for some
reason. To cope with this, the initiating server SHOULD start a
timer every time it finishes sending an ENRP_HANDLE_TABLE_REQUEST to
its mentor peer. If this timer expires without receiving a response
from the mentor peer, the initiating server SHOULD abort the current
download session and re-start a new handlespace download with a
backup mentor peer, if one is available.
Similarly, after sending out an ENRP_HANDLE_TABLE_RESPONSE, if the
mentor peer has still more data to send, it SHOULD start a session
timer. If this timer expires without receiving another request from
the initiating server, the mentor peer SHOULD abort the session,
cleaning out any resource and record of the session.
3.3. Handle PE Registration
To register itself with the handlespace, a PE sends an
ASAP_REGISTRATION message to its home ENRP server. The format of
ASAP_REGISTRATION message and rules of sending it are defined in [1].
In the ASAP_REGISTRATION message, the PE indicates the handle of the
pool it wishes to join in a pool handle parameter, and its complete
transport information and any load control information in a PE
parameter.
The ENRP server handles the ASAP_REGISTRATION message according to
the following rules:
1. If the named pool does not exist in the handlespace, the ENRP
server MUST creates a new pool with that handle in the
handlespace and add the PE to the pool as its first PE;
When a new pool is created, the overall member selection policy
of the pool MUST be set to the policy type indicated by the first
PE, the overall pool transport type MUST be set to the transport
type indicated by the PE, and the overall pool data/control
channel configuration MUST be set to what is indicated in the
Transport Use field of the User Transport parameter by the
registering PE.
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2. If the named pool already exists in the handlespace, but the
requesting PE is not currently a member of the pool, the ENRP
server will add the PE as a new member to the pool;
However, before adding the PE to the pool, the server MUST check
if the policy type, transport type, and transport usage indicated
by the registering PE is consistent with those of the pool. If
different, the ENRP server MUST reject the registration.
3. If the named pool already exists in the handlespace AND the
requesting PE is already a member of the pool, the ENRP server
SHOULD consider this as a re-registration case. The ENRP server
MUST perform the same tests on policy, transport type, transport
use, as described above. If the re-registration is accepted
after the test, the ENRP Server SHOULD replace the attributes of
the existing PE with the information carried in the received
ASAP_REGISTRATION message.
4. After accepting the registration, the ENRP server MUST assign
itself the owner of this PE. If this is a re-registration, the
ENRP server MUST take over ownership of this PE regardless of
whether the PE was previously owned by this server or by another
server. The ENRP server MUST also record the SCTP transport
address from which it received the ASAP_REGISTRATION in the ASAP
Transport parameter TLV inside the PE parameter of this PE.
5. The ENRP server may reject the registration due to other reasons
such as invalid values, lack of resource, authentication failure,
etc.
In all above cases, the ENRP server MUST reply to the requesting PE
with an ASAP_REGISTRATION_RESPONSE message. If the registration is
accepted, the ENRP server MUST set the 'R' flag in the
ASAP_REGISTRATION_RESPONSE to '0'. If the registration is rejected,
the ENRP server MUST indicate the rejection by setting the 'R' flag
in the ASAP_REGISTRATION_RESPONSE to '1'.
If the registration is rejected, the ENRP server SHOULD include the
proper error cause(s) in the ASAP_REGISTRATION_RESPONSE message.
If the registration is granted (either a new registration or a re-
registration case), the ENRP server MUST assign itself to be the home
ENRP server of the PE, i.e., to "own" the PE.
Implementation note: for better performance, the ENRP server may
find it both efficient and convenient to internally maintain two
separate PE lists or tables - one is for the PEs that are "owned"
by the ENRP server and the other for all the PEs owned by its
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peer(s).
Moreover, if the registration is granted, the ENRP server MUST take
the handlespace update action as described in Section 3.6 to inform
its peers about the change just made. If the registration is denied,
no message will be sent to its peers.
3.3.1. Rules on PE Re-registration
A PE may re-register itself to the handlespace with a new set of
attributes in order to, for example, extend its registration life,
change its load factor value, etc.
A PE may modify its load factor value at any time via re-
registration. Based on the number of PEs in the pool and the pool's
overall policy type, this operation allows the PE to dynamically
control its share of inbound messages received by the pool (also see
Section ???? in [1] for more on load control).
Moreover, when re-registering, the PE MUST NOT change its policy
type. The server MUST reject the re-registration if the PE attempt
to change its policy type. In the rejection, the server SHOULD
attach an error code "Pooling Policy Inconsistent".
Regardless whether it is the current owner of the PE, if the re-
registration is granted to the PE, the ENRP server MUST assign itself
to be the new home ENRP server of the PE.
Moreover, if the re-registration is granted, the ENRP server MUST
take the handlespace update action as described in Section 3.6 to
inform its peers about the change just made. If the re-registration
is denied, no message will be sent to its peers.
3.4. Handle PE De-registration
To remove itself from a pool, a PE sends an ASAP_DEREGISTRATION
message to its home ENRP server. The complete format of
ASAP_DEREGISTRATION message and rules of sending it are defined in
[1].
In the ASAP_DEREGISTRATION message the PE indicates the handle of the
pool it belongs to in a pool handle parameter and provides its PE
identifier.
Upon receiving the message, the ENRP server SHALL remove the PE from
its handlespace. Moreover, if the PE is the last one of the named
pool, the ENRP server will remove the pool from the handlespace as
well.
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If the ENRP server fails to find any record of the PE in its
handlespace, it SHOULD consider the de-registration granted and
completed, and send an ASAP_DEREGISTRATION_RESPONSE message to the
PE.
The ENRP server may reject the de-registration request for various
reasons, such as invalid parameters, authentication failure, etc.
In response, the ENRP server MUST send an
ASAP_DEREGISTRATION_RESPONSE message to the PE. If the de-
registration is rejected, the ENRP server MUST indicate the rejection
by including the proper Operational Error parameter.
It should be noted that de-registration does not stop the PE from
sending or receiving application messages.
Once the de-registration request is granted AND the PE removed from
its local copy of the handlespace, the ENRP server MUST take the
handlespace update action described in Section 3.6 to inform its
peers about the change just made. Otherwise, NO message SHALL be
send to its peers.
3.5. Pool Handle Translation
A PU uses the pool handle translation service of an ENRP server to
resolve a pool handle to a list of accessible transport addresses of
the member PEs of the pool.
This requires the PU to send an ASAP_HANDLE_RESOLUTION message to its
home ENRP server and in the ASAP_HANDLE_RESOLUTION message specify
the pool handle to be translated in a Pool Handle parameter.
Complete definition of the ASAP_HANDLE_RESOLUTION message and the
rules of sending it are defined in [1].
An ENRP server SHOULD be prepared to receive ASAP_HANDLE_RESOLUTION
requests from PUs either over an SCTP association on the well-know
SCTP port, or over a TCP connection on the well-know TCP port.
Upon reception of the ASAP_HANDLE_RESOLUTION message, the ENRP server
MUST first look up the pool handle in its handlespace. If the pool
exits, the home ENRP server MUST compose and send back an
ASAP_HANDLE_RESOLUTION_RESPONSE message to the requesting PU.
In the response message, the ENRP server SHOULD list all the PEs
currently registered in this pool, in a list of PE parameters. The
ENRP server MUST also include a pool member selection policy
parameter to indicate the overall member selection policy for the
pool, if the current pool member selection policy is not round-robin
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(if the overall policy is round-Robin, this parameter MAY be
omitted?).
If the named pool does not exist in the handlespace, the ENRP server
MUST reject the handle resolution request by responding with an
ASAP_HANDLE_RESOLUTION_RESPONSE message carrying a Unknown Poor
Handle error.
The complete format of ASAP_HANDLE_RESOLUTION_RESPONSE message and
the rules of receiving it are defined in [1].
3.6. Server Handlespace Update
This includes a set of update operations used by an ENRP server to
inform its peers when its local handlespace is modified, e.g.,
addition of a new PE, removal of an existing PE, change of pool or PE
properties.
3.6.1. Announcing Addition or Update of PE
When a new PE is granted registration to the handlespace or an
existing PE is granted a re-registration, the home ENRP server uses
this procedure to inform all its peers.
This is an ENRP announcement and is sent to all the peer of the home
ENRP server. See Section 3.1 on how announcements are sent.
An ENRP server MUST announce this update to all its peers in a
ENRP_HANDLE_UPDATE message with the Update Action field set to
ADD_PE, indicating the addition of a new PE or the modification of an
existing PE. The complete new information of the PE and the pool its
belongs to MUST be indicated in the message with a PE parameter and a
Pool Handle parameter, respectively.
The home ENRP server SHOULD fill in its server Id in the Sender
Server's ID field and leave the Receiver Server's ID blank (i.e., all
0's).
When a peer receives this ENRP_HANDLE_UPDATE message, it MUST take
the following actions:
1. If the named pool indicated by the pool handle does not exist in
its local copy of the handlespace, the peer MUST create the named
pool in its local handlespace and add the PE to the pool as the
first PE. It MUST then copy in all other attributes of the PE
carried in the message.
When the new pool is created, the overall member selection policy
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of the pool MUST be set to the policy type indicated by the PE.
2. If the named pool already exists in the peer's local copy of the
handlespace AND the PE does not exist, the peer MUST add the PE
to the pool as a new PE and copy in all attributes of the PE
carried in the message.
3. If the named pool exists AND the PE is already a member of the
pool, the peer MUST replace the attributes of the PE with the new
information carried in the message.
3.6.2. Announcing Removal of PE
When an existing PE is granted de-registration or is removed from its
handlespace for some other reasons (e.g., purging an unreachable PE,
see Section 3.7), the ENRP server MUST uses this procedure to inform
all its peers about the change just made.
This is an ENRP announcement and is sent to all the peer of the home
ENRP server. See Section 3.1 on how announcements are sent.
An ENRP server MUST announce the PE removal to all its peers in an
ENRP_HANDLE_UPDATE message with the Update Action field set to
DEL_PE, indicating the removal of an existing PE. The complete
information of the PE and the pool its belongs to MUST be indicated
in the message with a PE parameter and a Pool Handle parameter,
respectively.
[editor's note: only the pool handle and the PE's id are needed, it
should reduce the size of the message]
The sending server MUST fill in its server ID in the Sender Server's
ID field and leave the Receiver Server's ID blank (i.e., set to all
0's).
When a peer receives this ENRP_HANDLE_UPDATE message, it MUST first
find pool and the PE in its own handlespace, and then remove the PE
from its local handlespace. If the removed PE is the last one in the
pool, the peer MUST also delete the pool from its local handlespace.
If the peer fails to find the PE or the pool in its handlespace, it
SHOULD take no further actions.
3.7. Detecting and Removing Unreachable PE
Whenever a PU finds a PE unreachable (e.g., via an SCTP SEND.FAILURE
Notification, see section 10.2 of [8]), the PU SHOULD send an
ASAP_ENDPOINT_UNREACHABLE message to its home ENRP server. The
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message SHOULD contain the pool handle and the PE Id of the
unreachable PE.
Upon the reception of an ASAP_ENDPOINT_UNREACHABLE message, a server
MUST immediately send a point-to-point ASAP_ENDPOINT_KEEP_ALIVE
message to the PE in question (the 'H' flag in the message SHOULD be
set to '0' in this case). If this ASAP_ENDPOINT_KEEP_ALIVE fails
(e.g., it results in an SCTP SEND.FAILURE notification), the ENRP
server MUST consider the PE as truly unreachable and MUST remove the
PE from its handlespace and take actions described in Section 3.6.2.
If the ASAP_ENDPOINT_KEEP_ALIVE message is transmitted successfully
to the PE, the ENRP server MUST retain the PE in its handlespace.
Moreover, the server SHOULD keep a counter to record how many
ASAP_ENDPOINT_UNREACHABLE messages it has received reporting
reachability problem relating to this PE. If the counter exceeds the
protocol threshold MAX-BAD-PE-REPORT, the ENRP server SHOULD remove
the PE from its handlespace and take actions described in
Section 3.6.2.
Optionally, an ENRP server may also periodically send point-to-point
ASAP_ENDPOINT_KEEP_ALIVE (with 'H' flag set to '0') messages to each
of the PEs owned by the ENRP server in order to check their
reachability status. If the send of ASAP_ENDPOINT_KEEP_ALIVE to a PE
fails, the ENRP server MUST consider the PE as unreachable and MUST
remove the PE from its handlespace and take actions described in
Section 3.6.2. Note, if an ENRP server owns a large number of PEs,
the implementation should pay attention not to flood the network with
bursts of ASAP_ENDPOINT_KEEP_ALIVE messages. Instead, the
implementation should try to smooth out the ASAP_ENDPOINT_KEEP_ALIVE
message traffic over time.
The complete definition and rules of sending
ASAP_ENDPOINT_UNREACHABLE and receiving ASAP_ENDPOINT_KEEP_ALIVE
messages are described in [1].
3.8. Helping PE and PU to Discover Home ENRP Server
At its startup time, or whenever its current home ENRP server is not
providing services, a PE or PU will attempt to find a new home
server. For this reason, the PE or PU will need to maintain a list
of currently available ENRP servers in its scope.
To help the PE or PU maintaining this list, an ENRP server, if it is
enabled for multicast, SHOULD periodically send out an
ASAP_SERVER_ANNOUNCE message every SERVER-ANNOUNCE-CYCLE seconds to
the well-known ASAP multicast channel. And in the
ASAP_SERVER_ANNOUNCE message the ENRP server SHOULD include all the
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transport addresses available for ASAP communications. If the ENRP
server only supports SCTP for ASAP communications, the transport
information MAY be omitted in the ASAP_SERVER_ANNOUNCE message.
For the complete procedure of this, see Section 3.6?? in [1].
3.9. Maintaining Peer List and Monitoring Peer Status
An ENRP server MUST keep an internal record on the status of each of
its known peers. This record is referred to as the server's "peer
list"
3.9.1. Discovering New Peer
If a message of any type is received from a previously unknown peer,
the ENRP server MUST consider this peer a new peer in the operational
scope and add it to the peer list.
The ENRP server MUST send an ENRP_PRESENCE message with the Reply-
required flag set to '1' to the source address found in the arrived
message. This will force the new peer to reply with its own
ENRP_PRESENCE containing its full server information (see
Section 2.1).
[editor's note: should we ask for a peer list from the new peer? this
may help mending two split networks.]
3.9.2. Server Sending Heartbeat
Every PEER-HEARTBEAT-CYCLE seconds, an ENRP server MUST announce its
continued presence to all its peer with a ENRP_PRESENCE message. In
the ENRP_PRESENCE message, the ENRP server MUST set the
'Replay_required' flag to '0', indicating that no response is
required.
The arrival of this periodic ENRP_PRESENCE message will cause all its
peers to update their internal variable "peer.last.heard" for the
sending server (see Section 3.9.3 for more details).
3.9.3. Detecting Peer Server Failure
An ENRP server MUST keep an internal variable "peer.last.heard" for
each of its known peers and the value of this variable MUST be
updated to the current local time every time a message of any type
(point-to-point or announcement) is received from the corresponding
peer.
If a peer has not been heard for more than MAX-TIME-LAST-HEARD
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seconds, the ENRP server MUST immediately send a point-to-point
ENRP_PRESENCE with 'Reply_request' flag set to '1' to that peer.
If the send fails or the peer does not reply after MAX-TIME-NO-
RESPONSE seconds, the ENRP server MUST consider the peer server dead
and SHOULD initiate the takeover procedure defined in Section 3.10.
3.10. Taking-over a Failed Peer Server
In the following descriptions, We call the ENRP server that detects
the failed peer server and initiates the take-over the "initiating
server" and the failed peer server the "target server."
3.10.1. Initiate Server Take-over Arbitration
The initiating server SHOULD first start a take-over arbitration
process by announcing an ENRP_INIT_TAKEOVER message to all its peer
servers. See Section 3.1 on how announcements are sent. In the
message, the initiating server MUST fill in the Sender Server's ID
and Target Server's ID.
After announcing the ENRP_INIT_TAKEOVER message, the initiating
server SHOULD wait for an ENRP_INIT_TAKEOVER_ACK message from _each_
of its known peers, except of the target server. [editor's note: how
long should it wait?]
Each of the peer servers that receives the ENRP_INIT_TAKEOVER message
from the initiating server SHOULD take the following actions:
1. If the peer server finds that itself is the target server
indicated in the ENRP_INIT_TAKEOVER message, it MUST immediately
announce an ENRP_PRESENCE message to all its peer ENRP servers in
an attempt to stop this take-over process. This indicates a
false failure detection case by the initiating server.
2. If the peer server finds that itself has already started its own
take-over arbitration process on the same target server, it MUST
perform the following arbitration:
A. if the peer's server ID is smaller in value than the Sender
Server's ID in the arrived ENRP_INIT_TAKEOVER message, the
peer server SHOULD immediately abort its own take-over
attempt. Moreover, the peer SHOULD mark the target server as
"not active" on its internal peer list so that its status
will no longer be monitored by the peer, and reply the
initiating server with an ENRP_INIT_TAKEOVER_ACK message.
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B. Otherwise, the peer MUST ignore the ENRP_INIT_TAKEOVER
message and take no action.
3. If the peer finds that it is neither the target server nor is in
its own take-over process, the peer SHOULD: a) mark the target
server as "not active" on its internal peer list so that its
status will no longer be monitored by this peer, and b) reply to
the initiating server with an ENRP_INIT_TAKEOVER_ACK message.
Once the initiating server has received ENRP_INIT_TAKEOVER_ACK
message from _all_ of its currently known peers (except for the
target server), it SHOULD consider that it has won the arbitration
and SHOULD proceed to complete the take-over, following the steps
described in Section 3.10.2.
However, if it receives an ENRP_PRESENCE from the target server at
any point in the arbitration process, the initiating server SHOULD
immediately abort the take-over process and mark the status of the
target server as "active".
3.10.2. Take-over Target Peer Server
The initiating ENRP server SHOULD first send, via an announcement, a
ENRP_TAKEOVER_SERVER message to inform all its active peers that the
take-over is enforced. The target server's ID MUST be filled in the
message. The initiating server SHOULD then remove the target server
from its internal peer list.
Then it SHOULD examine its local copy of the handlespace and claim
ownership of each of the PEs originally owned by the target server,
by following these steps:
1. mark itself as the home ENRP server of each of the PEs originally
owned by the target server;
2. send a point-to-point ASAP_ENDPOINT_KEEP_ALIVE message, with the
'H' flag set to '1', to each of the PEs. This will trigger the
PE to adopt the initiating sever as its new home ENRP server;
When a peer receives the ENRP_TAKEOVER_SERVER message from the
initiating server, it SHOULD update its local peer list and PE cache
by following these steps:
1. remove the target server from its internal peer list;
2. update the home ENRP server of each PE in its local copy of the
handlespace to be the sender of the message, i.e., the initiating
server.
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3.11. Handlespace Data Auditing and Re-synchronization
Message losses or certain temporary breaks in network connectivity
may result in data inconsistency in the local handlespace copy of
some of the ENRP servers in an operational scope. Therefore, each
ENRP server in the operational scope SHOULD periodically verify that
its local copy of handlespace data is still in sync with that of its
peers.
This section defines the auditing and re-synchronization procedures
for an ENRP server to maintain its handlespace data consistency.
3.11.1. Auditing Procedures
The auditing of handlespace consistency is based on the following
procedures:
1. An ENRP server SHOULD keep a separate PE checksum (a 32-bit
integer internal variable) for each of its known peers and for
itself. For an ENRP server with 'k' known peers, we denote these
internal variables as "pe.checksum.pr0", "pe.checksum.pr1", ...,
"pe.checksum.prk", where "pe.checksum.pr0" is the server's own PE
checksum. The definition and detailed algorithm for calculating
these PE checksum variables are given in Section 3.11.2.
2. Each time an ENRP server sends out an ENRP_PRESENCE, it SHOULD
include in the message its current PE checksum (i.e.,
"pe.checksum.pr0").
3. When an ENRP server (server A) receives a PE checksum (carried in
an arrived ENRP_PRESENCE) from a peer ENRP server (server B),
server A SHOULD compare the PE checksum found in the
ENRP_PRESENCE with its own internal PE checksum of server B
(i.e., "pe.checksum.prB").
4. If the two values match, server A will consider that there is no
handlespace inconsistency between itself and server B and should
take no further actions.
5. If the two values do NOT match, server A SHOULD consider that
there is a handlespace inconsistency between itself and server B
and a re-synchronization process SHOULD be carried out
immediately with server B (see Section 3.11.3).
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3.11.2. PE Checksum Calculation Algorithm
When an ENRP server (server A) calculate an internal PE checksum for
a peer (server B), it MUST use the following algorithm.
Let us assume that in server A's internal handlespace there are
currently 'M' PEs that are owned by server B. Each of the 'M' PEs
will then contribute to the checksum calculation with the following
byte block:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Pool handle string of the pool the PE belongs (padded with :
: zeros to next 32-bit word boundary if needed) :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PE Id (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Note, these are not TLVs. This byte block gives each PE a unique
byte pattern in the scope. The 16-bit PE checksum for server B
"pe.checksum.prB" is then calculated over the byte blocks contributed
by the 'M' PEs one by one. The PE checksum calculation MUST use the
Internet algorithm described in [4].
Server A MUST calculate its own PE checksum (i.e., "pe.checksum.pr0")
in the same fashion, using the byte blocks of all the PEs owned by
itself.
Note, whenever an ENRP finds that its internal handlespace has
changed (e.g., due to PE registration/deregistration, receiving peer
updates, removing failed PEs, downloading handlespace pieces from a
peer, etc.), it MUST immediately update all its internal PE checksums
that are affected by the change.
Implementation Note: when the internal handlespace changes (e.g., a
new PE added or an existing PE removed), an implementation needs not
to re-calculate the affected PE checksum; it should instead simply
update the checksum by adding or subtracting the byte block of the
corresponding PE from the previous checksum value.
3.11.3. Re-synchronization Procedures
Once an ENRP server determines that there is inconsistency between
its local handlespace data and a peer's handlespace data with
regarding to the PEs owned by that peer, it SHOULD perform the
following steps to re-synchronize the data:
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1. The ENRP server SHOULD first "mark" every PE it knows about that
is owned by the peer in its local handlespace database;
2. The ENRP server SHOULD then send an ENRP_HANDLE_TABLE_REQUEST
message with W flag set to '1' to the peer to request a complete
list of PEs owned by the peer;
3. Upon reception of the ENRP_HANDLE_TABLE_REQUEST message with W
flag set to '1', the peer server SHOULD immediately respond with
an ENRP_HANDLE_TABLE_RESPONSE message listing all PEs currently
owned by the peer.
4. Upon reception of the ENRP_HANDLE_TABLE_RESPONSE message, the
ENRP server SHOULD transfer the PE entries carried in the message
into its local handlespace database. If an PE entry being
transferred already exists in its local database, the ENRP server
MUST replace the entry with the copy found in the message and
remove the "mark" from the entry.
5. After transferring all the PE entries from the received
ENRP_HANDLE_TABLE_RESPONSE message into its local database, the
ENRP server SHOULD check whether there are still PE entries that
remain "marked" in its local handlespace. If so, the ENRP server
SHOULD silently remove those "marked" entries.
Note, similar to what is described in Section 3.2.3, the peer may
reject the ENRP_HANDLE_TABLE_REQUEST or use more than one
ENRP_HANDLE_TABLE_RESPONSE message to respond.
3.12. Handling Unrecognized Message or Unrecognized Parameter
When an ENRP server receives an ENRP message with an unknown message
type or a message of known type that contains an unknown parameter,
it SHOULD handle the unknown message or the unknown parameter
according to the unrecognized message and parameter handling rules
defined in Sections 3 and 4 in [11].
According to the rules, if an error report to the message sender is
needed, the ENRP server that discovered the error SHOULD send back an
ENRP_ERROR message with proper error cause code.
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4. Variables and Thresholds
4.1. Variables
peer.last.heard - the local time that a peer server was last heard
(via receiving either a multicast or point-to-point message from
the peer).
pe.checksum.pr - the internal 32-bit PE checksum that an ENRP server
keeps for a peer. A separate PE checksum is kept for each of its
known peers as well as for itself.
4.2. Thresholds
MAX-NUMBER-SERVER-HUNT - the maximal number of attempts a sender
will make to contact an ENRP server (Default=3 times).
TIMEOUT-SERVER-HUNT - pre-set threshold for how long a sender will
wait for a response from an ENRP server (Default=5 seconds).
PEER-HEARTBEAT-CYCLE - the period for an ENRP server to announce a
heartbeat message to all its known peers. (Default=30 secs.)
SERVER-ANNOUNCE-CYCLE - the period for an ENRP server to announce a
SERVER_ANNOUNCE message to all PEs and PUs. (Default=5 secs.)
MAX-TIME-LAST-HEARD - pre-set threshold for how long an ENRP server
will wait before considering a silent peer server potentially
dead. (Default=61 secs.)
MAX-TIME-NO-RESPONSE - pre-set threshold for how long a message
sender will wait for a response after sending out a message.
(Default=5 secs.)
MAX-BAD-PE-REPORT - the maximal number of unreachability reports on
a PE that an ENRP server will allow before purging this PE from
the handlespace. (Default=3)
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5. Security Considerations
Threats Introduced by Rserpool and Requirements for Security in
Response to Threats [12] describes the threats to the Rserpool
architecture in detail and lists the security requirements in
response to each threat. From the threats described in this
document, the security services required for the Rserpool protocol
are enumerated below.
Threat 1) PE registration/deregistration flooding or spoofing
-----------
Security mechanism in response: ENRP server authenticates the PE
Threat 2) PE registers with a malicious ENRP server
-----------
Security mechanism in response: PE authenticates the ENRP server
Threat 1 and 2 taken together results in mutual authentication of the
ENRP server and the PE.
Threat 3) Malicious ENRP server joins the ENRP server pool
-----------
Security mechanism in response: ENRP servers mutually authenticate
Threat 4) A PU communicates with a malicious ENRP server for handle
resolution
-----------
Security mechanism in response: The PU authenticates the ENRP server
Threat 5) Replay attack
-----------
Security mechanism in response: Security protocol which has
protection from replay attacks
Threat 6) Corrupted data which causes a PU to have misinformation
concerning a pool handle resolution
-----------
Security mechanism in response: Security protocol which supports
integrity protection
Threat 7) Eavesdropper snooping on handlespace information
-----------
Security mechanism in response: Security protocol which supports data
confidentiality
Threat 8) Flood of ASAP_ENDPOINT_UNREACHABLE messages from the PU to
ENRP server
-----------
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Security mechanism in response: ASAP must control the number of
endpoint unreachable messages transmitted from the PU to the ENRP
server.
Threat 9) Flood of Endpoint_KeepAlive messages to the PE from the
ENRP server
-----------
Security mechanism in response: ENRP server must control the number
of Endpoint_KeepAlive messages to the PE
To summarize the threats 1-7 require security mechanisms which
support authentication, integrity, data confidentiality, protection
from replay attacks.
For Rserpool we need to authenticate the following:
PU <---- ENRP Server (PU authenticates the ENRP server)
PE <----> ENRP Server (mutual authentication)
ENRP server <-----> ENRP Server (mutual authentication)
We do not define any new security mechanisms specifically for
responding to threats 1-7. Rather we use existing IETF security
protocols to provide the security services required. TLS supports
all these requirements and MUST be implemented. The
TLS_RSA_WITH_AES_128_CBC_SHA ciphersuite MUST be supported at a
minimum by implementers of TLS for Rserpool. For purposes of
backwards compatibility, ENRP SHOULD support
TLS_RSA_WITH_3DES_EDE_CBC_SHA. Implementers MAY also support any
other ciphersuite.
Threat 8 requires the ASAP protocol to limit the number of
ASAP_ENDPOINT_UNREACHABLE messages (see Section 3.5??? in [1]) to the
ENRP server.
Threat 9 requires the ENRP protocol to limit the number of
Endpoint_KeepAlive messages to the PE (see Section x.y???).
5.1. Implementing Security Mechanisms
ENRP servers, PEs, PUs MUST implement TLS. ENRP servers and PEs must
support mutual authentication. ENRP servers must support mutual
authentication among themselves. PUs MUST authenticate ENRP servers.
ENRP servers and PEs SHOULD possess a site certificate whose subject
corresponds to their canonical hostname. PUs MAY have certificates
of their own for mutual authentication with TLS, but no provisions
are set forth in this document for their use. All Rserpool elements
that support TLS MUST have a mechanism for validating certificates
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received during TLS negotiation; this entails possession of one or
more root certificates issued by certificate authorities (preferably
well-known distributors of site certificates comparable to those that
issue root certificates for web browsers).
Implementations MUST support TLS with SCTP as described in RFC3436
[9] or TLS over TCP as described in RFC2246 [7]. When using TLS/SCTP
we must ensure that RSerPool does not use any features of SCTP that
are not available to an TLS/SCTP user. This is not a difficult
technical problem, but simply a requirement. When describing an API
of the RSerPool lower layer we have also to take into account the
differences between TLS and SCTP.
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6. Acknowledgements
The authors wish to thank John Loughney, Lyndon Ong, Walter Johnson,
Thomas Dreibholz, and many others for their invaluable comments and
feedback.
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7. References
7.1. Normative References
[1] Stewart, R., Xie, Q., Stillman, M., and M. Tuexen, "Aggregate
Server Access Protocol (ASAP)", draft-ietf-rserpool-asap-12
(work in progress), July 2005.
[2] Tuexen, M., Xie, Q., Stewart, R., Shore, M., Ong, L., Loughney,
J., and M. Stillman, "Requirements for Reliable Server
Pooling", RFC 3237, January 2002.
[3] Tuexen, M., Xie, Q., Stewart, R., Shore, M., Loughney, J., and
A. Silverton, "Architecture for Reliable Server Pooling",
draft-ietf-rserpool-arch-10 (work in progress), July 2005.
[4] Braden, R., Borman, D., and C. Partridge, "Computing the
Internet Checksum", RFC 1071, September 1988.
[5] Bradner, S., "The Internet Standards Process -- Revision 3",
BCP 9, RFC 2026, October 1996.
[6] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[7] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
RFC 2246, January 1999.
[8] Stewart, R., Xie, Q., Morneault, K., Sharp, C., Schwarzbauer,
H., Taylor, T., Rytina, I., Kalla, M., Zhang, L., and V.
Paxson, "Stream Control Transmission Protocol", RFC 2960,
October 2000.
[9] Jungmaier, A., Rescorla, E., and M. Tuexen, "TLS over SCTP",
RFC 3436, December 2002.
[10] Bellovin, S., Ioannidis, J., Keromytis, A., and R. Stewart, "On
the Use of Stream Control Transmission Protocol (SCTP) with
IPsec", RFC 3554, July 2003.
[11] Stewart, R., Xie, Q., Stillman, M., and M. Tuexen, "Aggregate
Server Access Protocol (ASAP) and Endpoint Handlespace
Redundancy Protocol (ENRP) Parameters",
draft-ietf-rserpool-common-param-09 (work in progress),
July 2005.
[12] Stillman, M., Gopal, R., Sengodan, S., Guttman, E., and M.
Holdrege, "Threats Introduced by Rserpool and Requirements for
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Security in Response to Threats",
draft-ietf-rserpool-threats-05 (work in progress), July 2005.
7.2. Informative References
[13] Eastlake, D., Crocker, S., and J. Schiller, "Randomness
Recommendations for Security", RFC 1750, December 1994.
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Authors' Addresses
Qiaobing Xie
Motorola, Inc.
1501 W. Shure Drive, 2-F9
Arlington Heights, IL 60004
US
Phone:
Email: qxie1@email.mot.com
Randall R. Stewart
Cisco Systems, Inc.
4875 Forest Drive
Suite 200
Columbia, SC 29206
USA
Phone:
Email: rrs@cisco.com
Maureen Stillman
Nokia
127 W. State Street
Ithaca, NY 14850
US
Phone:
Email: maureen.stillman@nokia.com
Michael Tuexen
Muenster Univ. of Applied Sciences
Stegerwaldstr. 39
48565 Steinfurt
Germany
Email: tuexen@fh-muenster.de
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Aron J. Silverton
Motorola, Inc.
1301 E. Algonquin Road
Room 2246
Schaumburg, IL 60196
USA
Phone: +1 847-576-8747
Email: aron.j.silverton@motorola.com
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Full Copyright Statement
Copyright (C) The Internet Society (2006).
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