Network Working Group R. Stewart
Internet-Draft Cisco Systems, Inc.
Expires: December 8, 2004 Q. Xie
Motorola, Inc.
M. Stillman
Nokia
M. Tuexen
June 9, 2004
Aggregate Server Access Protocol (ASAP)
draft-ietf-rserpool-asap-09.txt
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Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
Aggregate Server Access Protocol (ASAP) in conjunction with the
Endpoint Name Resolution Protocol (ENRP) [6] provides a high
availability data transfer mechanism over IP networks. ASAP uses a
name-based addressing model which isolates a logical communication
endpoint from its IP address(es), thus effectively eliminating the
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binding between the communication endpoint and its physical IP
address(es) which normally constitutes a single point of failure.
In addition, ASAP defines each logical communication destination as a
pool, providing full transparent support for server-pooling and load
sharing. It also allows dynamic system scalability - members of a
server pool can be added or removed at any time without interrupting
the service.
ASAP is designed to take full advantage of the network level
redundancy provided by the Stream Transmission Control Protocol
(SCTP) RFC2960 [4]. Each transport protocol to be used by Pool
Elements (PE) and Pool Users (PU) MUST have an accompanying
transports mapping document. Note that ASAP messages passed between
PE's and ENRP servers MUST use SCTP.
The high availability server pooling is gained by combining two
protocols, namely ASAP and ENRP, in which ASAP provides the user
interface for name to address translation, load sharing management,
and fault management while ENRP defines the high availability name
translation service.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1 Definitions . . . . . . . . . . . . . . . . . . . . . . . 5
1.2 Organization of this document . . . . . . . . . . . . . . 7
1.3 Scope of ASAP . . . . . . . . . . . . . . . . . . . . . . 7
1.3.1 Extent of the Namespace . . . . . . . . . . . . . . . 7
1.4 Conventions . . . . . . . . . . . . . . . . . . . . . . . 7
2. Message Definitions . . . . . . . . . . . . . . . . . . . . 8
2.1 ASAP Parameter Formats . . . . . . . . . . . . . . . . . . 8
2.2 ASAP Messages . . . . . . . . . . . . . . . . . . . . . . 8
2.2.1 REGISTRATION message . . . . . . . . . . . . . . . . . 9
2.2.2 DEREGISTRATION message . . . . . . . . . . . . . . . . 9
2.2.3 REGISTRATION_RESPONSE message . . . . . . . . . . . . 10
2.2.4 DEREGISTRATION_RESPONSE message . . . . . . . . . . . 10
2.2.5 NAME_RESOLUTION message . . . . . . . . . . . . . . . 11
2.2.6 NAME_RESOLUTION_RESPONSE message . . . . . . . . . . . 11
2.2.7 ENDPOINT_KEEP_ALIVE message . . . . . . . . . . . . . 12
2.2.8 ENDPOINT_KEEP_ALIVE_ACK message . . . . . . . . . . . 13
2.2.9 ENDPOINT_UNREACHABLE message . . . . . . . . . . . . . 13
2.2.10 SERVER_ANNOUNCE message . . . . . . . . . . . . . . 13
2.2.11 COOKIE message . . . . . . . . . . . . . . . . . . . 14
2.2.12 COOKIE_ECHO message . . . . . . . . . . . . . . . . 14
2.2.13 BUSINESS_CARD message . . . . . . . . . . . . . . . 14
2.2.14 PEER_ERROR message . . . . . . . . . . . . . . . . . 15
3. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.1 Registration . . . . . . . . . . . . . . . . . . . . . . . 16
3.2 Deregistration . . . . . . . . . . . . . . . . . . . . . . 18
3.3 Name resolution . . . . . . . . . . . . . . . . . . . . . 18
3.4 Endpoint keep alive . . . . . . . . . . . . . . . . . . . 19
3.5 Reporting unreachable endpoints . . . . . . . . . . . . . 20
3.6 ENRP server hunt procedures . . . . . . . . . . . . . . . 20
3.7 Handle ASAP to ENRP Communication Failures . . . . . . . . 22
3.7.1 SCTP Send Failure . . . . . . . . . . . . . . . . . . 22
3.7.2 T1-ENRPrequest Timer Expiration . . . . . . . . . . . 22
3.8 Cookie handling procedures . . . . . . . . . . . . . . . . 23
3.9 Business Card handling procedures . . . . . . . . . . . . 23
4. The ASAP Interfaces . . . . . . . . . . . . . . . . . . . . 25
4.1 Registration.Request Primitive . . . . . . . . . . . . . . 25
4.2 Deregistration.Request Primitive . . . . . . . . . . . . . 25
4.3 Cache.Populate.Request Primitive . . . . . . . . . . . . . 26
4.4 Cache.Purge.Request Primitive . . . . . . . . . . . . . . 26
4.5 Data.Send.Request Primitive . . . . . . . . . . . . . . . 26
4.5.1 Sending to a Pool Handle . . . . . . . . . . . . . . . 27
4.5.2 Pool Element Selection . . . . . . . . . . . . . . . . 28
4.5.3 Sending to a Pool Element Handle . . . . . . . . . . . 29
4.5.4 Send by Transport Address . . . . . . . . . . . . . . 30
4.5.5 Message Delivery Options . . . . . . . . . . . . . . . 31
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4.6 Data.Received Notification . . . . . . . . . . . . . . . . 32
4.7 Error.Report Notification . . . . . . . . . . . . . . . . 32
4.8 Examples . . . . . . . . . . . . . . . . . . . . . . . . . 33
4.8.1 Send to a New Pool . . . . . . . . . . . . . . . . . . 33
4.8.2 Send to a Cached Pool Handle . . . . . . . . . . . . . 34
4.9 PE send failure . . . . . . . . . . . . . . . . . . . . . 34
4.9.1 Translation.Request Primitive . . . . . . . . . . . . 35
4.9.2 Transport.Failure Primitive . . . . . . . . . . . . . 35
5. Timers, Variables, and Thresholds . . . . . . . . . . . . . 36
5.1 Timers . . . . . . . . . . . . . . . . . . . . . . . . . . 36
5.2 Variables . . . . . . . . . . . . . . . . . . . . . . . . 36
5.3 Thresholds . . . . . . . . . . . . . . . . . . . . . . . . 36
6. Security Considerations . . . . . . . . . . . . . . . . . . 37
6.1 Implementing Security Mechanisms . . . . . . . . . . . . . 38
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 40
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 41
8.1 Normative References . . . . . . . . . . . . . . . . . . . . 41
8.2 Informational References (non-normative) . . . . . . . . . . 41
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 42
Intellectual Property and Copyright Statements . . . . . . . 43
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1. Introduction
Aggregate Server Access Protocol (ASAP) in conjunction with ENRP [6]
provides a high availability data transfer mechanism over IP
networks. ASAP uses a name-based addressing model which isolates a
logical communication endpoint from its IP address(es), thus
effectively eliminating the binding between the communication
endpoint and its physical IP address(es) which normally constitutes a
single point of failure.
When multiple receiver instances exist under the same name, a.k.a, a
server pool, ASAP will select one Pool Element (PE), based on the
current load sharing policy indicated by the server pool, and deliver
the message to the selected PE.
While delivering the message, ASAP monitors the reachability of the
selected PE. If it is found unreachable, before notifying the sender
of the failure, ASAP can automatically select another PE (if one
exists) under that pool and attempt to deliver the message to that
PE. In other words, ASAP is capable of transparent fail-over amongst
instances of a server pool.
ASAP uses the Endpoint Name Resolution Protocol (ENRP) to provide a
high availability name space. ASAP is responsible for the
abstraction of the underlying transport technologies, load
distribution management, fault management, as well as the
presentation to the upper layer (i.e., the ASAP user) a unified
primitive interface.
When SCTP RFC2960 [4] is used as the transport layer protocol, ASAP
can seamlessly incorporate the link-layer redundancy provided by the
SCTP.
This document defines the ASAP portion of the high availability
server pool. ASAP depends on the services of a high availability
name space a.k.a. ENRP [6].
1.1 Definitions
This document uses the following terms:
ASAP User: Either a PE or PU that uses ASAP.
Operation scope: The part of the network visible to Pool Users by a
specific instance of the reliable server pooling protocols.
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Server pool (or Pool): A collection of servers providing the same
application functionality.
Pool handle (or pool name): A logical pointer to a pool. Each server
pool will be identifiable in the operation scope of the system by
a unique pool handle or "name".
Pool Element (PE): A server entity having registered to a pool.
Pool User (PU): A server Pool User.
Pool Element handle (PE handle): A logical pointer to a particular
Pool Element in a pool,
ENRP server: A server program running on a host that manages the name
space collectively with its peer ENRP servers and replies to the
service requests from any Pool User or Pool Element.
Home ENRP server: The ENRP server to which a Pool Element currently
uses. A PU or PE normally chooses the ENRP server on their local
host as the home ENRP server (if one exists). A PU or PE should
only have one home ENRP server at any given time. Having a "home"
ENRP server helps provide a mechanism to minimize the number of
associations a given PE will have.
ENRP client channel: The communication channel through which an ASAP
User (either a PE or PU) requests ENRP namespace 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, OR a well known list of transport
addresses for a group of ENRP servers spanning an operational
scope. All ENRP servers in an operation scope can communicate
with one another through this channel via either multicast OR
direct point to point SCTP associations.
ENRP name domain: Defined by the combination of the ENRP client
channel and the ENRP server channel in the operation scope.
Network Byte Order: Most significant byte first, a.k.a Big Endian.
Transport address: A Transport Address is traditionally defined by
Network Layer address, Transport Layer protocol and Transport
Layer port number. In the case of SCTP running over IP, a
transport address is defined by the combination of an IP address
and an SCTP port number (where SCTP is the Transport protocol).
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1.2 Organization of this document
Section 2 details ASAP message formats. In Section 3 we give the
detailed ASAP procedures for the ASAP implementer. And in Section 4
we give the details of the ASAP interface, focusing on the
communication primitives between the applications above ASAP and ASAP
itself, and the communications primitives between ASAP and SCTP (or
other transport layer). Also included in this discussion is relevant
timers and configurable parameters as appropriate. Section 5
provides threshold and protocol variables.
1.3 Scope of ASAP
The requirements for high availability and scalability do not imply
requirements on shared state and data. ASAP does not provide
transaction failover. If a host or application fails during
processing of a transaction this transaction may be lost. Some
services may provide a way to handle the failure, but this is not
guaranteed. ASAP MAY provide hooks to assist an application in
building a mechanism to share state but ASAP in itself will NOT share
any state.
1.3.1 Extent of the Namespace
The scope of the ASAP/ENRP is NOT Internet wide. The namespace is
neither hierarchical nor arbitrarily large like DNS. We propose a
flat peer-to-peer model. Pools of servers will exist in different
administrative domains. For example, suppose we want to use ASAP/
ENRP. First, the PU may use DNS to contact an ENRP server. Suppose
a PU in North America wishes to contact the server pool in Japan
instead of North America. The PU would use DNS to get the list of IP
addresses of the Japanese server pool domain, that is, the ENRP
client channel in Japan. From there the PU would query the ENRP
server and then directly contact the PE(s) of interest.
1.4 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
RFC2119 [2].
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2. Message Definitions
All messages as well as their fields described below shall be in
Network Byte Order during transmission. For fields with a length
bigger than 4 octets, a number in a pair of parentheses may follow
the field name to indicate the length of the field in number of
octets.
2.1 ASAP Parameter Formats
The basic message format and all parameter formats can be found in
ENRP-ASAP [5]. Note also that ALL ASAP messages exchanged between an
ENRP server and a PE MUST use SCTP as transport, while ASAP messages
exchanged between an ENRP server and a PU MUST use either SCTP or TCP
as transport. PE to PU data traffic MAY use any transport protocol
specified by the PE during registration.
2.2 ASAP Messages
This section details the individual messages used by ASAP. These
messages are composed of a standard message format found in Section 4
of ENRP-ASAP [5]. The parameter descriptions may also be found in
Section 3 of ENRP-ASAP [5].
The following ASAP message types are defined in this section:
Type Message Name
----- -------------------------
0x00 - (reserved by IETF)
0x01 - Registration
0x02 - Deregistration
0x03 - Registration Response
0x04 - Deregistration Response
0x05 - Name Resolution
0x06 - Name Resolution Response
0x07 - Endpoint Keep Alive
0x08 - Endpoint Keep Alive Acknowledgement
0x09 - Endpoint Unreachable
0x0a - Server Announce
0x0b - Cookie
0x0c - Cookie-Echo
0x0d - Business Card
0x0e - Peer Error
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2.2.1 REGISTRATION 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 = 0x1 |0|0|0|0|0|0|0|0| Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Pool Handle Parameter :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Pool Element Parameter :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The pool handle parameter field specifies the name to be registered.
The PE Parameter field MUST be filled in by the registrant endpoint
to declare its transport address, server pooling policy and value,
and other operation preferences. Note that the registration message
MUST use SCTP and the IP address(es) of the PE registered within the
Pool Element Parameter MUST be a subset of the addresses of the SCTP
association in respective of the transport protocol registered by the
PE.
2.2.2 DEREGISTRATION 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 = 0x2 |0|0|0|0|0|0|0|0| Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Pool Handle Parameter :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: PE Identifier Parameter :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+++
The PE sending the DEREGISTRATION shall fill in the pool handle and
the PE identifier parameter in order to allow the ENRP server to
verify the identity of the endpoint. Note that deregistration is NOT
allowed by proxy, in other words a PE may only deregister itself.
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2.2.3 REGISTRATION_RESPONSE 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 = 0x3 |0|0|0|0|0|0|0|R| Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Pool Handle Parameter :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: PE Identifier Parameter :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Operational Error (optional) :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
R (Reject) flag
When set to '1', indicate that the ENRP server that sent this message
has rejected the registration. Otherwise, the registration is
granted.
Operational Error
This optional TLV parameter is included if an error or some atypical
events occurred during the registration process. When the 'R' flag
is set to '1', this TLV, if present, indicates the cause of the
rejection. When the 'R' flag is set to '0', this TLV, if present,
serves as a warning to the registering PE, informing it that some of
its registration values may have been modified or overruled by the
ENRP server (e.g., the selection policy type overruled). If the
registration was successful and there is no warning this parameter is
not included.
2.2.4 DEREGISTRATION_RESPONSE 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 = 0x4 |0|0|0|0|0|0|0|0| Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Pool Handle Parameter :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: PE Identifier Parameter :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Operational Error (optional) :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Operational Error
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This optional TLV parameter is included if an error occurred during
the deregistration process. If the deregistration was successful
this parameter is not included.
2.2.5 NAME_RESOLUTION 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 = 0x5 |0|0|0|0|0|0|0|0| Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Pool Handle Parameter :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This message is sent to a ENRP server to request translation of the
Pool Handle to a list of Pool Elements. If sent from a PE the SCTP
association used for registration SHOULD be used.
2.2.6 NAME_RESOLUTION_RESPONSE 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 = 0x6 |0|0|0|0|0|0|0|0| Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Pool Handle Parameter :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Overall PE Selection Policy (optional) :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Pool Element Parameter 1 (optional) :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: ... :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Pool Element Parameter N (optional) :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Operational Error (optional) :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Overall PE Selection Policy:
This TLV is a PE selection policy parameter and can be present when
the response is positive. It indicates the overall selection policy
of the pool. If not present, round-robin is assumed. This TLV is
not present when the response is negative (i.e., a rejection).
Note, any load policy parameter inside the Pool Element Parameter (if
present) MUST be ignored, and MUST NOT be used to determine the
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overall pool policy.
Pool Element Parameters
When the response is positive, an array of PE TLVs are included,
indicating the current PEs and their information in the named pool.
In a positive response, at least one PE TLV MUST be present. When
the response is negative, no PE TLVs are included.
Operational Error
The presence of this TLV indicates that the response is negative
(i.e., the name resolution request was rejected by the ENRP server).
The cause code in this TLV (if present) will indicate the reason the
name resolution request was rejected (e.g., the requested pool handle
was not found).
2.2.7 ENDPOINT_KEEP_ALIVE 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 = 0x7 |0|0|0|0|0|0|0|0| Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Pool Handle Parameter :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This message is sent to a PE by the ENRP server as a "health" check.
If the transport level Heart Beat mechanism is insufficient, this
adds heartbeat messages with the goal of determining health status at
ASAP level in a possibly more timely fashion. (The transport level
Heart Beat may sometimes be considered insufficient due to that time
outs are set for too long or heartbeats are not frequent enough, or,
that the transport level Heart Beat mechanism's coverage is limited
only to the transport level at the two ends.)
Using ASAP keepalive also has additional value to the reliability of
fault detection when SCTP stack is in the kernel. In such a case,
while SCTP level heartbeat monitors the end-to-end connectivity
between the two SCTP stacks, ASAP keepalive monitors the end-to-end
liveliness of the ASAP layer above it.
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2.2.8 ENDPOINT_KEEP_ALIVE_ACK 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 = 0x8 |0|0|0|0|0|0|0|0| Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Pool Handle Parameter :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: PE Identifier Parameter :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This message is sent by the PE to the ENRP server has an
acknowledgment to the ENDPOINT_KEEP_ALIVE message.
2.2.9 ENDPOINT_UNREACHABLE 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 = 0x09 |0|0|0|0|0|0|0|0| Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Pool Handle Parameter :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: PE Identifier Parameter :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A PE or PU will send this message to an ENRP server to report the
unreachability of the specified PE.
2.2.10 SERVER_ANNOUNCE 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 = 0x0a |0|0|0|0|0|0|0|0| Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Transport param #1 :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Transport param #2 :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: ..... :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Transport param #n :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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This message is sent by an ENRP server such that PUs and PEs know the
transport layer information necessary to connect to the ENRP server.
The transport parameters are optional and only TCP and SCTP transport
parameters are allowed.
2.2.11 COOKIE 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 = 0x0b |0|0|0|0|0|0|0|0| Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Cookie Parameter :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This message is sent by a PE to a PU. It may only be sent when a
control channel exists between the PE and PU.
2.2.12 COOKIE_ECHO 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 = 0x0c |0|0|0|0|0|0|0|0| Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Cookie Parameter :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This message is sent by a PU to a PE in case of a failover. The
Cookie Parameter is one received latest from the failed PE.
2.2.13 BUSINESS_CARD message
This message is sent by a PU to a PE or from a PE to a PU. This
parameter MUST NOT be sent if a control channel does NOT exists
between the PE and PU.
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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 = 0xd |0|0|0|0|0|0|0|0| Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Pool Handle Parameter :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Pool Element Parameter-1 :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: .. :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Pool Element Parameter-N :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The sender of this message lists both the Pool that the sender
belongs to and a preferred list of failover candidates.
2.2.14 PEER_ERROR message
This message is used to report an operation error.
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 = 0xe |0|0|0|0|0|0|0|0| Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Operation Error Parameter :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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3. Procedures
This section will focus on the methods and procedures used by an
internal ASAP endpoint. Appropriate timers and recovery actions for
failure detection and management are also discussed.
3.1 Registration
When a PE wishes to join its server pool it MUST use the procedures
outlined in this section to register. Often the registration will be
triggered by a user request primitive (discussed in Section 4.1).
The ASAP endpoint MUST register using an SCTP association between the
ASAP endpoint and the ENRP server. If the ASAP endpoint has not
established its Home ENRP server it MUST follow the procedures
specified in Section 3.6 to establish its Home ENRP server.
Once the ASAP endpoint has established its Home ENRP server the
following procedures MUST be followed to register:
R1) The SCTP endpoint used to communicate with the ENRP server MUST
be bound to all IP addresses that will be used by the PE
(irregardless of what protocol will be used to service user
requests to the PE).
R2) The ASAP endpoint MUST formulate a Registration message as
defined in Section 2.2.1 In formulating the message the ASAP
endpoint MUST:
R2.1) Fill in the Pool Handle to specify which server pool the
ASAP endpoint wishes to join.
R2.2) Fill in a PE identifier using a good quality randomly
generated number (RFC1750 [9] provides some information on
randomness guidelines).
R2.3) Fill in the registration life time parameter with the number
of seconds that this registration is good for. Note a PE that
wishes to continue service MUST re-register after the
registration expires.
R2.4) Fill in a User Transport Parameter for the type of transport
and the data/control channel usage the PE is willing to
support. Note, to join an existing server pool, the PE MUST
follow the overall transport type and overall data/control
channel usage of the pool. Otherwise, the registration may be
rejected by the ENRP server.
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R2.5) Fill in the preferred Member selection policy.
R3) Send the Registration request to the Home ENRP server using SCTP.
R4) Start a T2-registration timer.
If the T2-registration timer expires before receiving a
REGISTRATION_RESPONSE message, or a SEND.FAILURE notification is
received from the SCTP layer, the ASAP endpoint shall start the
Server Hunt procedure (see Section 3.6) in an attempt to get service
from a different ENRP server. After establishing a new Home ENRP
server the ASAP endpoint SHOULD restart the registration procedure.
At the reception of the registration response, the ASAP endpoint MUST
stop the T2-Registration timer. If the response indicated success,
then the PE is now registered and will be considered an available
member of the server pool. If the registration response indicates a
failure, the ASAP endpoint must either re-attempt registration after
correcting the error or return a failure indication to the ASAP
endpoints upper layer. The ASAP endpoint MUST NOT re-attempt
registration without correcting the error condition.
The registration response may also indicate that the registration is
accepted with a warning, often indicating that the ENRP server might
have made modifications to the value of some registration attribute
or attributes (such as policy type, transport usage, etc.). When
this happens, the PE SHOULD immediately notify its upper layer about
the registration modifications. This gives the upper layer a chance,
for example, to withdraw itself from the pool if such modifications
are unacceptable for its operation.
At any time a registered PE MAY wish to re-register to either update
its member selection policy value or registration expiration time.
When re-registering the PE MUST use the same PE identifier.
After successful registration the PE MUST start a T4-reregistration
timer. At its expiration a re-registration SHOULD be made starting
at step R1 including (at completion) restarting the T4-reregistration
timer.
Note that an implementation SHOULD keep a record of the number of
registration attempts it makes in a local variable. If repeated
registration time-outs or failures occurs and the local count exceeds
the Threshold 'MAX-REG-ATTEMPT' the implementation SHOULD report the
error to its upper layer and stop attempting registration.
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3.2 Deregistration
In the event the PE wishes to deregister from its server pool
(normally via an upper layer requests see Section 4.2) it SHOULD use
the following procedures. Note that an alternate method of
deregistration is to NOT re-register and to allow the registration
lift time to expire.
When deregistering the PE SHOULD use the same SCTP association with
its Home ENRP server that was used for registration. To deregister
the ASAP endpoint MUST take the following actions:
D1) Fill in the Pool Handle parameter of the Deregistration message (
Section 2.2.2) using the same Pool Handle parameter sent during
registration.
D2) Fill in the PE Identifier. The identifier MUST be the same one
used during registration.
D3) Send the deregistration message to the Home ENRP server using the
SCTP association.
D4) Start a T3-Deregistration timer.
If the T3-Deregistration timer expires before receiving a
REGISTRATION_RESPONSE message, or a SEND.FAILURE notification is
received from the SCTP layer, the ASAP endpoint shall start the
Server Hunt procedure (see Section 3.6) in an attempt to get service
from a different ENRP server. After establishing a new Home ENRP
server the ASAP endpoint SHOULD restart the deregistration procedure.
At the reception of the deregistration response, the ASAP endpoint
MUST stop the T3-deregistration timer.
Note that after a successful deregistration the PE MAY still receive
requests for some period of time. The PE MAY wish to still remain
active and service these requests or may wish to ignore these
requests and exit.
3.3 Name resolution
At any time a PE or PU may wish to resolve a name. This usually will
occur when a Endpoint sends to a Pool handle ( Section 4.5.1) or
requests a cache population (Section 4.3) but may occur for other
reasons (e.g. the internal ASAP PE wishes to know its peers for
sending a message to all of them). When an Endpoint (PE or PU)
wishes to resolve a name it MUST take the following actions:
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NR1) Fill in a NAME_RESOLUTION message ( Section 2.2.5) with the Pool
Handle to be resolved.
NR2) If the endpoint does not have a Home ENRP server start the ENRP
Server Hunt procedures specified in Section 3.6 to obtain one.
Otherwise proceed to step NR3.
NR3) Send the NAME_RESOLUTION message to the Home ENRP server using
SCTP.
NR4) Start a T1-ENRPrequest timer.
If the T1-ENRPrequest timer expires before receiving a response
message, or a SEND.FAILURE notification is received from the SCTP
layer, the ASAP endpoint SHOULD start the Server Hunt procedure (see
Section 3.6) in an attempt to get service from a different ENRP
server. After establishing a new Home ENRP server the ASAP endpoint
SHOULD restart the name resolution procedure.
At the reception of the response message (i.e., a
NAME_RESOLUTION_RESPONSE) the endpoint MUST stop its T1-ENRPrequest
timer. After stopping the T1 timer the endpoint SHOULD process the
name response as appropriate (e.g. populate a local cache, give the
response to the ASAP user, and/or use the response to send the ASAP
users message).
Note that some ASAP endpoints MAY use a cache to minimize the number
of name resolutions made. If such a cache is used it SHOULD:
C1) Be consulted before requesting a name resolution.
C2) Have a stale timeout time associated with the cache so that even
in the event of a cache-hit, if the cache is "stale" it will cause
a new name_resolution to be issued to update the cache.
C3) In the case of a "stale" cache the implementation may in parallel
request an update and answer the request or block the user and
wait for an updated cache before proceeding with the users
request.
C4) If the cache is NOT stale, the endpoint SHOULD NOT make a
name_resolution request but instead use the entry from the cache.
3.4 Endpoint keep alive
Periodically an ENRP server may choose to "audit" a PE. It does this
by sending a ENDPOINT_KEEP_ALIVE message ( Section 2.2.7). Upon
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reception of an ENDPOINT_KEEP_ALIVE message the following actions
MUST be taken:
KA1) The PE must verify that the Pool Handle is correct and matches
the Pool Handle sent in its earlier Registration. If the Pool
Handle does not match silently discard the message.
KA2) Send a ENDPOINT_KEEP_ALIVE_ACK (Section 2.2.8) by:
KA2.1) Filling in the Pool Handle Parameter with the PE's Pool
Handle.
KA2.2) Fill in the PE Identifier that was used with this PE for
registration.
KA2.3) Send off the ENDPOINT_KEEP_ALIVE_ACK message via the
appropriate SCTP association for that ENRP server.
KA2.4) Adopt the sender of the ENDPOINT_KEEP_ALIVE message as the
new home ENRP server.
3.5 Reporting unreachable endpoints
Occasionally an ASAP endpoint may realize that a PE is unreachable.
This may occur by a specific SCTP error realized by the ASAP endpoint
or via an ASAP user report via the Transport.Failure Primitive
(Section 4.9.2). In either case the ASAP endpoint SHOULD report the
unavailability of the PE by sending an ENDPOINT_UNREACHABLE message
to its home ENRP server. The Endpoint should fill in the Pool Handle
and PE identifier of the unreachable endpoint. If the sender is a PE
the message MUST be sent via SCTP to the Endpoints Home ENRP server.
Note: an ASAP endpoint MUST report No more than once each time it
encounters such an event.
Note: when processing a Transport.Failure Primitive (Section 4.9.2)
the ASAP endpoint MUST NOT send a unreachable report unless the ASAP
endpoint has sent at least one message to the PE specified by the
primitive.
3.6 ENRP server hunt procedures
Each PU and PE manages a list of transport addresses of ENRP servers.
If the multicast capabilities are used an ENRP server MUST send
periodically every T6-Serverannounce a SERVER_ANNOUNE message
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(Section 2.2.10) including all the transport addresses available for
ASAP communication to the multicast channel.
If a SERVER_ANNOUNCE message is received by a PU or PE it SHOULD
insert all new included transport address in its list of ENRP server
addresses and start a T7-ENRPoutdate timer for each address. For all
already known addresses the T7-ENRPoutdate timers MUST be restarted.
If no transport parameters are included in the SERVER_ANNOUNCE
message the source IP address and the IANA registered ASAP port
number are used instead. It is also assumed that the transport
protocol used is SCTP. If a T7-ENRP timer for a transport address
expires the corresponding address is deleted from the list of
transport addresses.
If no multicast capabilities are used each PU and PE MUST have a
configured list of transport addresses of ENRP servers.
At its startup, or when it fails to send to (i.e., timed-out on a
service request) with its current home ENRP server, a PE or PU shall
establish its Home ENRP server, i.e. setup a TCP connection or SCTP
association with an ENRP server.
To establish a new association or connection the following rules MUST
be followed:
SH1) The PE or PU SHOULD try to establish an association or
connection with no more than three ENRP server addresses. An
endpoint MUST NOT try to establish more than three association or
connections at any single time.
SH2) The endpoint shall start a T5-Serverhunt timer.
SH3) If the endpoint establishes an association or connection it MUST
stop its T5-Serverhunt timer. The Endpoint SHOULD also reset the
T5-Serverhunt value to its initial value and then proceed to step
SH6.
SH4) If an association or connection establishment fails the endpoint
SHOULD try to establish an association or connection by using a
different transport address.
SH5) If the T5-Serverhunt timer expires the following should be
performed:
SH5.1) The endpoint MUST double the value of the T5-Serverhunt
timer.
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SH5.2) The endpoint SHOULD stop the establishment of associations
and connections.
SH5.2) The endpoint SHOULD repeat trying to establish an
association or connection by proceeding to step SH1. It SHOULD
attempt to select a different set of transport addresses to
connect to.
SH6) The PE or PU shall pick one of the ENRP servers that it was able
to establish an association or connection with, and send all its
subsequent the namespace service requests to this new home ENRP
server.
3.7 Handle ASAP to ENRP Communication Failures
Three types of failure may occur when the ASAP endpoint at an
endpoint tries to communicate with the ENRP server:
A) SCTP send failure
B) T1-ENRPrequest timer expiration
C) Registration failure
Registration failure is discussed in Section 3.1
3.7.1 SCTP Send Failure
This indicates that the SCTP layer failed to deliver a message sent
to the ENRP server. In other words, the ENRP server is currently
unreachable.
In such a case, the ASAP endpoint should not re-send the failed
message. Instead, it should discard the failed message and start the
ENRP server hunt procedure as described in Section 3.6
3.7.2 T1-ENRPrequest Timer Expiration
When a T1-ENRPrequest timer expires, the ASAP should re-send the
original request to the ENRP server and re-start the T1-ENRPrequest
timer. In parallel, a SERVER_HUNT message should be issued per
Section 3.6
This should be repeated up to 'MAX-REQUEST-RETRANSMIT' times. After
that, an Error.Report notification should be generated to inform the
ASAP user and the ENRP request message associated with the timer
should be discarded. Note that if an alternate ENRP server responds
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the ASAP endpoint SHOULD adopt the responding ENRP server as its new
"home" server and resend the request to the new "home" server.
3.8 Cookie handling procedures
Whenever a PE wants and a control channel exists it can send a Cookie
Message to the PU via the control channel. The ASAP layer at the PU
stores the Cookie parameter and discards an older one if it is
present.
If the ASAP layer detects a failure and initiates a failover to a
different PE, the ASAP layer sends the last received Cookie parameter
in a Cookie Echo message to the new PE. The upper layer may be
involved in the failover procedure.
This cookie mechanism can be used as a simple method for state
sharing. Therefore a cookie should be signed by the sending PE and
this should be verified by the receiving PE. The details of this are
out of scope of this document. It is only important that the PU
stores always the last received Cookie Parameter and sends that back
unmodified in case of a PE failure.
3.9 Business Card handling procedures
When communication begins between a PU and a PE (i.e. the first
message is sent from the PU to the PE) the ASAP layer in the PU
SHOULD send a Business card IF the sender is also registered as a PE.
A PE may also send back to a PU a business card as well. A Business
card MUST NOT be sent if a control channel does NOT exist between the
PU and PE. After communication as been established between a PE and
PU at any time either entity may update its failover distribution by
sending a new Business Card.
The business card serves two purposes (for both endpoints PU and PE).
First it lists the endpoints pool handle. For a PU contacting a PE
this is essential so that the PE may also gain the full benefits of
ASAP if the PU is also a PE. Secondly the business card tells the
receiver a failover order that is recommended to follow. This may
facilitate rendezvous between PE's as well as some control of load
redistribution upon the failure of any given PE.
Upon receipt of a Business Card Message (see Section 2.2.13) the
receiver SHOULD:
BC1) Unpack the business card, and if no entry exists in the
translation cache and one exists, populate the new Pool Handle
into the cache and request a NAME.RESOLUTION of the pool handle.
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BC2) Create a list for this PE of preferred failover order so that in
the event of a failure the preferred list will be used to guide
the ASAP endpoint in the selection of an alternate PE.
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4. The ASAP Interfaces
This chapter will focus primarily on the primitives and notifications
that form the interface between the ASAP-user and ASAP and that
between ASAP and its lower layer transport protocol (e.g., SCTP).
Note, the following primitive and notification descriptions are shown
for illustrative purposes. We believe that including these
descriptions in this document is important to the understanding of
the operation of many aspects of ASAP. But an ASAP implementation is
not required to use the exact syntax described in this section.
An ASAP User passes primitives to the ASAP sub-layer to request
certain actions. Upon the completion of those actions or upon the
detection of certain events, the ASAP will notify the ASAP user.
4.1 Registration.Request Primitive
Format: registration.request(poolHandle,
User Transport parameter(s))
The poolHandle parameter contains a NULL terminated ASCII string of
fixed length. The optional User Transport parameter(s) indicate
specific transport parameters and types to register with. If this
optional parameter is left off, then the SCTP endpoint used to
communicate with the ENRP server is used as the default User
Transport parameter. Note that any IP address contained within a
User Transport parameter MUST be a bound IP address in the SCTP
endpoint used to communicate with the ENRP server.
The ASAP user invokes this primitive to add itself to the namespace,
thus becoming a Pool Element of a pool. The ASAP user must register
itself with the ENRP server by using this primitive before other ASAP
users using the namespace can send message(s) to this ASAP user by
Pool Handle or by PE handle (see Section 4.5.1 and Section 4.5.3).
In response to the registration primitive, the ASAP endpoint will
send a REGISTRATION message to the home ENRP server (See Section
2.2.1 and Section 3.1), and start a T2-registration timer.
4.2 Deregistration.Request Primitive
Format: deregistration.request(poolHandle)
The ASAP PE invokes this primitive to remove itself from the Server
Pool. This should be used as a part of the graceful shutdown process
by the application.
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A DEREGISTRATION message will be sent by ASAP endpoint to the home
ENRP server (see Section 2.2.2 and Section 3.2).
4.3 Cache.Populate.Request Primitive
Format: cache.populate.request([Pool-Handle |
Pool-Element-Handle])
If the address type is a Pool handle and a local name translation
cache exists, the ASAP endpoint should initiate a mapping information
query by sending a NAME.RESOLUTION message on the Pool handle and
update it local cache when the response comes back from the ENRP
server.
If a Pool-Element-Handle is passed then the Pool Handle is unpacked
from the Pool-Element-Handle and the NAME.RESOLUTION message is sent
to the ENRP server for resolution. When the response message returns
from the ENRP server the local cache is updated.
Note that if the ASAP service does NOT support a local cache this
primitive performs NO action.
4.4 Cache.Purge.Request Primitive
Format: cache.purge.request([Pool-Handle | Pool-Element-Handle])
If the user passes a Pool handle and local name translation cache
exists, the ASAP endpoint should remove the mapping information on
the Pool handle from its local cache. If the user passes a
Pool-Element-Handle then the Pool handle within is used for the
cache.purge.request.
Note that if the ASAP service does NOT support a local cache this
primitive performs NO action.
4.5 Data.Send.Request Primitive
Format: data.send.request(destinationAddress, typeOfAddress,
message, sizeOfMessage, Options);
This primitive requests ASAP to send a message to some specified Pool
or Pool Element within the current Operational scope.
Depending on the address type used for the send request, the senders
ASAP endpoint may perform address translation and Pool Element
selection before sending the message out. This also MAY dictate the
creation of a local transport endpoint in order to meet the required
transport type.
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The data.send.request primitive can take different forms of address
types as described in the following sections.
4.5.1 Sending to a Pool Handle
In this case the destinationAddress and typeOfAddress together
indicates a pool handle.
This is the simplest form of send.data.request primitive. By
default, this directs ASAP to send the message to one of the Pool
Elements in the specified pool.
Before sending the message out to the pool, the senders ASAP endpoint
MUST first perform a pool handle to address translation. It may also
need to perform Pool Element selection if multiple Pool Elements
exist in the pool.
If the senders ASAP implementation does not support a local cache of
the mapping information or if it does not have the mapping
information on the pool in its local cache, it will transmit a
NAME.RESOLUTION message (see Section 2.2.5 and Section 3.3) to the
current home ENRP server, and MUST hold the outbound message in queue
while awaiting the response from the ENRP server (any further send
request to this pool before the ENRP server responds SHOULD also be
queued).
Once the necessary mapping information arrives from the ENRP server,
the senders ASAP will:
A) map the pool handle into a list of transport addresses of the
destination PE(s),
B) if multiple PEs exist in the pool, ASAP will choose one of them
and transmit the message to it. In that case, the choice of the
PE is made by ASAP endpoint of the sender based on the server
pooling policy as discussed in Section 4.5.2
C) Optionally create any transport endpoint that may be needed to
communicate with the PE selected.
D) if no transport association or connection exists towards the
destination PE, ASAP will establish any needed transport state,
E) send out the queued message(s) to the appropriate transport
connection using the appropriate send mechanism (e.g. for SCTP
the SEND primitive in RFC2960 [4] would be used), and,
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F) if the local cache is implemented, append/update the local cache
with the mapping information received in the ENRP server's
response. Also, record the local transport information (e.g. the
SCTP association id) if any new transport state was created.
For more on the ENRP server request procedures see ENRP [6].
Optionally, the ASAP endpoint of the sender may return a Pool Element
handle of the selected PE to the application after sending the
message. This PE handle can then be used for future transmissions to
that same PE (see Section 4.5.3).
Section 3.7 defines the fail-over procedures for cases where the
selected PE is found unreachable.
4.5.2 Pool Element Selection
Each time an ASAP user sends a message to a pool that contains more
than one PE, the senders ASAP endpoint must select one of the PEs in
the pool as the receiver of the current message. The selection is
done according to the current server pooling policy of the pool to
which the message is sent.
Note, no selection is needed if the ASAP_SEND_TOALL option is set
(see Section 4.5.5).
Together with the server pooling policy, each PE can also specify a
Policy Value for itself at the registration time. The meaning of the
policy value depends on the current server pooling policy of the
group. A PE can also change its policy value whenever it desires, by
re-registering itself with the namespace with a new policy value.
Re-registration shall be done by simply sending another REGISTRATION
to its home ENRP server (See Section 2.2.1).
Four basic server pooling policies are defined in ASAP, namely the
Round Robin, Least Used, Least Used Degrading and Weighted Round
Robin. The following sections describes each of these policies.
4.5.2.1 Round Robin Policy
When a ASAP endpoint sends messages by Pool Handle and Round-Robin is
the current policy of that Pool, the ASAP endpoint of the sender will
select the receiver for each outbound message by round-Robining
through all the registered PEs in that Pool, in an attempt to achieve
an even distribution of outbound messages. Note that in a large
server pool, the ENRP server MAY NOT send back all PEs to the ASAP
client. In this case the client or PU will be performing a round
robin policy on a subset of the entire Pool.
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4.5.2.2 Least Used Policy
When the destination Pool is under the Least Used server pooling
policy, the ASAP endpoint of the message sender will select the PE
that has the lowest policy value in the group as the receiver of the
current message. If more than one PE from the group share the same
lowest policy value, the selection will be done round Robin amongst
those PEs.
It is important to note that this policy means that the same PE will
be always selected as the message receiver by the sender until the
load control information of the pool is updated and changed in the
local cache of the sender (via a cache update see Section 3.3).
4.5.2.3 Least Used with Degradation Policy
This policy is the same as the Least Used policy with the exception
that, each time the PE with the lowest policy value is selected from
the Pool as the receiver of the current message, its policy value is
incremented, and thus it may no longer be the lowest value in the
Pool.
This provides a degradation of the policy towards round Robin policy
over time. As with the Least Used policy, every local cache update
at the sender will bring the policy back to Least Used with
Degradation.
4.5.2.4 Weighted Round Robin Policy
[TBD]
4.5.3 Sending to a Pool Element Handle
In this case the destinationAddress and typeOfAddress together
indicate an ASAP Pool Element handle.
This requests the ASAP endpoint to deliver the message to the PE
identified by the Pool Element handle.
The Pool Element handle should contain the Pool Handle and a
destination transport address of the destination PE or the Pool
Handle and the transport type. Other implementation dependant
elements may also be cached in a Pool Element handle.
The ASAP endpoint shall use the transport address and transport type
to identify the endpoint to communicate with. If no communication
state exists with the peer endpoint (and is required by the transport
protocol) the ASAP endpoint MAY setup the needed state and then
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invoke the SEND primitive for the particular transport protocol to
send the message to the PE.
In addition, if a local translation cache is supported the endpoint
will:
A) send out the message to the transport address (or association id)
designated by the PE handle.
B) determine if the Pool Handle is in the local cache.
If it is NOT, the endpoint will:
i) ask the home ENRP server for name resolution on pool handle by
sending a NAME.RESOLUTION message (see Section 2.2.5), and
ii) use the response to update the local cache.
If the pool handle is in the cache, the endpoint will only
update the pool handle if the cache is stale. A stale cache is
indicated by it being older than the protocol parameter
'stale.cache.value' (see Section 5.2).
Section 3.5 and Section 4.9 defines the fail-over procedures for
cases where the PE pointed to by the Pool Element handle is found
unreachable.
Optionally, the ASAP endpoint may return the actual Pool Element
handle to which the message was sent (this may be different from the
Pool Element handle specified when the primitive is invoked, due to
the possibility of automatic fail-over).
4.5.4 Send by Transport Address
In this case the destinationAddress and typeOfAddress together
indicate a transport address and transport type.
This directs the senders ASAP endpoint to send the message out to the
specified transport address.
No endpoint fail-over is support when this form of send request is
used. This form of send request effectively by-passes the ASAP
endpoint.
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4.5.5 Message Delivery Options
The Options parameter passed in the various forms of the above
data.send.request primitive gives directions to the senders ASAP
endpoint on special handling of the message delivery.
The value of the Options parameter is generated by bit-wise "OR"ing
of the following pre-defined constants:
ASAP_USE_DEFAULT: 0x0000 Use default setting.
ASAP_SEND_FAILOVER: 0x0001 Enables PE fail-over on this message. In
case where the first selected PE or the PE pointed to by the PE
handle is found unreachable, the sender's ASAP endpoint SHOULD
re-select an alternate PE from the same pool if one exists, and
silently re-send the message to this newly selected endpoint.
Note that this is a best-effort service. Applications should be
aware that messages can be lost during the failover process, even
if the underlying transport supports retrieval of unacknowledged
data (e.g. SCTP) (Example: messages acknowledged by the SCTP
layer at a PE, but not yet read by the PE when a PE failure
occurs.) In the case where the underlying transport does not
support such retrieval (e.g. TCP), any data already submitted by
ASAP to the transport layer MAY be lost upon failover.
ASAP_SEND_NO_FAILOVER: 0x0002 This option prohibits the senders ASAP
endpoint from re-sending the message to any alternate PE in case
that the first selected PE or the PE pointed to by the PE handle
is found unreachable. Instead, the senders ASAP endpoint shall
notify its upper layer about the unreachability with an
Error.Report and return any unsent data.
ASAP_SEND_TO_LAST: 0x0004 This option requests the senders ASAP
endpoint to send the message to the same PE in the pool that the
previous message destined to this pool was sent to.
ASAP_SEND_TO_ALL: 0x0008 When sending by Pool Handle, this option
directs the senders ASAP endpoint to send a copy of the message to
all the PEs, except for the sender itself if the sender is a PE,
in that pool.
ASAP_SEND_TO_SELF: 0x0010 This option only applies in combination
with ASAP_SEND_TO_ALL option. It permits the senders ASAP
endpoint also deliver a copy of the message to itself if the
sender is a PE of the pool (i.e., loop-back).
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ASAP_SCTP_UNORDER: 0x1000 This option requests the transport layer to
send the current message using un-ordered delivery (note the
underlying transport must support un-ordered delivery for this
option to be effective).
4.6 Data.Received Notification
Format: data.received(messageReceived, sizeOfMessage, senderAddress,
typeOfAddress)
When a new user message is received, the ASAP endpoint of the
receiver uses this notification to pass the message to its upper
layer.
Along with the message being passed, the ASAP endpoint of the
receiver should also indicate to its upper layer the message senders
address. The senders address can be in the form of either an SCTP
association id, TCP transport address, UDP transport address, or a
ASAP Pool Element handle.
A) If the name translation local cache is implemented at the
receiver's ASAP endpoint, a reverse mapping from the senders IP
address to the pool handle should be performed and if the mapping
is successful, the senders ASAP Pool Element handle should be
constructed and passed in the senderAddress field.
B) If there is no local cache or the reverse mapping is not
successful, the SCTP association id or other transport specific
identification (if SCTP is not being used) should be passed in the
senderAddress field.
4.7 Error.Report Notification
Format: error.report(destinationAddress, typeOfAddress,
failedMessage, sizeOfMessage)
An error.report should be generated to notify the ASAP user about
failed message delivery as well as other abnormalities.
The destinationAddress and typeOfAddress together indicates to whom
the message was originally sent. The address type can be either a
ASAP Pool Element handle, association id, or a transport address.
The original message (or the first portion of it if the message is
too big) and its size should be passed in the failedMessage and
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sizeOfMessage fields, respectively.
4.8 Examples
These examples assume an underlying SCTP transport between the PE and
PU. Other transports are possible but SCTP is utilized in the
examples for illustrative purposes. Note that all communication
between PU and ENRP server and PE and ENRP servers would be using
SCTP.
4.8.1 Send to a New Pool
This example shows the event sequence when a Pool User sends the
message "hello" to a pool which is not in the local translation cache
(assuming local caching is supported).
ENRP Server PU new-name:PEx
| | |
| +---+ |
| | 1 | |
| 2. NAME_RESOLUTION +---+ |
|<-------------------------------| |
| +---+ |
| | 3 | |
| 4. NAME_RESOLUTION_REPONSE +---+ |
|------------------------------->| |
| +---+ |
| | 5 | |
| +---+ 6. "hello1" |
| |---------------->|
| | |
1) The user at PU invokes:
data.send.request("new-name", name-type, "hello1", 6, 0);
The ASAP endpoint, in response, looks up the pool "new-name" in
its local cache but fails to find it.
2) The ASAP endpoint of PU queues the message, and sends a
NAME_RESOLUTION request to the ENRP server asking for all
information about pool "new-name".
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3) A T1-ENRPrequest timer is started while the ASAP endpoint is
waiting for the response from the ENRP server.
4) The ENRP Server responds to the query with a
NAME_RESOLUTION_REPONSE message that contains all the information
about pool "new-name".
5) ASAP at PU cancels the T1-ENRPrequest timer and populate its local
cache with information on pool "new-name".
6) Based on the server pooling policy of pool "new-name", ASAP at PU
selects the destination PE (PEx), sets up, if necessary, an SCTP
association towards PEx (explicitly or implicitly), and send out
the queued "hello1" user message.
4.8.2 Send to a Cached Pool Handle
This shows the event sequence when the ASAP user PU sends another
message to the pool "new-name" after what happened in Section 4.8.1.
ENRP Server PU new-name:PEx
| | |
| +---+ |
| | 1 | |
| +---+ 2. "hello2" |
| |---------------->|
| | |
1) The user at PU invokes:
pdata.send.request("new-name", name-type, "hello2", 6, 0);
The ASAP endpoint, in response, looks up the pool "new-name" in
its local cache and find the mapping information.
2) Based on the server pooling policy of "new-name", ASAP at PU
selects the PE (assume EPx is selected again), and sends out
"hello2" message (assume the SCTP association is already set up).
4.9 PE send failure
When the ASAP endpoint in a PE or PU attempts to send a message to a
PE and fails the failed sender will report the event as described in
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Section 3.5 .
Additional primitive are also defined in this section to support
those user applications that do not wish to use ASAP as the actual
transport.
4.9.1 Translation.Request Primitive
Format: translation.request(Pool-Handle)
If the address type is a Pool handle and a local name translation
cache exists, the ASAP endpoint should look within its translation
cache and return the current known transport types, ports and
addresses to the caller.
If the Pool handle does not exist in the local name cache or no name
cache exists, the ASAP endpoint will send a NAME.RESOLUTION request
using the Pool-Handle. Upon completion of the name resolution, the
ASAP endpoint should populate the local name cache (if a local name
cache is supported) and return the transport types, ports and
addresses to the caller.
4.9.2 Transport.Failure Primitive
Format: transport.failure(Pool-Handle, Transport-address)
If an external user encounters a failure in sending to a PE and is
NOT using ASAP it can use this primitive to report the failure to the
ASAP endpoint. ASAP will send ENDPOINT_UNREACHABLE to the "home"
ENRP server in response to this primitive. Note ASAP SHOULD NOT send
a ENDPOINT_UNREACHABLE UNLESS the user has actually made a previous
request to send data to the PE.
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5. Timers, Variables, and Thresholds
The following is a summary of the timers, variables, and pre-set
protocol constants used in ASAP.
5.1 Timers
T1-ENRPrequest - A timer started when a request is sent by ASAP to
the ENRP server (providing application information is queued).
Normally set to 15 seconds.
T2-registration - A timer started when sending a registration request
to the home ENRP server, normally set to 30 seconds.
T3-deregistration - A timer started when sending a deregistration
request to the home ENRP server, normally set to 30 seconds.
T4-reregistration - This timer is started after successful
registration into the ASAP name space and is used to cause a
re-registration at a periodic interval. This timer is normally
set to 10 minutes or 20 seconds less than the Life Timer parameter
used in the registration request (whichever is less).
T5-Serverhunt - This timer is used during the ENRP server hunt
procedure and is normally set to 120 seconds.
T6-Serverannounce - This timer gives the time between the sending of
consecutive SERVER_ANNOUNCE messages. It is normally set to 1
second.
T7-ENRPoutdate - This timer gives the time a server announcement is
valid. It is normally set to 5 seconds.
5.2 Variables
stale.cache.value - A threshold variable that indicates how long a
cache entry is valid for.
5.3 Thresholds
MAX-REG-ATTEMPT - The maximum number of registration attempts to be
made before a server hunt is issued.
MAX-REQUEST-RETRANSMIT - The maximum number of attempts to be made
when requesting information from the local ENRP server before a
server hunt is issued.
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6. Security Considerations
Threats Introduced by Rserpool and Requirements for Security in
Response to Threats [7] 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 name
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 namespace information
-----------
Security mechanism in response: Security protocol which supports data
confidentiality
Threat 8) Flood of 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
Endpoint_Unreachable messages (see Section 3.5) 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??? in [6]).
6.1 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
received during TLS negotiation; this entails possession of one or
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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
[8] or TLS over TCP as described in RFC2246 [3]. 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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7. Acknowledgments
The authors wish to thank Thomas Dreibholz, John Loughney, Lyndon
Ong, and many others for their invaluable comments.
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8. References
8.1 Normative References
[1] Bradner, S., "The Internet Standards Process -- Revision 3", BCP
9, RFC 2026, October 1996.
[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[3] Dierks, T., Allen, C., Treese, W., Karlton, P., Freier, A. and
P. Kocher, "The TLS Protocol Version 1.0", RFC 2246, January
1999.
[4] 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.
[5] Stewart, R., Xie, Q., Stillman, M. and M. Tuexen, "Aggregate
Server Access Protocol (ASAP) and Endpoint Name Resolution
Protocol (ENRP) Parameters", draft-ietf-rserpool-common-param-06
(work in progress), June 2004.
[6] Xie, Q., Stewart, R. and M. Stillman, "Enpoint Name Resolution
Protocol (ENRP)", draft-ietf-rserpool-enrp-08 (work in
progress), June 2004.
[7] Stillman, M., "Threats Introduced by Rserpool and Requirements
for Security in Response to Threats",
draft-ietf-rserpool-threats-02 (work in progress), Sept 2003.
[8] Jungmaier, A., Rescorla, E. and M. Tuexen, "TLS over SCTP", RFC
3436, December 2002.
8.2 Informational References (non-normative)
[9] Eastlake, D., Crocker, S. and J. Schiller, "Randomness
Recommendations for Security", RFC 1750, December 1994.
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Authors' Addresses
Randall R. Stewart
Cisco Systems, Inc.
8725 West Higgins Road
Suite 300
Chicago, IL 60631
USA
Phone: +1-815-477-2127
EMail: rrs@cisco.com
Qiaobing Xie
Motorola, Inc.
1501 W. Shure Drive, #2309
Arlington Heights, IL 60004
USA
Phone: +1-847-632-3028
EMail: qxie1@email.mot.com
Maureen Stillman
Nokia
127 W. State Street
Ithaca, NY 14850
USA
Phone: +1-607-273-0724
EMail: maureen.stillman@nokia.com
Michael Tuexen
Germany
Phone:
EMail: tuexen@fh-muenster.de
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