Reliable Server Pooling Applicability for IP Flow Information Exchange
University of Duisburg-Essen, Institute for Experimental Mathematics
Ellernstrasse 29
45326 Essen
Nordrhein-Westfalen
Germany
+49-201-1837637
+49-201-1837673
dreibh@iem.uni-due.de
http://www.iem.uni-due.de/~dreibh/
Nokia Siemens Networks
Atealaan 32
Herentals
2200
Belgium
+32-14-252081
lode.coene@nsn.com
University of Delaware
103 Smith Hall
Newark
DE 19716
USA
+1 302 831 8622
conrad@acm.org
Internet-Draft
This document describes the applicability of the Reliable Server
Pooling architecture to the IP Flow Information Exchange using the
Aggregate Server Access Protocol (ASAP) functionality of RSerPool only. Data
exchange in IPFIX between the router and the data collector can be provided
by a limited retransmission protocol.
Reliable Server Pooling provides protocols for providing highly
available services. The services are located in a pool of redundant
servers and if a server fails, another server will take over. The
only requirement put on these servers belonging to the pool is that if
state is maintained by the server, this state must be transferred
to the other server taking over.
The goal is to provide server-based redundancy. Transport and
network level redundancy are handle by the transport and network layer
protcols.
The application may choose to distribute its traffic over the servers
of the pool conforming to a certain policy.
The application wishing to make use of RSerPool protocols may use
different transport layers (such as UDP, TCP and SCTP). However, some
transport layers may have restrictions build in in the way they
might be operating in the RSerPool architecture and its protocols.
The scope of this document is to explain the way that a minimal
version of Reliable Server Pooling protocols have to be used in order
to provide a highly available service towards IP Flow Information
Exchange (IPFIX) protocols.
The terms are commonly identified in related work and can be found
in the Aggregate Server Access Protocol and Endpoint Handlespace Redundancy
Protocol Common Parameters document
IP flow information is exchanged between observation points and
collector points. The observation points may try to find out via the
Aggregate Server Access Protocol
(ASAP, see )
which collector point(s) are
active. Both the observation and the collector point may have
limitations for exchanging the information (observation point may
have limited buffer space and collectors points may be overburdened
with receiving lots of flow information from different observation
points).
The observation point will query the ENRP server for resolution of a
particular collector pool name and the ENRP server will return
a list of one or more collector points to the observation point.
The observation point will use its own transport protocols (TCP, UDP,
SCTP, SCTP with PR-SCTP extension) for exchanging the IPFIX data
between the observation point and the collector point.
If a collector point would fail, then the observation point will
send its data towards a different collector point,
belonging to the same collector pool.
Collector points will announce themselves to the ENRP server and
will be monitored for their availability. The observation point will
only query the ENRP server for server pool name resolution.
The exchange of IP flow information data between an observation point
and a collection point consists of massive amounts of data.
One collection point can service many observation points, therefore
transport protocols must do congestion control (example: modifying
the receive buffer space, thus reducing the incoming flow of data),
so that the collection point is not overburdened by its observation
points. Some data must arrive at the collector while other data
might arrive (if it gets lost: no problem). The choice of reliable
or partial reliable delivery has to be made by the observation
point
These requirements demand a protocol which provides variable
transport reliability of its data: it should be able to chose
the reliability by the IPFIX protocols on a a per-message base.
SCTP with PR-SCTP extension
is the only know protocol which
allows the choice of full, partial or unreliable delivery of
the message to its peer node. TCP will only allow fully reliable
delivery, while UDP only provides unreliable delivery and
NO congestion control.
The protocols used in the Reliable Server Pooling architecture only
try to increase the availability of the servers in the
network. RSerPool protocols do not contain any protocol mechanisms
which are directly related to user message authentication, integrity
and confidentiality functions. For such features, it depends on the
IPSEC protocols or on Transport Layer Security (TLS) protocols for
its own security and on the architecture and/or security features
of its user protocols.
The RSerPool architecture allows the use of different transport
protocols for its application and control data exchange. These
transport protocols may have mechanisms for reducing the risk of
blind denial-of-service attacks and/or masquerade attacks. If such
measures are required by the applications, then it is advised to
check the SCTP applicability statement
RFC2057 for guidance on this issue.
The RSerPool reference implementation RSPLIB can be found at
. It supports the functionalities
defined by
,
,
,
and
as well as the options
,
and
.
An introduction to this implementation is provided in
.
Security considerations for RSerPool systems are described by
.
This document introduces no additional considerations for IANA.
The authors wish to thank Maureen Stillman and many others
for their invaluable comments.