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rfc:rfc2647

Network Working Group D. Newman Request for Comments: 2647 Data Communications Category: Informational August 1999

         Benchmarking Terminology for Firewall Performance

Status of this Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard of any kind.  Distribution of this
 memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (1999).  All Rights Reserved.

Table of Contents

 1. Introduction...................................................2
 2. Existing definitions...........................................2
 3. Term definitions...............................................3
 3.1 Allowed traffic...............................................3
 3.2 Application proxy.............................................3
 3.3 Authentication................................................4
 3.4 Bit forwarding rate...........................................5
 3.5 Circuit proxy.................................................6
 3.6 Concurrent connections........................................6
 3.7 Connection....................................................7
 3.8 Connection establishment......................................9
 3.9 Connection establishment time.................................9
 3.10 Connection maintenance......................................10
 3.11 Conection overhead..........................................11
 3.12 Connection teardown.........................................11
 3.13 Connection teardown time....................................12
 3.14 Data source.................................................12
 3.15 Demilitarized zone..........................................13
 3.16 Firewall....................................................13
 3.17 Goodput.....................................................14
 3.18 Homed.......................................................15
 3.19 Illegal traffic.............................................15
 3.20 Logging.....................................................16
 3.21 Network address translation.................................16
 3.22 Packet filtering............................................17
 3.23 Policy......................................................17
 3.24 Protected network...........................................18
 3.25 Proxy.......................................................19
 3.26 Rejected traffic............................................19

Newman Informational [Page 1] RFC 2647 Firewall Performance Terminology August 1999

 3.27 Rule set....................................................20
 3.28 Security association........................................20
 3.29 Stateful packet filtering...................................21
 3.30 Tri-homed...................................................22
 3.31 Unit of transfer............................................22
 3.32 Unprotected network.........................................23
 3.33 User........................................................23
 4. Security considerations.......................................24
 5. References....................................................25
 6. Acknowledgments...............................................25
 7. Contact Information...........................................25
 8. Full Copyright Statement......................................26

1. Introduction

 This document defines terms used in measuring the performance of
 firewalls. It extends the terminology already used for benchmarking
 routers and switches with definitions specific to firewalls.
 Forwarding rate and connection-oriented measurements are the primary
 metrics used in this document.
 Why do we need firewall performance measurements? First, despite the
 rapid rise in firewall deployment, there is no standard method of
 performance measurement. Second, implementations vary widely, making
 it difficult to do direct performance comparisons. Finally, more and
 more organizations are deploying firewalls on internal networks
 operating at relatively high speeds, while most firewall
 implementations remain optimized for use over relatively low-speed
 wide-area connections. As a result, users are often unsure whether
 the products they buy will stand up to relatively heavy loads.

2. Existing definitions

 This document uses the conceptual framework established in RFCs 1242
 and 2544 (for routers) and RFC 2285 (for switches). The router and
 switch documents contain discussions of several terms relevant to
 benchmarking the performance of firewalls. Readers should consult the
 router and switch documents before making use of this document.
 This document uses the definition format described in RFC 1242,
 Section 2. The sections in each definition are: definition,
 discussion, measurement units (optional), issues (optional), and
 cross-references.

Newman Informational [Page 2] RFC 2647 Firewall Performance Terminology August 1999

3. Term definitions

3.1 Allowed traffic

 Definition:
   Packets forwarded as a result of the rule set of the device under
   test/system under test (DUT/SUT).
 Discussion:
   Firewalls typically are configured to forward only those packets
   explicitly permitted in the rule set. Forwarded packets must be
   included in calculating the bit forwarding rate or maximum bit
   forwarding rate of the DUT/SUT. All other packets must not be
   included in bit forwarding rate calculations.
   This document assumes 1:1 correspondence of allowed traffic offered
   to the DUT/SUT and forwarded by the DUT/SUT. There are cases where
   the DUT/SUT may forward more traffic than it is offered; for
   example, the DUT/SUT may act as a mail exploder or a multicast
   server. Any attempt to benchmark forwarding rates of such traffic
   must include a description of how much traffic the tester expects
   to be forwarded.
 Unit of measurement:
   not applicable
 Issues:
 See also:
   policy
   rule set

3.2 Application proxy

 Definition:
   A proxy service that is set up and torn down in response to a
   client request, rather than existing on a static basis.
 Discussion:
   Circuit proxies always forward packets containing a given port
   number if that port number is permitted by the rule set.
   Application proxies, in contrast, forward packets only once a
   connection has been established using some known protocol. When the
   connection closes, a firewall using applicaton proxies rejects
   individual packets, even if they contain port numbers allowed by a
   rule set.

Newman Informational [Page 3] RFC 2647 Firewall Performance Terminology August 1999

 Unit of measurement:
   not applicable
 Issues:
   circuit proxy
   rule sets
 See also:
   allowed traffic
   circuit proxy
   proxy
   rejected traffic
   rule set

3.3 Authentication

 Definition:
   The process of verifying that a user requesting a network resource
   is who he, she, or it claims to be, and vice versa.
 Discussion:
   Trust is a critical concept in network security. Any network
   resource (such as a file server or printer) typically requires
   authentication before granting access.
   Authentication takes many forms, including but not limited to IP
   addresses; TCP or UDP port numbers; passwords; external token
   authentication cards; and biometric identification such as
   signature, speech, or retina recognition systems.
   The entity being authenticated might be the client machine (for
   example, by proving that a given IP source address really is that
   address, and not a rogue machine spoofing that address) or a user
   (by proving that the user really is who he, she, or it claims to
   be).  Servers might also authenticate themselves to clients.
   Testers should be aware that in an increasingly mobile society,
   authentication based on machine-specific criteria such as an IP
   address or port number is not equivalent to verifying that a given
   individual is making an access request. At this writing systems
   that verify the identity of users are typically external to the
   firewall, and may introduce additional latency to the overall SUT.
 Unit of measurement:
   not applicable
 Issues:

Newman Informational [Page 4] RFC 2647 Firewall Performance Terminology August 1999

 See also:
   user

3.4 Bit forwarding rate

 Definition:
   The number of bits per second of allowed traffic a DUT/SUT can be
   observed to transmit to the correct destination interface(s) in
   response to a specified offered load.
 Discussion:
   This definition differs substantially from section 3.17 of RFC 1242
   and section 3.6.1 of RFC 2285.
   Unlike both RFCs 1242 and 2285, this definition introduces the
   notion of different classes of traffic: allowed, illegal, and
   rejected (see definitions for each term). For benchmarking
   purposes, it is assumed that bit forwarding rate measurements
   include only allowed traffic.
   Unlike RFC 1242, there is no reference to lost or retransmitted
   data.  Forwarding rate is assumed to be a goodput measurement, in
   that only data successfully forwarded to the destination interface
   is measured.  Bit forwarding rate must be measured in relation to
   the offered load.  Bit forwarding rate may be measured with
   differed load levels, traffic orientation, and traffic
   distribution.
   Unlike RFC 2285, this measurement counts bits per second rather
   than frames per second. Testers interested in frame (or frame-like)
   measurements should use units of transfer.
 Unit of measurement:
   bits per second
 Issues:
   Allowed traffic vs. rejected traffic
 See also:
   allowed traffic
   goodput
   illegal traffic
   rejected traffic
   unit of transfer

Newman Informational [Page 5] RFC 2647 Firewall Performance Terminology August 1999

3.5 Circuit proxy

 Definition:
   A proxy service that statically defines which traffic will be
   forwarded.
 Discussion:
   The key difference between application and circuit proxies is that
   the latter are static and thus will always set up a connection if
   the DUT/SUT's rule set allows it. For example, if a firewall's rule
   set permits ftp connections, a circuit proxy will always forward
   traffic on TCP port 20 (ftp-data) even if no control connection was
   first established on TCP port 21 (ftp-control).
 Unit of measurement:
   not applicable
 Issues:
   application proxy
   rule sets
 See also:
   allowed traffic
   application proxy
   proxy
   rejected traffic
   rule set

3.6 Concurrent connections

 Definition:
   The aggregate number of simultaneous connections between hosts
   across the DUT/SUT, or between hosts and the DUT/SUT.
 Discussion:
   The number of concurrent connections a firewall can support is just
   as important a metric for some users as maximum bit forwarding
   rate.
   While "connection" describes only a state and not necessarily the
   transfer of data, concurrency assumes that all existing connections
   are in fact capable of transferring data. If a data cannot be sent
   over a connection, that connection should not be counted toward the
   number of concurrent connections.
   Further, this definition assumes that the ability (or lack thereof)
   to transfer data on a given connection is solely the responsibility
   of the DUT/SUT. For example, a TCP connection that a DUT/SUT has

Newman Informational [Page 6] RFC 2647 Firewall Performance Terminology August 1999

   left in a FIN_WAIT_2 state clearly should not be counted. But
   another connection that has temporarily stopped transferring data
   because some external device has restricted the flow of data is not
   necessarily defunct. The tester should take measures to isolate
   changes in connection state to those effected by the DUT/SUT.
 Unit of measurement:
   Concurrent connections
   Maximum number of concurrent connections
 Issues:
 See also:
   connections
   connection establishment time
   connection overhead

3.7 Connection

 Definition:
   A state in which two hosts, or a host and the DUT/SUT, agree to
   exchange data using a known protocol.
 Discussion:
   A connection is an abstraction describing an agreement between two
   nodes: One agrees to send data and the other agrees to receive it.
   Connections might use TCP, but they don't have to. Other protocols
   such as ATM also might be used, either instead of or in addition to
   TCP connections.
   What constitutes a connection depends on the application. For a
   native ATM application, connections and virtual circuits may be
   synonymous. For TCP/IP applications on ATM networks (where multiple
   TCP connections may ride over a single ATM virtual circuit), the
   number of TCP connections may be the most important consideration.
   Additionally, in some cases firewalls may handle a mixture of
   native TCP and native ATM connections. In this situation, the
   wrappers around user data will differ. The most meaningful metric
   describes what an end-user will see.
   Data connections describe state, not data transfer. The existence
   of a connection does not imply that data travels on that connection
   at any given time, although if data cannot be forwarded on a
   previously established connection that connection should not be
   considered in any aggregrate connection count (see concurrent
   connections).

Newman Informational [Page 7] RFC 2647 Firewall Performance Terminology August 1999

   A firewall's architecture dictates where a connection terminates.
   In the case of application or circuit proxy firewalls, a connection
   terminates at the DUT/SUT. But firewalls using packet filtering or
   stateful packet filtering designs act only as passthrough devices,
   in that they reside between two connection endpoints. Regardless of
   firewall architecture, the number of data connections is still
   relevant, since all firewalls perform some form of connection
   maintenance; at the  very least, all check connection requests
   against their rule sets.
   Further, note that connection is not an atomic unit of measurement
   in that it does not describe the various steps involved in
   connection setup, maintenance, and teardown. Testers may wish to
   take separate measurements of each of these components.
   When benchmarking firewall performance, it's important to identify
   the connection establishment and teardown procedures, as these must
   not be included when measuring steady-state forwarding rates.
   Further, forwarding rates must be measured only after any security
   associations have been established.
   Though it seems paradoxical, connectionless protocols such as UDP
   may also involve connections, at least for the purposes of firewall
   performance measurement. For example, one host may send UDP packets
   to another across a firewall. If the destination host is listening
   on the correct UDP port, it receives the UDP packets. For the
   purposes of firewall performance measurement, this is considered a
   connection.
 Unit of measurement:
   concurrent connections
   connection
   connection establishment time
   maximum number of concurrent connections
   connection teardown time
 Issues:
   application proxy vs. stateful packet filtering
   TCP/IP vs. ATM
   connection-oriented vs. connectionless
 See also:
   data source
   concurrent connections
   connection establishment

Newman Informational [Page 8] RFC 2647 Firewall Performance Terminology August 1999

   connection establishment time
   connection teardown
   connection teardown time

3.8 Connection establishment

 Definition:
   The data exchanged between hosts, or between a host and the
   DUT/SUT, to initiate a connection.
 Discussion:
   Connection-oriented protocols like TCP have a proscribed
   handshaking procedure when launching a connection. When
   benchmarking firewall performance, it is import to identify this
   handshaking procedure so that it is not included in measurements of
   bit forwarding rate or UOTs per second.
   Testers may also be interested in measurements of connection
   establishment time through or with a given DUT/SUT.
 Unit of measurement:
   not applicable
 See also:
   connection
   connection establishement time
   connection maintenance
   connection teardown
 Issues:
   not applicable

3.9 Connection establishment time

 Definition:
   The length of time needed for two hosts, or a host and the DUT/SUT,
   to agree to set up a connection using a known protocol.
 Discussion:
   Each connection-oriented protocol has its own defined mechanisms
   for setting up a connection. For purposes of benchmarking firewall
   performance, this shall be the interval between receipt of the
   first bit of the first octet of the packet carrying a connection
   establishment request on a DUT/SUT interface until transmission of
   the last bit of the last octet of the last packet of the connection
   setup traffic headed in the opposite direction.

Newman Informational [Page 9] RFC 2647 Firewall Performance Terminology August 1999

   This definition applies only to connection-oriented protocols such
   as TCP. For connectionless protocols such as UDP, the notion of
   connection establishment time is not meaningful.
 Unit of measurement:
   Connection establishment time
 Issues:
 See also:
   concurrent connections
   connection
   connection maintenance

3.10 Connection maintenance

 Definition:
   The data exchanged between hosts, or between a host and the
   DUT/SUT, to ensure a connection is kept alive.
 Discussion:
   Some implementations of TCP and other connection-oriented protocols
   use "keep-alive" data to maintain a connection during periods where
   no user data is exchanged.
   When benchmarking firewall performance, it is useful to identfy
   connection maintenance traffic as distinct from UOTs per second.
   Given that maintenance traffic may be characterized by short bursts
   at periodical intervals, it may not be possible to describe a
   steady-state forwarding rate for maintenance traffic. One possible
   approach is to identify the quantity of maintenance traffic, in
   bytes or bits, over a given interval, and divide through to derive
   a measurement of maintenance traffic forwarding rate.
 Unit of measurement:
   maintenance traffic
   forwarding rate
 See also:
   connection
   connection establishment time
   connection teardown
   connection teardown time
 Issues:
   not applicable

Newman Informational [Page 10] RFC 2647 Firewall Performance Terminology August 1999

3.11 Connection overhead

 Definition:
   The degradation in bit forwarding rate, if any, observed as a
   result of the addition of one connection between two hosts through
   the DUT/SUT, or the addition of one connection from a host to the
   DUT/SUT.
 Discussion:
   The memory cost of connection establishment and maintenance is
   highly implementation-specific. This metric is intended to describe
   that cost in a method visible outside the firewall.
   It may also be desirable to invert this metric to show the
   performance improvement as a result of tearing down one connection.
 Unit of measurement:
   bit forwarding rate
 Issues:

3.12 Connection teardown

 Definition:
   The data exchanged between hosts, or between a host and the
   DUT/SUT, to close a connection.
 Discussion:
   Connection-oriented protocols like TCP follow a stated procedure
   when ending a connection. When benchmarking firewall performance,
   it is important to identify the teardown procedure so that it is
   not included in measurements of bit forwarding rate or UOTs per
   second.
   Testers may also be interested in measurements of connection
   teardown time through or with a given DUT/SUT.
 Unit of measurement:
   not applicable
 See also:
   connection teardown time
 Issues:
   not applicable

Newman Informational [Page 11] RFC 2647 Firewall Performance Terminology August 1999

3.13 Connection teardown time

 Definition:
   The length of time needed for two hosts, or a host and the DUT/SUT,
   to agree to tear down a connection using a known protocol.
 Discussion:
   Each connection-oriented protocol has its own defined mechanisms
   for dropping a connection. For purposes of benchmarking firewall
   performance, this shall be the interval between receipt of the
   first bit of the first octet of the packet carrying a connection
   teardown request on a DUT/SUT interface until transmission of the
   last bit of the last octet of the last packet of the connection
   teardown traffic headed in the opposite direction.
   This definition applies only to connection-oriented protocols such
   as TCP. For connectionless protocols such as UDP, the notion of
   connection teardown time is not meaningful.
 Unit of measurement:
   Connection teardown time
 Issues:
 See also:
   concurrent connections
   connection
   connection maintenance

3.14 Data source

 Definition:
   A host capable of generating traffic to the DUT/SUT.
 Discussion:
   One data source may emulate multiple users or hosts. In addition,
   one data source may offer traffic to multiple network interfaces on
   the DUT/SUT.
   The term "data source" is deliberately independent of any number of
   users. It is useful to think of data sources simply as traffic
   generators, without any correlation to any given number of users.
 Unit of measurement:
   not applicable
 Issues:
   user

Newman Informational [Page 12] RFC 2647 Firewall Performance Terminology August 1999

 See also:
   connection
   user

3.15 Demilitarized zone

 Definition:
   A network segment or segments located between protected and
   unprotected networks.
 Discussion:
   As an extra security measure, networks may be designed such that
   protected and unprotected segments are never directly connected.
   Instead, firewalls (and possibly public resources such as HTTP or
   FTP servers) reside on a so-called DMZ network.
   DMZ networks are sometimes called perimeter networks.
 Unit of measurement:
   not applicable
 Issues:
   Homed
 See also:
   protected network
   unprotected network

3.16 Firewall

 Definition:
   A device or group of devices that enforces an access control policy
   between networks.
 Discussion:
   While there are many different ways to accomplish it, all firewalls
   do the same thing: control access between networks.
   The most common configuration involves a firewall connecting two
   segments (one protected and one unprotected), but this is not the
   only possible configuration. Many firewalls support tri-homing,
   allowing use of a DMZ network. It is possible for a firewall to
   accommodate more than three interfaces, each attached to a
   different network segment.
   The criteria by which access are controlled are not specified here.
   Typically this has been done using network- or transport-layer
   criteria (such as IP subnet or TCP port number), but there is no

Newman Informational [Page 13] RFC 2647 Firewall Performance Terminology August 1999

   reason this must always be so. A growing number of firewalls are
   controlling access at the application layer, using user
   identification as the criterion. And firewalls for ATM networks may
   control access based on data link-layer criteria.
 Unit of measurement:
   not applicable
 Issues:
 See also:
   DMZ
   tri-homed
   user

3.17 Goodput

 Definition:
   The number of bits per unit of time forwarded to the correct
   destination interface of the DUT/SUT, minus any bits lost or
   retransmitted.
 Discussion:
   Firewalls are generally insensitive to packet loss in the network.
   As such, measurements of gross bit forwarding rates are not
   meaningful since (in the case of proxy-based and stateful packet
   filtering firewalls) a receiving endpoint directly attached to a
   DUT/SUT would not receive any data dropped by the DUT/SUT.
   The type of traffic lost or retransmitted is protocol-dependent.
   TCP and ATM, for example, request different types  of
   retransmissions.  Testers must observe retransmitted data for the
   protocol in use, and subtract this quantity from measurements of
   gross bit forwarding rate.
 Unit of measurement:
   bits per second
 Issues:
   allowed vs. rejected traffic
 See also:
   allowed traffic
   bit forwarding rate
   rejected traffic

Newman Informational [Page 14] RFC 2647 Firewall Performance Terminology August 1999

3.18 Homed

 Definition:
   The number of logical interfaces a DUT/SUT contains.
 Discussion:
   Firewalls typically contain at least two logical interfaces. In
   network topologies where a DMZ is used, the firewall usually
   contains at least three interfaces and is said to be tri-homed.
   Additional interfaces would make a firewall quad-homed, quint-
   homed, and so on.
   It is theoretically possible for a firewall to contain one physical
   interface and multiple logical interfaces. This configuration is
   discouraged for testing purposes because of the difficulty in
   verifying that no leakage occurs between protected and unprotected
   segments.
 Unit of measurement:
   not applicable
 Issues:
 See also:
   tri-homed

3.19 Illegal traffic

 Definition:
   Packets specified for rejection in the rule set of the DUT/SUT.
 Discussion:
   A buggy or misconfigured firewall might forward packets even though
   its rule set specifies that these packets be dropped. Illegal
   traffic differs from rejected traffic in that it describes all
   traffic specified for rejection by the rule set, while rejected
   traffic specifies only those packets actually dropped by the
   DUT/SUT.
 Unit of measurement:
   not applicable
 Issues:

Newman Informational [Page 15] RFC 2647 Firewall Performance Terminology August 1999

 See also:
   accepted traffic
   policy
   rejected traffic
   rule set

3.20 Logging

 Definition:
   The recording of user requests made to the firewall.
 Discussion:
   Firewalls typically log all requests they handle, both allowed and
   rejected. For many firewall designs, logging requires a significant
   amount of processing overhead, especially when complex rule sets
   are in use.
   The type and amount of data logged varies by implementation.
   Testers may find it desirable to log equivalent data when comparing
   different DUT/SUTs.
   Some systems allow logging to take place on systems other than the
   DUT/SUT.
 Unit of measurement:
   not applicable
 Issues:
   rule sets
 See also:
   allowed traffic
   connection
   rejected traffic

3.21 Network address translation

 Definition:
   A method of mapping one or more private, reserved IP addresses to
   one or more public IP addresses.
 Discussion:
   In the interest of conserving the IPv4 address space, RFC 1918
   proposed the use of certain private (reserved) blocks of IP
   addresses. Connections to public networks are made by use of a
   device that translates one or more RFC 1918 addresses to one or
   more public addresses--a network address translator (NAT).

Newman Informational [Page 16] RFC 2647 Firewall Performance Terminology August 1999

   The use of private addressing also introduces a security benefit in
   that RFC 1918 addresses are not visible to hosts on the public
   Internet.
   Some NAT implementations are computationally intensive, and may
   affect bit forwarding rate.
 Unit of measurement:
   not applicable
 Issues:
 See also:

3.22 Packet filtering

 Definition:
   The process of controlling access by examining packets based on the
   content of packet headers.
 Discussion:
   Packet-filtering devices forward or deny packets based on
   information in each packet's header, such as IP address or TCP port
   number. A packet-filtering firewall uses a rule set to determine
   which traffic should be forwarded and which should be blocked.
 Unit of measurement:
   not applicable
 Issues:
   static vs. stateful packet filtering
 See also:
   application proxy
   circuit proxy
   proxy
   rule set
   stateful packet filtering

3.23 Policy

 Definition:
   A document defining acceptable access to protected, DMZ, and
   unprotected networks.

Newman Informational [Page 17] RFC 2647 Firewall Performance Terminology August 1999

 Discussion:
   Security policies generally do not spell out specific
   configurations for firewalls; rather, they set general guidelines
   for what is and is not acceptable network access.
   The actual mechanism for controlling access is usually the rule set
   implemented in the DUT/SUT.
 Unit of measurement:
   not applicable
 Issues:
 See also:
   rule set

3.24 Protected network

 Definition:
   A network segment or segments to which access is controlled by the
   DUT/SUT.
 Discussion:
   Firewalls are intended to prevent unauthorized access either to or
   from the protected network. Depending on the configuration
   specified by the policy and rule set, the DUT/SUT may allow hosts
   on the protected segment to act as clients for servers on either
   the DMZ or the unprotected network, or both.
   Protected networks are often called "internal networks." That term
   is not used here because firewalls increasingly are deployed within
   an organization, where all segments are by definition internal.
 Unit of measurement:
 not applicable
 Issues:
 See also:
   demilitarized zone (DMZ)
   unprotected network
   policy
   rule set
   unprotected network

Newman Informational [Page 18] RFC 2647 Firewall Performance Terminology August 1999

3.25 Proxy

 Definition:
   A request for a connection made on behalf of a host.
 Discussion:
   Proxy-based firewalls do not allow direct connections between
   hosts.  Instead, two connections are established: one between the
   client host and the DUT/SUT, and another between the DUT/SUT and
   server host.
   As with packet-filtering firewalls, proxy-based devices use a rule
   set to determine which traffic should be forwarded and which should
   be rejected.
   There are two types of proxies: application proxies and circuit
   proxies.
 Unit of measurement:
   not applicable
 Issues:
   application
 See also:
   application proxy
   circuit proxy
   packet filtering
   stateful packet filtering

3.26 Rejected traffic

 Definition:
   Packets dropped as a result of the rule set of the DUT/SUT.
 Discussion:
   For purposes of benchmarking firewall performance, it is expected
   that firewalls will reject all traffic not explicitly permitted in
   the rule set. Dropped packets must not be included in calculating
   the bit forwarding rate or maximum bit forwarding rate of the
   DUT/SUT.
 Unit of measurement:
   not applicable
 Issues:

Newman Informational [Page 19] RFC 2647 Firewall Performance Terminology August 1999

 See also:
   allowed traffic
   illegal traffic
   policy
   rule set

3.27 Rule set

 Definition:
   The collection of access control rules that determines which
   packets the DUT/SUT will forward and which it will reject.
 Discussion:
   Rule sets control access to and from the network interfaces of the
   DUT/SUT. By definition, rule sets do not apply equally to all
   network interfaces; otherwise there would be no need for the
   firewall. For benchmarking purposes, a specific rule set is
   typically applied to each network interface in the DUT/SUT.
   The tester must describe the complete contents of the rule set of
   each DUT/SUT.
   To ensure measurements reflect only traffic forwarded by the
   DUT/SUT, testers are encouraged to include a rule denying all
   access except for those packets allowed by the rule set.
 Unit of measurement:
   not applicable
 Issues:
 See also:
   allowed traffic
   demilitarized zone (DMZ)
   illegal traffic
   policy
   protected network
   rejected traffic
   unprotected network

3.28 Security association

 Definition:
   The set of security information relating to a given network
   connection or set of connections.

Newman Informational [Page 20] RFC 2647 Firewall Performance Terminology August 1999

 Discussion:
   This definition covers the relationship between policy and
   connections. Security associations (SAs) are typically set up
   during connection establishment, and they may be reiterated or
   revoked during a connection.
   For purposes of benchmarking firewall performance, measurements of
   bit forwarding rate or UOTs per second must be taken after all
   security associations have been established.
 Unit of measurement:
   not applicable
 See also:
   connection
   connection establishment
   policy
   rule set

3.29 Stateful packet filtering

 Definition:
   The process of forwarding or rejecting traffic based on the
   contents of a state table maintained by a firewall.
 Discussion:
   Packet filtering and proxy firewalls are essentially static, in
   that they always forward or reject packets based on the contents of
   the rule set.
   In contrast, devices using stateful packet filtering will only
   forward packets if they correspond with state information
   maintained by the device about each connection. For example, a
   stateful packet filtering device will reject a packet on port 20
   (ftp-data) if no connection has been established over the ftp
   control port (usually port 21).
 Unit of measurement:
   not applicable
 Issues:
 See also:
   applicaton proxy
   packet filtering
   proxy

Newman Informational [Page 21] RFC 2647 Firewall Performance Terminology August 1999

3.30 Tri-homed

 Definition:
   A firewall with three network interfaces.
 Discussion:
   Tri-homed firewalls connect three network segments with different
   network addresses. Typically, these would be protected, DMZ, and
   unprotected segments.
   A tri-homed firewall may offer some security advantages over
   firewalls with two interfaces. An attacker on an unprotected
   network may compromise hosts on the DMZ but still not reach any
   hosts on the protected network.
 Unit of measurement:
   not applicable
 Issues:
   Usually the differentiator between one segment and another is its
   IP address. However, firewalls may connect different networks of
   other types, such as ATM or Netware segments.
 See also:
   homed

3.31 Unit of transfer

 Definition:
   A discrete collection of bytes comprising at least one header and
   optional user data.
 Discussion:
   This metric is intended for use in describing steady-state
   forwarding rate of the DUT/SUT.
   The unit of transfer (UOT) definition is deliberately left open to
   interpretation, allowing the broadest possible application.
   Examples of UOTs include TCP segments, IP packets, Ethernet frames,
   and ATM cells.
   While the definition is deliberately broad, its interpretation must
   not be. The tester must describe what type of UOT will be offered
   to the DUT/SUT, and must offer these UOTs at a consistent rate.
   Traffic measurement must begin after all connection establishment
   routines complete and before any connection completion routine
   begins.  Further, measurements must begin after any security
   associations (SAs) are established and before any SA is revoked.

Newman Informational [Page 22] RFC 2647 Firewall Performance Terminology August 1999

   Testers also must compare only like UOTs. It is not appropriate,
   for example, to compare forwarding rates by offering 1,500-byte
   Ethernet UOTs to one DUT/SUT and 53-byte ATM cells to another.
 Unit of measurement:
   Units of transfer
   Units of transfer per second
 Issues:
 See also:
   bit forwarding rate
   connection

3.32 Unprotected network

 Definition:
   A network segment or segments to which access is not controlled by
   the DUT/SUT.
 Discussion:
   Firewalls are deployed between protected and unprotected segments.
   The unprotected network is not protected by the DUT/SUT.
   Note that a DUT/SUT's policy may specify hosts on an unprotected
   network. For example, a user on a protected network may be
   permitted to access an FTP server on an unprotected network. But
   the DUT/SUT cannot control access between hosts on the unprotected
   network.
 Unit of measurement:
   not applicable
 Issues:
 See also:
   demilitarized zone (DMZ)
   policy
   protected network
   rule set

3.33 User

 Definition:
   A person or process requesting access to resources protected by the
   DUT/SUT.

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 Discussion:
   "User" is a problematic term in the context of firewall performance
   testing, for several reasons. First, a user may in fact be a
   process or processes requesting services through the DUT/SUT.
   Second, different "user" requests may require radically different
   amounts of DUT/SUT resources. Third, traffic profiles vary widely
   from one organization to another, making it difficult to
   characterize the load offered by a typical user.
   For these reasons, testers should not attempt to measure DUT/SUT
   performance in terms of users supported. Instead, testers should
   describe performance in terms of maximum bit forwarding rate and
   maximum number of connections sustained. Further, testers should
   use the term "data source" rather than user to describe traffic
   generator(s).
 Unit of measurement:
   not applicable
 Issues:
 See also:
   data source

4. Security Considerations

 The primary goal of this memo is to describe terms used in
 benchmarking firewall performance. However, readers should be aware
 that there is some overlap between performance and security issues.
 Specifically, the optimal configuration for firewall performance may
 not be the most secure, and vice-versa.
 Further, certain forms of attack may degrade performance. One common
 form of denial-of-service (DoS) attack bombards a firewall with so
 much rejected traffic that it cannot forward allowed traffic. DoS
 attacks do not always involve heavy loads; by definition, DoS
 describes any state in which a firewall is offered rejected traffic
 that prohibits it from forwarding some or all allowed traffic. Even a
 small amount of traffic may significantly degrade firewall
 performance, or stop the firewall altogether. Further, the safeguards
 in firewalls to guard against such attacks may have a significant
 negative impact on performance.
 Since the library of attacks is constantly expanding, no attempt is
 made here to define specific attacks that may affect performance.
 Nonetheless, any reasonable performance benchmark should take into

Newman Informational [Page 24] RFC 2647 Firewall Performance Terminology August 1999

 consideration safeguards against such attacks. Specifically, the same
 safeguards should be in place when comparing performance of different
 firewall implementations.

5. References

 Bradner, S., Ed., "Benchmarking Terminology for Network
         Interconnection Devices", RFC 1242, July 1991.
 Bradner, S. and J. McQuaid, "Benchmarking Methodology for Network
         Interconnect Devices", RFC 2544, March 1999.
 Mandeville, R., "Benchmarking Terminology for LAN Switching Devices",
         RFC 2285, February 1998.
 Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G. and E. Lear,
         "Address Allocation for Private Internets", BCP 5, RFC 1918,
         February 1996.

6. Acknowledgments

 The author wishes to thank the IETF Benchmarking Working Group for
 agreeing to review this document. Several other persons offered
 valuable contributions and critiques during this project: Ted Doty
 (Internet Security Systems), Kevin Dubray (Ironbridge Networks),
 Helen Holzbaur, Dale Lancaster, Robert Mandeville, Brent Melson
 (NSTL), Steve Platt (NSTL), Marcus Ranum (Network Flight Recorder),
 Greg Shannon, Christoph Schuba (Sun Microsystems), Rick Siebenaler,
 and Greg Smith (Check Point Software Technologies).

7. Contact Information

 David Newman
 Data Communications magazine
 3 Park Ave.
 31st Floor
 New York, NY 10016
 USA
 Phone: 212-592-8256
 Fax:   212-592-8265
 EMail: dnewman@data.com

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8. Full Copyright Statement

 Copyright (C) The Internet Society (1999).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

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