Subject: draft-ietf-bmwg-secperf-06.txt

From: Kevin Dubray <[email-masked]>
Date: Thu, 06 May 1999 07:47:26 -0400

Network Working Group                                          D. Newman
INTERNET-DRAFT                                       Data Communications
Expires in July 1999                                        January 1999

           Benchmarking Terminology for Firewall Performance
                    <draft-ietf-bmwg-secperf-06.txt>

Status of This Memo

  This document is an Internet-Draft.  Internet-Drafts are working
  documents of the Internet Engineering Task Force (IETF), its areas,
  and its working groups.  Note that other groups may also distribute
  working documents as Internet-Drafts.

  Internet-Drafts are draft documents valid for a maximum of six months
  and may be updated, replaced, or obsoleted by other documents at any
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  To view the entire list of current Internet-Drafts, please check the
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  munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or
  ftp.isi.edu (US West Coast).

1. Introduction......................................................2

2. Existing definitions..............................................3

3. Term definitions..................................................3

3.1 Allowed traffic..................................................3

3.2 Application proxy................................................4

3.3 Authentication...................................................4

3.4 Bit forwarding rate..............................................5

3.5 Circuit proxy....................................................5

3.6 Concurrent connections...........................................6

3.7 Connection.......................................................7

3.8 Connection establishment.........................................8

3.9 Connection establishment time....................................9

3.10 Connection maintenance..........................................9

3.11 Conection overhead.............................................10

3.12 Connection teardown............................................10

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3.13 Connection teardown time.......................................11

3.14 Data source....................................................11

3.15 Demilitarized zone.............................................12

3.16 Firewall.......................................................12

3.17 Goodput........................................................13

3.18 Homed..........................................................13

3.19 Illegal traffic................................................14

3.20 Logging........................................................14

3.21 Network address translation....................................15

3.22 Packet filtering...............................................15

3.23 Policy.........................................................16

3.24 Protected network..............................................16

3.25 Proxy..........................................................17

3.26 Rejected traffic...............................................17

3.27 Rule set.......................................................18

3.28 Security association...........................................18

3.29 Stateful packet filtering......................................19

3.30 Tri-homed......................................................19

3.31 Unit of transfer...............................................20

3.32 Unprotected network............................................20

3.33 User...........................................................21

4. Security considerations..........................................21

5. References.......................................................22

6. Acknowledgments..................................................22

7. Contact information..............................................23

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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 1944 (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.

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:

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  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.

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

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  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:

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

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  goodput
  illegal traffic
  rejected traffic
  unit of transfer

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 left
  in a FIN_WAIT_2 state clearly should not be counted. But another
  connection that has temporarily stopped transferring data because

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  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 MAY use TCP, but they don't have to. Other protocols such
  as ATM also may 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).

  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

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  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
  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.

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  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.

  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.

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  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

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

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  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

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.

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  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

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.

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  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
  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

3.18 Homed

Definition:
  The number of logical interfaces a DUT/SUT contains.

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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:

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

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  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).

  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.

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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.

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.

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  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

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

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  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:

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.

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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

3.30 Tri-homed

Definition:
  A firewall with three network interfaces.

Discussion:

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  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.

  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:

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  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.

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

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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--such as the recent Teardrop2 attack
  involving a few packet fragments--may significantly degrade firewall
  performance, or stop the firewall altogether. Further, the safeguards
  in firewalls to guard against such attacks may have 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 must take
  safeguards against such attacks into consideration. Specifically, the
  same safeguards must be in place when comparing performance of
  different firewall implementations.

5. References

  Bradner, S., editor. "Benchmarking Terminology for Network
  Interconnection Devices." RFC 1242.

  Bradner, S., and McQuaid, J. "Benchmarking Methodology for Network
  Interconnect Devices." RFC 1944.

  Mandeville, R. "Benchmarking Terminology for LAN Switching Devices."
  RFC 2285.

  Rekhter, Y., et al. "Address Allocation for Private Internets." RFC
  1918.

6. Acknowledgments

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  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 (NSTL), Dale Lancaster (Axent Technologies), Robert
  Mandeville (European Network Laboratories), Brent Melson (NSTL),
  Steve Platt (NSTL), Marcus Ranum (Network Flight Recorder), Greg
  Shannon (Ascend Communications), Christoph Schuba (Sun Microsystems),
  Rick Siebenaler (Cyberguard), 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
  212-592-8256 voice
  212-592-8265 fax
  [email-masked]

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