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

           Benchmarking Terminology for Firewall Performance
                    <draft-ietf-bmwg-secperf-05.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
   time.  It is inappropriate to use Internet- Drafts as reference
   material or to cite them other than as "work in progress."

   To view the entire list of current Internet-Drafts, please check the
   "1id-abstracts.txt" listing contained in the Internet-Drafts Shadow
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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

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


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     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

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

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   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.

   Measurement units:
   not applicable

   Issues:

   See also:
   policy

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   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.

   Measurement units:
   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) with restricted access MUST
   require 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 MAY 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 SHOULD 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

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   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.

   Measurement units:
   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). Any bit forwarding rate measurement MUST
   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.

   Units of measurement:
   bits per second

   Issues:
   Allowed traffic vs. rejected traffic

   See also:
   allowed traffic
   goodput
   illegal traffic
   rejected traffic
   unit of transfer

   3.5 Circuit proxy

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   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).

   Measurement units:
   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
   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.

   Measurement units:
   Concurrent connections

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   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
   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

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   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.

   Measurement units:
   concurrent connections
   connections
   connection establishment time
   maximum number of concurrent connections
   connection teardown time

   Issues:
   proxy-based 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.

   Testers may also be interested in measurements of connection
   establishment time through or with a given DUT/SUT.

   Measurement units:
   none


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   See also:
   connection
   connection establishement time
   connection maintenance
   connection teardown

   Issues:
   none

   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.

   Metric
   Connection establishment time

   Issues:

   See also:
   concurrent connections
   connection
   connection overhead

   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

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   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.

   Measurement units:
   maintenance traffic forwarding rate

   See also:
   connection
   connection establishment time
   connection teardown
   connection teardown time

   Issues:
   none

   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.

   Measurement units:
   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.

   Measurement units:
   none

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   See also:
   connection teardown time

   Issues:
   none

   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.

   Metric
   Connection teardown time

   Issues:

   See also:
   concurrent connections
   connection
   connection overhead

   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.

   Measurement units:
   not applicable

   Issues:

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   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 WWW or FTP
   servers) reside on a so-called DMZ network. To connect protected,
   DMZ, and unprotected networks with one device, the device MUST have
   at least three network interfaces.

   Multiple firewalls MAY bound the DMZ. In this case, the firewalls
   connecting the protected network with the DMZ and the DMZ with the
   unprotected network MUST each have at least two network interfaces.

   DMZ networks are sometimes called perimeter networks.

   Measurement units:
   not applicable

   Issues:
   Homed

   See also:
   unprotected network
   protected 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 is deliberately not

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   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.

   Measurement units:
   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.

   Discussion:

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   Firewalls MUST contain at least two logical interfaces. In network
   topologies where a DMZ is used, the firewall 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
   strongly discouraged for testing purposes because of the difficulty
   in verifying that no leakage occurs between protected and unprotected
   segments.

   Measurement units:
   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 may 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.

   Measurement units:
   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 MUST 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

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   SHOULD attempt to log equivalent data when comparing different
   DUT/SUTs.

   Logging MAY take place on systems other than the DUT/SUT.

   Measurement units:
   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.

   Measurement units:
   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.

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   Measurement units:
   not applicable

   Issues:
   static versus 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.

   Measurement units:
   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.

   Measurement units:

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   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.

   Measurement units:
   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:
   Firewalls MUST reject any 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.

   Measurement units:
   not applicable

   Issues:

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   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 MUST NOT apply equally to all
   network interfaces; otherwise there would be no need for the
   firewall. Therefore, a specific rule set MUST be 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 that testers measure only traffic forwarded or rejected by
   the DUT/SUT, each rule set MUST include a rule denying all access
   except for those packets allowed by the rule set.

   Measurement units:
   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.

   Discussion:
   This definition, taken verbatim from RFC 1825, 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

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   bit forwarding rate or UOTs per second MUST be taken after all
   security associations have been established.

   Measurement units:
   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).

   Measurement units:
   not applicable

   Issues:

   See also:
   applicaton proxy
   packet filter
   proxy

   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.

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   Measurement units:
   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.

   Measurement units:
   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.

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   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.

   Measurement units:
   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).

   Measurement units:
   not applicable

   Issues:

   See also:
   data source

4. Security considerations

   The primary goal of this memo is to describe terms used in

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   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

   Atkinson, R. "Security Architecture for the Internet Protocol." RFC
   1825.

   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

   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), Jim Hurd (NSTL), Dale Lancaster (Axent
   Technologies), Robert Mandeville (European Network Laboratories),
   Brent Melson (NSTL), Steve Platt (NSTL), Marcus Ranum (Network Flight
   Recorder Inc.), Greg Shannon (Ascend Communications), Christoph
   Schuba (Sun Microsystems), Rick Siebenaler (Cyberguard), and Greg
   Smith (Check Point Software Technologies).


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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
   dnewman@data.com












































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