Network Working Group                                         D. Newman
INTERNET-DRAFT                                      Data Communications
Expires in September 1998            H. Holzbaur, J. Hurd, and S. Platt
                                 National Software Testing Laboratories


           Benchmarking Terminology for Firewall Performance
                    <draft-ietf-bmwg-secperf-02.txt>

Status of This Memo

   This document is an Internet-Draft.  Internet-Drafts are working
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   1. Introduction ....................................................2
   2. Existing definitions ............................................3
   3. Term definitions ................................................3
     3.1 Allowed traffic ..............................................3
     3.2 Authentication ...............................................3
     3.3 Connection ...................................................4
     3.4 Data source ..................................................5
     3.5 Demilitarized zone (DMZ) .....................................5
     3.6 Dynamic proxy ................................................5
     3.7 Firewall .....................................................6
     3.8 Forwarding rate ..............................................6
     3.9 Goodput ......................................................7
     3.10 Homed .......................................................7
     3.11 Logging .....................................................8
     3.12 Network address translation (NAT) ...........................8
     3.13 Packet filtering ............................................9
     3.14 Perimeter network ...........................................9
     3.15 Policy .....................................................10
     3.16 Protected network ..........................................10
     3.17 Proxy ......................................................11
     3.18 Rejected traffic ...........................................11
     3.19 Rule set ...................................................11
     3.20 Session ....................................................12
     3.21 Stateful packet filtering ..................................13
     3.22 Tri-homed ..................................................13
     3.23 Unprotected network ........................................14
     3.24 User .......................................................14
4. Security considerations ...........................................15
5. References ........................................................15


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6. Acknowledgments ...................................................15
7. Contact information ...............................................16

. Introduction
   This document defines terms used in measuring the performance of
   firewalls. It extends the terminology already used for benchmarking
   routers and switches and adds terminology specific to firewalls. The
   primary metrics defined in this document are maximum forwarding rate
   and maximum number of connections.

   Why are firewall performance measurements needed? First, despite the
   rapid rise in firewall deployment, there is no standard means 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 low-speed wide-area
   connections. As a result, users are often unsure whether the products
   they buy will stand up to relatively heavy loads.

   We may also create additional terminology and methodology documents
   to define other types of network security products such as virtual
   private network (VPN) and encryption devices. This document, however,
   focuses solely on firewall terminology.

. 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.

. Term definitions

3.1 Allowed traffic

Definition:
Packets forwarded as a result of the rule set of the 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 forwarding rate or maximum forwarding rate of the
DUT/SUT. All other packets MUST NOT be included in forwarding rate
calculations.

Measurement units:
not applicable


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Issues:

See also:
policy
rule set

3.2 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 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

3.3 Connection

Definition:
A logical path established between two hosts, or between a host 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 forwarding rate.

Connections MAY be TCP sessions, but they don't have to be. Users of

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other connection-oriented protocols such as ATM may wish to use other
definitions of a connection, either instead of or in addition to TCP
connections.

What constitutes a connection depends on the application. For a "native
ATM" application like a video stream, connections and VCs can be
synonymous. For TCP/IP applications on ATM networks (where multiple TCP
sockets may ride over a single ATM virtual circuit), TCP sockets and
connections are synonymous.

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.

A firewall's architecture dictates where a connection is terminated. In
the case of proxy-based systems, a connection by definition 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.

Measurement units:
Maximum number of connections

Issues:
proxy-based vs. stateful packet filtering
TCP/IP vs. ATM

See also:
data source
session

3.4 Data source

Definition:
A station capable of generating traffic to the DUT/SUT.

Discussion:
One data source MAY emulate multiple users or stations. In addition, one
data source MAY offer traffic to multiple network interfaces on the
DUT/SUT.

Measurement units:
not applicable

Issues:
The term "data source" is deliberately independent of any number of

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users. It is useful to think of data sources simply as traffic
generators, without any correlation to any given number of users.

See also:
connection

3.5 Demilitarized zone (DMZ)

Definition:
A network segment or segments located between protected and unprotected
networks. DMZ networks are sometimes called perimeter networks.

Discussion:
As an extra security measure, networks are often designed such that
protected and unprotected segments are never directly connected.
Instead, firewalls (and possibly public resources such as WWW or FTP
servers) often reside on the 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.

Measurement units:
not applicable

Issues:
Homed

See also:
unprotected network
perimeter network
protected network

3.6 Dynamic 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:
Proxy services typically "listen" on a given TCP port number for client
requests. With static proxies, a firewall always forwards packets
containing a given TCP port number if that port number is permitted by
the rule set. Dynamic proxies, in contrast, forward TCP packets only
once an authenticated connection has been established. When the
connection closes, a firewall using dynamic proxies rejects individual
packets, even if they contain port numbers allowed by a rule set.

Measurement units:
not applicable

Issues:

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rule sets

See also:
allowed traffic
proxy
rejected traffic
rule set

3.7 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 is controlled is deliberately 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.

Measurement units:
not applicable

Issues:

See also:
DMZ
tri-homed
user

3.8 Forwarding rate

Definition:
The number of bits per second that a firewall can be observed to
transmit successfully to the correct destination interface 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 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

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interface is measured. Forwarding rate MUST be measured in relation to
the offered load. 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. Per-frame metrics are not meaningful in the context
of a flow of application data between endpoints.

Units of measurement:
bits per second

Issues:
Allowed traffic vs. rejected traffic

See also:
allowed traffic
goodput
rejected traffic

3.9 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 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 forwarding rate.

Unit of measurement:
bits per second

Issues:
allowed vs. rejected traffic

See also:
allowed traffic
forwarding rate
rejected traffic

3.10 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

3.11 Logging

Definition:
The recording of user requests made to the firewall.

Discussion:
Firewalls SHOULD 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
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
session

3.12 Network address translation (NAT)

Definition:
A method of mapping one or more private, reserved IP addresses to one or
more public IP addresses.

Discussion:

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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
forwarding rate.

Measurement units:
not applicable

Issues:

See also:

3.13  Packet filtering

Definition:
The process of controlling access by examining packets based on packet
header content.

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.

Measurement units:
not applicable

Issues:
static versus stateful packet filtering

See also:
dynamic proxy
proxy
rule set
stateful packet filtering

3.14 Perimeter network

Definition:
A network segment or segments located between protected and unprotected
networks. Perimeter networks are often called DMZ networks.

Discussion:
See the definition of DMZ for a discussion.

Measurement units:
not applicable

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Issues:
Tri-homed

See also:
demilitarized zone (DMZ)
unprotected network
protected network

3.15 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

3.16 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 stations 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:
not applicable

Issues:

See also:

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demilitarized zone (DMZ)
unprotected network
policy
rule set
unprotected network

3.17 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.

Proxies are generally application-specific.

Measurement units:
not applicable

Issues:
application

See also:
dynamic proxy
packet filtering
stateful packet filtering

3.18 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 forwarding
rate or maximum forwarding rate of the DUT/SUT.

Measurement units:
not applicable

Issues:

See also:
policy
rule set

3.19 Rule set


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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 order of rules within the rule set is critical. Firewalls generally
scan rule sets in a "top down" fashion, which is to say that the device
compares each packet received with each rule in the rule set until it
finds a rule that applies to the packet. Once the device finds an
applicable rule, it applies the actions defined in that rule (such as
forwarding or rejecting the packet) and ignores all subsequent rules.
For testing purposes, the rule set MUST conclude with a rule denying all
access.

Measurement units:
not applicable

Issues:

See also:
demilitarized zone (DMZ)
policy
protected network
rejected traffic
unprotected network

3.20 Session

Definition:
Data flowing through a previously established connection established
between two stations using a known protocol.

Discussion:
Because of the application-layer focus of many firewalls, sessions are a
more useful metric than the packet-based measurements used in
benchmarking routers and switches. Although firewall rule sets generally
work on a per-packet basis, it is ultimately sessions that a firewall
must handle. For example, the number of file transfer protocol (ftp)
sessions a DUT/SUT can handle concurrently is a more meaningful
measurement in benchmarking performance than the number of ftp "open"
packets it can reject. Further, a stateful packet filtering firewall
will not forward individual packets if those packets' headers conflict
with state information maintained by the firewall.

For purposes of this document, a session MUST be established using a
known protocol such as TCP. A traffic pattern is not considered a
session until it successfully completes the establishment procedures
defined by that protocol.

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Also for purposes of this document, a session constitutes the logical
connection between two end-stations and not the intermediate connections
that proxy-based firewalls may use.

Issues:
TCP/IP vs. ATM

See also:
connection
policy
proxy
rule set
stateful packet filtering

3.21 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 session. For example, a stateful packet filtering
device will reject a packet on port 20 (ftp-data) if no session has been
established over the ftp control port (usually port 21).

Measurement units:
not applicable

Issues:

See also:
dynamic proxy
packet filter
proxy

3.22 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

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compromise hosts on the DMZ but still not reach any hosts on the
protected network.

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

3.23 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.

Measurement units:
not applicable

Issues:

See also:
demilitarized zone (DMZ)
policy
protected network
rule set

3.24 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.

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For these reasons, we prefer not to measure DUT/SUT performance in terms
of users supported. Instead, we describe performance in terms of maximum
forwarding rate and maximum number of sessions sustained. Further, we
use the term "data source" rather than user to describe the traffic
generator(s).

Measurement units:
not applicable

Issues:

See also:
data source

. Security considerations

The primary goal of this memo is to describe terms used in measuring
firewall performance. However, readers should be aware that there is
some overlap between performance and security issues. Readers should be
aware that 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.

. 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.

. Acknowledgments

The authors wish 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), Shlomo Kramer (Check Point Software Technologies),
Robert Mandeville (European Network Laboratories), Brent Melson

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(National Software Testing Laboratories), Marcus Ranum (Network Flight
Recorder Inc.), Greg Shannon (Ascend Communications), Christoph Schuba
(Sun Microsystems), Rick Siebenaler (Cyberguard), and Greg Smith (Check
Point Software Technologies).

. Contact information

David Newman
Data Communications magazine
 Avenue of the Americas, 41st Floor
New York, NY 10020
USA
212-512-6182 voice
212-512-6833 fax
dnewman@data.com

Helen Holzbaur
National Software Testing Laboratories Inc.
 Ridge Pike
Conshohocken, PA 19428
USA
helen@nstl.com

Jim Hurd
National Software Testing Laboratories Inc.
 Ridge Pike
Conshohocken, PA 19428
USA
jimh@nstl.com

Steven Platt
National Software Testing Laboratories Inc.
 Ridge Pike
Conshohocken, PA 19428
USA
steve@nstl.com



















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