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


           Benchmarking Terminology for Firewall Performance
                    <draft-ietf-bmwg-secperf-01.txt>

Status of This Memo

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1. Introduction .......................................................2
2. Existing definitions ...............................................2
3. Term definitions ...................................................2
     3.1 Allowed traffic ..............................................2
     3.2 Authentication ...............................................3
     3.3 Data source ..................................................3
     3.4 Data connection ..............................................4
     3.5 Demilitarized zone (DMZ) .....................................4
     3.6 Dual-homed ...................................................5
     3.7 Dynamic proxy ................................................5
     3.8 External network .............................................6
     3.9 Homed ........................................................6
     3.10 Packet filtering ............................................6
     3.11 Perimeter network ...........................................7
     3.12 Policy ......................................................7
     3.13 Protected network ...........................................8
     3.14 Proxy .......................................................8
     3.15 Rejected traffic ............................................9
     3.16 Rule set ....................................................9
     3.17 Session .....................................................9
     3.18 Stateful inspection ........................................10
     3.19 Tri-homed ..................................................11
     3.20 User .......................................................11
4.  Security considerations ..........................................11
5. References ........................................................12
6. Acknowledgments ...................................................12
7. Contact Information ...............................................12

INTERNET-DRAFT      Firewall Performance Terminology      November 1997

. 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 deployment of firewalls, there is no standard method
   for benchmarking their performance. 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 draft-ietf-bmwg-lanswitch-07.txt (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

Issues:








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See also:
policy (3.12)
rule set (3.15)

3.2 Authentication

Definition:
The process of verifying that a client user or machine 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.

Authentication MAY work either by 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 by user (by proving that the
user really is who he or she claims to be). Servers SHOULD also
authenticate themselves to clients.

Measurement units:
Not applicable

Issues:
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 persons are typically external to the firewall, and may
introduce additional latency to the overall SUT.

See also:
user (3.20)

3.3 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:







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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, and not as a given number of users.

See also:
data connection (3.4)

3.4 Data connection

Definition:
A logical link established between two hosts, or between a host and the
DUT/SUT.

Discussion:
The number of concurrent data connections a firewall can field may be
just as important a metric for some users as the rate at which it can
forward traffic. Data connections MAY be TCP sessions, but they don't
have to be. Users of other connection-oriented protocols such as ATM may
wish to measure these, either instead of or in addition to TCP
connections.

Measurement units:
Number of connections

Issues:
A firewall's architecture dictates where the 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 inspection 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.

See also:
data source (3.3)

3.5 Demilitarized zone (DMZ)

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

Discussion:
As an extra security measure, networks are often designed such that
protected and external 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 external 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
external network MUST each have at least two network interfaces.







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Measurement units:
Not applicable

Issues:
Dual-homed
Homed

See also:
external network (3.8)
perimeter network (3.11)
protected network (3.13)

3.6 Dual-homed

Definition:
A firewall with at least two network interfaces.

Discussion:
Dual-homed firewalls connect two segments with different network
addresses.

Measurement units:
Not applicable

Issues:
Typically 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 (3.9)
Tri-homed (3.19)

3.7 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 (see section 3.14) 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 (3.1)
proxy (3.14)
rejected traffic (3.15)
rule set (3.16)

3.8 External network

Definition:
The segment or segments not protected by the network security DUT/SUT.

Discussion:
Firewalls are deployed between protected and unprotected segments. The
external network is not protected by the DUT/SUT.

Measurement units:
Not applicable

Issues:

See also:
demilitarized zone (DMZ) (3.5)
protected network (3.13)

3.9 Homed

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

Discussion:
Firewalls MUST contain at least two interfaces, using a dual-homed
configuration. 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.

Issues:
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 possibility of
leakage between protected and unprotected segments.

See also:
Dual-homed (3.6)
Tri-homed (3.19)

3.10 Packet filtering

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








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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 (see section 3.16) to determine which
traffic should be forwarded and which should be blocked.

Measurement units:
Not applicable

Issues:

See also:
dynamic proxy (3.7)
proxy (3.14)
rule set (3.16)
stateful inspection (3.18)

3.11 Perimeter network

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

Discussion:
See the definition of DMZ for a discussion.

Measurement units:
Not applicable

Issues:
Dual-homed
Tri-homed

See also:
Demilitarized zone (DMZ) (3.5)
external network (3.8)
protected network (3.13)

3.12 Policy

Definition:
A document defining acceptable use of protected, DMZ, and external
networks.

Discussion:
Security policies generally do not spell out specific configurations for
firewalls; rather, they set general guidelines for what it and is not
acceptable network behavior.

The actual mechanism for controlling access is usually the rule set (see
section 3.16) implemented in the DUT/SUT.

Measurement units:
Not applicable







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Issues:

See also:
Rule set (3.16)

3.13 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 external
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:
Demilitarized zone (DMZ) (3.5)
external network (3.8)
policy (3.12)
rule set (3.16)

3.14 Proxy

Definition:
A request for a connection made on behalf of a host.

Discussion:
Proxy-based firewalls never 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.

Measurement units:
Not applicable

Issues:

See also:







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dynamic proxy (3.7)
packet filtering (3.10)
stateful inspection (3.18)

3.15 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 (3.12)
rule set (3.16)

3.16 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 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) (3.5)
external network (3.8)
policy (3.12)







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protected network (3.13)
rejected traffic (3.15)

3.17 Session

Definition:
A logical 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 inspection 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.

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:

See also:
policy (3.12)
proxy (3.14)
rule set (3.16)
stateful inspection (3.18)

3.18 Stateful inspection

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 inspection will only forward packets
if they correspond with state information maintained by the device about
each session. For example, a stateful inspection device will reject a
packet on port 20 (ftp-data) if no session has been established over the
ftp control port (usually port 21).







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Measurement units:
Not applicable

Issues:

See also:
dynamic proxy (3.7)
packet filter (3.10)
proxy (3.14)

3.19 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
external segments.

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:
Dual-homed (3.6)
Homed (3.9)

3.20 User

Definition:
The person or machine 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 machine or
machines 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 users.

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).








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Measurement units:
Not applicable

Issues:

See also:
data source (3.3)

.  Security considerations
Security considerations are explicitly excluded from this memo. The
authors plan to address security and management concerns in a separate
proposal brought to the IETF's security directorate.

. 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, B. "Benchmarking Terminology for LAN Switching Devices."
ftp://ietf.org/internet-drafts/draft-ietf-bmwg-lanswitch-07.txt

Newman, D., and Melson, B. "Can Firewalls Take the Heat?" Data
Communications, November 21, 1995.
http://www.data.com/Lab_Tests/Firewalls.html

Newman, D., Holzbaur, H., and Bishop, K. "Firewalls: Don't Get Burned,"
Data Communications, March 21, 1997.
http://www.data.com/lab_tests/firewalls97.html

Ranum, M. "Firewall Performance Measurement Techniques: A Scientific
Approach." http://www.clark.net/pub/mjr/pubs/fwperf/intro.htm

Shannon, G. "Profile of Corporate Internet Application Traffic."
http://www.milkyway.com/libr/prof.html

. Acknowledgments
The authors wish to thank the IETF Benchmarking Working Group for
agreeing to review this document. Ted Doty (Internet Security Systems),
Shlomo Kramer (Check Point Software Technologies), Bob Mandeville
(European Network Laboratories), Brent Melson (National Software Testing
Laboratories), Marcus Ranum (Network Flight Recorder Inc.), Greg Shannon
(Ascend Communications), Rick Siebenaler (Cyberguard), and Greg Smith
(Check Point Software Technologies) offered valuable contributions and
critiques during this project.

. Contact Information
David Newman
Data Communications magazine
 Avenue of the Americas, 41st Floor
New York, NY 10020
USA







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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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