Behavior of and Requirements for Internet Firewalls
RFC 2979
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RFC - Informational
(October 2000; No errata)
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2015-11-11
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IAB
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plain text
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IAB state
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(None)
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Consensus Boilerplate |
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Unknown
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RFC Editor Note |
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Network Working Group N. Freed
Request for Comments: 2979 Sun
Category: Informational October 2000
Behavior of and Requirements for
Internet Firewalls
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2000). All Rights Reserved.
Abstract
This memo defines behavioral characteristics of and interoperability
requirements for Internet firewalls. While most of these things may
seem obvious, current firewall behavior is often either unspecified
or underspecified and this lack of specificity often causes problems
in practice. This requirement is intended to be a necessary first
step in making the behavior of firewalls more consistent across
implementations and in line with accepted IP protocol practices.
1. Introduction
The Internet is being used for an increasing number of mission
critical applications. Because of this many sites find isolated
secure intranets insufficient for their needs, even when those
intranets are based on and use Internet protocols. Instead they find
it necessary to provide direct communications paths between the
sometimes hostile Internet and systems or networks which either deal
with valuable data, provide vital services, or both.
The security concerns that inevitably arise from such setups are
often dealt with by inserting one or more "firewalls" on the path
between the Internet and the internal network. A "firewall" is an
agent which screens network traffic in some way, blocking traffic it
believes to be inappropriate, dangerous, or both.
Note that firewall functions are disjoint from network address
translation (NAT) functions -- neither implies the other, although
sometimes both are provided by the same device. This document only
discusses firewall functions.
Freed Informational [Page 1]
RFC 2979 Firewall Requirements October 2000
1.1. Requirements notation
This document occasionally uses terms that appear in capital letters.
When the terms "MUST", "SHOULD", "MUST NOT", "SHOULD NOT", and "MAY"
appear capitalized, they are being used to indicate particular
requirements of this specification. A discussion of the meanings of
these terms appears in RFC 2119 [2].
2. Characteristics
Firewalls either act as a protocol end point and relay (e.g., a SMTP
client/server or a Web proxy agent), as a packet filter, or some
combination of both.
When a firewall acts a protocol end point it may
(1) implement a "safe" subset of the protocol,
(2) perform extensive protocol validity checks,
(3) use an implementation methodology designed to minimize
the likelihood of bugs,
(4) run in an insulated, "safe" environment, or
(5) use some combination of these techniques in tandem.
Firewalls acting as packet filters aren't visible as protocol end
points. The firewall examines each packet and then
(1) passes the packet through to the other side unchanged,
(2) drops the packet entirely, or
(3) handles the packet itself in some way.
Firewalls typically base some of their decisions on IP source and
destination addresses and port numbers. For example, firewalls may
(1) block packets from the Internet side that claim a source
address of a system on the internal network,
(2) block TELNET or RLOGIN connections from the Internet to the
internal network,
(3) block SMTP and FTP connections to the Internet from internal
systems not authorized to send email or move files,
Freed Informational [Page 2]
RFC 2979 Firewall Requirements October 2000
(4) act as an intermediate server in handling SMTP and HTTP
connections in either direction, or
(5) require the use of an access negotiation and encapsulation
protocol such as SOCKS [1] to gain access to the Internet, to
the internal network, or both.
(This list of decision criteria is only intended to illustrate the
sorts of factors firewalls often consider; it is by no means
exhaustive, nor are all firewall products able to perform all the
operations on this list.)
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