On Firewalls in Internet Security
draft-gont-opsawg-firewalls-analysis-00
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| Last updated | 2015-09-14 | ||
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draft-gont-opsawg-firewalls-analysis-00
Operations Area Working Group F. Gont
Internet-Draft SI6 Networks / UTN-FRH
Intended status: Best Current Practice F. Baker
Expires: March 18, 2016 Cisco Systems
P. Hoffman
VPN Consortium
September 15, 2015
On Firewalls in Internet Security
draft-gont-opsawg-firewalls-analysis-00
Abstract
This document analyzes the role of firewalls in Internet security,
and suggests a line of reasoning about their usage. It analyzes
common kinds of firewalls and the claims made for them.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Drafts is at http://datatracker.ietf.org/drafts/current/.
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."
This Internet-Draft will expire on March 18, 2016.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Reasoning about Firewalls . . . . . . . . . . . . . . . . . . 3
3.1. The Role of Firewalls in Internet Security . . . . . . . 3
3.2. The End-to-End Principle . . . . . . . . . . . . . . . . 4
3.3. Building a communication . . . . . . . . . . . . . . . . 5
3.4. The middle way . . . . . . . . . . . . . . . . . . . . . 5
4. Common kinds of firewalls . . . . . . . . . . . . . . . . . . 6
4.1. Perimeter security: Protection from aliens and intruders 6
4.2. Pervasive access control . . . . . . . . . . . . . . . . 8
4.3. Intrusion Management: Contract and Reputation filters . . 8
5. Firewalling Strategies . . . . . . . . . . . . . . . . . . . 10
5.1. Blocking Traffic Unless It Is Explicitly Allowed (default
deny) . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6. Assumptions on IP addresses and Transport Protocol Port
Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
7. State Associated with Packet Filtering . . . . . . . . . . . 11
8. Enforcing Protocol Syntax at the Firewall . . . . . . . . . . 12
9. Performing Deep Packet Inspection . . . . . . . . . . . . . . 12
10. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 13
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
12. Security Considerations . . . . . . . . . . . . . . . . . . . 14
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
14.1. Normative References . . . . . . . . . . . . . . . . . . 14
14.2. Informative References . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction
The IETF has a long and fractured discussion on security. Many early
RFCs simply didn't address the topic - and said as much. When the
IESG started complaining about that, it was told that there was no
market interest in the topic that was measurable in money spent.
Those who *were* interested in the topic set forth frameworks, rules,
and procedures without necessarily explaining how they would be
useful in deployment, and dismissed questions as "from those who
don't understand." In many cases, as a result, deployments have been
underwhelming in both quantity and quality, and the Internet is noted
for its problems with security. What is clear is that people need to
think clearly about security, their own and that of others. What is
not clear is how to do so in a coherent and scalable manner.
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Prophylactic perimeter security in the form of firewalls, and the
proper use of them, have been a fractious sub-topic in this area.
This document suggests a line of reasoning about the use of
firewalls, and attempts to end the bickering on the topic, which is,
for the most part, of little value in illuminating the discussion.
It also analyzes common kinds of firewalls and the claims made for
them.
2. Terminology
In this document, a firewall is defined as a device or software that
imposes a policy whose effect is "a stated type of packets may or may
not pass from A to B". All modern firewalls allow an administrator
to change the policies in the firewall, although the ease of
administration for making those changes, and the granularity of the
policies, vary widely between firewalls and vendors.
Given this definition, it is easy to see that there is a perimeter
(the position between A and B) in which the specific security policy
applies. In typical deployed networks, there are usually some easy-
to-define perimeters. If two or more networks that are connected by
a single device, the perimeter is inside the device. If that device
is a firewall, it can impose a security policy at the shared
perimeters of those networks.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3. Reasoning about Firewalls
3.1. The Role of Firewalls in Internet Security
One could compare the role of firewalls in prophylactic perimeter
security to that of the human skin: the service that the skin
performs for the rest of the body is to keep common crud out, and as
a result prevent much damage and infection that could otherwise
occur. The body supplies prophylactic perimeter security for itself
and then presumes that the security perimeter has been breached; real
defenses against attacks on the body include powerful systems that
detect changes (anomalies) counterproductive to human health, and
recognizable attack syndromes such as common or recently-seen
diseases. One might well ask, in view of those superior defenses,
whether there is any value in the skin at all; the value is easily
stated, however. It is not in preventing the need for the stronger
solutions, but in making their expensive invocation less needful and
more focused.
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3.2. The End-to-End Principle
One common complaint about firewalls in general is that they violate
the End-to-End Principle [Saltzer]. The End-to-End Principle is
often incorrectly stated as requiring that "application specific
functions ought to reside in the end nodes of a network rather than
in intermediary nodes, provided they can be implemented 'completely
and correctly' in the end nodes" or that "there should be no state in
the network." What it actually says is heavily nuanced, and is a
line of reasoning applicable when considering any two communication
layers.
[Saltzer] "presents a design principle that helps guide placement
of functions among the modules of a distributed computer system.
The principle, called the end-to-end argument, suggests that
functions placed at low levels of a system may be redundant or of
little value when compared with the cost of providing them at that
low level."
In other words, the End-to-End Argument is not a prohibition against
e.g. lower layer retries of transmissions, which can be important in
certain LAN technologies, nor of the maintenance of state, nor of
consistent policies imposed for security reasons. It is, however, a
plea for simplicity. Any behavior of a lower communication layer,
whether found in the same system as the higher layer (and especially
application) functionality or in a different one, that from the
perspective of a higher layer introduces inconsistency, complexity,
or coupling extracts a cost. That cost may be in user satisfaction,
difficulty of management or fault diagnosis, difficulty of future
innovation, reduced performance, or other forms. Such costs need to
be clearly and honestly weighed against the benefits expected, and
used only if the benefit outweighs the cost.
From that perspective, introduction of a policy that prevents
communication under an understood set of circumstances, whether it is
to prevent access to pornographic sites or prevents traffic that can
be characterized as an attack, does not fail the End-to-End Argument;
there are any number of possible sites on the network that are
inaccessible at any given time, and the presence of such a policy is
easily explained and understood.
What does fail the End-to-End Argument is behavior that is
intermittent, difficult to explain, or unpredictable. If I can
sometimes reach a site and not at other times, or reach it using this
host or application but not another, I wonder why that is true, and
may not even know where to look for the issue.
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3.3. Building a communication
Any communication requires at least three components:
o a sender, someone or some thing that sends a message,
o a receiver, someone or some thing that receives the message, and
o a channel, which is a medium by which the message is communicated.
In the Internet, the IP network is the channel; it may traverse
something as simple as a directly connected cable or as complex as a
sequence of ISPs, but it is the means of communication. In normal
communications, a sender sends a message via the channel to the
receiver, who is willing to receive and operate on it. In contrast,
attacks are a form of harassment. A receiver exists, but is
unwilling to receive the message, has no application to operate on
it, or is by policy unwilling to. Attacks on infrastructure occur
when message volume overwhelms infrastructure or uses infrastructure
but has no obvious receiver.
By that line of reasoning, a firewall primarily protects
infrastructure, by preventing traffic that would attack it from it.
The best prophylactic might use a procedure for the dissemination of
Flow Specification Rules [RFC5575] to drop traffic sent by an
unauthorized or inappropriate sender or which has no host or
application willing to receive it as close as possible to the sender.
In other words, as discussed in Section 3.1, a firewall compares to
the human skin, and has as its primary purpose the prophylactic
defense of a network. By extension, the firewall also protects a set
of hosts and applications, and the bandwidth that serves them, as
part of a strategy of defense in depth. A firewall is not itself a
security strategy; the analogy to the skin would say that a body
protected only by the skin has an immune system deficiency and cannot
be expected to long survive. That said, every security solution has
a set of vulnerabilities; the vulnerabilities of a layered defense is
the intersection of the vulnerabilities of the various layers (e.g.,
a successful attack has to thread each layer of defense).
3.4. The middle way
There is therefore no one way to prevent attacks; there are different
kinds of firewalls, and they address different views of the network
(please see Section 4 for further discussion). A zone-based firewall
(Section 4.1) views the network as containing zones of trust, and
deems applications inside its zone of protection to be trustworthy.
A role-based firewall (Section 4.2) identifies parties on the basis
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of membership in groups, and prevents unauthorized communication
between groups. A reputation, anomaly, or signature-based intrusion
management system (Section 4.3) depends on active administration, and
permits known applications to communicate while excluding unknown or
known-evil applications. In each case, the host or application is
its own final bastion of defense, but preventing a host from
accepting incoming traffic (so-called "host firewalls") does not
defend infrastructure. Each type of prophylactic has a purpose, and
none of them is a complete prophylactic defense.
Each type of defense, however, can be assisted by enabling an
application running in a host to inform the network of what it is
willing to receive. As noted in Section 4.1, a zone-based firewall,
generally denies all incoming sessions and permits responses to
sessions initiated outbound from the zone, but can in some cases be
configured to also permit specific classes of incoming session
requests, such as WWW or SMTP to an appropriate server. A simple way
to enable a zone-based firewall to prevent attacks on infrastructure
(traffic to an un-instantiated address or to an application that is
off) while not impeding traffic that has a willing host and
application would be for the application to inform the firewall of
that willingness to receive. The Port Control Protocol [RFC6887], or
PCP, is an example of a protocol designed for that purpose.
4. Common kinds of firewalls
There are at least three common kinds of firewalls:
o Context or Zone-based firewalls, that protect systems within a
perimeter from systems outside it,
o Pervasive routing-based measures, which protect intermingled
systems from each other by enforcing role-based policies, and
o Systems that analyze application behavior and trigger on events
that are unusual, match a signature, or involve an untrusted peer.
4.1. Perimeter security: Protection from aliens and intruders
As discussed in [RFC6092], the most common kind of firewall is used
at the perimeter of a network. Perimeter security assumes two
things: that applications and equipment inside the perimeter are
under the control of the local administration and are therefore
probably doing reasonable things, and that applications and equipment
outside the perimeter are unknown. It may enforce simple permission
rules, such as that external web clients are permitted to access a
specific web server or that external SMTP MTAs are permitted to
access internal SMTP MTAs. Apart from those rules, a session may be
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initiated from inside the perimeter, and responses from outside will
be allowed through the firewall, but sessions may never be initiated
from outside.
In addition, perimeter firewalls often perform some level of testing,
either as application proxies or through deep packet inspection, to
verify that the protocol claimed to be being passed is in fact the
protocol being passed.
In many scenarios the existence and definition of zone-based
perimeter defenses is arguably a side-effect of the deployment of
Network Address Translation [RFC2993]. Since e.g. a single address
is shared among multiple systems, the NAT device needs to translate
both the IP addresses and the transport protocol ports in order to
multiplex multiple communication instances from different nodes in
the same external address. Thus, the NAT device must keep a state
table to know how to translate the IP addresses and transport
protocol ports of incoming packets. Packets originating from the
internal network will either match an existing entry in the state
table, or create a new one. On the other hand, packets originating
in the external network will either match an existing entry in the
state table, or be dropped. Thus, as a side effect, NATs implicitly
require that communication be initiated from the internal network,
and only allow return traffic from the external network.
Some applications make the mistake of coupling application identities
to network layer addresses, and hence employ such addresses in the
application protocol. Thus, Network Address Translation forces the
translator to interpret packet payloads and change addresses where
used by applications.
As a result, if the transport or application headers are not
understood by the translator, this has the effect of damaging or
preventing communication. Detection of such issues can be sold as a
security feature, although it is really a side-effect of a failure.
While this can have useful side-effects, such as preventing the
passage of attack traffic that masquerades as some well-known
protocol, it also has the nasty side-effect of making innovation
difficult. This has slowed the deployment of SCTP [RFC4960], since a
firewall will often not permit a protocol it doesn't know even if a
user behind it opens the session. When a new protocol or feature is
defined, the firewall needs to stop applying that rule, and that can
be difficult to make happen.
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4.2. Pervasive access control
Another access control model, often called "Role-based", tries to
control traffic in flight regardless of the perimeter. Given a rule
that equipment located in a given routing domain or with a specific
characteristic (such as "student dorms") should not be able to access
equipment in another domain or with a specific characteristic (such
as "academic records"), it might prevent routing from announcing the
second route in the domain of the first, or it might tag individual
packets ("I'm from the student dorm") and filter on those tags at
enforcement points throughout network. Such rules can be applied to
individuals as well as equipment; in that case, the host needs to tag
the traffic, or there must be a reliable correlation between
equipment and its user.
One common use of this model is in data centers, in which physical or
virtual machines from one tenant (which is not necessarily an "owner"
as much as it is a context in which the system is used) might be co-
resident with physical or virtual machines from another. Inter-
tenant attacks, espionage, and fraud are prevented by enforcing a
rule that traffic from systems used by any given tenant is only
delivered to other systems used by the same tenant. This might, of
course have nuances; under stated circumstances, identified systems
or identified users might be able to cross such a boundary.
The major impediment in deployment is complexity. The administration
has the option to assign policies for individuals on the basis of
their current location (e.g. as the cross-product of people,
equipment, and topology), meaning that policies can multiply wildly.
The administrator that applies a complex role-based access policy is
probably most justly condemned to live in the world he or she has
created.
4.3. Intrusion Management: Contract and Reputation filters
The model proposed in Advanced Security for IPv6 CPE
[I-D.vyncke-advanced-ipv6-security] could be compared to purchasing
an anti-virus software package for one's computer. The proposal is
to install a set of filters, perhaps automatically updated, that
identify "bad stuff" and make it inaccessible, while not impeding
anything else.
It depends on four basic features:
o A frequently-updated signature-based Intrusion Prevention System
which inspects a pre-defined set of protocols at all layers (from
layer-3 to layer-7) and uses a vast set of heuristics to detect
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attacks within one or several flows. Upon detection, the flow is
terminated and an event is logged for further optional auditing.
o A centralized reputation database that scores prefixes for degree
of trust. This is unlikely to be on addresses per se, since e.g.
temporary addresses [RFC4941] change regularly and frequently.
o Local correlation of attack-related information, and
o Global correlation of attacks seen, in a reputation database
The proposal doesn't mention anomaly-based intrusion detection, which
could be used to detect zero-day attacks and new applications or
attacks. This would be an obvious extension.
The comparison to anti-virus software is real; anti-virus software
uses similar algorithms, but on API calls or on data exchanged rather
than on network traffic, and for identified threats is often
effective.
The proposal also has weaknesses:
o People don't generally maintain anti-virus packages very well,
letting contracts expire,
o Reputation databases have a bad reputation for distributing
information which is incorrect or out of date,
o Anomaly-based analysis identifies changes but is often ineffective
in determining whether new application or application behaviors
are pernicious (false positives). Someone therefore has to
actively decide - a workload the average homeowner might have
little patience for, and
o Signature-based analysis applies to attacks that have been
previously identified, and must be updated as new attacks develop.
As a result, in a world in which new attacks literally arise
daily, the administrative workload can be intense, and reflexive
responses like accepting https certificates that are out of date
or the download and installation of unsigned software on the
assumption that the site admin is behind are themselves vectors
for attack.
Security has to be maintained to be useful, because attacks are
maintained.
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5. Firewalling Strategies
There is a great deal of tension in firewall policies between two
primary goals of networking: the security goal of "block traffic
unless it is explicitly allowed" and the networking goal of "trust
hosts with new protocols". The two inherently cannot coexist easily
in a set of policies for a firewall.
5.1. Blocking Traffic Unless It Is Explicitly Allowed (default deny)
Many networks enforce the so-called "default deny" policy, in which
traffic is blocked unless it is explicitly allowed. The rationale
for such policy is that it is easier to open "holes" in a firewall
for allowing specific protocols, than trying to block all protocols
that might be employed as an attack vectors; and that a network
should only support the protocols it has been explicitly designed to
support.
The drawback of this approach is that the security goal of "block
traffic unless it is explicitly allowed" prevents useful new
applications. This problem has been seen repeatedly over the past
decade: a new and useful application protocol is specified, but it
cannot get wide adoption because it is blocked by firewalls. The
result has been a tendency to try to run new protocols over
established applications, particularly over HTTP [RFC3205]. The
result is protocols that do not work as well they might if they were
designed from scratch.
Worse, the same goal prevents the deployment of useful transports
other than TCP, UDP, and ICMP. A conservative firewall that only
knows those three transports will block new transports such as SCTP
[RFC4960]; this in turn causes the Internet to not be able to grow in
a healthy fashion. Many firewalls will also block TCP and UDP
options they don't understand, and this has the same unfortunate
result.
6. Assumptions on IP addresses and Transport Protocol Port Numbers
In a number of scenarios, firewalls rules have traditionally been
specified in terms of the associated IP addresses and transport
protocol port numbers. In general, this assumes that the associated
IP addresses are stable, and that there is a "well known" transport
protocol port number associated with each application.
In the IPv4 world, IP addresses may be considered rather stable.
However, IPv6 introduces the concept of "temporary addresses"
[RFC4941] which, by definition, change over time. This may prevent
the enforcement of filtering policies based on specific IPv6
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addresses, or may lead to filtering based on a specific address
prefixes (as opposed to specific IPv6 addresses). In some scenarios,
from the point of view of enforcing filtering policies, it might be
desirable to disable temporary addresses altogether.
For example, an administrator might prefer that the caching DNS
server or SMTP MTA always employ the same source IPv6 address, as
opposed to the temporary addresses that change over time.
The server-side transport protocol port is generally the so-called
"well-known port" corresponding to the associated application. While
widespread, this practice should probably be considered a kludge/
short-cut rather than a "design principle" that can be relied upon
for the general case. For example, use of DNS SRV records [RFC2782],
or applications such as "portmapper" [Portmap] [RFC1833] might mean
that the associated transport protocol port number cannot be assumed
to be well-known, but rather needs to be dynamically learned.
7. State Associated with Packet Filtering
There are two main paradigms for packet filtering:
o Stateless filtering
o Stateful filtering
Stateless filtering implies that the decision on whether to allow or
block a specific packet is solely based on the contents of such
packet. One common example of such paradigm is the enforcement of
network ingress filtering [RFC2827], in which packets may be blocked
based on their IP addresses. Stateless filtering scales well, since
there are no state requirements on the filtering device other than
that associated with maintaining the filtering rules to be applied to
incoming packets.
On the other hand, stateful filtering implies that the decision on
whether to allow or block a packet is not only based on the contents
of the packet, but also on the existence (or lack of) previous
traffic/state associated with such packet. A common example of such
paradigm is a firewall that "allows outbound connection requests and
only allows return traffic from the external network" (such as the
policy implicitly enforced my most NAT devices). For obvious
reasons, the firewall needs to maintain state in order to be able to
enforce such policies. For example, a firewall may need to keep
track of all on-going communication instances, possibly applying
timeouts and garbage collection on the associated state table.
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Stateful filtering tends to allow more powerful packet filtering, at
the expense of increased state. Thus, stateful filtering may be
desirable when trying to perform deep packet inspection, but may be
undesirable when the firewall is meant to block some Denial of
Service attacks, since the firewall itself may become "the weakest
link in the chain".
8. Enforcing Protocol Syntax at the Firewall
Some firewalls try to enforce the protocol syntax by checking that
only packets complying with existing protocol definitions are
allowed. While this can have useful side-effects, such as preventing
the passage of attack traffic that masquerades as some well-known
protocol, it also has the nasty side-effect of making innovation
difficult. For example, one of the issues in the deployment of
Explicit Congestion Notification [RFC3168] has been that common
firewalls often test reserved/unused bits and require them to be set
to zero to close covert channels. When a new protocol or feature is
defined, the firewall needs to stop applying that rule, and that can
be difficult to make happen.
A somewhat related concept is that of traffic normalization (or
"scrubbing"), in which the filtering device can "normalize" traffic
by e.g. clearing bits that are expected to be cleared, changing some
protocol fields such that they are within "normal" ranges, etc. (see
e.g. the discussion of "traffic normalization" in [OpenBSD-PF]).
While this can have the useful effect of blocking DoS attacks to
sloppy implementations that do not enforce sanity checks on the
received packets, it also has the nasty side-effect of making
innovation difficult, or even breaking deployed protocols.
For example, some firewalls are known enforce a default packet
normalization policy that clears the TCP URG bit, as a result of
the TCP urgent mechanism being associated with some popular DoS
attacks. Widespread deployment of such firewalls has essentially
rendered the TCP urgent mechanism unusable, leading to its
eventual formal deprecation in [RFC6093].
9. Performing Deep Packet Inspection
While filtering packets based on the layer-3 protocol header fields
is rather simple and straight-forward, performing packet filtering
based on the upper layer protocols can be a challenging task.
For example, IP fragmentation may make this task quite challenging,
since even the very layer-4 protocol header could be present in a
non-first fragment. In a similar vein, IPv6 extension headers may
represent a challenge for a filtering device, since they can result
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in long IPv6 extension header chains [RFC7112]
[I-D.gont-v6ops-ipv6-ehs-packet-drops].
This problem is exacerbated as one tries to filter packets based on
upper layer protocol contents, since many of such protocols implement
some form of fragmentation/segmentation and reassembly. In many
cases, the reassembly process could possibly lead to different
results, and this may be exploited by attackers for circumventing
security controls [Ptacek1998] [RFC6274].
In general, the upper in the protocol stack that packet filtering is
performed, the more state that is required at the filtering device.
And when stateful packet filtering is warranted, its associated
security implications should be considered.
10. Recommendations
Zone-based firewalls, when used, SHOULD exclude all session
initiation from outside the zone regardless of attributes such as the
use of IPsec. They SHOULD also facilitate the use of a protocol such
as PCP by hosts to identify traffic (IPsec AH, IPsec ESP, transports
in general, or transports using specified destination port ranges)
that they are willing to receive, and interpret that into rules
permitting specified traffic to those specific systems. Being fully
automated and easily understood, such firewalls are appropriate for
networks with passive administration.
Role-based firewalls can be implemented using routing technology.
For example, if Alice should not be able to send a message to Bob,
Alice's routing system might not have a route to Bob, or Bob's
routing system might not have a route to Alice. Role-based firewalls
can also be implemented using filtering technology; Alice, Alice's
router, Bob's router, or Bob may have a filter that prevents
communication between them. While there can be issues in specific
cases, a routing implementation is generally more scalable and more
easily managed.
Reputation, anomaly, or signature-based intrusion management is
generally proprietary; a service maintains the list of exclusions,
which must be updated as new kinds of attacks are developed.
Implementations SHOULD be designed for frequent and scalable
updating.
As further discussed in Section 4.1, firewalls of any type SHOULD NOT
attempt to perform the kind of deep packet inspection and surgery
that is common with Network Address Translators [RFC2993]. There is
marginal value in detecting the spoofing of applications by attack
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traffic, but the side-effects of preventing protocol improvement and
application innovation are destructive and unnecessary.
11. IANA Considerations
This memo asks the IANA for no new parameters. It can before
publication as an RFC by the RFC Editor.
12. Security Considerations
This note reasons about security considerations. It introduces no
new ones.
13. Acknowledgements
This document is based on [I-D.ietf-opsawg-firewalls-00] authored by
Fred Baker, and [I-D.ietf-opsawg-firewalls-01] authored by Paul
Hoffman.
14. References
14.1. Normative References
[RFC1833] Srinivasan, R., "Binding Protocols for ONC RPC Version 2",
RFC 1833, DOI 10.17487/RFC1833, August 1995,
<http://www.rfc-editor.org/info/rfc1833>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC3205] Moore, K., "On the use of HTTP as a Substrate", BCP 56,
RFC 3205, DOI 10.17487/RFC3205, February 2002,
<http://www.rfc-editor.org/info/rfc3205>.
[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007,
<http://www.rfc-editor.org/info/rfc4941>.
[RFC6887] Wing, D., Ed., Cheshire, S., Boucadair, M., Penno, R., and
P. Selkirk, "Port Control Protocol (PCP)", RFC 6887,
DOI 10.17487/RFC6887, April 2013,
<http://www.rfc-editor.org/info/rfc6887>.
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[RFC7112] Gont, F., Manral, V., and R. Bonica, "Implications of
Oversized IPv6 Header Chains", RFC 7112,
DOI 10.17487/RFC7112, January 2014,
<http://www.rfc-editor.org/info/rfc7112>.
14.2. Informative References
[I-D.gont-v6ops-ipv6-ehs-packet-drops]
Gont, F., Hilliard, N., Doering, G., LIU, S., and W.
Kumari, "Operational Implications of IPv6 Packets with
Extension Headers", draft-gont-v6ops-ipv6-ehs-packet-
drops-00 (work in progress), July 2015.
[I-D.ietf-opsawg-firewalls-00]
Baker, F., "On Firewalls in Internet Security", draft-
ietf-opsawg-firewalls-00 (work in progress), June 2012.
[I-D.ietf-opsawg-firewalls-01]
Baker, F. and P. Hoffman, "On Firewalls in Internet
Security", draft-ietf-opsawg-firewalls-01 (work in
progress), October 2012.
[I-D.vyncke-advanced-ipv6-security]
Vyncke, E., Yourtchenko, A., and M. Townsley, "Advanced
Security for IPv6 CPE", draft-vyncke-advanced-
ipv6-security-03 (work in progress), October 2011.
[OpenBSD-PF]
OpenBSD, , "pf(4) manual page: pf -- packet filter", 2015,
<http://www.openbsd.org/cgi-bin/man.cgi/OpenBSD-
current/man4/pf.4&query=pf>.
[Portmap] Wikipedia, , "Portmap", 2014,
<https://en.wikipedia.org/wiki/Portmap>.
[Ptacek1998]
Ptacek, T. and T. Newsham, "Insertion, Evasion and Denial
of Service: Eluding Network Intrusion Detection", 1998,
<http://www.aciri.org/vern/Ptacek-Newsham-Evasion-98.ps>.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981,
<http://www.rfc-editor.org/info/rfc793>.
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
DOI 10.17487/RFC2782, February 2000,
<http://www.rfc-editor.org/info/rfc2782>.
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[RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering:
Defeating Denial of Service Attacks which employ IP Source
Address Spoofing", BCP 38, RFC 2827, DOI 10.17487/RFC2827,
May 2000, <http://www.rfc-editor.org/info/rfc2827>.
[RFC2993] Hain, T., "Architectural Implications of NAT", RFC 2993,
DOI 10.17487/RFC2993, November 2000,
<http://www.rfc-editor.org/info/rfc2993>.
[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP",
RFC 3168, DOI 10.17487/RFC3168, September 2001,
<http://www.rfc-editor.org/info/rfc3168>.
[RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol",
RFC 4960, DOI 10.17487/RFC4960, September 2007,
<http://www.rfc-editor.org/info/rfc4960>.
[RFC5575] Marques, P., Sheth, N., Raszuk, R., Greene, B., Mauch, J.,
and D. McPherson, "Dissemination of Flow Specification
Rules", RFC 5575, DOI 10.17487/RFC5575, August 2009,
<http://www.rfc-editor.org/info/rfc5575>.
[RFC6092] Woodyatt, J., Ed., "Recommended Simple Security
Capabilities in Customer Premises Equipment (CPE) for
Providing Residential IPv6 Internet Service", RFC 6092,
DOI 10.17487/RFC6092, January 2011,
<http://www.rfc-editor.org/info/rfc6092>.
[RFC6093] Gont, F. and A. Yourtchenko, "On the Implementation of the
TCP Urgent Mechanism", RFC 6093, DOI 10.17487/RFC6093,
January 2011, <http://www.rfc-editor.org/info/rfc6093>.
[RFC6274] Gont, F., "Security Assessment of the Internet Protocol
Version 4", RFC 6274, DOI 10.17487/RFC6274, July 2011,
<http://www.rfc-editor.org/info/rfc6274>.
[Saltzer] Saltzer, J., Reed, D., and D. Clark, "End-to-end arguments
in system design", ACM Transactions on Computer Systems
(TOCS) v.2 n.4, p277-288, Nov 1984.
Authors' Addresses
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Fernando Gont
SI6 Networks / UTN-FRH
Evaristo Carriego 2644
Haedo, Provincia de Buenos Aires 1706
Argentina
Phone: +54 11 4650 8472
Email: fgont@si6networks.com
URI: http://www.si6networks.com
Fred Baker
Cisco Systems
Santa Barbara, California 93117
USA
Email: fred@cisco.com
Paul Hoffman
VPN Consortium
Email: paul.hoffman@vpnc.org
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