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None.                                                          C. Morrow
Internet-Draft                                        UUNET Technologies
Expires: October 12, 2006                                       G. Jones
                                                   The MITRE Corporation
                                                               V. Manral
                                                              IPInfusion
                                                            May 12, 2006


          Filtering Capabilities for IP Network Infrastructure
                    draft-ietf-opsec-filter-caps-01

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
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   This Internet-Draft will expire on October 12, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   [I-D.practices] lists operator practices related to securing
   networks.  This document lists filtering capabilities needed to
   support those practices.

   Capabilities are defined without reference to specific technologies.



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   This is done to leave room for deployment of new technologies that
   implement the capability.  Each capability cites the practices it
   supports.  Current implementations that support the capability are
   cited.  Special considerations are discussed as appropriate listing
   operational and resource constraints, limitations of current
   implementations, tradeoffs, etc.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  6
     1.1.  Threat Model . . . . . . . . . . . . . . . . . . . . . . .  6
     1.2.  Capabilities or Requirements ? . . . . . . . . . . . . . .  7
     1.3.  Format . . . . . . . . . . . . . . . . . . . . . . . . . .  7
     1.4.  Definitions  . . . . . . . . . . . . . . . . . . . . . . .  7
   2.  Functional Capabilities  - Filtering non-transit traffic
       (management plane) . . . . . . . . . . . . . . . . . . . . . .  9
     2.1.  Filtering TO the Device  . . . . . . . . . . . . . . . . .  9
       2.1.1.  Ability to Filter Traffic on All Interfaces TO the
               Device . . . . . . . . . . . . . . . . . . . . . . . .  9
       2.1.2.  Ability to Filter Traffic To the Device  . . . . . . . 10
       2.1.3.  Ability to Filter Traffic To the Device - Minimal
               Performance Degradation  . . . . . . . . . . . . . . . 10
       2.1.4.  Ability to Filter To the Device - Specify Filter
               Actions  . . . . . . . . . . . . . . . . . . . . . . . 12
       2.1.5.  Ability to Filter To the Device - Log Filter
               Actions  . . . . . . . . . . . . . . . . . . . . . . . 13
       2.1.6.  Ability to Filter To the Device - Specify Log
               Granularity  . . . . . . . . . . . . . . . . . . . . . 14
       2.1.7.  Ability to Filter To the Device - Ability to
               Filter Protocols . . . . . . . . . . . . . . . . . . . 15
       2.1.8.  Ability to Filter To the Device - Ability to
               Filter Addresses . . . . . . . . . . . . . . . . . . . 15
       2.1.9.  Ability to Filter To the Device - Ability to
               Filter Protocol Header Fields  . . . . . . . . . . . . 16
       2.1.10. Ability to Filter To the Device - Ability to
               Filter Inbound and Outbound  . . . . . . . . . . . . . 17
       2.1.11. Ability to Filter To the Device - Ability to
               Accurately Count Filter Hits . . . . . . . . . . . . . 18
       2.1.12. Ability to Filter To the Device - Ability to
               Display Filter Counters  . . . . . . . . . . . . . . . 19
       2.1.13. Ability to Filter To the Device - Ability to
               Display Filter Counters per Filter Application . . . . 20
       2.1.14. Ability to Filter To the Device - Ability to Reset
               Filter Counters  . . . . . . . . . . . . . . . . . . . 21
       2.1.15. Ability to Filter To the Device - Filter Counters
               are Accurate . . . . . . . . . . . . . . . . . . . . . 22
     2.2.  Rate Limit TO the Device . . . . . . . . . . . . . . . . . 22



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       2.2.1.  Ability to Rate limit Traffic on All Interfaces TO
               the Device . . . . . . . . . . . . . . . . . . . . . . 22
       2.2.2.  Ability to Rate Limit Traffic To the Device  . . . . . 23
       2.2.3.  Ability to Rate Limit Traffic To the Device -
               Minimal Performance Degradation  . . . . . . . . . . . 24
       2.2.4.  Ability to Rate Limit To the Device - Specify Rate
               Limit Actions  . . . . . . . . . . . . . . . . . . . . 26
       2.2.5.  Ability to Rate Limit To the Device - Log Rate
               Limit Actions  . . . . . . . . . . . . . . . . . . . . 27
       2.2.6.  Ability to Rate Limit To the Device - Specify Log
               Granularity  . . . . . . . . . . . . . . . . . . . . . 28
       2.2.7.  Ability to Rate Limit To the Device - Ability to
               Rate Limit Protocols . . . . . . . . . . . . . . . . . 28
       2.2.8.  Ability to Rate Limit To the Device - Ability to
               Rate Limit Addresses . . . . . . . . . . . . . . . . . 29
       2.2.9.  Ability to Rate Limit To the Device - Ability to
               Rate Limit Protocol Header Fields  . . . . . . . . . . 30
       2.2.10. Ability to Rate Limit To the Device - Ability to
               Rate Limit Inbound and Outbound  . . . . . . . . . . . 31
       2.2.11. Ability to Rate Limit To the Device - Ability to
               Accurately Count Rate Limit Hits . . . . . . . . . . . 32
       2.2.12. Ability to Rate Limit To the Device - Ability to
               Display Rate Limit Counters  . . . . . . . . . . . . . 33
       2.2.13. Ability to Rate Limit To the Device - Ability to
               Display Rate Limit Counters per Rate Limit
               Application  . . . . . . . . . . . . . . . . . . . . . 33
       2.2.14. Ability to Rate Limit To the Device - Ability to
               Reset Rate Limit Counters  . . . . . . . . . . . . . . 34
       2.2.15. Ability to Rate Limit To the Device - Rate Limit
               Counters are Accurate  . . . . . . . . . . . . . . . . 35
   3.  Functional Capabilities  - Filtering transit traffic (data
       plane) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
     3.1.  Filtering THROUGH the Device . . . . . . . . . . . . . . . 37
       3.1.1.  Ability to Filter Traffic on All Interfaces
               THROUGH the Device . . . . . . . . . . . . . . . . . . 37
       3.1.2.  Ability to Filter Traffic Through the Device . . . . . 38
       3.1.3.  Ability to Filter Traffic Through the Device -
               Minimal Performance Degradation  . . . . . . . . . . . 38
       3.1.4.  Ability to Filter Through the Device - Specify
               Filter Actions . . . . . . . . . . . . . . . . . . . . 40
       3.1.5.  Ability to Filter Through the Device - Log Filter
               Actions  . . . . . . . . . . . . . . . . . . . . . . . 41
       3.1.6.  Ability to Filter Through the Device - Specify Log
               Granularity  . . . . . . . . . . . . . . . . . . . . . 42
       3.1.7.  Ability to Filter Through the Device - Ability to
               Filter Protocols . . . . . . . . . . . . . . . . . . . 43
       3.1.8.  Ability to Filter Through the Device - Ability to
               Filter Addresses . . . . . . . . . . . . . . . . . . . 43



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       3.1.9.  Ability to Filter Through the Device - Ability to
               Filter Protocol Header Fields  . . . . . . . . . . . . 44
       3.1.10. Ability to Filter Through the Device - Ability to
               Filter Inbound and Outbound  . . . . . . . . . . . . . 45
       3.1.11. Ability to Filter Through the Device - Ability to
               Accurately Count Filter Hits . . . . . . . . . . . . . 46
       3.1.12. Ability to Filter Through the Device - Ability to
               Display Filter Counters  . . . . . . . . . . . . . . . 47
       3.1.13. Ability to Filter Through the Device - Ability to
               Display Filter Counters per Filter Application . . . . 48
       3.1.14. Ability to Filter Through the Device - Ability to
               Reset Filter Counters  . . . . . . . . . . . . . . . . 49
       3.1.15. Ability to Filter Through the Device - Filter
               Counters are Accurate  . . . . . . . . . . . . . . . . 50
     3.2.  Rate Limit THROUGH the Device  . . . . . . . . . . . . . . 50
       3.2.1.  Ability to Rate limit Traffic on All Interfaces
               THROUGH the Device . . . . . . . . . . . . . . . . . . 51
       3.2.2.  Ability to Rate Limit Traffic Through the Device . . . 51
       3.2.3.  Ability to Rate Limit Traffic Through the Device -
               Minimal Performance Degradation  . . . . . . . . . . . 52
       3.2.4.  Ability to Rate Limit Through the Device - Specify
               Rate Limit Actions . . . . . . . . . . . . . . . . . . 54
       3.2.5.  Ability to Rate Limit Through the Device - Log
               Rate Limit Actions . . . . . . . . . . . . . . . . . . 55
       3.2.6.  Ability to Rate Limit Through the Device - Specify
               Log Granularity  . . . . . . . . . . . . . . . . . . . 56
       3.2.7.  Ability to Rate Limit Through the Device - Ability
               to Rate Limit Protocols  . . . . . . . . . . . . . . . 57
       3.2.8.  Ability to Rate Limit Through the Device - Ability
               to Rate Limit Addresses  . . . . . . . . . . . . . . . 57
       3.2.9.  Ability to Rate Limit Through the Device - Ability
               to Rate Limit Protocol Header Fields . . . . . . . . . 58
       3.2.10. Ability to Rate Limit Through the Device - Ability
               to Rate Limit Inbound and Outbound . . . . . . . . . . 59
       3.2.11. Ability to Rate Limit Through the Device - Ability
               to Accurately Count Rate Limit Hits  . . . . . . . . . 60
       3.2.12. Ability to Rate Limit Through the Device - Ability
               to Display Rate Limit Counters . . . . . . . . . . . . 61
       3.2.13. Ability to Rate Limit Through the Device - Ability
               to Display Rate Limit Counters per Rate Limit
               Application  . . . . . . . . . . . . . . . . . . . . . 62
       3.2.14. Ability to Rate Limit Through the Device - Ability
               to Reset Rate Limit Counters . . . . . . . . . . . . . 63
       3.2.15. Ability to Rate Limit Through the Device - Rate
               Limit Counters are Accurate  . . . . . . . . . . . . . 64
   4.  Functional Capabilities  - Filtering Layer 2 Attributes . . . . 65
     4.1.  Filtering Layer 2  . . . . . . . . . . . . . . . . . . . . 65
       4.1.1.  Ability to partition layer-2 network to provide



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               different levels of security . . . . . . . . . . . . . 65
       4.1.2.  Ability to restrict access to specified hardware
               (MAC) addresses  . . . . . . . . . . . . . . . . . . . 66
       4.1.3.  Ability to restrict based on layer-2 packet type
               [etherType] field  . . . . . . . . . . . . . . . . . . 67
   5.  Additional Operational Practices . . . . . . . . . . . . . . . 68
     5.1.  Profile Current Traffic  . . . . . . . . . . . . . . . . . 68
     5.2.  Block Malicious Packets  . . . . . . . . . . . . . . . . . 68
     5.3.  Limit Sources of Management  . . . . . . . . . . . . . . . 68
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 69
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 70
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 70
     7.2.  Non-normative References . . . . . . . . . . . . . . . . . 70
   Appendix A.  Acknowledgments . . . . . . . . . . . . . . . . . . . 71
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 72
   Intellectual Property and Copyright Statements . . . . . . . . . . 73



































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1.  Introduction

   This document is defined in the context of [I-D.practices].
   [I-D.practices] defines the goals, motivation, scope, definitions,
   intended audience,threat model, potential attacks and give
   justifications for each of the practices.  Many of the capabilities
   listed here refine or add to capabilities listed in [RFC3871]

1.1.  Threat Model

   Threats in today's networked environment range from simple packet
   floods with overwhelming bandwidth toward a leaf network to subtle
   attacks aimed at subverting known vulnerabilities in existing
   applications.  The attacked network or host might not be an end user,
   it may be the networking device or links inside the provider core.

   Networks must have the ability to place mitigation in order to limit
   these threats.  These mitigation steps could include routing updates,
   traffic filters, and routing filters.  It is possible that the
   mitigation steps might have to affect transit traffic as well as
   traffic destined to the device on which the mitigation steps are
   activated.

   The scope of the threat includes simply denying services to an
   individual customer on one side of the scale to exploiting a newly
   discovered protocol vulnerability which affects the entire provider
   core.  The obvious risk to the business requires mitigation
   capabilities which can span this range of threats.

   Threat: An indication of impending danger or harm to the network or
   its parts.  This could be formed from the projected loss of revenue
   to the business.  Additionally, it could be formed from the increased
   cost to the business caused by the event. (more interfaces, more
   bandwidth, more personnel to support the increased size or
   complexity)

   Risk: The possibility of suffering harm or loss of network services
   due to a threat.

   Attack: To set upon with violent force the network or its parts.
   Typically this is a form of flood of packets to or through a network.
   This could also be a much smaller stream of packets created with the
   intent of exploiting a vulnerability in the infrastructure of the
   network.

   Asset: Either a customer, network device or network link.  Any of
   these could be assets from a business perspective.




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   These terms are more completely defined in RFC2828 we have added some
   scope specific information only.

1.2.  Capabilities or Requirements ?

   Capabilities may or may not be requirements.  That is a local
   determination that must be made by each operator with reference to
   the policies that they must support.  It is hoped that this document,
   together with [I-D.practices] will assist operators in identifying
   their security capability requirements and communicating them clearly
   to vendors.

1.3.  Format

   Each capability has the following subsections:

   o  Capability (what)

   o  Supported Practices (why)

   o  Current Implementations (how)

   o  Considerations (caveats, resource issues, protocol issues, etc.)

   The Capability section describes a feature to be supported by the
   device.  The Supported Practice section cites practices described in
   [I-D.practices] that are supported by this capability.  The Current
   Implementation section is intended to give examples of
   implementations of the capability, citing technology and standards
   current at the time of writing.  See [RFC3631].  It is expected that
   the choice of features to implement the capabilities will change over
   time.  The Considerations section lists operational and resource
   constraints, limitations of current implementations, tradeoffs, etc.

   [EDITORS NOTE: this is a first draft.  At least two editing passes
   will be made over the capabilities listed below in future drafts: one
   will break out compound capabilities into individual capabilities,
   the other will try to align the supported practices with the
   practices listed in [I-D.practices]]

1.4.  Definitions

   RFC 2119 Keywords

      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].




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      The use of the RFC 2119 keywords is an attempt, by the editor, to
      assign the correct requirement levels ("MUST", "SHOULD",
      "MAY"...).  It must be noted that different organizations,
      operational environments, policies and legal environments will
      generate different requirement levels.














































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2.  Functional Capabilities     - Filtering non-transit traffic (management
    plane)

   The capabilities in this section are intended to list testable,
   functional capabilities that are needed to operate devices securely.
   Focusing on filtering non-transit packets on devices, controlling
   access to the management plane.

2.1.  Filtering TO the Device

2.1.1.  Ability to Filter Traffic on All Interfaces TO the Device

   Capability.



      The device provides a means to filter IP packets on any interface
      implementing IP that are non-transit packets.


   Supported Practices.



      *  Profile Current Traffic ([I-D.practices] Section x.x.x)

      *  Block Malicious Packets (Section 5.2)

      *  Limit Sources of Management (Section 5.3)


   Current Implementations.



      Many devices currently implement access control lists or filters
      that allow filtering based on protocol and/or source/destination
      address and or source/destination port and allow these filters to
      be applied to interfaces.


   Considerations.









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      None.


2.1.2.  Ability to Filter Traffic To the Device

   Capability.



      It is possible to apply the filtering mechanism to traffic that is
      addressed directly to the device via any of its interfaces -
      including loopback interfaces.


   Supported Practices.



      *  This allows the operator to apply filters that protect the
         device itself from attacks and unauthorized access.


   Current Implementations.



      Many devices currently implement access control lists or filters
      that allow filtering based on protocol and/or source/destination
      address and or source/destination port and allow these filters to
      be applied to services offered by the device.

      Examples of this might include filters that permit only BGP from
      peers and SNMP and SSH from an authorized management segment and
      directed to the device itself, while dropping all other traffic
      addressed to the device.


   Considerations.



      None.


2.1.3.  Ability to Filter Traffic To the Device - Minimal Performance
        Degradation





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   Capability.



      The device provides a means to filter packets without significant
      performance degradation.  This specifically applies to stateless
      packet filtering operating on layer 3 (IP) and layer 4 (TCP or
      UDP) headers, as well as normal packet forwarding information such
      as incoming and outgoing interfaces.

      The device is able to apply stateless packet filters on ALL
      interfaces (up to the maximum number possible) simultaneously and
      with multiple filters per interface (e.g., inbound and outbound).

      The filtering of traffic destined to interfaces on the device,
      including the loopback interface, should not degrade performance
      significantly.


   Supported Practices.



      *  This enables the implementation of filters on whichever
         services necessary.  To the extent that filtering causes
         degradation, it may not be possible to apply filters that
         implement the appropriate policies.


   Current Implementations.



      Another way of stating the capability is that filter performance
      should not be the limiting factor in device throughput.  If a
      device is capable of forwarding 30Mb/sec without filtering, then
      it should be able to forward the same amount with filtering in
      place.


   Considerations.



      The definition of "significant" is subjective.  At one end of the
      spectrum it might mean "the application of filters may cause the
      box to crash".  At the other end would be a throughput loss of
      less than one percent with tens of thousands of filters applied.



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      The level of performance degradation that is acceptable will have
      to be determined by the operator.

      Repeatable test data showing filter performance impact would be
      very useful in evaluating this capability.  Tests should include
      such information as packet size, packet rate, number of interfaces
      tested (source/destination), types of interfaces, routing table
      size, routing protocols in use, frequency of routing updates, etc.

      This capability does not address stateful filtering, filtering
      above layer 4 headers or other more advanced types of filtering
      that may be important in certain operational environments.


2.1.4.  Ability to Filter To the Device - Specify Filter Actions

   Capability.



      The device provides a mechanism to allow the specification of the
      action to be taken when a filter rule matches.  Actions include
      "permit" (allow the traffic), "reject" (drop with appropriate
      notification to sender), and "drop" (drop with no notification to
      sender).


   Supported Practices.



      *  This capability is essential to the use of filters to enforce
         policy.


   Current Implementations.



      Assume that your management devices for deployed networking
      devices live on several subnets, use several protocols, and are
      controlled by several different parts of your organization.  There
      might exist a reason to have disparate policies for access to the
      devices from these parts of the organization.







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      Actions such as "permit", "deny", "drop" are essential in defining
      the security policy for the services offered by the network
      devices.


   Considerations.



      While silently dropping traffic without sending notification may
      be the correct action in security terms, consideration should be
      given to operational implications.  See [RFC3360] for
      consideration of potential problems caused by sending
      inappropriate TCP Resets.


2.1.5.  Ability to Filter To the Device - Log Filter Actions

   Capability.



      It is possible to log all filter actions.  The logging capability
      is able to capture at least the following data:

      *  permit/deny/drop status

      *  source and destination IP address

      *  source and destination ports (if applicable to the protocol)

      *  which network element received the packet (interface, MAC
         address or other layer 2 information that identifies the
         previous hop source of the packet).




   Supported Practices.



      *  Logging is essential for auditing, incident response, and
         operations







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   Current Implementations.



      Actions such as "permit", "deny", "drop" are essential in defining
      the security policy for the services offered by the network
      devices.  Auditing the frequency, sources and destinations of
      these attempts is essential for tracking ongoing issues today.


   Considerations.



      Logging can be burdensome to the network device, at no time should
      logging cause performance degradation to the device or services
      offered on the device.


2.1.6.  Ability to Filter To the Device - Specify Log Granularity

   Capability.



      It is possible to enable/disable logging on a per rule basis.


   Supported Practices.



      *  The ability to tune the granularity of logging allows the
         operator to log the information that is desired and only the
         information that is desired.  Without this capability, it is
         possible that extra data (or none at all) would be logged,
         making it more difficult to find relevant information.


   Current Implementations.



      If a filter is defined that has several rules, and one of the
      rules denies telnet (tcp/23) connections, then it should be
      possible to specify that only matches on the rule that denies
      telnet should generate a log message.




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   Considerations.



      None.


2.1.7.  Ability to Filter To the Device - Ability to Filter Protocols

   Capability.



      The device provides a means to filter traffic based on the value
      of the protocol field in the IP header.


   Supported Practices.



      *  Being able to filter on protocol is necessary to allow
         implementation of policy, secure operations and for support of
         incident response.


   Current Implementations.



      Some denial of service attacks are based on the ability to flood
      the victim with ICMP traffic.  One quick way (admittedly with some
      negative side effects) to mitigate the effects of such attacks is
      to drop all ICMP traffic headed toward the victim.


   Considerations.



      None.


2.1.8.  Ability to Filter To the Device - Ability to Filter Addresses







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   Capability.



      The function is able to control the flow of traffic based on
      source and/or destination IP address or blocks of addresses such
      as Classless Inter-Domain Routing (CIDR) blocks.


   Supported Practices.



      *  The capability to filter on addresses and address blocks is a
         fundamental tool for establishing boundaries between different
         networks.


   Current Implementations.



      One example of the use of address based filtering is to implement
      ingress filtering per [RFC2827].


   Considerations.



      None.


2.1.9.  Ability to Filter To the Device - Ability to Filter Protocol
        Header Fields

   Capability.



      The filtering mechanism supports filtering based on the value(s)
      of any portion of the protocol headers for IP, ICMP, UDP and TCP.
      It supports filtering of all other protocols supported at layer 3
      and 4.  It supports filtering based on the headers of higher level
      protocols.  It is possible to specify fields by name (e.g.,
      "protocol = ICMP") rather than bit- offset/length/numeric value
      (e.g., 72:8 = 1).




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   Supported Practices.



      *  Being able to filter on portions of the header is necessary to
         allow implementation of policy, secure operations, and support
         incident response.


   Current Implementations.



      This capability implies that it is possible to filter based on TCP
      or UDP port numbers, TCP flags such as SYN, ACK and RST bits, and
      ICMP type and code fields.  One common example is to reject
      "inbound" TCP connection attempts (TCP, SYN bit set+ACK bit clear
      or SYN bit set+ACK,FIN and RST bits clear).  Another common
      example is the ability to control what services are allowed in/out
      of a network.  It may be desirable to only allow inbound
      connections on port 80 (HTTP) and 443 (HTTPS) to a network hosting
      web servers.


   Considerations.



      None.


2.1.10.  Ability to Filter To the Device - Ability to Filter Inbound and
         Outbound

   Capability.



      It is possible to filter both incoming and outgoing traffic on any
      interface.


   Supported Practices.



      *  This capability allows flexibility in applying filters at the
         place that makes the most sense.  It allows invalid or



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         malicious traffic to be dropped as close to the source as
         possible.


   Current Implementations.



      It might be desirable on a border router, for example, to apply an
      egress filter outbound on the interface that connects a site to
      its external ISP to drop outbound traffic that does not have a
      valid internal source address.  Inbound, it might be desirable to
      apply a filter that blocks all traffic from a site that is known
      to forward or originate lots of junk mail.


   Considerations.



      None.


2.1.11.  Ability to Filter To the Device - Ability to Accurately Count
         Filter Hits

   Capability.



      The device supplies a facility for accurately counting all filter
      matches.


   Supported Practices.



      *  Accurate counting of filter rule matches is important because
         it shows the frequency of attempts to violate policy.  This
         enables resources to be focused on areas of greatest need.


   Current Implementations.







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      Assume, for example, that a ISP network implements anti-spoofing
      egress filters (see [RFC2827]) on interfaces of its edge routers
      that support single-homed stub networks.  Counters could enable
      the ISP to detect cases where large numbers of spoofed packets are
      being sent.  This may indicate that the customer is performing
      potentially malicious actions (possibly in violation of the ISPs
      Acceptable Use Policy), or that system(s) on the customers network
      have been "owned" by hackers and are being (mis)used to launch
      attacks.


   Considerations.



      None.


2.1.12.  Ability to Filter To the Device - Ability to Display Filter
         Counters

   Capability.



      The device provides a mechanism to display filter counters.


   Supported Practices.



      *  Information that is collected is not useful unless it can be
         displayed in a useful manner.


   Current Implementations.



      Assume there is a router with four interfaces.  One is an up-link
      to an ISP providing routes to the Internet.  The other three
      connect to separate internal networks.  Assume that a host on one
      of the internal networks has been compromised by a hacker and is
      sending traffic with bogus source addresses.  In such a situation,
      it might be desirable to apply ingress filters to each of the



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      internal interfaces.  Once the filters are in place, the counters
      can be examined to determine the source (inbound interface) of the
      bogus packets.


   Considerations.



      None.


2.1.13.  Ability to Filter To the Device - Ability to Display Filter
         Counters per Filter Application

   Capability.



      If it is possible for a filter to be applied more than once at the
      same time, then the device provides a mechanism to display filter
      counters per filter application.


   Supported Practices.



      *  It may make sense to apply the same filter definition
         simultaneously more than one time (to different interfaces,
         etc.).  If so, it would be much more useful to know which
         instance of a filter is matching than to know that some
         instance was matching somewhere.


   Current Implementations.



      One way to implement this capability would be to have the counter
      display mechanism show the interface (or other entity) to which
      the filter has been applied, along with the name (or other
      designator) for the filter.  For example if a filter named
      "desktop_outbound" applied two different interfaces, say,
      "ethernet0" and "ethernet1", the display should indicate something
      like "matches of filter 'desktop_outbound' on ethernet0 ..." and
      "matches of filter 'desktop_outbound' on ethernet1 ..."




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   Considerations.



      None.


2.1.14.  Ability to Filter To the Device - Ability to Reset Filter
         Counters

   Capability.



      It is possible to reset counters to zero on a per filter basis.

      For the purposes of this capability it would be acceptable for the
      system to maintain two counters: an "absolute counter", C[now],
      and a "reset" counter, C[reset].  The absolute counter would
      maintain counts that increase monotonically until they wrap or
      overflow the counter.  The reset counter would receive a copy of
      the current value of the absolute counter when the reset function
      was issued for that counter.  Functions that display or retrieve
      the counter could then display the delta (C[now] - C[reset]).


   Supported Practices.



      *  This allows operators to get a current picture of the traffic
         matching particular rules/filters.


   Current Implementations.



      Assume that filter counters are being used to detect internal
      hosts that are infected with a new worm.  Once it is believed that
      all infected hosts have been cleaned up and the worm removed, the
      next step would be to verify that.  One way of doing so would be
      to reset the filter counters to zero and see if traffic indicative
      of the worm has ceased.







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   Considerations.



      None.


2.1.15.  Ability to Filter To the Device - Filter Counters are Accurate

   Capability.



      Filter counters are accurate.  They reflect the actual number of
      matching packets since the last counter reset.  Filter counters
      are be capable of holding up to 2^32 - 1 values without
      overflowing and should be capable of holding up to 2^64 - 1
      values.


   Supported Practices.



      *  Inaccurate data can not be relied on as the basis for action.
         Underreported data can conceal the magnitude of a problem.


   Current Implementations.



      If N packets matching a filter are sent to/through a device, then
      the counter should show N matches.


   Considerations.



      None.


2.2.  Rate Limit TO the Device

2.2.1.  Ability to Rate limit Traffic on All Interfaces TO the Device





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   Capability.



      The device provides a means to rate limit IP packets on any
      interface implementing IP that are non-transit packets.


   Supported Practices.



      *  Profile Current Traffic ([I-D.practices] Section x.x.x)

      *  Block Malicious Packets (Section 5.2)

      *  Limit Sources of Management (Section 5.3)


   Current Implementations.



      Many devices currently implement rate limits that allow rate
      limiting based on protocol and/or source/destination address and
      or source/destination port or raw bandwidth and allow these limits
      to be applied to interfaces.


   Considerations.



      None.


2.2.2.  Ability to Rate Limit Traffic To the Device

   Capability.



      It is possible to apply the rate-limiting mechanism to traffic
      that is addressed directly to the device via any of its interfaces
      - including loopback interfaces.






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   Supported Practices.



      *  This allows the operator to apply rate-limits that protect the
         device itself from attacks and unauthorized access.


   Current Implementations.



      Many devices currently implement rate-limits that allow limiting
      based on protocol and/or source/destination address and or source/
      destination port and allow these limits to be applied to services
      offered by the device.

      Examples of this might include rate-limits that permit BGP traffic
      rates up to 100 megabits per second from an authorized peer, while
      dropping all other traffic addressed to the device which exceeds
      this limit.


   Considerations.



      None.


2.2.3.  Ability to Rate Limit Traffic To the Device - Minimal
        Performance Degradation

   Capability.



      The device provides a means to rate-limit packets without
      significant performance degradation.

      The device is able to apply rate-limits on ALL interfaces (up to
      the maximum number possible) simultaneously and with multiple
      rate-limits per interface (e.g., inbound, outbound, differing
      traffic classifications in either direction).







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      The rate-limiting of traffic destined to interfaces on the device,
      including the loopback interface, should not degrade performance
      significantly.


   Supported Practices.



      *  This enables the implementation of rate-limits on whichever
         services are necessary.  To the extent that rate-limiting
         causes degradation, it may not be possible to apply rate-limits
         that implement the appropriate policies.


   Current Implementations.



      Another way of stating the capability is that rate-limit
      performance should not be the limiting factor in device
      throughput.  If a device is capable of forwarding 30Mb/sec without
      rate-limits, then it should be able to forward the same amount
      with rate-limits in place.


   Considerations.



      The definition of "significant" is subjective.  At one end of the
      spectrum it might mean "the application of rate-limits may cause
      the box to crash".  At the other end would be a throughput loss of
      less than one percent with tens of thousands of rate-limits
      applied.  The level of performance degradation that is acceptable
      will have to be determined by the operator.

      Repeatable test data showing rate-limiting performance impact
      would be very useful in evaluating this capability.  Tests should
      include such information as packet size, packet rate, number of
      interfaces tested (source/destination), types of interfaces,
      routing table size, routing protocols in use, frequency of routing
      updates, etc.








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2.2.4.  Ability to Rate Limit To the Device - Specify Rate Limit Actions

   Capability.



      The device provides a mechanism to allow the specification of the
      action to be taken when a rate-limit rule matches.  Actions
      include "permit" (allow the traffic), "reject" (drop with
      appropriate notification to sender), and "drop" (drop with no
      notification to sender).


   Supported Practices.



      *  This capability is essential to the use of rate limits to
         enforce policy.


   Current Implementations.



      Assume that your management devices for deployed networking
      devices live on several subnets, use several protocols, and are
      controlled by several different parts of your organization.  There
      might exist a reason to have disparate policies for access to the
      devices from these parts of the organization.  Further you may
      want to limit traffic levels for these types of traffic from these
      known sources.

      Actions such as "permit", "deny", "drop" are essential in defining
      the security policy for the services offered by the network
      devices.


   Considerations.



      While silently dropping traffic without sending notification may
      be the correct action in security terms, consideration should be
      given to operational implications.  See [RFC3360] for
      consideration of potential problems caused by sending
      inappropriate TCP Resets.




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2.2.5.  Ability to Rate Limit To the Device - Log Rate Limit Actions

   Capability.



      It is possible to log rate limit actions.  The logging capability
      is able to capture at least the following data:

      *  permit/deny/drop status

      *  source and destination IP address

      *  source and destination ports (if applicable to the protocol)

      *  which network element received the packet (interface, MAC
         address or other layer 2 information that identifies the
         previous hop source of the packet).




   Supported Practices.



      *  Logging is essential for auditing, incident response, and
         operations


   Current Implementations.



      Actions such as "permit", "deny", "drop" are essential in defining
      the security policy for the services offered by the network
      devices.  Auditing the frequency, sources and destinations of
      these attempts is essential for tracking ongoing issues today.


   Considerations.



      Logging can be burdensome to the network device, at no time should
      logging cause performance degradation to the device or services
      offered on the device.




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2.2.6.  Ability to Rate Limit To the Device - Specify Log Granularity

   Capability.



      It is possible to enable/disable logging on a per rule basis.


   Supported Practices.



      *  The ability to tune the granularity of logging allows the
         operator to log the information that is desired and only the
         information that is desired.  Without this capability, it is
         possible that extra data (or none at all) would be logged,
         making it more difficult to find relevant information.


   Current Implementations.



      If a rate limit is defined that has several rules, and one of the
      rules denies telnet (tcp/23) connections, then it should be
      possible to specify that only matches on the rule that denies
      telnet should generate a log message.


   Considerations.



      None.


2.2.7.  Ability to Rate Limit To the Device - Ability to Rate Limit
        Protocols

   Capability.



      The device provides a means to rate limit traffic based on the
      value of the protocol field in the IP header.





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   Supported Practices.



      *  Being able to rate limit on protocol is necessary to allow
         implementation of policy, secure operations and for support of
         incident response.


   Current Implementations.



      Some denial of service attacks are based on the ability to flood
      the victim with ICMP traffic.  One quick way (admittedly with some
      negative side effects) to mitigate the effects of such attacks is
      to rate limit all ICMP traffic headed toward the victim.


   Considerations.



      None.


2.2.8.  Ability to Rate Limit To the Device - Ability to Rate Limit
        Addresses

   Capability.



      The function is able to control the flow of traffic based on
      source and/or destination IP address or blocks of addresses such
      as Classless Inter-Domain Routing (CIDR) blocks.


   Supported Practices.



      *  The capability to rate limit on addresses and address blocks is
         a fundamental tool for establishing boundaries between
         different networks.






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   Current Implementations.



      One example of the use of address based rate limits is to
      implement ingress filtering per [RFC2827].


   Considerations.



      None.


2.2.9.  Ability to Rate Limit To the Device - Ability to Rate Limit
        Protocol Header Fields

   Capability.



      The rate limit mechanism supports rate limiting based on the
      value(s) of any portion of the protocol headers for IP, ICMP, UDP
      and TCP.  It supports rate limiting of all other protocols
      supported at layer 3 and 4.  It supports rate limiting based on
      the headers of higher level protocols.  It is possible to specify
      fields by name (e.g., "protocol = ICMP") rather than bit- offset/
      length/numeric value (e.g., 72:8 = 1).


   Supported Practices.



      *  Being able to rate limit on portions of the header is necessary
         to allow implementation of policy, secure operations, and
         support incident response.


   Current Implementations.



      This capability implies that it is possible to rate limit based on
      TCP or UDP port numbers, TCP flags such as SYN, ACK and RST bits,
      and ICMP type and code fields.  One common example is to reject
      "inbound" TCP connection attempts (TCP, SYN bit set+ACK bit clear



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      or SYN bit set+ACK,FIN and RST bits clear).  Another common
      example is the ability to control what services are allowed in/out
      of a network.  It may be desirable to only allow inbound
      connections on port 80 (HTTP) and 443 (HTTPS) to a network hosting
      web servers.


   Considerations.



      None.


2.2.10.  Ability to Rate Limit To the Device - Ability to Rate Limit
         Inbound and Outbound

   Capability.



      It is possible to rate limit both incoming and outgoing traffic on
      any interface.


   Supported Practices.



      *  This capability allows flexibility in applying rate limits at
         the place that makes the most sense.  It allows invalid or
         malicious traffic to be dropped as close to the source as
         possible.


   Current Implementations.



      It might be desirable on a router to apply an egress rate limit to
      its external connections to limit outbound traffic that does not
      have a high priority.  Inbound, it might be desirable to apply a
      rate limit to all traffic of a certain classification in order to
      preserve limited resources on the router's management components.







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   Considerations.



      None.


2.2.11.  Ability to Rate Limit To the Device - Ability to Accurately
         Count Rate Limit Hits

   Capability.



      The device supplies a facility for accurately counting all rate
      limit matches.


   Supported Practices.



      *  Accurate counting of rate limit rule matches is important
         because it shows the frequency of attempts to violate policy.
         This enables resources to be focused on areas of greatest need.


   Current Implementations.



      Assume, for example, that a ISP network implements anti-spoofing
      egress rate limits (see [RFC2827]) on interfaces of its edge
      routers that support single-homed stub networks.  Counters could
      enable the ISP to detect cases where large numbers of spoofed
      packets are being sent.  This may indicate that the customer is
      performing potentially malicious actions (possibly in violation of
      the ISPs Acceptable Use Policy), or that system(s) on the
      customers network have been compromised by hackers and are being
      (mis)used to launch attacks.


   Considerations.








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      None.


2.2.12.  Ability to Rate Limit To the Device - Ability to Display Rate
         Limit Counters

   Capability.



      The device provides a mechanism to display rate limit counters.


   Supported Practices.



      *  Information that is collected is not useful unless it can be
         displayed in a useful manner.


   Current Implementations.



      Assume there is a router with four interfaces.  One is an up-link
      to an ISP providing routes to the Internet.  The other three
      connect to separate internal networks.  Assume that a host on one
      of the internal networks has been compromised by a hacker and is
      sending traffic with bogus source addresses.  In such a situation,
      it might be desirable to apply ingress rate limits to each of the
      internal interfaces.  Once the rate limits are in place, the
      counters can be examined to determine the source (inbound
      interface) of the bogus packets.


   Considerations.



      None.


2.2.13.  Ability to Rate Limit To the Device - Ability to Display Rate
         Limit Counters per Rate Limit Application






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   Capability.



      If it is possible for a rate limit to be applied more than once at
      the same time, then the device provides a mechanism to display
      rate limit counters per rate limit application.


   Supported Practices.



      *  It may make sense to apply the same rate limit definition
         simultaneously more than one time (to different interfaces,
         etc.).  If so, it would be much more useful to know which
         instance of a rate limit is matching than to know that some
         instance was matching somewhere.


   Current Implementations.



      One way to implement this capability would be to have the counter
      display mechanism show the interface (or other entity) to which
      the rate limit has been applied, along with the name (or other
      designator) for the rate limit.  For example if a rate limit named
      "desktop_outbound" applied two different interfaces, say,
      "ethernet0" and "ethernet1", the display should indicate something
      like "matches of rate limit 'desktop_outbound' on ethernet0 ..."
      and "matches of rate limit 'desktop_outbound' on ethernet1 ..."


   Considerations.



      None.


2.2.14.  Ability to Rate Limit To the Device - Ability to Reset Rate
         Limit Counters








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   Capability.



      It is possible to reset counters to zero on a per rate limit
      basis.

      For the purposes of this capability it would be acceptable for the
      system to maintain two counters: an "absolute counter", C[now],
      and a "reset" counter, C[reset].  The absolute counter would
      maintain counts that increase monotonically until they wrap or
      overflow the counter.  The reset counter would receive a copy of
      the current value of the absolute counter when the reset function
      was issued for that counter.  Functions that display or retrieve
      the counter could then display the delta (C[now] - C[reset]).


   Supported Practices.



      *  This allows operators to get a current picture of the traffic
         matching particular rules/rate limit.


   Current Implementations.



      Assume that rate limit counters are being used to detect internal
      hosts that are infected with a new worm.  Once it is believed that
      all infected hosts have been cleaned up and the worm removed, the
      next step would be to verify that.  One way of doing so would be
      to reset the rate limit counters to zero and see if traffic
      indicative of the worm has ceased.


   Considerations.



      None.


2.2.15.  Ability to Rate Limit To the Device - Rate Limit Counters are
         Accurate





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   Capability.



      Rate limit counters are accurate.  They reflect the actual number
      of matching packets since the last counter reset.  Rate limit
      counters are be capable of holding up to 2^32 - 1 values without
      overflowing and should be capable of holding up to 2^64 - 1
      values.


   Supported Practices.



      *  Inaccurate data can not be relied on as the basis for action.
         Underreported data can conceal the magnitude of a problem.


   Current Implementations.



      If N packets matching a Rate limit are sent to/through a device,
      then the counter should show N matches.


   Considerations.



      None.



















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3.  Functional Capabilities     - Filtering transit traffic (data plane)

   The capabilities in this section are intended to list testable,
   functional capabilities that are needed to operate devices securely.
   Focusing on filtering transit packets on devices, controlling the
   data plane.

3.1.  Filtering THROUGH the Device

3.1.1.  Ability to Filter Traffic on All Interfaces THROUGH the Device

   Capability.



      The device provides a means to filter IP packets on any interface
      implementing IP that are transit packets.


   Supported Practices.



      *  Profile Current Traffic ([I-D.practices] Section x.x.x)

      *  Block Malicious Packets (Section 5.2)

      *  Limit Sources of Management (Section 5.3)


   Current Implementations.



      Many devices currently implement access control lists or filters
      that allow filtering based on protocol and/or source/destination
      address and or source/destination port and allow these filters to
      be applied to interfaces.


   Considerations.



      None.






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3.1.2.  Ability to Filter Traffic Through the Device

   Capability.



      It is possible to apply the filtering mechanism to traffic that is
      flowing through the device via any of its interfaces - transit
      traffic.


   Supported Practices.



      *  This allows the operator to apply filters that protect the
         networks supported by the device from attacks and unauthorized
         access.


   Current Implementations.



      Many devices currently implement access control lists or filters
      that allow filtering based on protocol and/or source/destination
      address and or source/destination port and allow these filters to
      be applied to interfaces of the device for the purposes of
      protecting the networks that connect to the device.

      Examples of this might include filters that permit only HTTP from
      known good sources and SMTP and SSH from a known subset of the
      entire network, while dropping all other traffic.


   Considerations.



      None.


3.1.3.  Ability to Filter Traffic Through the Device - Minimal
        Performance Degradation







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   Capability.



      The device provides a means to filter packets without significant
      performance degradation.  This specifically applies to stateless
      packet filtering operating on layer 3 (IP) and layer 4 (TCP or
      UDP) headers, as well as normal packet forwarding information such
      as incoming and outgoing interfaces.

      The device is able to apply stateless packet filters on ALL
      interfaces (up to the maximum number possible) simultaneously and
      with multiple filters per interface (e.g., inbound and outbound).

      The filtering of traffic through the device should not degrade
      performance significantly.


   Supported Practices.



      *  This enables the implementation of filters on necessary
         services for the networks supported by the device.  To the
         extent that filtering causes degradation, it may not be
         possible to apply filters that implement the appropriate
         policies.


   Current Implementations.



      Another way of stating the capability is that filter performance
      should not be the limiting factor in device throughput.  If a
      device is capable of forwarding 30Mb/sec without filtering, then
      it should be able to forward the same amount with filtering in
      place.


   Considerations.



      The definition of "significant" is subjective.  At one end of the
      spectrum it might mean "the application of filters may cause the
      box to crash".  At the other end would be a throughput loss of
      less than one percent with tens of thousands of filters applied.



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      The level of performance degradation that is acceptable will have
      to be determined by the operator.

      Repeatable test data showing filter performance impact would be
      very useful in evaluating this capability.  Tests should include
      such information as packet size, packet rate, number of interfaces
      tested (source/destination), types of interfaces, routing table
      size, routing protocols in use, frequency of routing updates, etc.

      This capability does not address stateful filtering, filtering
      above layer 4 headers or other more advanced types of filtering
      that may be important in certain operational environments.


3.1.4.  Ability to Filter Through the Device - Specify Filter Actions

   Capability.



      The device provides a mechanism to allow the specification of the
      action to be taken when a filter rule matches.  Actions include
      "permit" (allow the traffic), "reject" (drop with appropriate
      notification to sender), and "drop" (drop with no notification to
      sender).


   Supported Practices.



      *  This capability is essential to the use of filters to enforce
         policy.


   Current Implementations.



      Assume that your network's services live on several subnets, use
      several protocols, and are controlled by several different parts
      of your organization.  There might exist a reason to have
      disparate policies for access to the devices from these parts of
      the organization.







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      Actions such as "permit", "deny", "drop" are essential in defining
      the security policy for the services offered by the network
      devices.


   Considerations.



      While silently dropping traffic without sending notification may
      be the correct action in security terms, consideration should be
      given to operational implications.  See [RFC3360] for
      consideration of potential problems caused by sending
      inappropriate TCP Resets.


3.1.5.  Ability to Filter Through the Device - Log Filter Actions

   Capability.



      It is possible to log all filter actions.  The logging capability
      is able to capture at least the following data:

      *  permit/deny/drop status

      *  source and destination IP address

      *  source and destination ports (if applicable to the protocol)

      *  which network element received the packet (interface, MAC
         address or other layer 2 information that identifies the
         previous hop source of the packet).




   Supported Practices.



      *  Logging is essential for auditing, incident response, and
         operations







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   Current Implementations.



      Actions such as "permit", "deny", "drop" are essential in defining
      the security policy for the services offered by the network
      devices.  Auditing the frequency, sources and destinations of
      these attempts is essential for tracking ongoing issues today.


   Considerations.



      Logging can be burdensome to the network device, at no time should
      logging cause performance degradation to the device or services
      offered on the device.


3.1.6.  Ability to Filter Through the Device - Specify Log Granularity

   Capability.



      It is possible to enable/disable logging on a per rule basis.


   Supported Practices.



      *  The ability to tune the granularity of logging allows the
         operator to log the information that is desired and only the
         information that is desired.  Without this capability, it is
         possible that extra data (or none at all) would be logged,
         making it more difficult to find relevant information.


   Current Implementations.



      If a filter is defined that has several rules, and one of the
      rules denies telnet (tcp/23) traffic, then it should be possible
      to specify that only matches on the rule that denies telnet should
      generate a log message.




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   Considerations.



      None.


3.1.7.  Ability to Filter Through the Device - Ability to Filter
        Protocols

   Capability.



      The device provides a means to filter traffic based on the value
      of the protocol field in the IP header.


   Supported Practices.



      *  Being able to filter on protocol is necessary to allow
         implementation of policy, secure operations and for support of
         incident response.


   Current Implementations.



      Some denial of service attacks are based on the ability to flood
      the victim with ICMP traffic.  One quick way (admittedly with some
      negative side effects) to mitigate the effects of such attacks is
      to drop all ICMP traffic headed toward the victim.


   Considerations.



      None.


3.1.8.  Ability to Filter Through the Device - Ability to Filter
        Addresses





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   Capability.



      The function is able to control the flow of traffic based on
      source and/or destination IP address or blocks of addresses such
      as Classless Inter-Domain Routing (CIDR) blocks.


   Supported Practices.



      *  The capability to filter on addresses and address blocks is a
         fundamental tool for establishing boundaries between different
         networks.


   Current Implementations.



      One example of the use of address based filtering is to implement
      ingress filtering per [RFC2827].


   Considerations.



      None.


3.1.9.  Ability to Filter Through the Device - Ability to Filter
        Protocol Header Fields

   Capability.



      The filtering mechanism supports filtering based on the value(s)
      of any portion of the protocol headers for IP, ICMP, UDP and TCP.
      It supports filtering of all other protocols supported at layer 3
      and 4.  It supports filtering based on the headers of higher level
      protocols.  It is possible to specify fields by name (e.g.,
      "protocol = ICMP") rather than bit- offset/length/numeric value
      (e.g., 72:8 = 1).




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   Supported Practices.



      *  Being able to filter on portions of the header is necessary to
         allow implementation of policy, secure operations, and support
         incident response.


   Current Implementations.



      This capability implies that it is possible to filter based on TCP
      or UDP port numbers, TCP flags such as SYN, ACK and RST bits, and
      ICMP type and code fields.  One common example is to reject TCP
      connection attempts (TCP, SYN bit set+ACK bit clear or SYN bit
      set+ACK,FIN and RST bits clear).  Another common example is the
      ability to control what services are allowed in/out of a network.
      It may be desirable to only allow inbound connections on port 80
      (HTTP) and 443 (HTTPS) to a network hosting web servers.


   Considerations.



      None.


3.1.10.  Ability to Filter Through the Device - Ability to Filter
         Inbound and Outbound

   Capability.



      It is possible to filter both incoming and outgoing traffic on any
      interface.


   Supported Practices.



      *  This capability allows flexibility in applying filters at the
         place that makes the most sense.  It allows invalid or
         malicious traffic to be dropped as close to the source as



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         possible.


   Current Implementations.



      It might be desirable on a border router, for example, to apply an
      egress filter outbound on the interface that connects a site to
      its external ISP to drop outbound traffic that does not have a
      valid internal source address.  Inbound, it might be desirable to
      apply a filter that blocks all traffic from a site that is known
      to forward or originate lots of junk mail.


   Considerations.



      None.


3.1.11.  Ability to Filter Through the Device - Ability to Accurately
         Count Filter Hits

   Capability.



      The device supplies a facility for accurately counting all filter
      matches.


   Supported Practices.



      *  Accurate counting of filter rule matches is important because
         it shows the frequency of attempts to violate policy.  This
         enables resources to be focused on areas of greatest need.


   Current Implementations.








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      Assume, for example, that a ISP network implements anti-spoofing
      egress filters (see [RFC2827]) on interfaces of its edge routers
      that support single-homed stub networks.  Counters could enable
      the ISP to detect cases where large numbers of spoofed packets are
      being sent.  This may indicate that the customer is performing
      potentially malicious actions (possibly in violation of the ISPs
      Acceptable Use Policy), or that system(s) on the customers network
      have been "owned" by hackers and are being (mis)used to launch
      attacks.


   Considerations.



      None.


3.1.12.  Ability to Filter Through the Device - Ability to Display
         Filter Counters

   Capability.



      The device provides a mechanism to display filter counters.


   Supported Practices.



      *  Information that is collected is not useful unless it can be
         displayed in a useful manner.


   Current Implementations.



      Assume there is a router with four interfaces.  One is an up-link
      to an ISP providing routes to the Internet.  The other three
      connect to separate internal networks.  Assume that a host on one
      of the internal networks has been compromised by a hacker and is
      sending traffic with bogus source addresses.  In such a situation,
      it might be desirable to apply ingress filters to each of the
      internal interfaces.  Once the filters are in place, the counters
      can be examined to determine the source (inbound interface) of the



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      bogus packets.


   Considerations.



      None.


3.1.13.  Ability to Filter Through the Device - Ability to Display
         Filter Counters per Filter Application

   Capability.



      If it is possible for a filter to be applied more than once at the
      same time, then the device provides a mechanism to display filter
      counters per filter application.


   Supported Practices.



      *  It may make sense to apply the same filter definition
         simultaneously more than one time (to different interfaces,
         etc.).  If so, it would be much more useful to know which
         instance of a filter is matching than to know that some
         instance was matching somewhere.


   Current Implementations.



      One way to implement this capability would be to have the counter
      display mechanism show the interface (or other entity) to which
      the filter has been applied, along with the name (or other
      designator) for the filter.  For example if a filter named
      "desktop_outbound" applied two different interfaces, say,
      "ethernet0" and "ethernet1", the display should indicate something
      like "matches of filter 'desktop_outbound' on ethernet0 ..." and
      "matches of filter 'desktop_outbound' on ethernet1 ..."






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   Considerations.



      None.


3.1.14.  Ability to Filter Through the Device - Ability to Reset Filter
         Counters

   Capability.



      It is possible to reset counters to zero on a per filter basis.

      For the purposes of this capability it would be acceptable for the
      system to maintain two counters: an "absolute counter", C[now],
      and a "reset" counter, C[reset].  The absolute counter would
      maintain counts that increase monotonically until they wrap or
      overflow the counter.  The reset counter would receive a copy of
      the current value of the absolute counter when the reset function
      was issued for that counter.  Functions that display or retrieve
      the counter could then display the delta (C[now] - C[reset]).


   Supported Practices.



      *  This allows operators to get a current picture of the traffic
         matching particular rules/filters.


   Current Implementations.



      Assume that filter counters are being used to detect internal
      hosts that are infected with a new worm.  Once it is believed that
      all infected hosts have been cleaned up and the worm removed, the
      next step would be to verify that.  One way of doing so would be
      to reset the filter counters to zero and see if traffic indicative
      of the worm has ceased.







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   Considerations.



      None.


3.1.15.  Ability to Filter Through the Device - Filter Counters are
         Accurate

   Capability.



      Filter counters are accurate.  They reflect the actual number of
      matching packets since the last counter reset.  Filter counters
      are be capable of holding up to 2^32 - 1 values without
      overflowing and should be capable of holding up to 2^64 - 1
      values.


   Supported Practices.



      *  Inaccurate data can not be relied on as the basis for action.
         Underreported data can conceal the magnitude of a problem.


   Current Implementations.



      If N packets matching a filter are sent to/through a device, then
      the counter should show N matches.


   Considerations.



      None.


3.2.  Rate Limit THROUGH the Device






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3.2.1.  Ability to Rate limit Traffic on All Interfaces THROUGH the
        Device

   Capability.



      The device provides a means to rate limit IP packets on any
      interface implementing IP that are transit packets.


   Supported Practices.



      *  Profile Current Traffic ([I-D.practices] Section x.x.x)

      *  Block Malicious Packets (Section 5.2)

      *  Limit Sources of Management (Section 5.3)


   Current Implementations.



      Many devices currently implement rate limits that allow rate
      limiting based on protocol and/or source/destination address and
      or source/destination port or raw bandwidth and allow these limits
      to be applied to interfaces.


   Considerations.



      None.


3.2.2.  Ability to Rate Limit Traffic Through the Device

   Capability.









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      It is possible to apply the rate-limiting mechanism to traffic
      that is transiting the device via any of its interfaces.


   Supported Practices.



      *  This allows the operator to apply rate-limits that protect the
         networks transiting the device from attacks and unauthorized
         access.


   Current Implementations.



      Many devices currently implement rate-limits that allow limiting
      based on protocol and/or source/destination address and or source/
      destination port and allow these limits to be applied to services
      offered by the networks which transit the device.

      Examples of this might include rate-limits that permit SSH traffic
      rates up to 100 megabits per second from an authorized peer, while
      dropping all other traffic addressed to the network which exceeds
      this limit.


   Considerations.



      None.


3.2.3.  Ability to Rate Limit Traffic Through the Device - Minimal
        Performance Degradation

   Capability.



      The device provides a means to rate-limit packets without
      significant performance degradation.







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      The device is able to apply rate-limits on ALL interfaces (up to
      the maximum number possible) simultaneously and with multiple
      rate-limits per interface (e.g., inbound, outbound, differing
      traffic classifications in either direction).

      The rate-limiting of traffic destined to networks transiting the
      device should not degrade performance significantly.


   Supported Practices.



      *  This enables the implementation of rate-limits on whichever
         services are necessary.  To the extent that rate-limiting
         causes degradation, it may not be possible to apply rate-limits
         that implement the appropriate policies.


   Current Implementations.



      Another way of stating the capability is that rate-limit
      performance should not be the limiting factor in device
      throughput.  If a device is capable of forwarding 30Mb/sec without
      rate-limits, then it should be able to forward the same amount
      with rate-limits in place.


   Considerations.



      The definition of "significant" is subjective.  At one end of the
      spectrum it might mean "the application of rate-limits may cause
      the box to crash".  At the other end would be a throughput loss of
      less than one percent with tens of thousands of rate-limits
      applied.  The level of performance degradation that is acceptable
      will have to be determined by the operator.

      Repeatable test data showing rate-limiting performance impact
      would be very useful in evaluating this capability.  Tests should
      include such information as packet size, packet rate, number of
      interfaces tested (source/destination), types of interfaces,
      routing table size, routing protocols in use, frequency of routing
      updates, etc.




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3.2.4.  Ability to Rate Limit Through the Device - Specify Rate Limit
        Actions

   Capability.



      The device provides a mechanism to allow the specification of the
      action to be taken when a rate-limit rule matches.  Actions
      include "permit" (allow the traffic), "reject" (drop with
      appropriate notification to sender), and "drop" (drop with no
      notification to sender).


   Supported Practices.



      *  This capability is essential to the use of rate limits to
         enforce policy.


   Current Implementations.



      Assume that your management devices for deployed networking
      devices live on several subnets, use several protocols, and are
      controlled by several different parts of your organization.  There
      might exist a reason to have disparate policies for access to the
      devices from these parts of the organization.  Further you may
      want to limit traffic levels for these types of traffic from these
      known sources as close to the sources as possible via interface
      rate limits implemented on the supporting network devices for
      those source networks.

      Actions such as "permit", "deny", "drop" are essential in defining
      the security policy for the services offered by the network
      devices.


   Considerations.









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      While silently dropping traffic without sending notification may
      be the correct action in security terms, consideration should be
      given to operational implications.  See [RFC3360] for
      consideration of potential problems caused by sending
      inappropriate TCP Resets.


3.2.5.  Ability to Rate Limit Through the Device - Log Rate Limit
        Actions

   Capability.



      It is possible to log rate limit actions.  The logging capability
      is able to capture at least the following data:

      *  permit/deny/drop status

      *  source and destination IP address

      *  source and destination ports (if applicable to the protocol)

      *  which network element received the packet (interface, MAC
         address or other layer 2 information that identifies the
         previous hop source of the packet).




   Supported Practices.



      *  Logging is essential for auditing, incident response, and
         operations


   Current Implementations.



      Actions such as "permit", "deny", "drop" are essential in defining
      the security policy for the services offered by the network
      devices.  Auditing the frequency, sources and destinations of
      these attempts is essential for tracking ongoing issues today.





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   Considerations.



      Logging can be burdensome to the network device, at no time should
      logging cause performance degradation to the device or services
      offered on the device.


3.2.6.  Ability to Rate Limit Through the Device - Specify Log
        Granularity

   Capability.



      It is possible to enable/disable logging on a per rule basis.


   Supported Practices.



      *  The ability to tune the granularity of logging allows the
         operator to log the information that is desired and only the
         information that is desired.  Without this capability, it is
         possible that extra data (or none at all) would be logged,
         making it more difficult to find relevant information.


   Current Implementations.



      If a rate limit is defined that has several rules, and one of the
      rules denies telnet (tcp/23) connections, then it should be
      possible to specify that only matches on the rule that denies
      telnet should generate a log message.


   Considerations.



      None.






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3.2.7.  Ability to Rate Limit Through the Device - Ability to Rate Limit
        Protocols

   Capability.



      The device provides a means to rate limit traffic based on the
      value of the protocol field in the IP header.


   Supported Practices.



      *  Being able to rate limit on protocol is necessary to allow
         implementation of policy, secure operations and for support of
         incident response.


   Current Implementations.



      Some denial of service attacks are based on the ability to flood
      the victim with ICMP traffic.  One quick way (admittedly with some
      negative side effects) to mitigate the effects of such attacks is
      to rate limit all ICMP traffic headed toward the victim.


   Considerations.



      None.


3.2.8.  Ability to Rate Limit Through the Device - Ability to Rate Limit
        Addresses

   Capability.



      The function is able to control the flow of traffic based on
      source and/or destination IP address or blocks of addresses such
      as Classless Inter-Domain Routing (CIDR) blocks.




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   Supported Practices.



      *  The capability to rate limit on addresses and address blocks is
         a fundamental tool for establishing boundaries between
         different networks.


   Current Implementations.



      One example of the use of address based rate limits is to
      implement ingress filtering per [RFC2827].


   Considerations.



      None.


3.2.9.  Ability to Rate Limit Through the Device - Ability to Rate Limit
        Protocol Header Fields

   Capability.



      The rate limit mechanism supports rate limiting based on the
      value(s) of any portion of the protocol headers for IP, ICMP, UDP
      and TCP.  It supports rate limiting of all other protocols
      supported at layer 3 and 4.  It supports rate limiting based on
      the headers of higher level protocols.  It is possible to specify
      fields by name (e.g., "protocol = ICMP") rather than bit- offset/
      length/numeric value (e.g., 72:8 = 1).


   Supported Practices.



      *  Being able to rate limit on portions of the header is necessary
         to allow implementation of policy, secure operations, and
         support incident response.




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   Current Implementations.



      This capability implies that it is possible to rate limit based on
      TCP or UDP port numbers, TCP flags such as SYN, ACK and RST bits,
      and ICMP type and code fields.  One common example is to reject
      "inbound" TCP connection attempts (TCP, SYN bit set+ACK bit clear
      or SYN bit set+ACK,FIN and RST bits clear).  Another common
      example is the ability to control what services are allowed in/out
      of a network.  It may be desirable to only allow inbound
      connections on port 80 (HTTP) and 443 (HTTPS) to a network hosting
      web servers.


   Considerations.



      None.


3.2.10.  Ability to Rate Limit Through the Device - Ability to Rate
         Limit Inbound and Outbound

   Capability.



      It is possible to rate limit both incoming and outgoing traffic on
      any interface to or from any transiting network.


   Supported Practices.



      *  This capability allows flexibility in applying rate limits at
         the place that makes the most sense.  It allows invalid or
         malicious traffic to be dropped as close to the source as
         possible.


   Current Implementations.







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      It might be desirable on a router to apply an egress rate limit to
      its external connections to limit outbound traffic that does not
      have a high priority.  Inbound, it might be desirable to apply a
      rate limit to all traffic of a certain classification in order to
      preserve limited resources on the sported networks behind the
      device.


   Considerations.



      None.


3.2.11.  Ability to Rate Limit Through the Device - Ability to
         Accurately Count Rate Limit Hits

   Capability.



      The device supplies a facility for accurately counting all rate
      limit matches.


   Supported Practices.



      *  Accurate counting of rate limit rule matches is important
         because it shows the frequency of attempts to violate policy.
         This enables resources to be focused on areas of greatest need.


   Current Implementations.



      Assume, for example, that a ISP network implements anti-spoofing
      egress rate limits (see [RFC2827]) on interfaces of its edge
      routers that support single-homed stub networks.  Counters could
      enable the ISP to detect cases where large numbers of spoofed
      packets are being sent.  This may indicate that the customer is
      performing potentially malicious actions (possibly in violation of
      the ISPs Acceptable Use Policy), or that system(s) on the



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      customers network have been compromised by hackers and are being
      (mis)used to launch attacks.


   Considerations.



      None.


3.2.12.  Ability to Rate Limit Through the Device - Ability to Display
         Rate Limit Counters

   Capability.



      The device provides a mechanism to display rate limit counters.


   Supported Practices.



      *  Information that is collected is not useful unless it can be
         displayed in a useful manner.


   Current Implementations.



      Assume there is a router with four interfaces.  One is an up-link
      to an ISP providing routes to the Internet.  The other three
      connect to separate internal networks.  Assume that a host on one
      of the internal networks has been compromised by a hacker and is
      sending traffic with bogus source addresses.  In such a situation,
      it might be desirable to apply ingress rate limits to each of the
      internal interfaces.  Once the rate limits are in place, the
      counters can be examined to determine the source (inbound
      interface) of the bogus packets.


   Considerations.






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      None.


3.2.13.  Ability to Rate Limit Through the Device - Ability to Display
         Rate Limit Counters per Rate Limit Application

   Capability.



      If it is possible for a rate limit to be applied more than once at
      the same time, then the device provides a mechanism to display
      rate limit counters per rate limit application.


   Supported Practices.



      *  It may make sense to apply the same rate limit definition
         simultaneously more than one time (to different interfaces,
         etc.).  If so, it would be much more useful to know which
         instance of a rate limit is matching than to know that some
         instance was matching somewhere.


   Current Implementations.



      One way to implement this capability would be to have the counter
      display mechanism show the interface (or other entity) to which
      the rate limit has been applied, along with the name (or other
      designator) for the rate limit.  For example if a rate limit named
      "desktop_outbound" applied two different interfaces, say,
      "ethernet0" and "ethernet1", the display should indicate something
      like "matches of rate limit 'desktop_outbound' on ethernet0 ..."
      and "matches of rate limit 'desktop_outbound' on ethernet1 ..."


   Considerations.








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      None.


3.2.14.  Ability to Rate Limit Through the Device - Ability to Reset
         Rate Limit Counters

   Capability.



      It is possible to reset counters to zero on a per rate limit
      basis.

      For the purposes of this capability it would be acceptable for the
      system to maintain two counters: an "absolute counter", C[now],
      and a "reset" counter, C[reset].  The absolute counter would
      maintain counts that increase monotonically until they wrap or
      overflow the counter.  The reset counter would receive a copy of
      the current value of the absolute counter when the reset function
      was issued for that counter.  Functions that display or retrieve
      the counter could then display the delta (C[now] - C[reset]).


   Supported Practices.



      *  This allows operators to get a current picture of the traffic
         matching particular rules/rate limit.


   Current Implementations.



      Assume that rate limit counters are being used to detect internal
      hosts that are infected with a new worm.  Once it is believed that
      all infected hosts have been cleaned up and the worm removed, the
      next step would be to verify that.  One way of doing so would be
      to reset the rate limit counters to zero and see if traffic
      indicative of the worm has ceased.


   Considerations.







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      None.


3.2.15.  Ability to Rate Limit Through the Device - Rate Limit Counters
         are Accurate

   Capability.



      Rate limit counters are accurate.  They reflect the actual number
      of matching packets since the last counter reset.  Rate limit
      counters are be capable of holding up to 2^32 - 1 values without
      overflowing and should be capable of holding up to 2^64 - 1
      values.


   Supported Practices.



      *  Inaccurate data can not be relied on as the basis for action.
         Underreported data can conceal the magnitude of a problem.


   Current Implementations.



      If N packets matching a Rate limit are sent to/through a device,
      then the counter should show N matches.


   Considerations.



      None.











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4.  Functional Capabilities     - Filtering Layer 2 Attributes

   The capabilities in this section are intended to list testable,
   functional capabilities that are needed to operate devices securely.

   A layer-2 domain permits all devices in the domain to establish
   communication at layer-2.  Devices thus connected have an implicit
   trust relationship among themselves.  If there are devices in a
   layer-2 domain which are at different trust levels, we may want to
   filter traffic between such devices based on the trust levels or any
   other fields in the layer-2 header.  The following filtering
   capabilities are required at layer-2.

4.1.  Filtering Layer 2

4.1.1.  Ability to partition layer-2 network to provide different levels
        of security

   Capability.

      The device provides a means to partition the physical layer-2
      domain into multiple virtual domains, thus allowing the filtering
      of unwarranted traffic.




   Supported Practices.



      *  Being able to partition a layer-2 domain provides the same
         level of security within a layer-2 domain as can be guaranteed
         if they were different layer-2 domains.


   Current Implementations.



      Most Ethernet networks use the concept of VLAN [8021Q] to
      partition a layer-2 broadcast domain.  Private VLAN's [PVLAN]
      allow further partitioning of VLANs's into smaller domains.








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   Considerations.



      Not all layer-2 network technologies may lend themselves to
      virtual partitioning.


4.1.2.  Ability to restrict access to specified hardware (MAC) addresses

   Capability.

      The device provides a means to filter traffic based on the source
      and/ or destination hardware address.




   Supported Practices.



      *  Being able to filter on hardware Address provides an ability to
         block frames between devices in the same layer-2 domain to
         communicate.


   Current Implementations.



      The ability to filter and monitor traffic in layer-2 allows for
      security at layer-2 itself, between devices on the same network.
      Allowing filtering based on hardware address allows a simple
      filtering interface to the administrator to apply simple policy
      rules.


   Considerations.



      Different Link layer technologies use different addressing
      mechanisms.







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4.1.3.  Ability to restrict based on layer-2 packet type [etherType]
        field

   Capability.

      The device provides a means to filter packets based on the packet
      type field in the layer-2 header.




   Supported Practices.



      *  Being able to filter on packets based on the packet type field
         helps in preventing packets not understandable by a particular
         device to be processed by it.


   Current Implementations.



      The ability to filter and monitor traffic in layer-2 allows for
      security at layer-2 itself.  This capability can also prevent IPX
      packets to inadvertently be sent to an IP device and vice versa.


   Considerations.



      None.

















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5.  Additional Operational Practices

   This section describes practices not covered in [I-D.practices].
   They are included here to provide justification for capabilities that
   reference them.

5.1.  Profile Current Traffic

   Discuss practice.  Use same format as [I-D.practices].

5.2.  Block Malicious Packets

   Discuss practice.  Use same format as [I-D.practices].

5.3.  Limit Sources of Management

   Discuss practice.  Use same format as [I-D.practices].


































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6.  Security Considerations

   General

      Security is the subject matter of this entire memo.  The
      capabilities listed cite practices in [I-D.practices] that they
      are intended to support.  [I-D.practices] defines the threat
      model, practices and lists justifications for each practice.











































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7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

7.2.  Non-normative References

   [8021Q]    "802.1Q - Virtual LANs", IEEE Standard 802.1Q - Virtual
              LANs, August 2001.

   [I-D.practices]
              Kaeo, M., "Operational Security Current Practices",
              Internet-Draft (to be published)
              draft-ietf-opsec-current-practices-00, February 2005.

   [PVLAN]    HomChaudhuri, S. and M. Foschiano, "Private VLANs:
              Addressing VLAN scalability and security issues in a
              multi-client environment", Internet Draft (to be
              published) draft-sanjib-private-vlan-02, June 2004.

   [RFC2828]  Shirey, R., "Internet Security Glossary", RFC rfc2828.txt,
              May 2000.

   [RFC3631]  Bellovin, S. and J. Schiller, "Security Mechanisms for the
              Internet", RFC 3631, December 2003.

   [RFC3871]  Jones, G., "Operational Security Requirements for Large
              Internet Service Provider (ISP) IP Network
              Infrastructure", RFC 3871, September 2004.




















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Appendix A.  Acknowledgments

   The editors gratefully acknowledges the contributions of:

   o  xxx

   o  yyy

   o  The MITRE Corporation for supporting development of this document.
      NOTE: The editor's affiliation with The MITRE Corporation is
      provided for identification purposes only, and is not intended to
      convey or imply MITRE's concurrence with, or support for, the
      positions, opinions or viewpoints expressed by the editor.

   o  Others who have provided significant feedback are: zzz

   o  This listing is intended to acknowledge contributions, not to
      imply that the individual or organizations approve the content of
      this document.

   o  Apologies to those who commented on/contributed to the document
      and were not listed.





























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Authors' Addresses

   Christopher L. Morrow
   UUNET Technologies
   21830 UUNet Way
   Ashburn, Virginia  21047
   U.S.A.

   Phone: +1 703 886 3823
   Email: chris@uu.net


   George M. Jones
   The MITRE Corporation
   7515 Colshire Drive, M/S WEST
   McLean, Virginia  22102-7508
   U.S.A.

   Phone: +1 703 488 9740
   Email: gmjones@mitre.org


   Vishwas Manral
   IPInfusion,
   Bangalore,
   India

   Phone: +91-98456-61911
   Email: vishwas@ipinfusion.com






















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