<pre>Network Working Group                                       T. Killalea
Request for Comments: 3013                                    neart.org
BCP: 46                                                   November 2000
Category: Best Current Practice


 <span class="h1">Recommended Internet Service Provider Security Services and Procedures</span>

Status of this Memo

   This document specifies an Internet Best Current Practices for the
   Internet Community, and requests discussion and suggestions for
   improvements.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

Abstract

   The purpose of this document is to express what the engineering
   community as represented by the IETF expects of Internet Service
   Providers (ISPs) with respect to security.

   It is not the intent of this document to define a set of requirements
   that would be appropriate for all ISPs, but rather to raise awareness
   among ISPs of the community's expectations, and to provide the
   community with a framework for discussion of security expectations
   with current and prospective service providers.






















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Table of Contents

   <a href="#section-1">1</a> Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-2">2</a>
     <a href="#section-1.1">1.1</a> Conventions Used in this Document. . . . . . . . . . . . . . <a href="#page-3">3</a>
   <a href="#section-2">2</a> Communication. . . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-3">3</a>
     <a href="#section-2.1">2.1</a> Contact Information. . . . . . . . . . . . . . . . . . . . . <a href="#page-3">3</a>
     <a href="#section-2.2">2.2</a> Information Sharing. . . . . . . . . . . . . . . . . . . . . <a href="#page-4">4</a>
     <a href="#section-2.3">2.3</a> Secure Channels. . . . . . . . . . . . . . . . . . . . . . . <a href="#page-4">4</a>
     <a href="#section-2.4">2.4</a> Notification of Vulnerabilities and Reporting Incidents. . . <a href="#page-4">4</a>
     2.5 ISPs and Computer Security Incident Response Teams (CSIRTs). 5
   <a href="#section-3">3</a> Appropriate Use Policy . . . . . . . . . . . . . . . . . . . . . <a href="#page-5">5</a>
     <a href="#section-3.1">3.1</a> Announcement of Policy . . . . . . . . . . . . . . . . . . . <a href="#page-6">6</a>
     <a href="#section-3.2">3.2</a> Sanctions. . . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-6">6</a>
     <a href="#section-3.3">3.3</a> Data Protection. . . . . . . . . . . . . . . . . . . . . . . <a href="#page-6">6</a>
   <a href="#section-4">4</a> Network Infrastructure . . . . . . . . . . . . . . . . . . . . . <a href="#page-6">6</a>
     <a href="#section-4.1">4.1</a> Registry Data Maintenance. . . . . . . . . . . . . . . . . . <a href="#page-6">6</a>
     <a href="#section-4.2">4.2</a> Routing Infrastructure . . . . . . . . . . . . . . . . . . . <a href="#page-7">7</a>
     <a href="#section-4.3">4.3</a> Ingress Filtering on Source Address. . . . . . . . . . . . . <a href="#page-7">7</a>
     <a href="#section-4.4">4.4</a> Egress Filtering on Source Address . . . . . . . . . . . . . <a href="#page-8">8</a>
     <a href="#section-4.5">4.5</a> Route Filtering. . . . . . . . . . . . . . . . . . . . . . . <a href="#page-8">8</a>
     <a href="#section-4.6">4.6</a> Directed Broadcast . . . . . . . . . . . . . . . . . . . . . <a href="#page-8">8</a>
   <a href="#section-5">5</a> Systems Infrastructure . . . . . . . . . . . . . . . . . . . . . <a href="#page-9">9</a>
     <a href="#section-5.1">5.1</a> System Management. . . . . . . . . . . . . . . . . . . . . . <a href="#page-9">9</a>
     <a href="#section-5.2">5.2</a> No Systems on Transit Networks . . . . . . . . . . . . . . . <a href="#page-9">9</a>
     <a href="#section-5.3">5.3</a> Open Mail Relay. . . . . . . . . . . . . . . . . . . . . . . <a href="#page-9">9</a>
     <a href="#section-5.4">5.4</a> Message Submission . . . . . . . . . . . . . . . . . . . . . <a href="#page-9">9</a>
   <a href="#section-6">6</a> References . . . . . . . . . . . . . . . . . . . . . . . . . . .<a href="#page-10">10</a>
   <a href="#section-7">7</a> Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . .<a href="#page-12">12</a>
   <a href="#section-8">8</a> Security Considerations. . . . . . . . . . . . . . . . . . . . .<a href="#page-12">12</a>
   <a href="#section-9">9</a> Author's Address . . . . . . . . . . . . . . . . . . . . . . . .<a href="#page-12">12</a>
   <a href="#section-10">10</a> Full Copyright Statement. . . . . . . . . . . . . . . . . . . .<a href="#page-13">13</a>

<span class="h2"><a class="selflink" id="section-1" href="#section-1">1</a> Introduction</span>

   The purpose of this document is to express what the engineering
   community as represented by the IETF expects of Internet Service
   Providers (ISPs) with respect to security.  This document is
   addressed to ISPs.

   By informing ISPs of what this community hopes and expects of them,
   the community hopes to encourage ISPs to become proactive in making
   security not only a priority, but something to which they point with
   pride when selling their services.

   Under no circumstances is it the intention of this document to
   dictate business practices.





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   In this document we define ISPs to include organisations in the
   business of providing Internet connectivity or other Internet
   services including but not restricted to web hosting services,
   content providers and e-mail services.  We do not include in our
   definition of an ISP organisations providing those services for their
   own purposes.

   This document is offered as a set of recommendations to ISPs
   regarding what security and attack management arrangements should be
   supported, and as advice to users regarding what they should expect
   from a high quality service provider.  It is in no sense normative in
   its own right.  In time it is likely to become dated, and other
   expectations may arise.  However, it does represent a snapshot of the
   recommendations of a set of professionals in the field at a given
   point in the development of the Internet and its technology.

<span class="h3"><a class="selflink" id="section-1.1" href="#section-1.1">1.1</a> Conventions Used in this Document</span>

   The key words "REQUIRED", "MUST", "MUST NOT", "SHOULD", "SHOULD NOT",
   and "MAY" in this document are to be interpreted as described in "Key
   words for use in RFCs to Indicate Requirement Levels" [<a href="./rfc2119" title="&quot;Key words for use in RFCs to Indicate Requirement Levels&quot;">RFC2119</a>].

<span class="h2"><a class="selflink" id="section-2" href="#section-2">2</a> Communication</span>

   The community's most significant security-related expectations of
   ISPs relate to the availability of communication channels for dealing
   with security incidents.

<span class="h3"><a class="selflink" id="section-2.1" href="#section-2.1">2.1</a> Contact Information</span>

   ISPs SHOULD adhere to [<a href="./rfc2142" title="&quot;Mailbox Names for Common Services, Roles and Functions&quot;">RFC2142</a>], which defines the mailbox SECURITY
   for network security issues, ABUSE for issues relating to
   inappropriate public behaviour and NOC for issues relating to network
   infrastructure.  It also lists additional mailboxes that are defined
   for receiving queries and reports relating to specific services.

   ISPs may consider using common URLs for expanded details on the above
   (e.g., <a href="http://www.ISP-name-here.net/security/">http://www.ISP-name-here.net/security/</a>).

   In addition, ISPs have a duty to make sure that their contact
   information, in Whois, in routing registries [<a href="./rfc1786" title="&quot;Representation of IP Routing Policies in a Routing Registry (ripe-81++)&quot;">RFC1786</a>] or in any
   other repository, is complete, accurate and reachable.









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<span class="h3"><a class="selflink" id="section-2.2" href="#section-2.2">2.2</a> Information Sharing</span>

   ISPs SHOULD have clear policies and procedures on the sharing of
   information about a security incident with their customers, with
   other ISPs, with Incident Response Teams, with law enforcement or
   with the press and general public.

   ISPs should have processes in place to deal with security incidents
   that traverse the boundaries between them and other ISPs.

<span class="h3"><a class="selflink" id="section-2.3" href="#section-2.3">2.3</a> Secure Channels</span>

   ISPs SHOULD be able to conduct such communication over a secure
   channel.  Note, however, that in some jurisdictions secure channels
   might not be permitted.

<span class="h3"><a class="selflink" id="section-2.4" href="#section-2.4">2.4</a> Notification of Vulnerabilities and Reporting of Incidents</span>

   ISPs SHOULD be proactive in notifying customers of security
   vulnerabilities in the services they provide.  In addition, as new
   vulnerabilities in systems and software are discovered they should
   indicate whether their services are threatened by these risks.

   When security incidents occur that affect components of an ISP's
   infrastructure the ISP should promptly report to their customers

      -  who is coordinating response to the incident

      -  the vulnerability

      -  how service was affected

      -  what is being done to respond to the incident

      -  whether customer data may have been compromised

      -  what is being done to eliminate the vulnerability

      -  the expected schedule for response, assuming it can be
         predicted

   Many ISPs have established procedures for notifying customers of
   outages and service degradation.  It is reasonable for the ISP to use
   these channels for reporting security-related incidents.  In such
   cases, the customer's security point of contact might not be the
   person notified.  Rather, the normal point of contact will receive
   the report.  Customers should be aware of this and make sure to route
   such notifications appropriately.



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<span class="h3"><a class="selflink" id="section-2.5" href="#section-2.5">2.5</a> Incident Response and Computer Security Incident Response Teams</span>
   (CSIRTs)

   A Computer Security Incident Response Team (CSIRT) is a team that
   performs, coordinates, and supports the response to security
   incidents that involve sites within a defined constituency.  The
   Internet community's expectations of CSIRTs are described in
   "Expectations for Computer Security Incident Response" [<a href="./rfc2350" title="&quot;Expectations for Computer Security Incident Response&quot;">RFC2350</a>].

   Whether or not an ISP has a CSIRT, they should have a well-advertised
   way to receive and handle reported incidents from their customers.
   In addition, they should clearly document their capability to respond
   to reported incidents, and should indicate if there is any CSIRT
   whose constituency would include the customer and to whom incidents
   could be reported.

   Some ISPs have CSIRTs.  However it should not be assumed that either
   the ISP's connectivity customers or a site being attacked by a
   customer of that ISP can automatically avail themselves of the
   services of the ISP's CSIRT.  ISP CSIRTs are frequently provided as
   an added-cost service, with the team defining as their constituency
   only those who specifically subscribe to (and perhaps pay for)
   Incident Response services.

   Thus it's important for ISPs to publish what incident response and
   security resources they make available to customers, so that the
   customers can define their incident response escalation chain BEFORE
   an incident occurs.

   Customers should find out whether their ISP has a CSIRT, and if so
   what the charter, policies and services of that team are.  This
   information is best expressed using the CSIRT template as shown in
   <a href="#appendix-D">Appendix D</a> of "Expectations for Computer Security Incident Response"
   [<a href="./rfc2350" title="&quot;Expectations for Computer Security Incident Response&quot;">RFC2350</a>].

<span class="h2"><a class="selflink" id="section-3" href="#section-3">3</a> Appropriate Use Policy</span>

   Every ISP SHOULD have an Appropriate Use Policy (AUP).

   Whenever an ISP contracts with a customer to provide connectivity to
   the Internet that contract should be governed by an AUP.  The AUP
   should be reviewed each time the contract is up for renewal, and in
   addition the ISP should proactively notify customers as policies are
   updated.

   An AUP should clearly identify what customers shall and shall not do
   on the various components of a system or network, including the type




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   of traffic allowed on the networks.  The AUP should be as explicit as
   possible to avoid ambiguity or misunderstanding.  For example, an AUP
   might prohibit IP spoofing.

<span class="h3"><a class="selflink" id="section-3.1" href="#section-3.1">3.1</a> Announcement of Policy</span>

   In addition to communicating their AUP to their customers ISPs should
   publish their policy in a public place such as their web site so that
   the community can be aware of what the ISP considers appropriate and
   can know what action to expect in the event of inappropriate
   behaviour.

<span class="h3"><a class="selflink" id="section-3.2" href="#section-3.2">3.2</a> Sanctions</span>

   An AUP should be clear in stating what sanctions will be enforced in
   the event of inappropriate behaviour.

<span class="h3"><a class="selflink" id="section-3.3" href="#section-3.3">3.3</a> Data Protection</span>

   Many jurisdictions have Data Protection Legislation.  Where such
   legislation applies, ISPs should consider the personal data they hold
   and, if necessary, register themselves as Data Controllers and be
   prepared to only use the data in accordance with the terms of the
   legislation.  Given the global nature of the Internet ISPs that are
   located where no such legislation exists should at least familiarise
   themselves with the idea of Data Protection by reading a typical Data
   Protection Act (e.g., [<a href="#ref-DPR1998" title="&quot;Data Protection Act 1998 (c. 29)&quot;">DPR1998</a>]).

<span class="h2"><a class="selflink" id="section-4" href="#section-4">4</a> Network Infrastructure</span>

   ISPs are responsible for managing the network infrastructure of the
   Internet in such a way that it is

      -  reasonably resistant to known security vulnerabilities

      -  not easily hijacked by attackers for use in subsequent attacks

<span class="h3"><a class="selflink" id="section-4.1" href="#section-4.1">4.1</a> Registry Data Maintenance</span>

   ISPs are commonly responsible for maintaining the data that is stored
   in global repositories such as the Internet Routing Registry (IRR)
   and the APNIC, ARIN and RIPE databases.  Updates to this data should
   only be possible using strong authentication.

   ISPs should publicly register the address space that they assign to
   their customers so that there is more specific contact information
   for the delegated space.




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<span class="h3"><a class="selflink" id="section-4.2" href="#section-4.2">4.2</a> Routing Infrastructure</span>

   An ISP's ability to route traffic to the correct destination may
   depend on routing policy as configured in routing registries
   [<a href="./rfc1786" title="&quot;Representation of IP Routing Policies in a Routing Registry (ripe-81++)&quot;">RFC1786</a>].  If so, and if the registry supports it, they should
   ensure that the registry information that they maintain can only be
   updated using strong authentication, and that the authority to make
   updates is appropriately restricted.

   Due care should also be taken in determining in whose routing
   announcements you place greater trust when a choice of routes are
   available to a destination.  In the past bogus announcements have
   resulted in traffic being 'black holed', or worse, hijacked.

   BGP authentication [<a href="./rfc2385" title="&quot;Protection of BGP Sessions via the TCP MD5 Signature Option&quot;">RFC2385</a>] SHOULD be used with routing peers.

<span class="h3"><a class="selflink" id="section-4.3" href="#section-4.3">4.3</a> Ingress Filtering on Source Address</span>

   The direction of such filtering is from the edge site (customer) to
   the Internet.

   Attackers frequently cover their tracks by using forged source
   addresses.  To divert attention from their own site the source
   address they choose will generally be from an innocent remote site or
   indeed from those addresses that are allocated for private Internets
   [<a href="./rfc1918" title="&quot;Address Allocation for Private Internets&quot;">RFC1918</a>].  In addition, forged source addresses are frequently used
   in spoof-based attacks in order to exploit a trust relationship
   between hosts.

   To reduce the incidence of attacks that rely on forged source
   addresses ISPs should do the following.  At the boundary router with
   each of their customers they should proactively filter all traffic
   coming from the customer that has a source address of something other
   than the addresses that have been assigned to that customer.  For a
   more detailed discussion of this topic see [<a href="./rfc2827" title="&quot;Network Ingress Filtering: Defeating Denial of Service Attacks which employ IP Source Address Spoofing&quot;">RFC2827</a>].

   There are (rare) circumstances where ingress filtering is not
   currently possible, for example on large aggregation routers that
   cannot take the additional load of applying packet filters.  In
   addition, such filtering can cause difficulty for mobile users.
   Hence, while the use of this technique to prevent spoofing is
   strongly encouraged, it may not always be feasible.

   In these rare cases where ingress filtering at the interface between
   the customer and the ISP is not possible, the customer should be
   encouraged to implement ingress filtering within their networks.  In
   general filtering should be done as close to the actual hosts as
   possible.



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<span class="h3"><a class="selflink" id="section-4.4" href="#section-4.4">4.4</a> Egress Filtering on Source Address</span>

   The direction of such filtering is from the Internet to the edge site
   (customer).

   There are many applications in widespread use on the Internet today
   that grant trust to other hosts based only on ip address (e.g., the
   Berkeley 'r' commands).  These are susceptible to IP spoofing, as
   described in [<a href="#ref-CA-95.01.IP.spoofing" title="&quot;IP Spoofing Attacks and Hijacked Terminal Connections&quot;">CA-95.01.IP.spoofing</a>].  In addition, there are
   vulnerabilities that depend on the misuse of supposedly local
   addresses, such as 'land' as described in [<a href="#ref-CA-97.28.Teardrop_Land" title="&quot;IP Denial-of-Service Attacks&quot;">CA-97.28.Teardrop_Land</a>].

   To reduce the exposure of their customers to attacks that rely on
   forged source addresses ISPs should do the following.  At the
   boundary router with each of their customers they should proactively
   filter all traffic going to the customer that has a source address of
   any of the addresses that have been assigned to that customer.

   The circumstances described in 4.3 in which ingress filtering isn't
   feasible apply similarly to egress filtering.

<span class="h3"><a class="selflink" id="section-4.5" href="#section-4.5">4.5</a> Route Filtering</span>

   Excessive routing updates can be leveraged by an attacker as a base
   load on which to build a Denial of Service attack.  At the very least
   they will result in performance degradation.

   ISPs should filter the routing announcements they hear, for example
   to ignore routes to addresses allocated for private Internets, to
   avoid bogus routes and to implement "BGP Route Flap Dampening"
   [<a href="./rfc2439" title="&quot;BGP Route Flap Damping&quot;">RFC2439</a>] and aggregation policy.

   ISPs should implement techniques that reduce the risk of putting
   excessive load on routing in other parts of the network.  These
   include 'nailed up' routes, aggressive aggregation and route
   dampening, all of which lower the impact on others when your internal
   routing changes in a way that isn't relevant to them.

<span class="h3"><a class="selflink" id="section-4.6" href="#section-4.6">4.6</a> Directed Broadcast</span>

   The IP protocol allows for directed broadcast, the sending of a
   packet across the network to be broadcast on to a specific subnet.
   Very few practical uses for this feature exist, but several different
   security attacks (primarily Denial of Service attacks making use of
   the packet multiplication effect of the broadcast) use it.
   Therefore, routers connected to a broadcast medium MUST NOT be
   configured to allow directed broadcasts onto that medium [<a href="./rfc2644" title="&quot;Changing the Default for Directed Broadcasts in Routers&quot;">RFC2644</a>].




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<span class="h2"><a class="selflink" id="section-5" href="#section-5">5</a> Systems Infrastructure</span>

   The way an ISP manages their systems is crucial to the security and
   reliability of their network.  A breach of their systems may
   minimally lead to degraded performance or functionality, but could
   lead to loss of data or the risk of traffic being eavesdropped (thus
   leading to 'man-in-the-middle' attacks).

   It's widely accepted that it's easier to build secure systems if
   different services (such as mail, news and web-hosting) are kept on
   separate systems.

<span class="h3"><a class="selflink" id="section-5.1" href="#section-5.1">5.1</a> System Management</span>

   All systems that perform critical ISP functions such as mail, news
   and web-hosting, should be restricted such that access to them is
   only available to the administrators of those services.  That access
   should be granted only following strong authentication, and should
   take place over an encrypted link.  Only the ports on which those
   services listen should be reachable from outside of the ISP's systems
   networks.

   ISPs should stay up to date for more secure methods of providing
   services as they become available (e.g., IMAP/POP AUTHorize Extension
   for Simple Challenge/Response, [<a href="./rfc2195" title="&quot;IMAP/POP AUTHorize Extension for Simple Challenge/Response&quot;">RFC2195</a>]).

<span class="h3"><a class="selflink" id="section-5.2" href="#section-5.2">5.2</a> No Systems on Transit Networks</span>

   Systems should not be attached to transit network segments.

<span class="h3"><a class="selflink" id="section-5.3" href="#section-5.3">5.3</a> Open Mail Relay</span>

   ISPs should take active steps to prevent their mail infrastructure
   from being used by 'spammers' to inject Unsolicited Bulk E-mail (UBE)
   while hiding the sender's identity [<a href="./rfc2505" title="&quot;Anti-Spam Recommendations for SMTP MTAs&quot;">RFC2505</a>].  While not all
   preventive steps are appropriate for every site, the most effective
   site-appropriate methods should be used.

   ISPs should also strongly encourage their customers to take the
   necessary steps to prevent this activity on their own systems.

<span class="h3"><a class="selflink" id="section-5.4" href="#section-5.4">5.4</a> Message Submission</span>

   Message submissions should be authenticated using the AUTH SMTP
   service extension as described in the "SMTP Service Extension for
   Authentication" [<a href="./rfc2554" title="&quot;SMTP Service Extension for Authentication&quot;">RFC2554</a>].





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   SMTP AUTH is preferred over IP address-based submission restrictions
   in that it gives the ISP's customers the flexibility of being able to
   submit mail even when not connected through the ISP's network (for
   example, while at work), is more resistant to spoofing, and can be
   upgraded to newer authentication mechanisms as they become available.

   In addition, to facilitate the enforcement of security policy, it is
   strongly recommended that messages be submitted using the MAIL SUBMIT
   port (587) as discussed in "Message Submission" [<a href="./rfc2476" title="&quot;Message Submission&quot;">RFC2476</a>], rather
   than through the SMTP port (25).  In this way the SMTP port (25) can
   be restricted to local delivery only.

   The reason for this is to be able to differentiate between inbound
   local delivery and relay (i.e., allow customers to send email via the
   ISP's SMTP service to arbitrary receivers on the Internet).  Non-
   authenticated SMTP should only be allowed for local delivery.

   As more and more mail clients support both SMTP AUTH and the message
   submission port (either explicitly or by configuring the SMTP port),
   ISPs may find it useful to require that customers submit messages
   using both the submission port and SMTP AUTH; permitting only inbound
   mail on port 25.

   These measures (SMTP AUTH and the submission port) not only protect
   the ISP from serving as a UBE injection point via third-party relay,
   but also help in tracking accountability for message submission in
   the case where a customer sends UBE.

<span class="h2"><a class="selflink" id="section-6" href="#section-6">6</a> References</span>

   [<a id="ref-CA-95.01.IP.spoofing">CA-95.01.IP.spoofing</a>]   "IP Spoofing Attacks and Hijacked Terminal
                            Connections",
                            <a href="ftp://info.cert.org/pub/cert_advisories/">ftp://info.cert.org/pub/cert_advisories/</a>

   [<a id="ref-CA-97.28.Teardrop_Land">CA-97.28.Teardrop_Land</a>] "IP Denial-of-Service Attacks",
                            <a href="ftp://info.cert.org/pub/cert_advisories/">ftp://info.cert.org/pub/cert_advisories/</a>

   [<a id="ref-DPR1998">DPR1998</a>]                The UK "Data Protection Act 1998 (c. 29)",
                            <a href="http://www.hmso.gov.uk/acts/acts1998/19980029.htm">http://www.hmso.gov.uk/acts/acts1998/</a>
                            <a href="http://www.hmso.gov.uk/acts/acts1998/19980029.htm">19980029.htm</a>

   [<a id="ref-RFC1786">RFC1786</a>]                Bates, T., Gerich, E., Joncheray, L.,
                            Jouanigot, J., Karrenberg, D., Terpstra, M.
                            and J. Yu, "Representation of IP Routing
                            Policies in a Routing Registry (ripe-81++)",
                            <a href="./rfc1786">RFC 1786</a>, March 1995.





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   [<a id="ref-RFC1834">RFC1834</a>]                Gargano, J. and K. Weiss, "Whois and Network
                            Information Lookup Service", <a href="./rfc1834">RFC 1834</a>,
                            August 1995.

   [<a id="ref-RFC1835">RFC1835</a>]                Deutsch, P., Schoultz, R., Faltstrom, P. and
                            C. Weider, "Architecture of the WHOIS++
                            service", <a href="./rfc1835">RFC 1835</a>, August 1995.

   [<a id="ref-RFC1918">RFC1918</a>]                Rekhter, Y., Moskowitz, B., Karrenberg, D.,
                            de Groot, G. J. and E. Lear, "Address
                            Allocation for Private Internets", <a href="https://www.rfc-editor.org/bcp/bcp5">BCP 5</a>,
                            <a href="./rfc1918">RFC 1918</a>, February 1996.

   [<a id="ref-RFC2119">RFC2119</a>]                Bradner, S., "Key words for use in RFCs to
                            Indicate Requirement Levels", <a href="https://www.rfc-editor.org/bcp/bcp14">BCP 14</a>, <a href="./rfc2119">RFC</a>
                            <a href="./rfc2119">2119</a>, March 1997.

   [<a id="ref-RFC2142">RFC2142</a>]                Crocker, D., "Mailbox Names for Common
                            Services, Roles and Functions", <a href="./rfc2142">RFC 2142</a>,
                            May 1997.

   [<a id="ref-RFC2195">RFC2195</a>]                Klensin, J., Catoe, R. and P. Krumviede,
                            "IMAP/POP AUTHorize Extension for Simple
                            Challenge/Response", <a href="./rfc2195">RFC 2195</a>, September
                            1997.

   [<a id="ref-RFC2196">RFC2196</a>]                Fraser, B., "Site Security Handbook", FYI 8,
                            <a href="./rfc2196">RFC 2196</a>, September 1997.

   [<a id="ref-RFC2350">RFC2350</a>]                Brownlee, N. and  E. Guttman, "Expectations
                            for Computer Security Incident Response",
                            <a href="https://www.rfc-editor.org/bcp/bcp21">BCP 21</a>, <a href="./rfc2350">RFC 2350</a>, June 1998.

   [<a id="ref-RFC2385">RFC2385</a>]                Heffernan, A., "Protection of BGP Sessions
                            via the TCP MD5 Signature Option", <a href="./rfc2385">RFC 2385</a>,
                            August 1998.

   [<a id="ref-RFC2439">RFC2439</a>]                Chandra R., Govindan R. and C. Villamizar,
                            "BGP Route Flap Damping", <a href="./rfc2439">RFC 2439</a>, November
                            1998.

   [<a id="ref-RFC2476">RFC2476</a>]                Gellens R. and J. Klensin, "Message
                            Submission", <a href="./rfc2476">RFC 2476</a>, December 1998.

   [<a id="ref-RFC2505">RFC2505</a>]                Lindberg, G., "Anti-Spam Recommendations for
                            SMTP MTAs", <a href="https://www.rfc-editor.org/bcp/bcp30">BCP 30</a>, <a href="./rfc2505">RFC 2505</a>, February 1999.





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   [<a id="ref-RFC2554">RFC2554</a>]                Myers, J., "SMTP Service Extension for
                            Authentication", <a href="./rfc2554">RFC 2554</a>, March 1999.

   [<a id="ref-RFC2644">RFC2644</a>]                Senie, D., "Changing the Default for
                            Directed Broadcasts in Routers", <a href="https://www.rfc-editor.org/bcp/bcp34">BCP 34</a>, <a href="./rfc2644">RFC</a>
                            <a href="./rfc2644">2644</a>, August 1999.

   [<a id="ref-RFC2827">RFC2827</a>]                Ferguson, P. and D. Senie, "Network Ingress
                            Filtering: Defeating Denial of Service
                            Attacks which employ IP Source Address
                            Spoofing", <a href="https://www.rfc-editor.org/bcp/bcp38">BCP 38</a>, <a href="./rfc2827">RFC 2827</a>, May 2000.

<span class="h2"><a class="selflink" id="section-7" href="#section-7">7</a> Acknowledgements</span>

   I gratefully acknowledge the constructive comments received from
   Nevil Brownlee, Randy Bush, Bill Cheswick, Barbara Y. Fraser, Randall
   Gellens, Erik Guttman, Larry J. Hughes Jr., Klaus-Peter Kossakowski,
   Michael A. Patton, Don Stikvoort and Bill Woodcock.

<span class="h2"><a class="selflink" id="section-8" href="#section-8">8</a> Security Considerations</span>

   This entire document discusses security issues.

<span class="h2"><a class="selflink" id="section-9" href="#section-9">9</a> Author's Address</span>

   Tom Killalea
   Lisi/n na Bro/n
   Be/al A/tha na Muice
   Co. Mhaigh Eo
   IRELAND

   Phone: +1 206 266-2196
   EMail: tomk@neart.org


















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<span class="h2"><a class="selflink" id="section-10" href="#section-10">10</a> Full Copyright Statement</span>

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

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Acknowledgement

   Funding for the RFC Editor function is currently provided by the
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