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Versions: 00                                                            
Internet Draft                                        Tristan Debeaupuis
GRIP Working Group                                                Editor
Expires on                                     Herve Schauer Consultants
15 February 2000                                          15 August 1999

                Site Security Handbook Addendum for ISPs
                    <draft-ietf-grip-ssh-add-00.txt>

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This memo and its companions are discussed on the GRIP working group
   mailing list, grip-wg[-request]@uu.net.

Copyright Notice

   Copyright (C) The Internet Society (1999).  All Rights Reserved.

Abstract

   This addendum to the Site Security Handbook [RFC2196] is providing a
   checklist for the general Internet community to use when discussing
   security with Internet Service Providers (ISPs).  These questions can
   serve as a framework for discussion of security expectations with
   current and prospective service providers.  Regrettably, such a
   discussion rarely takes place today.

Debeaupuis                                              [Page 1]


INTERNET-DRAFT  Site Security Handbook Addendum for ISPs    11 July 1999

   This document is addressed to Internet service purchasing decision-
   makers (consumers).  Three types of consumers are considered in this
   document:  connectivity consumers, hosting service consumers, and co-
   located consumers.

   Additionally, in informing ISPs of what the community will be ask-
   ing of them, a further goal is 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.  It has been argued
   that vendors begin to care about security only when prompted by
   consumers.  We hope that these documents will encourage both parties
   to more readily express how much they care about security, and that
   discussion between the community and its ISPs will be increased.

   Note that these are broad categories and individual consumers may not
   fall exactly into these categories; as such, not all questions will
   apply to all consumers, nor will all questions apply to all ISPs.

   Companion documents, [RFCisp] and [RFCsshadd], express the general
   Internet community's expectations of ISPs with respect to security.

   The questions have been collected together into Appendix A for easy
   reference.

Table of Contents

1. Purpose of This Work  . . . . . . . . . . . . . . . . . . . . . .   3
2. Audience  . . . . . . . . . . . . . . . . . . . . . . . . . . . .   4
2.1. Conventions Used in this Document . . . . . . . . . . . . . . .   5
3. Incident Response . . . . . . . . . . . . . . . . . . . . . . . .   5
3.1. ISPs and Security Incident Response Teams (SIRTs) . . . . . . .   5
3.2. Assistance with Inbound Security Incidents  . . . . . . . . . .   6
3.3. Assistance with Outbound or Transit Security Incidents  . . . .   6
3.4. Communication and Authentication  . . . . . . . . . . . . . . .   7
4. Protection of the Community . . . . . . . . . . . . . . . . . . .   7
4.1. Data Protection . . . . . . . . . . . . . . . . . . . . . . . .   7
4.2. Training  . . . . . . . . . . . . . . . . . . . . . . . . . . .   8
5. Network Infrastructure  . . . . . . . . . . . . . . . . . . . . .   8
5.1. Routers . . . . . . . . . . . . . . . . . . . . . . . . . . . .   8
5.2. Switches, Terminal Servers, Modems and other Network
Devices  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   9
5.3. Anonymous telnet and other unlogged connections . . . . . . . .  10
5.4. The Network Operation Centre (NOC) and Network Management
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  10
5.5. Physical Security . . . . . . . . . . . . . . . . . . . . . . .  11
5.6. Routing Infrastructure  . . . . . . . . . . . . . . . . . . . .  12
5.7. Ingress Filtering on Source Address . . . . . . . . . . . . . .  13

Debeaupuis                                              [Page 2]


INTERNET-DRAFT  Site Security Handbook Addendum for ISPs    11 July 1999

5.8. Egress Filtering on Source Address  . . . . . . . . . . . . . .  13
5.9. Route Filtering . . . . . . . . . . . . . . . . . . . . . . . .  14
5.10. Directed Broadcast . . . . . . . . . . . . . . . . . . . . . .  14
6. Systems Infrastructure  . . . . . . . . . . . . . . . . . . . . .  15
6.1. Policy  . . . . . . . . . . . . . . . . . . . . . . . . . . . .  15
6.2. System Management . . . . . . . . . . . . . . . . . . . . . . .  15
6.3. Backup  . . . . . . . . . . . . . . . . . . . . . . . . . . . .  16
6.4. Software Distribution . . . . . . . . . . . . . . . . . . . . .  16
7. Domain Name Service (DNS) . . . . . . . . . . . . . . . . . . . .  17
7.1. DNS Server Administration . . . . . . . . . . . . . . . . . . .  17
7.2. Authoritative Domain Name Service . . . . . . . . . . . . . . .  17
7.3. Resolution Service  . . . . . . . . . . . . . . . . . . . . . .  18
8. Email and Mail Services . . . . . . . . . . . . . . . . . . . . .  18
8.1. Mail Server Administration  . . . . . . . . . . . . . . . . . .  19
8.2. Secure Mail . . . . . . . . . . . . . . . . . . . . . . . . . .  19
8.3. Open Mail Relay . . . . . . . . . . . . . . . . . . . . . . . .  20
8.4. Message Submission  . . . . . . . . . . . . . . . . . . . . . .  20
8.5. POP and IMAP Services . . . . . . . . . . . . . . . . . . . . .  21
9. News Service (NNTP) . . . . . . . . . . . . . . . . . . . . . . .  21
9.1. News Server Administration  . . . . . . . . . . . . . . . . . .  21
9.2. Article Submission  . . . . . . . . . . . . . . . . . . . . . .  22
9.3. Control Messages  . . . . . . . . . . . . . . . . . . . . . . .  22
9.4. Newsfeed Filters  . . . . . . . . . . . . . . . . . . . . . . .  22
10. Web-hosting Services . . . . . . . . . . . . . . . . . . . . . .  23
10.1. Webhosting Server Administration . . . . . . . . . . . . . . .  23
10.2. Server Side Programs . . . . . . . . . . . . . . . . . . . . .  24
10.3. Data and Databases . . . . . . . . . . . . . . . . . . . . . .  25
10.4. Logs and Statistics Reporting  . . . . . . . . . . . . . . . .  26
10.5. Push and Streaming Services  . . . . . . . . . . . . . . . . .  26
10.6. Commerce . . . . . . . . . . . . . . . . . . . . . . . . . . .  26
10.7. Content Loading and Distributed Authoring  . . . . . . . . . .  27
10.8. Search Engines and other tools . . . . . . . . . . . . . . . .  27
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . .  28
12. Security Considerations  . . . . . . . . . . . . . . . . . . . .  30
13. Editor Information . . . . . . . . . . . . . . . . . . . . . . .  30
14. Full Copyright Statement . . . . . . . . . . . . . . . . . . . .  30

1.  Purpose of This Work

   This handbook is a guide to setting computer security policies and
   procedures for sites that have systems on the Internet (however, the
   information provided should also be useful to sites not yet connected
   to the Internet).  This guide lists issues and factors that a site
   must consider when setting their own policies. It makes a number of
   recommendations and provides discussions of relevant areas.

Debeaupuis                                              [Page 3]


INTERNET-DRAFT  Site Security Handbook Addendum for ISPs    11 July 1999

   This guide is only a framework for setting security policies and pro¡
   cedures.  In order to have an effective set of policies and proce¡
   dures, a site will have to make many decisions, gain agreement, and
   then communicate and implement these policies.

2.  Audience

   The audience for this document are system and network administrators,
   and decision makers (typically "middle management") at sites.  For
   brevity, we will use the term "administrator" throughout this docu¡
   ment to refer to system and network administrators.

   This document is not directed at programmers or those trying to cre¡
   ate secure programs or systems.  The focus of this document is on the
   policies and procedures that need to be in place to support the tech¡
   nical security features that a site may be implementing.

   The primary audience for this work are sites that are members of the
   Internet community.  However, this document should be useful to any
   site that allows communication with other sites.  As a general guide
   to security policies, this document may also be useful to sites with
   isolated systems.

   The purpose of this document is to express the general Internet com¡
   munity's expectations of Internet Service Providers (ISPs) with
   respect to security.

   In this document, we define ISPs to include organizations in the
   business of providing Internet connectivity or other Internet ser¡
   vices including, but not restricted to, Web hosting services, content
   providers and email service providers. We do not include in our defi¡
   nition of an ISP organizations providing those services for their own
   purposes."

   A goal is that customers could have a framework that facilitates the
   discussion of security with prospective service providers; regret¡
   tably, such a discussion rarely takes place today.

   Additionally, in informing ISPs of what the community hopes and
   expects of them, a further goal is to encourage ISPs to become proac¡
   tive 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 dic¡
   tate business practices.

   This document is addressed to Internet service purchasing decision-

Debeaupuis                                              [Page 4]


INTERNET-DRAFT  Site Security Handbook Addendum for ISPs    11 July 1999

   makers (customers) and to ISPs.

   It has been argued that vendors begin to care about security only
   when prompted by customers.  I hope that this document will encourage
   both parties to more readily express how much they care about secu¡
   rity, and that discussion between the community and its ISPs will be
   increased.

2.1.  Conventions Used in this Document

   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" [RFC2119].

3.  Incident Response

   A Security Incident Response Team (SIRT) is a team that performs,
   coordinates, and supports the response to security incidents that
   involve sites within a defined constituency.  The Internet commu¡
   nity's expectations of SIRTs are described in "Expectations for Com¡
   puter Security Incident Response" [RFC2350].

   Whether or not an ISP has a SIRT, 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.

3.1.  ISPs and Security Incident Response Teams (SIRTs)

   Some ISPs have SIRTs.  However it should not be assumed that either
   the ISP's connectivity customers or a site being attacked by a cus¡
   tomer of that ISP can automatically avail themselves of the services
   of the ISP's SIRT.  ISP SIRTs 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 to determine what incident response and security
   resources are available to you, and define your incident response
   escalation chain BEFORE an incident occurs.

   Customers should find out whether their ISP has a SIRT, and if so

Debeaupuis                                              [Page 5]


INTERNET-DRAFT  Site Security Handbook Addendum for ISPs    11 July 1999

   what the charter, policies and services of that team are.  This
   information is best expressed using the SIRT template as shown in
   Appendix D of "Expectations for Computer Security Incident Response"
   [RFC2350].  If the ISP doesn't have a SIRT they should describe what
   role if any they will take in incident response, and should indicate
   if there is any SIRT whose constituency would include the customer
   and to whom incidents could be reported.

3.2.  Assistance with Inbound Security Incidents

   When a security incident targeting one of their connectivity cus¡
   tomers occurs ISPs should inform the customer of the attack. The ISP
   may also provide assistance to
      - trace the 'apparent' origin of the attack and attempt to
        determine the veracity of each step in the path (keeping in
        mind that the source address may be spoofed).  In cases where
        the source address is spoofed the ISP could trace the point
        at which the bogusly addressed traffic entered the ISP's
        network.

      - obtain contact information for the source of the attack using
        whois [RFC1834 and RFC1835], the DNS [RFC1034 and RFC1035] or
        relevant common mailbox names [RFC2142].

      - collect and protect evidence of the incident and guard against
        its destruction or unintentional announcement.

      If the event continues then, at the customer's request, ISPs may
      also assist by logging in order to further diagnose the problem,
      or by filtering certain types of traffic.

3.3.  Assistance with Outbound or Transit Security Incidents

   In the case where one of their connectivity customers appears to be
   the source of a security incident an ISP will frequently be con¡
   tacted.  The ISP may facilitate the administrators at the source and
   the target of the incident getting in contact with each other, nor¡
   mally by passing contact information for the target to the ISP's cus¡
   tomer.

   An ISP may also be contacted to assist with incidents that traverse
   their network but use bogus source addresses, such as SYN flooding
   attacks [CA-96.21.tcpsynflooding].  Assistance in this case might
   consist of using network traces on a hop by hop basis to identify the

Debeaupuis                                              [Page 6]


INTERNET-DRAFT  Site Security Handbook Addendum for ISPs    11 July 1999

   point at which the bogusly addressed traffic entered the ISP's net¡
   work.  In tracing such incidents it's frequently necessary to coordi¡
   nate with adjacent ISPs to form a complete chain of response teams
   along the path of the attack.

3.4.  Communication and Authentication

   ISPs SHOULD have clear policies and procedures on the sharing of
   information about a security incident with their customers, with
   other ISPs or SIRTs, with law enforcement or with the press and gen¡
   eral public.

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

4.  Protection of the Community

   ISPs play a crucial role in helping to improve the security of the
   Internet.  This and following sections describe a number of issues
   which, should they be addressed by ISPs in a coordinated and timely
   way, would have a very positive effect on the security of the net¡
   work, and would make it much more difficult for the perpetrators to
   cover their tracks.

   Later sections cover in some detail issues related to specific ser¡
   vices such as ingress filtering and open mail relays. Such issues, if
   addressed by all the ISPs in a concerted way, could have a very posi¡
   tive effect.

4.1.  Data Protection

   Many jurisdictions have Data Protection Legislation.  Where such leg¡
   islation 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., [DPR1998]).

Debeaupuis                                              [Page 7]


INTERNET-DRAFT  Site Security Handbook Addendum for ISPs    11 July 1999

4.2.  Training

   It's important that all ISP staff be trained to be security-conscious
   at all times and to be able to make appropriate use of tools that
   enhance security.  Some issues that they should be particularly aware
   of include the use of secure channels for confidential information,
   the risk of attacks that use social engineering, management of data
   used for authentication, and so on.

5.  Network Infrastructure

   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

5.1.  Routers

   Routers are an excellent platform from which to launch a security
   attack, as well as being attractive targets of themselves.

   Many routers allow an attacker to do dangerous things such as:
      - sniff transit traffic

      - manipulate routing tables to redirect traffic

      - manipulate interface states to disrupt service

      - create routing flaps which could potentially cause Denial of
        Service for large parts of the Internet

      - create packets with spoofed addresses, and with any desired
      flags
        set

      - initiate ICMP packet storms and other Denial of Service attacks

      - ³black hole³ traffic (e.g., by holding a local route to a null
      or
        invalid interface, by holding a local route to an invalid
        next-hop (one which does not itself have a corresponding route,
        and does not have a default), or worst yet, by using a dynamic
        routing protocol to advertise availability of a low-cost route
        and thus actively drawing traffic toward the black hole)

Debeaupuis                                              [Page 8]


INTERNET-DRAFT  Site Security Handbook Addendum for ISPs    11 July 1999

      - launder connections to third-party destinations, facilitated by
        the router's lack of logging
      Such threats are amplified because of the central part in the net¡
      working infrastructure that routers occupy, and the large band¡
      width frequently available to them.

      So access to routers SHOULD be based on one-time passwords or bet¡
      ter (e.g., Kerberos) and should be as restricted as possible.
      Connections to the router should be logged to a different system.

      If the router supports different levels of authorisation these
      levels should be used to restrict privileged access to the router.

      Sessions should be encrypted to prevent sessions or data from
      being stolen and to avoid replay attacks.

      Routers should not run the 'small services', which are often
      enabled by default.  These may include bootp, chargen, daytime,
      discard, echo and finger.

5.2.  Switches, Terminal Servers, Modems and other Network Devices

   ISPs should be similarly vigilant in their configuration of other
   network devices.  Unfortunately many such devices deployed in the
   field support only minimal authentication, do authorisation on an
   all-or-nothing basis and do little or no logging.  In the past ISPs
   have been left with no trail to follow after their switches were
   reconfigured, their terminal servers were used to launch attacks on
   third parties or their Uninterruptable Power Supplies were shut down.

   Where possible access to such devices should be restricted only to
   legitimate network administrators.

   Network infrastructure devices frequently don't support extensive
   internal logging because they have no long-term storage, like hosts'
   hard drives.  Many support syslog or SNMP traps however, or at least
   a short internal event log or debugging mode which can be captured
   through the console or a through a remote logging session.

   Router or switch configurations should always be maintained on a file
   server, so that they can be restored to previous configuration easily
   and quickly.  These backup configurations should obviously be pro¡
   tected so that they cannot be transferred by unauthorised parties, or
   overwritten with new bogus configurations.

Debeaupuis                                              [Page 9]


INTERNET-DRAFT  Site Security Handbook Addendum for ISPs    11 July 1999

5.3.  Anonymous telnet and other unlogged connections

   There are many network devices ranging from low-end routers to print¡
   ers that accept telnet connections without prompting for a password.
   Obviously such devices, many of which don't maintain audit trails,
   are very popular among attackers who wish to cover their tracks.

   If ISPs have such devices on their own network they should restrict
   access to them.  In addition, they should encourage their customers
   to block access to such devices from outside of the customer's net¡
   work.

   The use of telnet to manage network elements is strongly discouraged.

5.4.  The Network Operation Centre (NOC) and Network Management

   A NOC is a crucial part of an ISP's infrastructure, and should be
   operated with appropriate regard to security.

   A NOC frequently has management control over the configuration infor¡
   mation of network devices, and should be vigilant in restricting
   access to that information.  Loading of configuration information
   into network devices is still frequently done using the TFTP protocol
   [RFC1350], which not only lacks authentication and uses an insecure
   channel, but calls for great care in configuration at the server end
   [CA-91:18.Active.Internet.tftp.Attacks].

   A NOC will generally perform a network monitoring function by polling
   (e.g., with ICMP Echo) a set of network devices periodically.  In
   selecting the set of devices to be polled the crucial role of the
   devices in 5.2 shouldn't be overlooked.

   Beyond simple polling a NOC may also use a network management proto¡
   col such as SNMP to communicate with network devices.  Usually this
   will be used to 'get' the value of various variables, such as the
   number of packets received on a particular interface.  However the
   protocol can be used to 'set' variables, perhaps with serious results
   (e.g., the device can be reconfigured).  In any case, SNMPv1 uses
   only trivial authentication.  Where possible SNMP should be used as a
   read-only tool to 'get' information from remote devices, and the
   information gotten should be treated as confidential.

   A further use of SNMP is in trap reporting, whereby a management sta¡
   tion is notified when certain exceptions occur.  This information
   should also be considered confidential, and the NOC should take care
   that such trap reporting cannot of itself become a Denial of Service

Debeaupuis                                             [Page 10]


INTERNET-DRAFT  Site Security Handbook Addendum for ISPs    11 July 1999

   attack.

5.5.  Physical Security

   The physical security of every installation should be given appropri¡
   ate consideration.  This is particularly so for co-located facilities
   to which people from different organisations and with different secu¡
   rity policies have access.

   Three types of co-location arrangements are of particular interest:

      - customers co-locating equipment at an ISP's facility

      - ISPs co-locating equipment at an external facility with
        authorised 'remote hands'

      - ISPs co-locating equipment at an external facility with no
        authorised physical access

      The first case is most likely to directly concern the customer.
      If an ISP has a co-location facility for the hosting of customer-
      owned equipment many issues arise surrounding customer access to
      their co- located equipment.

      Ideally every customer would have a fully enclosed locking 'cage',
      akin to a small room with walls and ceiling of heavy wire mesh
      fencing, containing the racks in which their equipment is mounted.
      Customers are allowed access to their own cage under escort by one
      of the ISP's employees, or with keys that grant access specifi¡
      cally to their cage.

      This assignment of separate cages is expensive in terms of space
      however, so many ISPs compromise by putting all co-located equip¡
      ment together in a single machine room, and managing the actions
      of escorted customers very closely.  However this may be insuffi¡
      cient to prevent mishaps such as the accidental disconnection of
      another customer's equipment.  If a single machine room is used
      then the ISP should provide separate locking cabinets for each co-
      location customer in preference to an open common area.

      A customer should always be supervised while in the physical pres¡
      ence of any equipment that is not their own, and should not be
      allowed to touch, photograph, or examine equipment belonging to
      another customer.

      Also of concern is layer 2 security of co-located equipment.

Debeaupuis                                             [Page 11]


INTERNET-DRAFT  Site Security Handbook Addendum for ISPs    11 July 1999

      Customer equipment should not be allowed to share a physical net¡
      work segment with hosts belonging to anyone else, whether another
      customer or the ISP themselves.  It's common for crackers to
      exploit weak security or unencrypted remote logins on co-located
      customer-owned equipment to take control of that equipment and put
      it into promiscuous listening mode on the local network segment,
      thereby potentially compromising the privacy and security of any
      other devices on that segment.

      When ISPs co-locate network infrastructure components outside of
      their own premises, such as at peering points or remote POPs,
      security considerations are extremely important.  These locations
      often play a pivotal role in the network topology, and may be par¡
      ticular targets for attack or vulnerable to accidents.  Equipment
      should ideally be fully enclosed in locking cabinets or cages to
      limit physical access.  If on-site spares are kept, they should
      likewise be protected from tampering.  Whenever possible, security
      systems and logging card-swipe locks should be employed.  Instal¡
      lations should be inspected periodically for the addition of unau¡
      thorised equipment which might be used to 'tap' a connection.  As
      with any other facility, hosts should not be attached to transit
      segments, and hosts should never have unused physical interfaces
      attached to network segments.

5.6.  Routing Infrastructure

   An ISP's ability to route traffic to the correct destination depends
   on routing policy as configured in the routing registries [RFC1786].
   ISPs should ensure that the registry information that they maintain
   can only be updated using strong authentication, and that the author¡
   ity 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 ³black holed³, or worse, hijacked.  BGP
   authentication should be used with routing peers.

   The internal routing protocol that an ISP uses should be chosen with
   security in mind.  It should not be configured with the assumption
   that route recalculations are rare and expensive as this would leave
   the way open for a Denial of Service attack.  Routing updates should
   use the highest level of authentication supported by the internal
   routing protocol.

   If more specific routes to parts of the ISP's allocated address space

Debeaupuis                                             [Page 12]


INTERNET-DRAFT  Site Security Handbook Addendum for ISPs    11 July 1999

   are heard from external peers then the ISP needs to be judicious in
   deciding whether to accept the announcement.  Only ISPs who have
   allowed their CIDR address allocations to become fragmented (by
   allowing customers to take addressess with them when they change
   providers) have to face this decision.

5.7.  Ingress Filtering on Source Address

   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
   [RFC1918].  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 [RFC2267].

   There are (rare) circumstances where ingress filtering is not cur¡
   rently 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 pos¡
   sible.

5.8.  Egress Filtering on Source Address

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

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   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 [CA-95.01.IP.spoofing].  In addition, there are vulnera¡
   bilities that depend on the misuse of supposedly local addresses,
   such as 'land' as described in [CA-97.28.TeardropLand].

   To reduce the exposure of their customers to attacks that rely on
   forged source addresses ISPs should do the following.  At the bound¡
   ary router with each of their customers they should proactively fil¡
   ter 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 5.7 in which ingress filtering isn't
   feasible apply similarly to egress filtering.

5.9.  Route Filtering

   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 route dampening 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 dampen¡
   ing, all of which lower the impact on others when your internal rout¡
   ing changes in a way that isn't relevant to them.

5.10.  Directed Broadcast

   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.  There¡
   fore, routers connected to a broadcast medium SHOULD NOT be config¡
   ured to allow directed broadcasts onto that medium as explain in
   [RFC2644].

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   If it is a packet to which the router would respond if received as a
   unicast, it MAY send a (single) response.  If it is not responding
   (either because it's not appropriate, or because it's been configured
   not to) it MAY send an ICMP error.  It is also appropriate to
   silently discard such packets.  In any case such packets should be
   counted to detect possible attempts to abuse this feature.

6.  Systems Infrastructure

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

   In general a 'horses for courses' approach to the provision of sys¡
   tems services should be adopted (i.e., separate systems should be
   used to deliver each distinct service).  Apart from the benefits that
   accrue in terms of easing systems administration it's widely acknowl¡
   edged that it's much easier to build secure systems if different ser¡
   vices (such as mail, news and web-hosting) are kept on separate sys¡
   tems.

   The services discussed in later sections will all benefit from strong
   security at a lower layer when IPSec is deployed.

6.1.  Policy

   An ISP's policy with regard to privacy, authentication, accountabil¡
   ity, application of security patches, availability and violations
   reporting should all be of interest to their customers, and should be
   published in a public place such as the ISP's web site.

   A more detailed discussion of Security Policy can be found in the
   Site Security Handbook [RFC2196].

6.2.  System Management

   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

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   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.

   If the ISP provides login accounts to customers then the systems that
   support this service should be isolated from the rest of the ISP's
   systems networks.

   If applications such as rdist are used for software distribution and
   synchronisation then they should be used over a secure channel and
   with strong authentication, for example over Secure Shell (ssh)
   [SSH1997].

   A system should not be attached to transit segments.

   If reusable passwords are permitted then users should be educated
   about how to choose and care for a password, and proactive password
   checks, password aging and password guessers should be employed.

6.3.  Backup

   The importance of backups need not be stressed here.  However backups
   can become the weakest link in a system's security if appropriate
   care isn't taken of backup media.

   If backups are done across the network then a secure channel should
   be used.  If volumes are dumped to staging disks during the backup
   process then access to the images on those staging disks should be as
   restricted as possible.

   Backups take on additional significance as audit data following a
   security incident.

   Ageing backup media should be destroyed rather than discarded.

   The customers of a system or service should be informed of what is
   and is not backed up.  Further, if customers have been informed that
   certain data is not backed up then it should not be backed up.

6.4.  Software Distribution

   ISPs frequently engage in application software distribution.  The
   integrity of the software should be assured by distributing with it a
   checksum that has been produced with a strong digest function such as

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   SHA-1 [SHA].

7.  Domain Name Service (DNS)

   The DNS is critical to the daily activities of millions of Internet
   users.  Regrettably applications have frequently placed blind trust
   in the information contained in the DNS, and in the availability of
   the DNS.  However prior to DNSSEC [RFC2065] the DNS protocol lacked
   security, while widely used implementations of the DNS protocol con¡
   tain further severe vulnerabilities [VIX1995].

   While this section indicates some methods in which the DNS can be
   made more trustworthy and reliable it cannot be stressed too strongly
   that name based authentication is inherently insecure.

7.1.  DNS Server Administration

   In addition to issues raised in section 6 ISPs will need to address
   the following issues in administering their DNS servers:
      - Service Monitoring.
        The service availability (ability to answer queries) should be
        monitored.

      - Clock synchronisation.
        Servers should synchronise their clocks using the NTP protocol
        [RFC1305] with authentication.  At least two NTP servers should
        be used.

7.2.  Authoritative Domain Name Service

   An Authoritative Server is one that knows the content of a DNS zone
   from local knowledge, and thus can answer queries about that zone
   without needing to query other servers.  Customers should consider
   [RFC2182] when choosing secondary DNS servers.

   ISPs commonly operate as secondary (or slave) servers for their cus¡
   tomers, and these servers may provide service for thousands of zones.
   Regardless of the number of zones, administrators of these servers
   should familiarise themselves with the Operational Criteria for Root
   Name Servers [RFC2010] as a basis for deciding how to provide highly
   available service.  In particular they should follow these guide¡
   lines:

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      - Recursion should be disabled for queries.

      - Zone transfer should be restricted.
        Apart from the significant load presented by zone transfer
        with resultant exposure to Denial of Service attacks, ISPs
        should recognise that some of their customers will consider the
        contents of their zone files to be private.

      - Performance Monitoring.
        Key variables such as queries per second and average latency
        should be monitored.

7.3.  Resolution Service

   ISPs commonly operate DNS resolution service for their customers.  In
   this scenario customers configure their DNS resolver (client) to
   resolve queries from the ISP's DNS resolution servers.  For resolu¡
   tion servers ISPs should follow these guidelines:

      - Recursion must be enabled for queries.
        An implication is that ISPs should not use the same servers for
        resolution service and authoritative DNS service.

      - Zone transfer should be disallowed.
        Even though there may be no zones to transfer, allowing zone
        transfers would expose the servers to Denial of Service attacks.

      - Performance Monitoring.
        Key variables such as queries per second and average latency
        should be monitored.  In addition, the hosts generating the
        highest number of requests should be periodically reported.

      - Name server software.
        A name server package should be run that is not vulnerable to
        server cache poisoning where malicious or misleading data
        received from a remote name server is cached and is then made
        available to resolvers that request the cached data.

8.  Email and Mail Services

   Email has been the target of some of the most widely reported secu¡
   rity attacks, as well as thousands of juvenile hoaxes and pranks.

   ISPs have a major role in protecting the community from abuse and in
   educating their customers in appropriate technologies and in

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   appropriate uses of the technology.

8.1.  Mail Server Administration

   In configuring mail servers ISPs should follow these guidelines:

      - Mail software.
        If possible software that uses a separate receiving/sending
      agent
        and a processing agent should be used.  A goal is that the
        receiving/sending agent, which interfaces with remote mail
        servers, can be run with reduced privilege.

      - Restrict remote message queue starting.
        On-demand queue runs (to facilitate customers who receive mail
      at
        their own domain and don't have permanent connections) should be
        restricted, preferably using a strong authentication mechanism.
        Remote message queue starting is implemented using a variety of
        mechanisms, one of which is the ETRN SMTP service extension as
        described in [RFC1985].

      - Disable VRFY and EXPN.
        No more should be revealed about local users or delivery
        mechanisms than is necessary.

      - Clock synchronisation.
        Servers should synchronise their clocks using the NTP protocol
        [RFC1305] with authentication.  At least two NTP servers should
        be used.

      - Exception Reporting.
        Exceptional conditions such as repeated authentication failures,
        mail loops and abnormal queue length should be trapped and
        reported.

      - Restrict Access to mail logs.
        Mail logs should only be readable by system administrators.

8.2.  Secure Mail

As indicated in 2.6, It's critical that ISPs, and in particular their
Security Incident Response personnel, have access to tools that allow
them to exchange email securely.

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8.3.  Open Mail Relay

   An SMTP mail server is said to be running as an 'open' mail relay if
   it is willing to accept and relay to non-local destinations mail mes¡
   sages that do not originate locally (i.e., neither the originator nor
   the recipient address is local).  Such open relays are frequently
   used by 'spammers' to inject their Unsolicited Bulk E-mail (UBE)
   while hiding their identity.  There are only very limited circum¡
   stances in which an administrator can make a justifiable case for
   leaving a mail relay on the Internet completely open.

   The processes for restricting relaying are well documented.  It's
   regrettable that some major software vendors ship their Message
   Transfer Agents (MTAs) with relaying open by default.

   While this is an issue for the whole community, ISPs should be par¡
   ticularly vigilant in disabling open relaying on mail servers that
   they manage because their high-bandwidth connectivity makes them the
   preferred injection point for UBE.

   ISPs should also strongly encourage their customers to disable open
   relaying on their mail servers.  Sanctions for running an open mail
   relay should be covered in an ISP's AUP.

8.4.  Message Submission

   To facilitate the enforcement of security policy message submission
   should be done through the MAIL SUBMIT port (587) as proposed in the
   work in progress called "Message Submission and Relay", rather than
   through the SMTP port (25).  In addition, message submissions should
   be authenticated using the AUTH SMTP service extension as described
   in the work in progess called "SMTP Service Extension for Authentica¡
   tion".  In this way the SMTP port (25) can be restricted to local
   delivery only.

   These two measures not only protect the ISP from serving as a UBE
   injection point, but also help in tracking accountability for message
   submission in the case where a customer sends UBE.  Furthermore,
   using the Submit port with SMTP AUTH has additional advantages 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 authentica¡
   tion mechanisms as they become available.

   The (undocumented) XTND XMIT POP3 extension which allows clients to

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   send mail through the POP3 session rather than using SMTP may also be
   considered.  It also provides a way to support mobile users at sites
   where open relaying is disabled, and has the benefit of an authenti¡
   cated connection and a better audit trail.

8.5.  POP and IMAP Services

   ISPs who provide POP or IMAP access to mailboxes to their customers
   should, at a minimum, support the CRAM-MD5 [RFC2195] or APOP
   [RFC1939] authentication mechanisms.  Support for stronger mechanisms
   should be considered, as should disabling plaintext (user/password)
   authentication.

9.  News Service (NNTP)

   As in the case of SMTP, the NNTP protocol [RFC977] used by News suf¡
   fers from a lack of authentication, so it's trivial to forge news
   postings.  Forgeries can bypass the moderation process, cancel legit¡
   imate articles and create havoc for sites that maintain an active
   file.

   The lack of encryption in the protocol and the manner in which many
   news systems are maintained lead to privacy issues in that it's easy
   for others to detect what newsgroups and articles you are reading.

9.1.  News Server Administration

   In configuring news servers ISPs should follow these guidelines:
      - News software.
        A news software package should be run that is not vulnerable to
        maliciously formed news control messages or buffer overflows.

      - Disable other services.
        Given news' propensity to consume all available disk space and
        CPU cycles it's particularly important that news systems do not
        perform other services.

      - Do not interpret batches.
        If incoming batches of articles are supported they should not
        be fed to a command interpreter.

      - Restrict Access to news logs.

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        News logs should only be readable by system administrators.

      - Authenticate approved headers.
        If possible support for cryptographic authentication of approved
        messages should be supported, particularly in the case of group
        control messages.

9.2.  Article Submission

   As many of the issues relating to open mail relays (8.3) apply to
   news, ISPs should restrict article submission only to approved cus¡
   tomers.  Further, the networks from which posting is allowed and the
   newsgroups to which posting is allowed should be as restricted as
   possible.

9.3.  Control Messages

   Control messages attempt to cause the news server to take action
   beyond filing and passing on the article.  Certain control messages,
   because of the ease with which they can be forged, should be handled
   with care.  While it is up to the ISP to decide whether to take
   action they must at least propagate control messages even if they do
   not understand them.

      - 'whogets', 'sendsys', 'version' should be ignored by ISPs.

      - While 'cancel' messages must be acted on and propagated their
        sheer volume can sometimes swamp service, and the fact that much
        of that volume is computer-generated is worrying.

      - Systems that require the maintenance of an active file should
        exercise extreme caution in choosing which if any group control
        messages (checkgroups, newgroup, rmgroup) will be acted upon.

9.4.  Newsfeed Filters

   The most obvious form of security problem with news is 'leakage' of
   articles which are intended to have only restricted circulation.  The
   flooding algorithm is extremely good at finding any path by which
   articles can leave a subnet with supposedly restrictive boundaries.
   Substantial administrative effort is required to ensure that local
   newsgroups remain local [SPE1994].

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   ISPs who provide customers with the ability to remotely manipulate
   their inbound filters should use strong authentication for this ser¡
   vice.

   ISPs should not propagate articles that are excessively crossposted.
   10 or more cross-postings is commonly considered to be excessive.

   ISPs should impose an upper limit on the article size that they will
   propagate.

10.  Web-hosting Services

   Sites frequently choose to out-source the operation and administra¡
   tion of their site to an ISP, and security is often a prominent moti¡
   vator for doing so.  The hosting of such sites and provision of
   related services is the subject of this section.  Further information
   on the topic can be found in [GAR1997] and [HUG1995].

10.1.  Webhosting Server Administration

   In addition to issues raised in section 6 ISPs will need to address
   the following issues in administering their web-hosting servers:

      - Service Monitoring.
        The service availability (ability to answer HTTP requests)
      should
        be monitored.

      - Clock synchronisation.
        Servers should synchronise their clocks using the NTP protocol
        [RFC1305] with authentication.  At least two NTP servers should
        be used.

      - DNS.
        DNS lookups should not be performed on web clients when they
        connect because they expose the web servers to DNS-based Denial
        of Service attacks, and they adversely affect performance.

      - Process User and Group.
        The web daemon should be run as a user and group that is set up
        specifically for that purpose, and that user/group should have
        minimal privilege.  This user should be different from the
        maintainers of the web content.

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      - DocumentRoot.
        Everything below this directory should be subject to the
        strictest scrutiny.  If possible chroot should be used to change
        the HTTP daemon's root directory.

      - UserDir.
        Users other than administrators should not be permitted on the
        server.  If users have accounts then the 'UserDir' directive, if
        permitted, should not access their private accounts.  In
        particular, scripts should not be permitted to be run from their
        accounts.

      - Partitioning of Virtual Sites.
        A single server that hosts multiple sites (virtual domains)
        SHOULD be set up such that all data, programs and logs for the
        different sites are partitioned from each other such that no
        access to the configuration or data of each other's sites is
        possible.  In addition, it should not be possible to access the
        data or programs of one customer's site using a URL that has
        the name of another customer's site in it's host part.

      - Access Control.
        Restricted access to certain parts of a site should be
        facilitated using a strong authentication mechanism such as a
        certificate or a one-time password device.  An alternative is
        to use well-chosen passwords in conjunction with SSL which at
        least avoids passwords being passed across the network in
        plaintext.

      - Security Patches and Service Packs.
        The stakes in running a web server are particularly high, so
        administrators should be particularly vigilant in applying
        security patches and Service Packs as they are released.

10.2.  Server Side Programs

   Server side programs such as those that use the Common Gateway Inter¡
   face (CGI) or other server side interfaces are important to the flex¡
   ibility of the web as a communications medium.  However that flexi¡
   bility introduces security risks and a weak program might threaten
   all of the virtual hosts on the server that runs it.  An ISP's policy
   with regard to what programs it will allow is a good indicator of
   security policy in general.

   ISPs should consider the guidelines on server side programs and CGIs:
      - Security Policy.

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        ISPs should give their customers clear guidelines about how to
        write secure programs for their hosting environment, and give
        specific indications about what programming practices will
      result
        in a program being rejected.

      - Program Installation.
        Customers should not be allowed to install their own programs.
        All programs and scripts should be submitted to the ISP first to
        be checked for conformance with security policy.  The programs
        SHOULD be installed such that only the server administrators
      have
        permission to modify them.

      - Process User and Group.
        Programs should be run as a user and group that is set up
        specifically for that purpose, and that user/group should have
        minimal privilege (many sites use 'nobody').

      - Display by Browsers.
        Programs SHOULD never be allowed to be viewed by browsers.  One
        implication of that is that they SHOULD NOT be put under the
        DocumentRoot.

      - Partitioning of Virtual Sites.
        Programs SHOULD NOT be accessible through the site of another
        customer on the same server, or to the webmaster of that other
        customer.

      - User Input.
        Expressions SHOULD NOT be evaluated based on user input except
        when used with the equivalent of Perl's tainting features.

      - Processing Limit.
        All programs SHOULD have a limit set on real and CPU time, and
      on
        the amount of disk space that they can consume.

      - Paths.
        All paths SHOULD be full or starting at DocumentRoot, and the
        PATH variable should be set by the server administrator.

10.3.  Data and Databases

   Data that is written by server-side programs should be considered
   confidential.  To prevent them being read by browsers their permis¡
   sion should be such that they're not readable by the web daemon

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   process.

   If access to a back-end database is provided then programs that
   facilitate such access should have the least privilege that is abso¡
   lutely necessary.

   Data that relates to state management (cookies) that is stored on the
   server should be considered confidential and should not be accessible
   from browsers.

10.4.  Logs and Statistics Reporting

   The logs generated by the web daemon process can be useful from the
   security viewpoint in providing an audit trail of site activity, how¡
   ever their more common use is for billing and for market and site
   analysis.

   These logs should be considered highly confidential.

   - The only manipulation of them done by the ISP should be that
     which is necessary to generate billing information and
     periodically rotate them.

   - They should be stored outside of DocumentRoot to prevent access
     by a browser to them.

   - Access to them, whether in raw or summarised format, should be
     provided to the customer over a secure channel.

10.5.  Push and Streaming Services

ISPs frequently provide their customers with the ability to deliver con¡
tent using protocols other than HTTP.  Where such add-on services are
provided, both the customer and the ISP should be aware of the security
implications of providing such services.

10.6.  Commerce

   Many ISPs set up the means whereby their customers can sell goods and
   services through their web-hosted sites.  Though a server that can
   exchange information with a browser over SSL is sometimes described
   as a 'secure server' this term can be misleading, and ISPs that host

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   commerce applications should consider the following:

      - Encrypted Transactions.
        Transactions should never be stored on the server in unencrypted
        form.  Public key cryptography may be used such that only the
        customer can decrypt the transactions.  However even when
        transactions are passed directly to a financial institution and
        to the customer some part of the transaction will have to be
        stored by the ISP for audit trail purposes.

      - Transaction Transfer.
        If transactions are not processed immediately but instead are
        transferred to the customer in batches then that transfer should
        occur over a secure channel such as SSL and only after strong
        authentication has taken place.  Transaction files should be
        carefully rotated so that every transaction occurs exactly once.

      - Backups.
        If transactions are written to backup media then the physical
        security of the backup media should be assured.

10.7.  Content Loading and Distributed Authoring

   The loading of content onto the ISP's server should happen over a
   secure channel.

   If server support for Distributed Authoring tools is enabled, then
   this should be administered with great care to ensure that strong
   authentication takes place and that access is given only to the cus¡
   tomer's virtual site, and only to that customer's content maintainer.

10.8.  Search Engines and other tools

   ISPs frequently install tools such as search engines, link checkers
   and so on for use by their customers.  Many such tools create a very
   great processing overhead when run and so running them on-demand
   should not be allowed to avoid Denial of Service attacks.

   Search engines should be configured so that their searches are
   restricted to those parts of a site that are available to all.

   The output of link checkers should be considered confidential, and
   should only be available to the content maintainer of the customer's
   site.

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11.  References

[CA-91:18.Active.Internet.tftp.Attacks] "Active Internet tftp
  Attacks", ftp://info.cert.org/pub/certadvisories/

[CA-95.01.IP.spoofing] "IP Spoofing Attacks and Hijacked Terminal
  Connections", ftp://info.cert.org/pub/certadvisories/

[CA-96.21.tcpsynflooding] "TCP SYN Flooding and IP Spoofing
  Attacks", ftp://info.cert.org/pub/certadvisories/

[CA-97.28.TeardropLand] "IP Denial-of-Service Attacks",
  ftp://info.cert.org/pub/certadvisories/

[DPR1998] The UK "Data Protection Act 1998 (c. 29)",
  http://www.hmso.gov.uk/acts/acts1998/19980029.htm

[GAR1997] Garfinkel, S., "Web Security and Commerce",
  O'Reilly and Associates, Sebastopol, CA, 1997.

[HUG1995] Hughes Jr., L., "Actually Useful Internet Security
  Techniques", New Riders Publishing, Indianapolis, IN, 1995.

[RFC977] Kantor, B and P. Lapsley, "Network News Transfer Protocol",
  RFC 977, February 1986.

[RFC1350] Sollins, K. R., "The TFTP Protocol (revision 2)", STD 33,
  RFC 1350, July 1992.

[RFC1034] Mockapetris, P. V., "Domain names - concepts and
  facilities", STD 13, RFC 1034, November 1987.

[RFC1035] Mockapetris, P. V., "Domain names - implementation and
  specification", STD 13, RFC 1035, November 1987.

[RFC1305] Mills, D., "Network Time Protocol (Version 3)
  Specification, Implementation", RFC 1305, March 1992.

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

[RFC1834] Gargano, J., and K. Weiss, "Whois and Network Information
  Lookup Service", RFC 1834, August 1995.

[RFC1835] Deutsch, P., Schoultz, R., Faltstrom, P., and C. Weider,
  "Architecture of the WHOIS++ service", RFC 1835, August 1995.

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[RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.
  J., and E. Lear, "Address Allocation for Private Internets", BCP 5,
  RFC 1918, February 1996.

[RFC1939] Myers, J., and M. Rose, "Post Office Protocol - Version
  3", RFC 1939, May 1996.

[RFC1985] De Winter, J. "SMTP Service Extension for Remote Message
  Queue Starting", RFC 1985, August 1996.

[RFC2010] Manning, B., and P. Vixie, "Operational Criteria for Root
  Name Servers", RFC 2010, October 1996.

[RFC2065] Eastlake 3rd, D., and C. Kaufman, "Domain Name System
  Security Extensions", RFC 2065, January 1997.

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

[RFC2142] Crocker, D., "Mailbox Names for Common Services, Roles and
  Functions", RFC 2142, May 1997.

[RFC2195] Klensin, J., Catoe, R., and P. Krumviede, "IMAP/POP
  AUTHorize Extension for Simple Challenge/Response", RFC 2195,
  September 1997.

[RFC2196] Fraser, B., "Site Security Handbook", RFC 2196, September
  1997.

[RFC2267] Ferguson, P., and D. Senie, "Network Ingress Filtering:
  Defeating Denial of Service Attacks which employ IP Source
  Address Spoofing", RFC 2267, January 1998.

[RFC2350] Brownlee, N., and  E. Guttman, "Expectations for Computer
  Security Incident Response", RFC 2350, June 1998.

[SHA] NIST, FIPS PUB 180-1: Secure Hash Standard, April 1995.

[SPE1994] Spencer, H., "News Article Format and Transmission",
  ftp://ftp.zoo.toronto.edu/pub/news.txt.Z

[SSH1997] SSH (secure Shell) Remote Login Program,
  http://www.cs.hut.fi/ssh/

[VIX1995] Vixie, P., "DNS and BIND Security Issues",
     ftp://ftp.vix.com/pri/vixie/bindsec.psf, 1995.

[RFC2644] Senie, D. "Changing the Default for Directed Broadcasts in

Debeaupuis                                             [Page 29]


INTERNET-DRAFT  Site Security Handbook Addendum for ISPs    11 July 1999

     Routers", RFC 2644, August 1999.

12.  Security Considerations

   This entire document discusses security issues.

13.  Editor Information

   Tristan Debeaupuis
   Herve Schauer Consultants
   142, rue de Rivoli
   75001 Paris
   France

   Phone: +33 141 409 700

   Email: Tristan.Debeaupuis@hsc.fr

14.  Full Copyright Statement

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implmentation may be prepared, copied, published and
   distributed, in whole or in part, without restriction of any kind,
   provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this doc¡
   ument itself may not be modified in any way, such as by removing the
   copyright notice or references to the Internet Society or other
   Internet organisations, except as needed for the purpose of develop¡
   ing Internet standards in which case the procedures for copyrights
   defined in the Internet Standards process must be followed, or as
   required to translate it into languages other than English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION

Debeaupuis                                             [Page 30]


INTERNET-DRAFT  Site Security Handbook Addendum for ISPs    11 July 1999

   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MER¡
   CHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."

Debeaupuis                                             [Page 31]