Internet Engineering Task Force                            Tom Killalea
Valid for six months                                          June 1999

          Security Expectations for Internet Service Providers


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
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Copyright Notice

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


   The purpose of this document is to express the general Internet
   community's expectations 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.

Table of Contents

   1 Introduction
     1.1 Conventions Used in this Document

   2 Communication
     2.1 Contact Information
     2.2 Information Sharing
     2.3 Secure Channels
     2.4 Notification of Vulnerabilities and Reporting Incidents
     2.5 ISPs and Computer Security Incident Response Teams (CSIRTs)

   3 Appropriate Use Policy
     3.1 Announcement of Policy
     3.2 Sanctions
     3.3 Data Protection

   4 Network Infrastructure
     4.1 Registry Data Maintenance
     4.2 Routing Infrastructure
     4.3 Ingress Filtering on Source Address
     4.4 Egress Filtering on Source Address
     4.5 Route Filtering
     4.6 Directed Broadcast

   5 Systems Infrastructure
     5.1 System Management
     5.2 No Systems on Transit Networks
     5.3 Open Mail Relay
     5.4 Message Submission

   6 References

   7 Acknowledgements

   8 Security Considerations

   9 Author's Address

   10 Full Copyright Statement

1 Introduction

   The purpose of this document is to express the general Internet
   community's expectations of Internet Service Providers (ISPs) with
   respect to security.  This document is addressed to ISPs.

   By informing ISPs of what the 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.

1.1 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].

2 Communication

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

2.1 Contact Information

   ISPs SHOULD adhere to [RFC2142], 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

   In addition, ISPs have a duty to make sure that their contact
   information, in Whois, in the routing registry [RFC1786] or in any
   other repository, is complete, accurate and reachable.

2.2 Information Sharing

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

2.3 Secure Channels

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

2.4 Notification of Vulnerabilities and Reporting of Incidents

   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

2.5 Incident Response and Computer Security Incident Response Teams

   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" [RFC2350].

   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
   Appendix D of "Expectations for Computer Security Incident Response"

3 Appropriate Use Policy

   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

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

3.1 Announcement of Policy

   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

3.2 Sanctions

   An AUP should be clear in stating what sanctions will be enforced in
   the event of inappropriate behaviour, and ISPs should be forthcoming
   in announcing to the community when such sanctions are imposed.

3.3 Data Protection

   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., [DPR1998]).

4 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

4.1 Registry Data Maintenance

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

   ISPs should 'SWIP' (Shared WhoIs Project) the address space that they
   assign to their customers so that there is more specific contact
   information for the delegated space.

4.2 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
   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 should be used with routing peers.

4.3 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
   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

4.4 Egress Filtering on Source Address

   The direction of such filtering is from the Internet to the edge site

   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
   vulnerabilities that depend on the misuse of supposedly local
   addresses, such as 'land' as described in [CA-97.28.Teardrop_Land].

   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 5.7 in which ingress filtering isn't
   feasible apply similarly to egress filtering.

4.5 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 "BGP Route Flap Dampening"
   [RFC2439] 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.

4.6 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.
   Therefore, routers connected to a broadcast medium SHOULD NOT be
   configured to allow directed broadcasts onto that medium.

   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.

   See the work in progress [DRAFT-SENIE] for further discussion of this

5 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
   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.

5.1 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
   take place over an encrypted link.  Only the ports on which those
   services listen should be reachable from outside of the ISP's systems

   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, [RFC2195]).

5.2 No Systems on Transit Networks

   Systems should not be attached to transit network segments.

5.3 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
   messages 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
   circumstances 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
   particularly 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.

5.4 Message Submission

   To facilitate the enforcement of security policy message submission
   should be done through the MAIL SUBMIT port (587) as discussed in
   "Message Submission" [RFC2476], 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 Authentication".  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
   authentication mechanisms as they become available.

   The (undocumented) XTND XMIT POP3 extension which allows clients to
   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
   authenticated connection and a better audit trail.

6 References

   [CA-95.01.IP.spoofing] "IP Spoofing Attacks and Hijacked Terminal

   [CA-97.28.Teardrop_Land] "IP Denial-of-Service Attacks",


   [DPR1998] The UK "Data Protection Act 1998 (c. 29)",

   [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.

   [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.

   [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

   [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.

   [RFC2439] Chandra R., Govindan R., and C. Villamizar, "BGP Route
     Flap Damping", RFC 2439, November 1998.

   [RFC2476] Gellens R., and J. Klensin, "Message Submission",
     RFC 2476, December 1998.

7 Acknowledgements

   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.

8 Security Considerations

   This entire document discusses security issues.

9 Author's Address

   Tom Killalea
   1516 2nd Ave
   Seattle, WA 98101

   Phone: +1 206 694-2196

10 Full Copyright Statement

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

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   This document and the information contained herein is provided on an

This document expires December 25, 1999.