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Versions: 00 01                                                         
Opsec Working Group                                              J. Gill
Internet-Draft                                          Verizon Business
Intended status: Best Current                                   D. Lewis
Practice                                                        P. Quinn
Expires: October 8, 2007                              Cisco Systems Inc.
                                                          P. Schoenmaker
                                                             NTT America
                                                           April 6, 2007

                Service Provider Infrastructure Security

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   The list of current Internet-Drafts can be accessed at

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   This Internet-Draft will expire on October 8, 2007.

Copyright Notice

   Copyright (C) The IETF Trust (2007).


   This RFC describes best current practices for implementing Service
   Provider network infrastructure protection for network elements.
   This RFC complements and extends RFC 2267 and RFC 3704.  RFC 2267
   provides guidelines for filtering traffic on the ingress to service

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   provider networks.  RFC 3704 expands the recommendations described in
   RFC 2267 to address operational filtering guidelines for single and
   multi-homed environments.  The focus of those RFCs is on filtering
   packets on ingress to a network, regardless of destination, if those
   packets have a spoofed source address, or if the source address fall
   within "reserved" address space.  Deployment of RFCs 2267 and 3704
   has limited the effects of denial of service attacks by dropping
   ingress packets with spoofed source addresses, which in turn offers
   other benefits by ensuring that packets coming into a network
   originate from validly allocated and consistent sources.  This
   document focuses solely on traffic destined to elements of the the
   network infrastructure itself.  This document presents techniques
   that, together with network edge ingress filtering and RFC 2267 and
   RFC 3704, provides a defense in depth approach for infrastructure
   protection.  This document does not present recommendations for
   protocol validation (i.e. "sanity checking") nor does it address
   guidelines for general security configuration.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Overview of Infrastructure Protection Techniques . . . . . . .  4
     2.1.  Edge Remarking . . . . . . . . . . . . . . . . . . . . . .  5
     2.2.  Device and Element Protection  . . . . . . . . . . . . . .  5
     2.3.  Infrastructure Hiding  . . . . . . . . . . . . . . . . . .  5
   3.  Edge Infrastructure Access Control Lists . . . . . . . . . . .  5
     3.1.  Constructing the Access List . . . . . . . . . . . . . . .  5
     3.2.  Other Traffic  . . . . . . . . . . . . . . . . . . . . . .  6
     3.3.  Edge Infrastructure Conclusion . . . . . . . . . . . . . .  6
   4.  Edge Rewrite/Remarking . . . . . . . . . . . . . . . . . . . .  7
     4.1.  Edge Rewrite/Remarking Discussion  . . . . . . . . . . . .  7
     4.2.  Edge Rewriting/Remarking Performance Considerations  . . .  8
   5.  Device/Element Protection  . . . . . . . . . . . . . . . . . .  8
     5.1.  Service Specific Access Control  . . . . . . . . . . . . .  8
       5.1.1.  Common Services  . . . . . . . . . . . . . . . . . . .  8
     5.2.  Aggregate Device Access Control  . . . . . . . . . . . . .  9
       5.2.1.  IP Fragments . . . . . . . . . . . . . . . . . . . . .  9
       5.2.2.  Performance Considerations . . . . . . . . . . . . . .  9
       5.2.3.  Access Control Implementation Guide  . . . . . . . . .  9
     5.3.  Device Access Authorization and Accounting . . . . . . . . 10
   6.  Infrastructure Hiding  . . . . . . . . . . . . . . . . . . . . 10
     6.1.  Use Less IP  . . . . . . . . . . . . . . . . . . . . . . . 10
     6.2.  MPLS Techniques  . . . . . . . . . . . . . . . . . . . . . 10
     6.3.  IGP Configuration  . . . . . . . . . . . . . . . . . . . . 11
     6.4.  Route Advertisement Control  . . . . . . . . . . . . . . . 11
       6.4.1.  Route Announcement Filtering . . . . . . . . . . . . . 11
       6.4.2.  Address Core Out of RFC 1918 Space . . . . . . . . . . 11
     6.5.  Further obfuscation  . . . . . . . . . . . . . . . . . . . 12
   7.  IPv6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     7.1.  Use IPv6 Edge Infrastructure Access Control Lists  . . . . 13
     7.2.  IPv6 Infrastructure Hiding . . . . . . . . . . . . . . . . 13
   8.  IP Multicast . . . . . . . . . . . . . . . . . . . . . . . . . 13
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 13
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 14
     11.2. Informative References . . . . . . . . . . . . . . . . . . 14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
   Intellectual Property and Copyright Statements . . . . . . . . . . 17

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1.  Introduction

   This RFC describes best current practices for implementing Service
   Provider network infrastructure protection.  This document both
   refines and extends the filtering best practices outlined in RFC 2267
   [RFC2267] and RFC 3704 [RFC3704] and focuses only on traffic destined
   to the network infrastructure itself to protect the service provider
   network from denial of service and other attacks.  This document
   presents techniques that, together with network edge ingress
   filtering and RFC 2267 [RFC2267] and RFC 3704 [RFC3704], provides a
   defense in depth approach for infrastructure protection.

   Attacks targeting the network infrastructure can take many forms,
   including bandwidth saturation to crafted packets destined to a
   router.  These attacks might use spoofed or non spoofed source
   addresses.  Regardless of the nature of the attack, the network
   infrastructure must be protected from both accidental floods and
   intentional attacks.  Additionally, this protection will assist in
   preventing the network elements from being used as reflectors in
   attacks against others.

   The techniques outlined in this document and described in section 2
   below, describe best practices for infrastructure protection: edge
   policy (filtering and precedence), per device traffic policy
   enforcement for packets destined to a device and, limiting of address
   and routing visibility to reduce exposure to limit core network --
   that is provider (P) and provider edge (PE) infrastructure --
   attacks.  This document is targeted at network operators seeking to
   limit their exposure to risks associated with denial of service
   targeting the infrastructure.  These techniques are designed to be
   used in addition to specific protocol or application security
   features implemented in network devices.

   Infrastructure protection is a complex topic.  While the best
   practices outlines in this document do not provide perfect
   protection, they can significantly improve the protection of the
   network infrastructure.

2.  Overview of Infrastructure Protection Techniques

   This section provides an overview of recommended techniques that may
   be used to protect network infrastructure.  The areas described below
   are not exhaustive; other mechanisms can be used to provide
   additional protection.  The techniques discussed in this document
   have been widely deployed and have proven operational security
   benefits in large networks.

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2.1.  Edge Remarking

   Edge Remarking, detailed in section 4, ensures that ingress IP
   precedence or DSCP values match expected values within the context of
   security.  This provides another layer of defense, particularly for
   traffic permitted through any of the Edge Infrastructure Access
   Control Lists.  This document focuses only on using Edge Remarking
   best practices to enforce security policies.

2.2.  Device and Element Protection

   Each network infrastructure device should enforce local rules for
   traffic destined to itself.  These rules can take the form of filters
   (permit/deny) or rate limiting rules that allow ingress traffic at
   specified rates.  These should complement any existing Edge
   Infrastructure Access Control Lists and are described in more detail
   in section 5.  The deployment of these local device protection rules
   complements the edge techniques by protecting the device from traffic
   that: i) was permitted but violates device policy, ii) could not be
   filtered at the edge, iii) entered the network on an interface that
   did not have ingress filtering enabled.

2.3.  Infrastructure Hiding

   Hiding the infrastructure of the network provides an elegant
   mechanism for protecting the network infrastructure.  If the
   destination of an attack is to an infrastructure address that is
   unreachable, attacks become far more difficult.  Infrastructure
   hiding can be achieved in several ways: i) MPLS techniques ii) IGP
   configuration iii) Route advertisement control.  Section 6 addresses
   these infrastructure hiding techniques in detail.

3.  Edge Infrastructure Access Control Lists

   Edge Infrastructure Access Control Lists (EIACLs) are a specific
   implementation of the more general Ingress Access List.  As opposed
   to generic ingress filtering which denies data (sometimes referred to
   as user) plane traffic, edge infrastructure access control lists do
   not attempt to deny transit traffic; rather, this form of access
   control limits traffic destined to infrastructure equipment while
   permitting -- if needed, explicitly -- traffic through the network.

3.1.  Constructing the Access List

   Edge Infrastructure Access Control Lists permit only required traffic
   destined to the network infrastructure, while allowing data plane
   traffic to flow through unfiltered.  The basic premise of EIACLs is

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   that only a relatively limited subset of traffic sourced from outside
   an AS should be allowed to transit towards a core router and that by
   explicitly permitting only that known and understood traffic the core
   devices are not subjected to unnecessary traffic that might result in
   a denial of service.  Since edge infrastructure access control lists
   protect only the infrastructure, the development of the list differs
   somewhat from "traditional" access filter lists:

   1.  Review addressing scheme, and identify address block(s) that
       represent core devices.

   2.  Determine what traffic must be destined to the core devices from
       outside the AS.

   3.  Create a filter that allows the required traffic, denies all
       traffic destined to the core address block and then finally,
       permits all other traffic.

   4.  Optionally, prior to implementing the deny action for all traffic
       destined to the core address block, a log action may be used and
       the results of the deny actions evaluated.

   As with other ingress filtering techniques, EIACLs are applied on
   ingress interfaces, as close to the edge as possible.  Comprehensive
   coverage (i.e. on as many interfaces as possible) yields the most

3.2.  Other Traffic

   In addition to the explicitly permitted traffic, EIACLs can be
   combined with other common edge filters such as: 1.  Source spoof
   prevention (as per RFC 3704 [RFC3704]) by denying internal AS
   addresses as external sources. 2.  Filtering of reserved addresses
   (e.g.  RFC 1918 [RFC1918] addresses) since traffic should not be
   sourced from reserved address. 3.  Other unneeded or unnecessary
   traffic.  Filtering this traffic can be part of the list explicitly
   or implicitly; explicit filters often provide log-able information
   that can be of use during a security audit.

3.3.  Edge Infrastructure Conclusion

   Edge Infrastructure Access Control Lists provide a very effective
   first line of defense.  EIACLs are not perfect and cannot protect the
   network against every attack.  Furthermore, to be manageable, EIACLs
   must be able to clearly and simply identify infrastructure address
   space.  To be effective, the EIACLs should be deployed as widely as
   possible at the edge of the network on devices that support the
   required filtering performance characteristics.

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   The potential impact on the device's performance must be taken into
   consideration when deploying EIACLs.

4.  Edge Rewrite/Remarking

   Typically edge packet rewrite/remarking deals primarily with traffic
   passing through a device.  However, IP Precedence/DSCP values are
   used in prioritizing traffic sent to the devices as well.  RFC 1812
   [RFC1812] section 5.3 defines the use of IP Precedence in IPv4
   packets for routing, management and control traffic.  In addition,
   the RFC [RFC1812] recommends that devices use a mechanism for
   providing preferential forwarding for packets marked as routing,
   management or control traffic using IP Preference bits 6 or 7 (110 or
   111 in binary).  RFC 2474 [RFC2474] defines DSCP and the
   compatibility of IP Preference bits when using DSCP.

   All packets received by customer- and peer-facing Provider Edge (PE)
   router interfaces with IP Preference values of 6 or 7 or DSCP bits of
   11xxxx, as specified in RFC2474 [RFC2474] Differentiated Services
   Field Definition, should have the IP Preference bits rewritten.
   Routing traffic received from customer- and peer-facing interfaces
   can safely have the IP Preference bits rewritten because only a
   limited number of protocols are transmitted beyond the first PE
   router.  The bits may be rewritten to any value other than IP
   Preference values 6 or 7, or any DSCP value other than 11xxxx.  The
   new value can be based on the network operators IP Preference or DSCP
   policy.  If no policy exists the bits should be rewritten to 0.  In
   cases where control, management, and routing traffic enters the
   provider network via the customer and peer facing interfaces policy
   should be employed to ensure proper prioritization of critical
   traffic.  EIACLs may be be used facilitate the proper classification
   of traffic.  To offer fully transparent service, a provider may not
   wish to modify the IP precedence on transit traffic through the
   network.  If a provider has alternate means of applying different
   prioritization to router management and control traffic and transit
   traffic then rewriting IP precedence bits is not required.

4.1.  Edge Rewrite/Remarking Discussion

   By default router vendors do not differentiate an interface on a PE
   router connected to a P router from an interface connected to a CE
   router.  As a result any packet with the proper IP Preference or DSCP
   bits set may receive the same preferential forwarding behavior as
   legitimate routing, management, and control traffic.  A malicious
   attack may be able to take advantage of the vulnerability to increase
   the effectiveness of the attack or to attack the routing, management,
   and/or control traffic directly.  The forwarding prioritization given

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   to routing, management, and control traffic by default leaves devices
   vulnerable to indirect attacks to the infrastructure.  By rewriting
   the IP Precedence at the PE protection is provided for both traffic
   through the network along with traffic that is to the network that is
   not blocked by other methods discussed in this document.  This
   document assumes that all customer and peer facing interfaces cannot
   be trusted for inter- domain diff-serv.  In cases where a trust
   relationship exists for inter-domain diff-serv, diff-serv bits
   1xxxxxxx do not have to be rewritten.

4.2.  Edge Rewriting/Remarking Performance Considerations

   The potential impact on the device's performance must be taken into
   consideration when rewriting/remarking IP Precedence/DSCP bits.
   Devices may require additional resources to rewrite/remark packets
   compared to merely forwarding them.

5.  Device/Element Protection

   Even with the widest possible deployment of the techniques described
   above in section 3, Infrastructure Edge Access Control, the
   individual devices of the network must implement access control
   mechanisms.  In addition to the cases incomplete or imperfect
   deployment of edge infrastructure controls, threats may come from
   from trusted sources within the perimeter of the network.

5.1.  Service Specific Access Control

   Many vendor's implementation of service specific controls are not
   made with overall system availability as a primary concern.  With
   this in mind, it is recommended that these controls be used in
   conjunction with any aggregate mechanisms to control device access as
   well as techniques like EIACLs and Core Hiding.  There are many
   practical examples available of vendor specific service security
   mechanisms, the references section provides links to several of them.
   These should guide the operator in securing the services that they

5.1.1.  Common Services

   While each service implemented by network equipment manufacturers
   differs in its available security features there are some common
   services and security features for those services that have been
   widely deployed.  The most important first step for the operator is
   to disable any unneeded/unused services.  This reduces the device's
   profile.  If the device is not listening to a port, it is much more
   difficult to attack via that port.  Second, the operator should

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   utilize the services access control mechanisms to limit the access to
   the devices service to only required sources.  Examples of per
   service security are using virtual terminal access control lists, or
   SNMP Community access control lists.

5.2.  Aggregate Device Access Control

   Aggregating the security policy -- as opposed to defining it on a per
   service basis -- allows for a simplified view of the access policies
   traffic going to the device.  Many vendors leverage this simplified
   view to allow for the policy to be implemented in hardware,
   protecting the device's control plane.  A key requirement of these
   mechanisms is that it must not impact transit data plane traffic.

5.2.1.  IP Fragments

   Traffic destined to a router is not typically fragmented.  Use of
   mechanisms to deny fragments to the device are recommended.

5.2.2.  Performance Considerations

   Care should be taken to understand a vendors implementation of
   aggregate device access control and to make sure that device
   operation is not impaired during DoS attacks against the device.

5.2.3.  Access Control Implementation Guide

   Implementing a complex set of access controls for all traffic going
   to and from a router is non trivial.  The following is a recommended
   set of steps that has been used successfully by many carriers.

   1.  Develop list of required protocols.

   2.  Develop source address requirements: Determine destination
       interface on router Does the protocol access a single interface?
       Does the protocol access many interfaces?  Does the protocol
       access a virtual or physical interfaces?

   3.  Prior to implementing with a deny, it is recommended to test the
       behavior with the action of "log" and observe the results

   4.  Deployment should be an iterative process: Start with relatively
       open lists then tighten as needed

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5.3.  Device Access Authorization and Accounting

   Operators should use per command authorization and accounting
   wherever possible.  Aside from their utility in mitigating other
   security threats, they provide an invaluable tool in the post event

6.  Infrastructure Hiding

   Hiding the infrastructure of the network provides one layer of
   protection to the devices that make up the network core.  By hiding
   those devices (making them unreachable) successful execution of
   denial of service attacks becomes far more difficult.  Before
   implementing measures to make network infrastructure unreachable from
   outside consider carefully that these actions can create limitations
   that staff, customers, and applications may not expect and weigh
   these results against the additional security afforded by a hiding
   the network core.  The following sections present different options
   for accomplishing infrastructure hiding.  The operator should
   carefully consider the merits of each approach based on their
   network's architecture.

6.1.  Use Less IP

   One way to reduce exposure of network infrastructure is to use
   unnumbered links wherever possible.  This is particularly useful in
   the simple case of a customer with single link used as their default
   path to the Internet.  Not only can such a configuration reduce the
   exposure of the equipment on both ends of the link to malicious
   attack, the overall effort required to manage a link can be reduced
   considerably with a simplified configuration and without the
   additional overhead and expense of managing the IP addresses.

6.2.  MPLS Techniques

   While it may not be feasible to hide the entire infrastructure of
   large networks, it is certainly possible to reduce exposure of
   critical core infrastructure by hiding the existence and complexity
   of that infrastructure using an MPLS mesh where TTL is not
   decremented as packets pass through it as described in RFC 3443
   [RFC3443].  In this manner the number, addresses, and even existence
   of intermediary devices can be hidden from traffic as it passes
   through the core.  As pointed out by RFC 4381 [RFC4381], not only can
   this method hide the structure, it simplifies access restrictions to
   core devices. e.g.  Core equipment addresses are inaccessible from
   the "Public Internet" VPN.  The fact that this technique is
   transparent from a layer-3 viewpoint recommends it to providers of

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   public services.  Because basic external troubleshooting and presents
   to all external views a simplified network structure with few
   potential target addresses exposed it offers a better balance of
   security against effort than most techniques for public networks.

6.3.  IGP Configuration

   Using a non-IP control plane for the core routing protocol can
   substantially reduce the number of IP addresses that comprise (and
   therefore, expose) the core.  This simplifies the task of maintaining
   edge ACLs or route announcement filters.  IS-IS is an elegant and
   mature protocol that some operators have found suitable for this

6.4.  Route Advertisement Control

6.4.1.  Route Announcement Filtering

   Inasmuch as it is unavoidable that some network elements must be
   configured with IP addresses, it may be possible to assign these
   address out of netblocks for which the routing advertisement can be
   filtered out, thereby limiting possible sources of traffic to core
   netblocks down to customers for whom you provide a default route, or
   direct peers who would make the effort to create a static route for
   your core netblock into your AS.  By assigining address for network
   infrastructure out of a limited number of address blocks which are
   well known to internal network administrators, the operator can
   greatly simplify EIACL configuration.  This can also minimise the
   frequency with which ACLs need to be updated based on changes in the
   network.  This can also have performance implications, especially for
   equipment where the length of ACLs is limited.  By keeping ACLs short
   they may be deployable on a wider range of existing equipment.
   Further, it may be possible in those situations where customer point-
   to-point links must be numbered, to address such links out of another
   range of addresses for which announcements could be similarly
   filtered.  While this has implications for a customer's ability to
   remote-monitor their circuit, this can often be overcome with
   application of an address from the customer's routed space to the CPE

6.4.2.  Address Core Out of RFC 1918 Space

   In addition to filtering the visibility of core addresses to the
   wider Internet, it may be possible to use private RFC 1918 [RFC1918]
   netblocks for numbering infrastructure when IP addresses are required
   (eg, loopbacks).  This added level of obscurity takes prevention of
   wide distribution of your infrastructure address space one step
   further.  Many networks filter out packets with RFC 1918 [RFC1918]

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   address at ingress/ egress points as a matter of course.  In this
   circumstance, tools such as traceroute can work for operations and
   support staff but not from outside networks.  Care should be taken to
   limit reverse-resolution of descriptive DNS names to queries from
   internal/support groups.  The fact that this technique can break
   simple troubleshooting tools such as traceroute may frustrate
   customers who expect to be able to perform basic troubleshooting
   tasks on their own.  Campus or corporate networks may find some
   advantage to this configuration, on balance.  Use caution when
   employing this technique, particularly in public internet service
   provider environments.

6.5.  Further obfuscation

   The strategy of changing services to run on ports different from the
   default and well-known ones will not protect you from a determined
   attacker.  It can, however, provide some level of protection from
   many attack tools, worms, auto-rooters, etc.  Should they find access
   to the infrastructure equipment in some way.  Again, this does
   nothing to restrict access, nor to make network devices more
   difficult to reach.  As with the other methods, a careful
   consideration of how much effort and management each strategy
   requires must be weighed against the protection that it provides and
   the necessity of that protection in light of all measures taken to
   protect a network.

7.  IPv6

   IPv6 Networks contain the same infrastructure security risks as IPv4.
   All techniques described in this document for IPv4 should be directly
   applicable to IPv6 networks.  Limitations exist where devices do not
   have feature parity between IPv4 and IPv6.  Different techniques
   maybe required where IPv4 and IPv6 networks deviate in
   implementation.  Multi-vendor networks can create greater
   difficulties when each vendor does not have feature parity with each
   other.  Hardware differences in devices that support both IPv4 and
   IPv6 must also be taken into consideration.  Because IPv6 uses a
   longer address space the scaling, and performance characteristics of
   ACLs maybe lower for IPv6 vs IPv4.  The fields or number of fields
   that an ACL can match on may also differ.  The fact that all PE
   devices do not support all the recommended IPv6 security features
   should not preclude the implementation of the recommendations in this
   document on the devices that do support the security features.  With
   the number of Network Operators deploying IPv6 growing, along with
   the continued availability of IPv6 Tunnel services, connecting to the
   IPv6 Internet is less difficult.  Dual stack IPv6 networks run on
   Networks with speeds equal to IPv4.  Neither the edge nor the core

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   limit potential IPv6 attacks.  Despite the increased deployment of
   IPv6 it still does not have the same level of operational experience
   as IPv4.

7.1.  Use IPv6 Edge Infrastructure Access Control Lists

   IPv6 Infrastructure security policy will be similar to the IPv4
   policy for EIACLs, Edge remarking and Device and Element protection.
   Construction of the IPv6 EIACL should use the same process as the
   IPv4 EIACL.  The construction of the EIACL can be made less difficult
   with IPv6 because of the sparse address assignment capability given
   the larger total address space.  IPv6 DSCP bits should be rewritten
   in the same manner that IPv4 DSCP bits.  Differences between DSCP
   rewriting of IPv4 and IPv6 will minimal except in cases where the
   device capabilities differ between IPv4 and IPv6.  Device and Element
   protection should be created using the same methods described in this
   document for IPv4.  The policy may differ for IPv6 from IPv4 in cases
   where services are exclusively IPv4 or exclusively IPv6.  Services
   not used with IPv6 should be disabled.

7.2.   IPv6 Infrastructure Hiding

   Network operators may deploy IPv4 differently from IPv6 in their
   network.  Providers may use native forwarding for IPv6 while using
   MPLS for IPv4, other combinations.  IPv6 infrastructure hiding should
   have parity with IPv4 infrastructure hiding even if the technique
   used is different.  Implementation of IPv6 route advertisement
   control for infrastructure hiding is difficult when using global
   address space.  Registeries assign fewer large blocks of IPv6 space
   compared to IPv4.  Providers cannot control the announcement of
   infrastructure global IPv6 blocks for infrastructure hiding without
   deaggregating their IPv6 announcements.

8.  IP Multicast

   IP Multicast behaves differently from IP unicast therefore must be
   secured in a different manner.  Some of the protocols used with
   multicast rely on IP unicast to transport the routing, and control
   information.  Unicast based protocols should be secured using the
   technique described in much of this document.  Multicast security is
   better addressed in a multicast specific security document.

9.  Security Considerations

   This entire document is concerned with security.

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10.  Acknowledgements

   Don Smith provided invaluable comments and suggestions.  Pat Cain,
   Ross Callon, Vince Fuller, Barry Greene, George Jones, David Meyer,
   Peka Savola reviewed this document and provided feedback.

11.  References

11.1.  Normative References

   [RFC1812]  Baker, F., Ed., "Requirements for IP Version 4 Routers",
              June 1995.

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

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

   [RFC2474]  Nichols, K., Blake, S., Baker, F., Black, D., "Definition
              of the Differentiated Services Field (DS Field) in the
              IPv4 and IPv6 Headers", December 1998.

   [RFC3443]  Agarwal, P., Akyol, B., "Time To Live (TTL) Processing in
              Multi-Protocol Label Switching (MPLS) Networks",
              January 2003.

   [RFC3704]  Baker, F., Savola, P., "Ingress Filtering for Multihomed
              Networks", March 2004.

   [RFC4381]  Behringer, M., "Analysis of the Security of BGP/MPLS IP
              Virtual Private Networks (VPNs)", February 2006.

11.2.  Informative References

   [AKIN]     "Hardening Cisco Routers", T. Akin, O'Reilly Media,
              2002, ISBN 0596001665.

   [CYMRU-J]  "JUNOS Secure Template", S. Gill, Team Cymru, March 2005,

   [CYMRU-C]  "Secure IOS Template", R. Thomas, Team Cymru, March 2007,

   [GREENE]   "Cisco ISP Essentials", B. Greene and P. Smith,
              Cisco Press, 2002, ISBN 1587050412.

   [NANOG-M]  "Implications of Securing Backbone Router
              Infrastructure", R. McDowell, NANOG 31, May 2004.

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   [RFC2334]  Narten, T., and H. Alverstand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", October 1998.

   [RFC2827]  Ferguson, P., Senie, D., "Network Ingress Filtering:
              Defeating Denial of Service Attacks which employ IP Source
              Address Spoofing", May 2000.

   [RFC3669]  Bradner, S., "Intellectual Property Rights in IETF
              Technology", February 2004.

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

   [RFC3978]  Bradner, S., Ed., "IETF Rights in Contributions",
              February 2004.

   [RFC4778]  Kaeo, M., "Current Operational Security Practices in
              Internet Service Provider Environments", January 2007.

Authors' Addresses

   James Gill
   Verizon Business
   22001 Louden County Parkway
   Ashburn, VA  20147

   Phone: +1-703-886-3834
   Email: james.gill@verizonbusiness.com
   URI:   www.verizonbusiness.com

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   Darrel Lewis
   Cisco Systems Inc.
   170 West Tasman Dr.
   San Jose, CA  95134

   Phone: +1-408-853-3653
   Email: darlewis@cisco.com
   URI:   www.cisco.com

   Paul Quinn
   Cisco Systems Inc.
   170 West Tasman Drive
   San Jose, CA  95134

   Phone: +1-408-527-3560
   Email: paulq@cisco.com
   URI:   www.cisco.com

   Peter Schoenmaker
   NTT America
   101 Park Ave., FL 41
   New York, NY  10178

   Phone: +1-202-808-2298
   Email: pds@ntt.net

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