[Docs] [txt|pdf|xml|html] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03 04 05 06 07 08 09 10 11 RFC 7404

OPsec Working Group                                         M. Behringer
Internet-Draft                                                 E. Vyncke
Intended status: Informational                                     Cisco
Expires: August 17, 2014                               February 13, 2014


        Using Only Link-Local Addressing Inside an IPv6 Network
                      draft-ietf-opsec-lla-only-07

Abstract

   In an IPv6 network it is possible to use only link-local addresses on
   infrastructure links between routers.  This document discusses the
   advantages and disadvantages of this approach to help the decision
   process for a given network.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on August 17, 2014.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.




Behringer & Vyncke       Expires August 17, 2014                [Page 1]


Internet-Draft               Link-Local Only               February 2014


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Using Link-Local Address on Infrastructure Links  . . . . . .   2
     2.1.  The Approach  . . . . . . . . . . . . . . . . . . . . . .   2
     2.2.  Advantages  . . . . . . . . . . . . . . . . . . . . . . .   3
     2.3.  Caveats . . . . . . . . . . . . . . . . . . . . . . . . .   5
     2.4.  Internet Exchange Points  . . . . . . . . . . . . . . . .   6
     2.5.  Summary . . . . . . . . . . . . . . . . . . . . . . . . .   7
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   6.  Informative References  . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   An infrastructure link between a set of routers typically does not
   require global or unique local addresses [RFC4193].  Using only link-
   local addressing on such links has a number of advantages.  For
   example, that routing tables do not need to carry link addressing,
   and can therefore be significantly smaller.  This helps to decrease
   failover times in certain routing convergence events.  An interface
   of a router is also not reachable beyond the link boundaries,
   therefore reducing the attack horizon.

   This document discusses the advantages and caveats of this approach.

2.  Using Link-Local Address on Infrastructure Links

   This document discusses the approach of using only link-local
   addresses (LLA) on all router interfaces on infrastructure links.
   Routers don't typically need to receive packets from hosts or nodes
   outside the network.  For a network operator, there may be reasons to
   use greater than link-local scope addresses on infrastructure
   interfaces for certain operational tasks, such as pings to an
   interface or traceroutes across the network.  This document discusses
   such cases and proposes alternative procedures.

2.1.  The Approach

   In this approach neither globally routed IPv6 addresses nor unique
   local addresses are configured on infrastructure links.  In the
   absence of specific global or unique local address definitions, the
   default behavior of routers is to use link-local addresses notably
   for routing protocols.





Behringer & Vyncke       Expires August 17, 2014                [Page 2]


Internet-Draft               Link-Local Only               February 2014


   The sending of ICMPv6 [RFC4443] error messages (packet-too-big, time-
   exceeded...) is required for routers.  Therefore, another interface
   must be configured with an IPv6 address with a greater scope than
   link-local.  This address will usually be a loopback interface with a
   global scope address belonging to the operator and part of an
   announced prefix (with a suitable prefix length) to avoid being
   dropped by other routers implementing [RFC3704].  This is
   implementation dependent.  For the remainder of this document we will
   refer to this interface as a "loopback interface".

   [RFC6724] recommends that greater than link-local scope IPv6
   addresses are used as the source IPv6 address for all generated
   ICMPv6 messages sent to a non link-local address, with the exception
   of ICMPv6 redirect messages, as defined in [RFC4861] section 4.5.

   The effect on specific traffic types is as follows:

   o  Most control plane protocols, such as BGP [RFC4271], ISIS [IS-IS],
      OSPFv3 [RFC5340], RIPng [RFC2080], PIM [RFC4609] work by default
      or can be configured to work with link-local addresses.
      Exceptions are explained in the caveats section (Section 2.3).

   o  Management plane traffic, such as SSH [RFC4251], Telnet [RFC0495],
      SNMP [RFC1157], and ICMPv6 echo request [RFC4443], can use the
      address of the router loopback interface as the destination
      address.  Router management can also be done over out-of-band
      channels.

   o  ICMP error messages are usually sourced from a loopback interface
      with a greater than link-local address scope.  [RFC4861] section
      4.5 explains one exception: ICMP redirect messages can also be
      sourced from a link-local address.

   o  Data plane traffic is forwarded independently of the link address
      type.

   o  Neighbor discovery (neighbor solicitation and neighbor
      advertisement) is done by using link-local unicast and multicast
      addresses.  Therefore neighbor discovery is not affected.

   We therefore conclude that it is possible to construct a working
   network in this way.

2.2.  Advantages

   The following list of advantages is in no particular order.





Behringer & Vyncke       Expires August 17, 2014                [Page 3]


Internet-Draft               Link-Local Only               February 2014


   Smaller routing tables: Since the routing protocol only needs to
   carry one global address (the loopback interface) per router, it is
   smaller than the traditional approach where every infrastructure link
   address is carried in the routing protocol.  This reduces memory
   consumption, and increases the convergence speed in some routing
   failover cases.  Because the Forwarding Information Base to be
   downloaded to line cards is smaller and there are fewer prefixes in
   the Routing Information Base, the routing algorithm is accellerated.
   Note: smaller routing tables can also be achieved by putting
   interfaces in passive mode for the Interior Gateway Protocol (IGP).

   Simpler address management: Only loopback interface addresses need to
   be considered in an addressing plan.  This also allows for easier
   renumbering.

   Lower configuration complexity: link-local addresses require no
   specific configuration, thereby lowering the complexity and size of
   router configurations.  This also reduces the likelihood of
   configuration mistakes.

   Simpler DNS: Less routable address space in use also means less
   reverse and forward mapping DNS resource records to maintain.

   Reduced attack surface: Every routable address on a router
   constitutes a potential attack point: a remote attacker can send
   traffic to that address.  Examples are a TCP SYN flood (see
   [RFC4987]), or SSH brute force password attacks.  If a network only
   uses the addresses of the router loopback interface(s), only those
   addresses need to be protected from outside the network.  This may
   ease protection measures, such as infrastructure access control
   lists.

   Without using link-local addresses, it is still possible to achieve
   the same result if the network addressing scheme is set up such that
   all link and loopback interfaces have greater than link-local
   addresses and are aggregatable, and if the infrastructure access list
   covers that entire aggregated space.  See also [RFC6752] for further
   discussion on this topic.

   [RFC6860] describes another approach to hide addressing on
   infrastructure links for OSPFv2 and OSPFv3, by modifying the existing
   protocols.  This document does not modify any protocol, however it
   works only for IPv6.








Behringer & Vyncke       Expires August 17, 2014                [Page 4]


Internet-Draft               Link-Local Only               February 2014


2.3.  Caveats

   The caveats listed in this section are in no particular order.

   Interface ping: if an interface doesn't have a routable address, it
   can only be pinged from a node on the same link.  Therefore, it is
   not possible to ping a specific link interface remotely.  A possible
   workaround is to ping the loopback address of a router instead.  In
   most cases today, it is not possible to see which link the packet was
   received on; however, [RFC5837] suggests including the interface
   identifier of the interface a packet was received on in the ICMPv6
   response; it must be noted that there are few implementations of this
   ICMPv6 extension.  With this approach it would be possible to ping a
   router on the addresses of loopback interfaces, yet see which
   interface the packet was received on.  To check liveliness of a
   specific interface, it may be necessary to use other methods, such as
   connecting to the router via SSH and checking locally or using SNMP.

   Traceroute: similar to the ping case, a reply to a traceroute packet
   would come from the address of a loopback interface, and current
   implementations do not display the specific interface the packets
   came in on.  Also here, [RFC5837] provides a solution.  As in the
   ping case above, it is not possible to traceroute to a particular
   interface if it only has a link-local address.

   Hardware dependency: LLAs are usually EUI-64 based, hence, they
   change when the MAC address is changed.  This could pose problem in a
   case where the routing neighbor must be configured explicitly (e.g.
   BGP) and a line card needs to be physically replaced hence changing
   the EUI-64 LLA and breaking the routing neighborship.  LLAs can be
   statically configured such as fe80::1 and fe80::2 which can be used
   to configure any required static routing neighborship.  However, this
   static LLA configuration may be more complex to operate than
   statically configured greater than link-local addresses, because the
   link scope must also be considered, as in this example: 'BGP neighbor
   fe80::1%eth0 is down'.

   Network Management System (NMS) toolkits: if there is any NMS tool
   that makes use of interface IP address of a router to carry out any
   of its NMS functions, then it would no longer work if the interface
   does not have a routable address.  A possible workaround for such
   tools is to use the routable address of the router loopback interface
   instead.  Most vendor implementations allow the specification of
   loopback interface addresses for SYSLOG, IPfix, and SNMP.  The
   protocol LLDP (IEEE 802.1AB-2009) runs directly over Ethernet and
   does not require any IPv6 address, so dynamic network discovery is
   not hindered when using LLDP.  But, network discovery based on NDP
   cache content will only display the link-local addresses and not the



Behringer & Vyncke       Expires August 17, 2014                [Page 5]


Internet-Draft               Link-Local Only               February 2014


   addresses of the loopback interfaces; therefore, network discovery
   should rather be based on the Route Information Base to detect
   adjacent nodes.

   MPLS and RSVP-TE [RFC3209] allows establishing MPLS LSP on a path
   that is explicitly identified by a strict sequence of IP prefixes or
   addresses (each pertaining to an interface or a router on the path).
   This is commonly used for Fast Re-Route (FRR).  However, if an
   interface uses only a link-local address, then such LSPs cannot be
   established.  At the time of writing this document, there is no
   workaround for this case; therefore, where RSVP-TE is being used, the
   approach described in this document does not work.

2.4.  Internet Exchange Points

   Internet Exchange Points (IXPs) have a special importance in the
   global Internet, because they connect a high number of networks in a
   single location, and because a significant part of Internet traffic
   passes through at least one IXP.  An IXP requires therefore a very
   high level of security.  The address space used on an IXP is
   generally known, as it is registered in the global Internet Route
   Registry, or it is easily discoverable through traceroute.  The IXP
   prefix is especially critical, because practically all addresses on
   this prefix are critical systems in the Internet.

   Apart from general device security guidelines, there are generally
   two additional ways to raise security (see also
   [I-D.ietf-opsec-bgp-security]):

   1.  Not to announce the prefix in question, and

   2.  To drop all traffic from remote locations destined to the IXP
       prefixes.

   Not announcing the prefix of the IXP would frequently result in
   traceroute and similar packets (required for PMTUd) to be dropped due
   to uRPF checks.  Given that PMTUd is critical, this is generally not
   acceptable.  Dropping all external traffic to the IXP prefix is hard
   to implement, because if only one service provider connected to an
   IXP does not filter correctly, then all IXP routers are reachable
   from at least that service provider network.

   As the prefix used in the IXP is usually longer than a /48, it is
   frequently dropped by route filters on the Internet having the same
   net effect as not announcing the prefix.

   Using link-local addresses on the IXP may help in this scenario.  In
   this case, the generated ICMPv6 packets would be generated from



Behringer & Vyncke       Expires August 17, 2014                [Page 6]


Internet-Draft               Link-Local Only               February 2014


   loopback interfaces or from any other interface with a globally
   routable address without any configuration.  However in this case,
   each service provider would use his own address space, making a
   generic attack against all devices on the IXP harder.  All of an
   IXP's loopback interface addresses can be discovered by a potential
   attacker with a simple traceroute; a generic attack is therefore
   still possible, but it would require more work.

   In some cases service providers carry the IXP addresses in their IGP
   for certain forms of traffic engineering across multiple exit points.
   Link-local addresses cannot be used for this purpose; in this case,
   the service provider would have to employ other methods of traffic
   engineering.

   If an Internet Exchange Point is using a global prefix registered for
   this purpose, a traceroute will indicate whether the trace crosses an
   IXP rather than a private interconnect.  If link local addressing is
   used instead, a traceroute will not provide this distinction.

2.5.  Summary

   Using exclusively link-local addressing on infrastructure links has a
   number of advantages and disadvantages, which are both described in
   detail in this document.  A network operator can use this document to
   evaluate whether using link-local addressing on infrastructure links
   is a good idea in the context of his/her network or not.  This
   document makes no particular recommendation either in favour or
   against.

3.  Security Considerations

   Using LLAs only on infrastructure links reduces the attack surface of
   a router: loopback interfaces with routed addresses are still
   reachable and must be secured, but infrastructure links can only be
   attacked from the local link.  This simplifies security of control
   and management planes.  The approach does not impact the security of
   the data plane.  The link-local-only approach does not address
   control plane [RFC6192] attacks generated by data plane packets (such
   as hop-limit expiration or packets containing a hop-by-hop extension
   header).

4.  IANA Considerations

   There are no IANA considerations or implications that arise from this
   document.






Behringer & Vyncke       Expires August 17, 2014                [Page 7]


Internet-Draft               Link-Local Only               February 2014


5.  Acknowledgements

   The authors would like to thank Salman Asadullah, Brian Carpenter,
   Bill Cerveny, Benoit Claise, Rama Darbha, Simon Eng, Wes George,
   Fernando Gont, Jen Linkova, Harald Michl, Janos Mohacsi, Ivan
   Pepelnjak, and Alvaro Retana for their useful comments about this
   work.

6.  Informative References

   [I-D.ietf-opsec-bgp-security]
              Durand, J., Pepelnjak, I., and G. Doering, "BGP operations
              and security", draft-ietf-opsec-bgp-security-02 (work in
              progress), January 2014.

   [IS-IS]    ISO/IEC 10589, , "Intermediate System to Intermediate
              System Intra-Domain Routing Exchange Protocol for use in
              Conjunction with the Protocol for Providing the
              Connectionless-mode Network Service (ISO 8473)", June
              1992.

   [RFC0495]  McKenzie, A., "Telnet Protocol specifications", RFC 495,
              May 1973.

   [RFC1157]  Case, J., Fedor, M., Schoffstall, M., and J. Davin,
              "Simple Network Management Protocol (SNMP)", STD 15, RFC
              1157, May 1990.

   [RFC2080]  Malkin, G. and R. Minnear, "RIPng for IPv6", RFC 2080,
              January 1997.

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, December 2001.

   [RFC3704]  Baker, F. and P. Savola, "Ingress Filtering for Multihomed
              Networks", BCP 84, RFC 3704, March 2004.

   [RFC4193]  Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
              Addresses", RFC 4193, October 2005.

   [RFC4251]  Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
              Protocol Architecture", RFC 4251, January 2006.

   [RFC4271]  Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
              Protocol 4 (BGP-4)", RFC 4271, January 2006.





Behringer & Vyncke       Expires August 17, 2014                [Page 8]


Internet-Draft               Link-Local Only               February 2014


   [RFC4443]  Conta, A., Deering, S., and M. Gupta, "Internet Control
              Message Protocol (ICMPv6) for the Internet Protocol
              Version 6 (IPv6) Specification", RFC 4443, March 2006.

   [RFC4609]  Savola, P., Lehtonen, R., and D. Meyer, "Protocol
              Independent Multicast - Sparse Mode (PIM-SM) Multicast
              Routing Security Issues and Enhancements", RFC 4609,
              October 2006.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              September 2007.

   [RFC4987]  Eddy, W., "TCP SYN Flooding Attacks and Common
              Mitigations", RFC 4987, August 2007.

   [RFC5340]  Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
              for IPv6", RFC 5340, July 2008.

   [RFC5837]  Atlas, A., Bonica, R., Pignataro, C., Shen, N., and JR.
              Rivers, "Extending ICMP for Interface and Next-Hop
              Identification", RFC 5837, April 2010.

   [RFC6192]  Dugal, D., Pignataro, C., and R. Dunn, "Protecting the
              Router Control Plane", RFC 6192, March 2011.

   [RFC6724]  Thaler, D., Draves, R., Matsumoto, A., and T. Chown,
              "Default Address Selection for Internet Protocol Version 6
              (IPv6)", RFC 6724, September 2012.

   [RFC6752]  Kirkham, A., "Issues with Private IP Addressing in the
              Internet", RFC 6752, September 2012.

   [RFC6860]  Yang, Y., Retana, A., and A. Roy, "Hiding Transit-Only
              Networks in OSPF", RFC 6860, January 2013.

Authors' Addresses

   Michael Behringer
   Cisco
   Building D, 45 Allee des Ormes
   Mougins  06250
   France

   Email: mbehring@cisco.com






Behringer & Vyncke       Expires August 17, 2014                [Page 9]


Internet-Draft               Link-Local Only               February 2014


   Eric Vyncke
   Cisco
   De Kleetlaan, 6A
   Diegem  1831
   Belgium

   Email: evyncke@cisco.com












































Behringer & Vyncke       Expires August 17, 2014               [Page 10]


Html markup produced by rfcmarkup 1.129b, available from https://tools.ietf.org/tools/rfcmarkup/