[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
Operational Security Capabilities for M. Behringer
IP Network Infrastructure E. Vyncke
Internet-Draft Cisco
Intended status: Informational February 12, 2013
Expires: August 16, 2013
Using Only Link-Local Addressing Inside an IPv6 Network
draft-ietf-opsec-lla-only-03
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 16, 2013.
Copyright Notice
Copyright (c) 2013 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 16, 2013 [Page 1]
Internet-Draft Link-Local Only February 2013
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . . 3
2. Using Link-Local Address on Infrastructure Links . . . . . . . 3
2.1. The Approach . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Advantages . . . . . . . . . . . . . . . . . . . . . . . . 4
2.3. Caveats . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.4. Internet Exchange Points . . . . . . . . . . . . . . . . . 6
2.5. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Security Considerations . . . . . . . . . . . . . . . . . . . . 8
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.1. Normative References . . . . . . . . . . . . . . . . . . . 8
6.2. Informative References . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
Behringer & Vyncke Expires August 16, 2013 [Page 2]
Internet-Draft Link-Local Only February 2013
1. Introduction
An infrastructure link between a set of routers typically does not
require global or even unique local addressing [RFC4193]. Using
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.
We propose to configure neither globally routable IPv6 addresses nor
unique local addresses on infrastructure links of routers, wherever
possible. We recommend to use exclusively link-local addresses on
such links.
This document discusses the advantages and caveats of this approach.
Note: [I-D.ietf-ospf-prefix-hiding] describes another approach for
OPSFv2 and OSPFv3 by modifying the existing protocols while this
document does not modify any protocol but works only for IPv6.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC2119 [RFC2119] when
they appear in ALL CAPS. These words may also appear in this
document in lower case as plain English words, absent their normative
meanings.
2. Using Link-Local Address on Infrastructure Links
This document proposes to use only link-local addresses (LLA) on all
router interfaces on infrastructure links. Routers typically do not
need to be reached from nodes of the network, nor from outside the
network. For an network operator there may be reasons to send
packets to an infrastructure link for certain monitoring tasks; many
of those tasks could also be handled differently, not requiring
routable address space on infrastructure links.
2.1. The Approach
Neither global 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 16, 2013 [Page 3]
Internet-Draft Link-Local Only February 2013
These link-local addresses SHOULD be hard-coded to prevent the change
of EUI-64 addresses when changing of MAC address (such as after
changing a network interface card).
ICMPv6 [RFC4443] error messages (packet-too-big, time-exceeded...)
are required for routers, therefore a loopback interface must be
configured with an IPv6 address with a greater scope than link-local
(this will usually be a global scope). This greater than link-local
scope IPv6 address must be used as the source IPv6 address for all
generated ICMPv6 messages sent to a non link-local address and must
belong to the operator and be part of an announced prefix (with a
suitable prefix length) to avoid being dropped by other routers
implementing [RFC3704].
The effect on specific traffic types is as follows:
o Control plane protocols, such as BGP, ISIS, OSPFv3, RIPng, PIM
work by default or can be configured to work with link-local
addresses.
o Management plane traffic, such as SSH, Telnet, SNMP, ICMP echo
request ... can be addressed to loopback addresses of routers with
a greater than link-local scope address. Router management can
also be done over out-of-band channels.
o ICMP error message can be sourced from a loopback address. They
must not be sourced from link-local addresses when the destination
is non link-local.
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
Smaller routing tables: Since the routing protocol only needs to
carry one loopback address per router, it is smaller than in the
traditional approach where every infrastructure link addresses are
carried in the routing protocol. This reduces memory consumption,
and increases the convergence speed in some routing failover cases
(notably because the Forwarding Information Base to be downloaded to
line cards are smaller but also because there are less prefixes in
Behringer & Vyncke Expires August 16, 2013 [Page 4]
Internet-Draft Link-Local Only February 2013
the Routing Information Base hence accelerating the routing
algorithm). Note: smaller routing tables can also be achieved by
putting interfaces in passive mode for the IGP.
Reduced attack surface: Every routable address on a router
constitutes a potential attack point: a remote attacker can send
traffic to that address, for example a TCP SYN flood, or he can
intent SSH brute force password attacks. If a network only uses
loopback addresses for the routers, only those loopback addresses
need to be protected from outside the network. This may ease
protection measures, such as infrastructure access control lists. If
the addressing scheme is set up such that all link addresses and all
loopback addresses are aggregatable, and if the infrastructure access
list covers that entire aggregated space, then changing to link-local
addresses does not reduce the attack surface significantly. See also
[I-D.ietf-grow-private-ip-sp-cores] for further discussion on this
topic.
Lower configuration complexity: LLAs require no specific
configuration (except when they are statically configured), 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 DNS
mappings to maintain.
2.3. Caveats
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 [RFC5837] suggests to include the
interface identifier of the interface a packet was received on in the
ICMP response; it must be noted that there are little implemention of
this ICMP extension. With this approach it would be possible to ping
a router on the loopback address, yet see which interface the packet
was received on. To check liveliness of a specific interface it may
be necessary to use other methods, for example to connect to the
router via SSH and to check locally or use SNMP.
Traceroute: Similar to the ping case, a reply to a traceroute packet
would come from a loopback address with a greater than link-local
address. Today this does not display the specific interface the
packets came in on. Also here, RFC5837 [RFC5837] provides a
solution.
Behringer & Vyncke Expires August 16, 2013 [Page 5]
Internet-Draft Link-Local Only February 2013
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. But, LLAs can
be statically configured such as fe80::1 and fe80::2 which can be
used to configure any required static routing neighborship. This
static configuration is similar in complexity to statically
configured greater than link-local addresses, however, it is only
required where routing peers are explicitly configured.
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 NMS functions, then it would no longer work, if the interface is
missing routable address. A possible workaround for such tools is to
use the routable loopback address of the router instead. Most vendor
implementations allow the specification of the loopback address for
SYSLOG, IPfix, SNMP. 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 loopback global address; 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 proposed 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 significant part of Internet traffic
pass through at least one IXP. An IXP with all the service provider
nodes 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
Behringer & Vyncke Expires August 16, 2013 [Page 6]
Internet-Draft Link-Local Only February 2013
two additional ways to raise security (see also
[I-D.jdurand-bgp-security]):
1. Not to announce the prefix in question, and
2. To drop all traffic destined to the IXP prefixes from traffic
from remote locations.
Not announcing the prefix of the IXP however 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 on an IXP
routes does not filter correctly, then all IXP routers are reachable
from at least that service provider network.
As the prefix used in IXP is usually longer than a /48 it is
frequently dropped by route filters on the Internet having the same
net effect as not announced the prefix.
Using link-local addresses on the IXP may help in this scenario. In
this case, the generated ICMP packets would be generated from
loopback interfaces or from any other interfaces with globally
routable sources 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. Also all the
loopback addresses on the IXP can be discovered by a potential
attacker by a simple traceroute; a generic attack is therefore still
possible, but it would require significantly more work.
In some cases service providers carry the IXP addresses in their IGP
for certain forms of traffic engineering across multiple exit points.
If link local addresses are used, these cannot be used for this
purpose; in this case, the service provider would have to employ
other methods of traffic engineering.
2.5. Summary
Using link-local addressing only on infrastructure links has a number
of advantages, such as a smaller routing table size and a reduced
attack surface. It also simplifies router configurations. However,
the way certain network management tasks are carried out today has to
be adapted to provide the same level of detail, for example interface
identifiers in traceroute.
Behringer & Vyncke Expires August 16, 2013 [Page 7]
Internet-Draft Link-Local Only February 2013
3. Security Considerations
Using LLAs only on infrastructure links reduces the attack surface of
a router: loopback addresses 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 proposal does not impact the security of
the data plane. This proposal 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).
As in the traditional approach, this approach relies on the
assumption that all routers can be trusted due to physical and
operational security.
4. IANA Considerations
There are no IANA considerations or implications that arise from this
document.
5. Acknowledgements
The authors would like to thank Salman Asadullah, Brian Carpenter,
Benoit Claise, Simon Eng, Wes George, Janos Mohacsi, Alvaro Retana,
Ivan Pepelnjak, and Harald Michl for their useful comments about this
work.
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
6.2. Informative References
[I-D.ietf-grow-private-ip-sp-cores]
Kirkham, A., "Issues with Private IP Addressing in the
Internet", draft-ietf-grow-private-ip-sp-cores-07 (work in
progress), July 2012.
[I-D.ietf-ospf-prefix-hiding]
Yang, Y., Retana, A., and A. Roy, "Hiding Transit-only
Networks in OSPF", draft-ietf-ospf-prefix-hiding-07 (work
in progress), December 2012.
Behringer & Vyncke Expires August 16, 2013 [Page 8]
Internet-Draft Link-Local Only February 2013
[I-D.jdurand-bgp-security]
Durand, J., Pepelnjak, I., and G. Doering, "BGP operations
and security", draft-jdurand-bgp-security-02 (work in
progress), September 2012.
[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.
[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.
[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.
Authors' Addresses
Michael Behringer
Cisco
Building D, 45 Allee des Ormes
Mougins, 06250
France
Email: mbehring@cisco.com
Eric Vyncke
Cisco
De Kleetlaan, 6A
Diegem, 1831
Belgium
Email: evyncke@cisco.com
Behringer & Vyncke Expires August 16, 2013 [Page 9]
Html markup produced by rfcmarkup 1.129d, available from
https://tools.ietf.org/tools/rfcmarkup/