Internet DRAFT - draft-behringer-lla-only
draft-behringer-lla-only
Network Working Group M. Behringer
Internet-Draft E. Vyncke
Intended status: Informational Cisco
Expires: January 17, 2013 July 16, 2012
Using Only Link-Local Addressing Inside an IPv6 Network
draft-behringer-lla-only-01
Abstract
This document proposes to use only IPv6 link-local addresses on
infrastructure links between routers, wherever possible. It
discusses the advantages and disadvantages of this approach to aide
the decision process for a given network,
Status of this Memo
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Copyright (c) 2012 IETF Trust and the persons identified as the
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . . 3
2. Using Link-Local Address on Infrastructure Links . . . . . . . 3
2.1. The Suggested Approach . . . . . . . . . . . . . . . . . . 3
2.2. Advantages . . . . . . . . . . . . . . . . . . . . . . . . 4
2.3. Caveats and Possible Workarounds . . . . . . . . . . . . . 5
2.4. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. Normative References . . . . . . . . . . . . . . . . . . . 7
6.2. Informative References . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7
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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.
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] 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 from users 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; we
suggest that many of those tasks could also be handled differently,
not requiring routable address space on infrastructure links.
2.1. The Suggested 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. These link-local addresses
MAY 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...) are required for
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routers, therefore a loopback interface MUST be configured with a
global scope IPv6 address. This global scope IPv6 address MUST be
used as the source IPv6 address for all generated ICMPv6 messages.
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 global scope address. Router management can also be done over
out-of-band channels.
o ICMP error message can also be sourced from the global scope
loopback 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
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.
Note: smaller routing tables can also be achieved by putting
interfaces in passive mode for the IGP.
Reduced attack surface: Every globally 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 significantly
eases protection measures, such as infrastructure access control
lists. See also [I-D.ietf-grow-private-ip-sp-cores] for further
discussion on this topic.
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Lower configuration complexity: LLAs require no specific
configuration, thereby lowering the complexity and size of router
configurations. This also reduces the likelihood of configuration
mistakes.
Simpler DNS: Less address space in use also means less DNS mappings
to maintain.
2.3. Caveats and Possible Workarounds
Interface ping: If an interface doesn't have a globally 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 implemented of this 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.
Traceroute: Similar to the ping case, a reply to a traceroute packet
would come from a loopback address with a global address. Today this
does not display the specific interface the packets came in on. Also
here, RFC5837 [RFC5837] provides a solution.
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.
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 globally routable
address. A possible workaround for such tools is to use the globally
routable lopback address of the router instead.
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 FRR. However, if an interface uses only a
link-local address, then such LSPs can not be established. A
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possible workaround is to use loose sequence of IP prefixes or
addresses (each pertaining to a router) to identify an explicit path
along with shared-risk-link-group (to not use a set of common
interfaces).
2.4. 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 has to be
adapted to provide the same level of detail, for example interface
identifiers in traceroute.
3. Security Considerations
Using LLAs only on infrastructure links reduces the attack surface of
a router: Loopback addresses with globally 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).
As in the traditional approach, also 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, Janos Mohacsi and
Wes George for their useful comments about this work.
6. References
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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-05 (work in
progress), June 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.
[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
400 Avenue Roumanille, Bat 3
Biot, 06410
France
Email: mbehring@cisco.com
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Eric Vyncke
Cisco
De Kleetlaan, 6A
Diegem, 1831
Belgium
Email: evyncke@cisco.com
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