--- 1/draft-ietf-opsec-lla-only-01.txt 2012-10-22 21:14:21.369510550 +0200 +++ 2/draft-ietf-opsec-lla-only-02.txt 2012-10-22 21:14:21.389509104 +0200 @@ -1,19 +1,19 @@ Operational Security Capabilities for M. Behringer IP Network Infrastructure E. Vyncke Internet-Draft Cisco -Intended status: Informational September 21, 2012 -Expires: March 25, 2013 +Intended status: Informational October 22, 2012 +Expires: April 25, 2013 Using Only Link-Local Addressing Inside an IPv6 Network - draft-ietf-opsec-lla-only-01 + draft-ietf-opsec-lla-only-02 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 @@ -23,21 +23,21 @@ 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 March 25, 2013. + This Internet-Draft will expire on April 25, 2013. Copyright Notice Copyright (c) 2012 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 @@ -47,29 +47,30 @@ the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. 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 and Possible Workarounds . . . . . . . . . . . . . 5 - 2.4. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . 6 - 3. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 - 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 - 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7 - 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 - 6.1. Normative References . . . . . . . . . . . . . . . . . . . 7 - 6.2. Informative References . . . . . . . . . . . . . . . . . . 7 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8 + 2.3. Caveats . . . . . . . . . . . . . . . . . . . . . . . . . . 5 + 2.4. Internet Exchange Points . . . . . . . . . . . . . . . . . 6 + 2.5. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . 7 + 3. Security Considerations . . . . . . . . . . . . . . . . . . . . 7 + 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8 + 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8 + 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 + 6.1. Normative References . . . . . . . . . . . . . . . . . . . 8 + 6.2. Informative References . . . . . . . . . . . . . . . . . . 8 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9 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, @@ -110,40 +111,43 @@ 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. 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 + 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 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 to avoid being dropped by other routers + (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 also be sourced from the loopback address. + 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. @@ -165,30 +169,28 @@ 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. 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. + 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 greater-than-link-local address space in use also - means less DNS mappings to maintain because DNS is not really - suitable to contain link-local addresses as DNS has no clue to the - link scope. + Simpler DNS: Less routable address space in use also means less DNS + mappings to maintain. -2.3. Caveats and Possible Workarounds +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 @@ -208,33 +210,90 @@ 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. 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. + 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 FRR. However, if an interface uses only a - link-local address, then such LSPs can not be established. A - 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). + 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. Summary +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 + 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. 3. Security Considerations @@ -252,42 +311,47 @@ 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 - for their useful comments about this work. + Benoit Claise, Simon Eng, Wes George, Janos Mohacsi, Alvaro Retana, + Ivan Pepelnjak 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-05 (work in progress), July 2012. + [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.