IPv6 Operations F. Baker Internet-Draft Cisco Systems Intended status: Informational W. Harrop Expires: January 26, 2010 G. Armitage CAIA, Swinburne University of Technology July 25, 2009 IPv4 and IPv6 Greynets draft-baker-v6ops-greynet-01 Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on January 26, 2010. Copyright Notice Copyright (c) 2009 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 in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Baker, et al. Expires January 26, 2010 [Page 1] Internet-Draft IPv4 and IPv6 Greynets July 2009 Abstract This note discusses a feature to support building Greynets for IPv4 and IPv6. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Deploying Greynets . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Deployment using routing - Darknets . . . . . . . . . . . . 4 2.2. Deployment using tunnels - Greynets . . . . . . . . . . . . 4 2.3. Other filters . . . . . . . . . . . . . . . . . . . . . . . 6 3. Implications for router design . . . . . . . . . . . . . . . . 6 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 7.1. Normative References . . . . . . . . . . . . . . . . . . . 8 7.2. Informative references . . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8 Baker, et al. Expires January 26, 2010 [Page 2] Internet-Draft IPv4 and IPv6 Greynets July 2009 1. Introduction Darknets, also called "Network Telescopes" among other things, have been deployed by several organizations including CAIDA, Team Cymru, and the University of Michigan, to look at traffic directed to addresses in blocks that are not in actual use. Such traffic becomes visible by either direct capture (it is routed to a collector) or by virtue of its backscatter (its resulting in ICMP traffic or transport layer resets). [Harrop] defines a 'Greynet' by extension, in these words: Darknets are often proposed to monitor for anomalous, externally sourced traffic, and require large, contiguous blocks of unused IP addresses - not always feasible for enterprise network operators. We introduce and evaluate the Greynet - a region of IP address space that is sparsely populated with "darknet" addresses interspersed with active (or "lit") IP addresses. Based on a small sample of traffic collected within a university campus network we saw that relatively sparse greynets can achieve useful levels of network scan detection. In other words, instead of setting aside prefixes that an attacker might attempt to probe and in so doing court discovery, Harrop proposed that individual (or small groups of adjacent) addresses in subnets be set aside for the purpose, using different host identifiers in each subnet to make it more difficult for an address scan to detect them. The concept has value in the sense that it is harder to map the addresses or prefixes out of an attacker's search pattern, as their presence is more obscure. Harrop's research was carried out using IPv4 [RFC0791], and yielded interesting information. It has been observed [RFC5157] that address scanning is less effective in IPv6 [RFC2460] networks, as there are more addresses to scan. The observation is of limited value, in that there are other approaches to identifying IPv6 systems, such as reading the 'Received:' lines in SMTP envelopes. Such attacks can be limited by the use of Privacy Addresses [RFC4941], which periodically change, rendering such historical information less useful, but the fact is that such analytic methods exist. Greynets are a tool that can be used to isolate and analyze them. 2. Deploying Greynets Corporate IT departments and other network operators frequently run collectors or other kinds of sensors. A collector is a computer Baker, et al. Expires January 26, 2010 [Page 3] Internet-Draft IPv4 and IPv6 Greynets July 2009 system on the Internet that is expressly set up to attract and "trap" nefarious attempts to penetrate computer systems. Such systems may simply record the attempt or the datagram that initiated the attempt (darknets/greynets), or they may act as a decoy, luring in potential attacks in order to study their activities and study their methods (honey pots). To accomplish this, we separate nefarious traffic from that which is likely normal and important, studying one and facilitating the other. 2.1. Deployment using routing - Darknets One obvious way to isolate and identify nefarious traffic is to realize that it is sent to a prefix or address that is not instantiated. If a campus uses an IPv4 /24 prefix or an IPv6 /56 prefix but contains less than 100 actual subnets, for example, we might use only odd numbered subnets (128 of the 256 available in that prefix), and not quite all of those. Knowing that the active prefixes are more specific and therefore attract appropriate traffic, we might also advertise the default prefix from the collector, attracting traffic directed to the uninstantiated prefixes in that routing domain. A second question involves mimicking a host under attack; the collector may simply record this uninvited traffic, or may reply as a honeypot system. 2.2. Deployment using tunnels - Greynets IPv4 subnets usually have some unallocated space in them, if only because CIDR allocates O(2^n) addresses to an IP Subnet and there are not exactly that many systems there. Similarly, with active IPv6 prefixes, even a very large switched LAN is likely to use a small fraction of the available addresses. This is by design, as discussed in section 2.5.1 of [RFC4291]. If the addresses are distributed reasonably randomly among the possible values, the likelihood of an attacker guessing what addresses are in actual use is limited. This gives us an opportunity with respect to unused addresses within a IP prefix. Routers use IPv4 ARP [RFC0826] and IPv6 Neighbor Discovery [RFC4861] to determine the MAC address of a neighbor to which a datagram needs to be sent. Both specifications intend that when a datagram arrives at a router serving the target prefix, but which doesn't know the MAC address of the intended destination, it should: Baker, et al. Expires January 26, 2010 [Page 4] Internet-Draft IPv4 and IPv6 Greynets July 2009 o Enqueue the datagram, o Emit a Neighbor Solicitation or ARP Request, o Await a Neighbor Advertisement or ARP Response, and o On receipt, dequeue and forward the datagram. Once the host's MAC address is in the router's tables (and in so doing the address proven valid), the matter is not an issue. In [Harrop], the Greynet is described as being instantiated on an end-host that replies to ARP Requests for all 'dark' IP addresses. However, a small modification to router behaviour can augment this model. As well as queuing or dropping a datagram that has triggered an ARP Request or Neighbor Solicitation, the router forwards a copy of this datagram over an independent link to the Greynet's analytic equipment. This independent link may be a different physical interface, a circuit, VLAN, tunnel, or in fact any place such a datagram could be handled. The analytic equipment will now receive two types of datagrams. Of most interest will be those destined for 'dark' IP addresses. Of less interest will be the irregular case where a datagram arrives for a legitimate local neighbour who has, for some temporary reason, no MAC address in the router's tables. Datagrams arriving for an IP destination for which an ARP reply (or Neighbor Advertisement) has not yet received might also be forwarded to the analytical equipment over the independent link - or might not, if they are considered to be unlikely to provide new analytic information. Analytic equipment, depending on the router to recognize 'dark' IP addresses in this manner, can easily track arrival patterns of datagrams destined to unused parts of the network. It may also optionally chose to respond to such datagrams, acting as a honeypot to elicit further datagrams from the remote source. If the collector replies directly, the attacker may be able to identify the fact through information in or about the datagram - datagrams sent to the same IP Subnet may come back with different TTL values, for example. Hence, it may be advisable for the collector to send the reply back through the tunnel and therefore as if from the same IP Subnet. Naturally the collector in this scenario should not respond to datagrams destined for 'lit' IP addresses - the intended destination will eventually respond to the router's ARP or Neighbor Solicitation anyway. Baker, et al. Expires January 26, 2010 [Page 5] Internet-Draft IPv4 and IPv6 Greynets July 2009 2.3. Other filters An obvious extension of the concept would include traffic identified by other filters as appropriate to send to the collector. For example, one might configure the system to forward traffic failing a unicast reverse forwarding path (uRPF) check [RFC2827] to the collector via the same tunnel. 3. Implications for router design The implication for router design applies to the IPv4 ARP and IPv6 Neighbor Discovery algorithms. It might be interesting to provide, under configuration control, the ability to forward arriving datagrams that trigger an ARP Request or Neighbor Solicit, and then fail to receive the intended response, to an interface, circuit, VLAN, or tunnel to an analytic system. 4. IANA Considerations This memo asks the IANA for no new parameters. Note to RFC Editor: This section will have served its purpose if it correctly tells IANA that no new assignments or registries are required, or if those assignments or registries are created during the RFC publication process. From the author's perspective, it may therefore be removed upon publication as an RFC at the RFC Editor's discretion. 5. Security Considerations This note describes a tool for managing IPv4 and IPv6 network security. Like any tool, it has limitations and possible attacks. If discarding traffic under overload is a good thing, then holding and subsequently forwarding the traffic instead places a potential load on the network and the router in question, and as such represents a possible attack. Such an attack has obvious mitigations, however; one simply, in a manner the operator deems appropriate, selects a subset of the traffic to forward and discards the rest. In addition, this attack is not new; it is only changed in character. A stream that would instantiate the attack today results in a load of ARP or Neighbor Solicit messages that all listening hosts must intelligently discard. The new attack additionally consumes bandwidth that is presumably set aside specifically for that purpose. Baker, et al. Expires January 26, 2010 [Page 6] Internet-Draft IPv4 and IPv6 Greynets July 2009 The question of exactly what subset of traffic is interesting and economical to forward is intentionally left open. Key questions in algorithm design include what can be learned from a given sample (are bursts happening, and if so with what data?), what the impact on the router and other equipment in question is, how that might be mitigated, etc. Possible selection algorithms dependent only on state and algorithms typically available in a router include: o All datagrams triggering an ARP Request or Neighbor Solicit, o The subset of those that are not responded to within some stated interval and are therefore likely dark, o The subset of those that are new; if the address is currently being solicited, forwarding redundant data may not be useful. o All such datagrams up to some rate, o All such datagrams matching (or not matching) a specified filter rule, o etc. 6. Acknowledgements Algorithms for learning about Internet attack behavior by observing backscatter traffic have been used by CAIDA, University of Michigan, Team Cymru, and others. Harrop extended them in his research. This formulation of the notion originated in a discussion among the authors in 2005. This note grew out of a conversation with Paul Vixie and Rhette Marsh on Internet traffic sensors; they also made useful comments on it. Albert Manfredi commented on the distinction between a LAN (as defined by IEEE 802) and an IP subnet. Tim Chown [RFC5157] has observed that, at least at this time, address scanning attacks in IPv6 have not been reported in the wild. Rhette Marsh has suggested the structure of such an attack, however, and Fred Baker has suggested approaches based on addressing information exchanged by applications. Hence, we believe that such issues may be relevant to IPv6 in the future, when IPv6 is a more interesting target. 7. References Baker, et al. Expires January 26, 2010 [Page 7] Internet-Draft IPv4 and IPv6 Greynets July 2009 7.1. Normative References [Harrop] Harrop, W. and G. Armitage, "Greynets: a definition and evaluation of sparsely populated darknets", IEEE LCN IEEE 30th Conference on Local Computer Networks, 2005. [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981. [RFC0826] Plummer, D., "Ethernet Address Resolution Protocol: Or converting network protocol addresses to 48.bit Ethernet address for transmission on Ethernet hardware", STD 37, RFC 826, November 1982. [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998. [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, February 2006. [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, September 2007. [RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy Extensions for Stateless Address Autoconfiguration in IPv6", RFC 4941, September 2007. 7.2. Informative references [RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering: Defeating Denial of Service Attacks which employ IP Source Address Spoofing", BCP 38, RFC 2827, May 2000. [RFC5157] Chown, T., "IPv6 Implications for Network Scanning", RFC 5157, March 2008. Authors' Addresses Fred Baker Cisco Systems Santa Barbara, California 93117 USA Email: fred@cisco.com Baker, et al. Expires January 26, 2010 [Page 8] Internet-Draft IPv4 and IPv6 Greynets July 2009 Warren Harrop CAIA, Swinburne University of Technology Hawthorn, Victoria 3122 Australia Email: wazz@bud.cc.swin.edu.au Grenville Armitage CAIA, Swinburne University of Technology Hawthorn, Victoria 3122 Australia Email: garmitage@swin.edu.au Baker, et al. Expires January 26, 2010 [Page 9]