Internet Engineering Task Force (IETF)                          F. Baker
Request for Comments: 6018                                 Cisco Systems
Category: Informational                                        W. Harrop
ISSN: 2070-1721                                              G. Armitage
                                      Swinburne University of Technology
                                                          September 2010
Internet Engineering Task Force (IETF)                          F. Baker
Request for Comments: 6018                                 Cisco Systems
Category: Informational                                        W. Harrop
ISSN: 2070-1721                                              G. Armitage
                                      Swinburne University of Technology
                                                          September 2010

IPv4 and IPv6 Greynets

IPv4和IPv6 Greynets



This note discusses a feature to support building Greynets for IPv4 and IPv6.


Status of This Memo


This document is not an Internet Standards Track specification; it is published for informational purposes.


This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documents approved by the IESG are a candidate for any level of Internet Standard; see Section 2 of RFC 5741.

本文件是互联网工程任务组(IETF)的产品。它代表了IETF社区的共识。它已经接受了公众审查,并已被互联网工程指导小组(IESG)批准出版。并非IESG批准的所有文件都适用于任何级别的互联网标准;见RFC 5741第2节。

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at


Copyright Notice


Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved.

版权所有(c)2010 IETF信托基金和确定为文件作者的人员。版权所有。

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. 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.

本文件受BCP 78和IETF信托有关IETF文件的法律规定的约束(自本文件出版之日起生效。请仔细阅读这些文件,因为它们描述了您对本文件的权利和限制。从本文件中提取的代码组件必须包括信托法律条款第4.e节中所述的简化BSD许可证文本,并提供简化BSD许可证中所述的无担保。

Table of Contents


   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 2
     1.1.  History and Experience  . . . . . . . . . . . . . . . . . . 3
   2.  Deploying Greynets  . . . . . . . . . . . . . . . . . . . . . . 4
     2.1.  Deployment Using Routing - Darknets . . . . . . . . . . . . 4
     2.2.  Deployment Using Sparse Address Space - Greynets  . . . . . 4
     2.3.  Other Filters . . . . . . . . . . . . . . . . . . . . . . . 6
   3.  Implications for Router Design  . . . . . . . . . . . . . . . . 6
   4.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 7
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 8
     6.1.  Normative References  . . . . . . . . . . . . . . . . . . . 8
     6.2.  Informative References  . . . . . . . . . . . . . . . . . . 8
   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 2
     1.1.  History and Experience  . . . . . . . . . . . . . . . . . . 3
   2.  Deploying Greynets  . . . . . . . . . . . . . . . . . . . . . . 4
     2.1.  Deployment Using Routing - Darknets . . . . . . . . . . . . 4
     2.2.  Deployment Using Sparse Address Space - Greynets  . . . . . 4
     2.3.  Other Filters . . . . . . . . . . . . . . . . . . . . . . . 6
   3.  Implications for Router Design  . . . . . . . . . . . . . . . . 6
   4.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 7
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 8
     6.1.  Normative References  . . . . . . . . . . . . . . . . . . . 8
     6.2.  Informative References  . . . . . . . . . . . . . . . . . . 8
1. Introduction
1. 介绍

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).


Darknets, of course, have two problems. As their address spaces become known, attackers stop probing them, so they are less effective. Also, the administrators of those prefixes are pressured by Regional Internet Registry (RIR) policy and business requirements to deploy them in active networks.

当然,黑暗有两个问题。当它们的地址空间变得已知时,攻击者停止探测它们,因此它们的效率较低。此外,这些前缀的管理员受到区域Internet Registry(RIR)策略和业务需求的压力,必须将它们部署到活动网络中。

[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.


1.1. History and Experience
1.1. 历史和经验

The research supporting this proposal includes two prototypes, one with IPv4 [RFC0791] and one with IPv6 [RFC2460]. Both have limitations, being research experiments as opposed to deployment of a finished product.


The original research was done by Warren Harrop and documented in [Harrop]. This was IPv4-only. His premise was that one would put a virtual or physical machine on a LAN that one was not otherwise using, and use it to identify scans of various kinds. As reported in his paper, the concept worked effectively in a prototype deployment at the Centre for Advanced Internet Architectures (CAIA), Swinburne University of Technology. The basic reason was that there was a reasonable expectation on the part of a potential attacker that a given address might be represented, and there was no pattern that would enable the attacker to predict which addresses were being used in this way. CAIA developed and released a prototype FreeBSD-based Greynet system in 2008 built around this premise [Armitage].

最初的研究由Warren Harrop完成,并记录在[Harrop]中。这只是IPv4。他的前提是将虚拟机或物理机放在一个局域网上,然后用它来识别各种扫描。正如他的论文所报道的,这个概念在斯文本科技大学高级互联网架构(CAIA)中心的原型部署中有效地工作。基本原因是,潜在攻击者有一个合理的预期,即给定的地址可能会被表示,并且没有任何模式使攻击者能够预测以这种方式使用的地址。CAIA于2008年开发并发布了一个基于FreeBSD的Greynet原型系统,该系统就是围绕这个前提而构建的[Armitage]。

Baker's addition to his concept started from the router, the idea that the router would be highly likely to encounter any such scan if it came from off-LAN, and the fact that the router would have to use Address Resolution Protocol (ARP) or Neighbor Discovery (ND) to identify -- or fail to identify -- the machine in question. In effect, any address that is not currently instantiated in the subnet acts as a Greynet trigger address. This clearly also works for any system that would implement ARP or ND, but the router is an obvious focal point in any subnet.


Tim Chown, of the School of Electronics and Computer Science, University of Southampton, offered privately to do some research on it, and had Owen Stephens do a Linux prototype in spring 2010. They demonstrated that the technology was straightforward to implement and in fact worked in a prototype IPv6 implementation.

南安普敦大学电子与计算机科学学院的Tim Chown私下里为这项研究做了一些研究,并让Owen Stephens在2010春季做了一个Linux原型。他们证明了这项技术易于实现,事实上,它在IPv6原型实现中起到了作用。

The question that remains with IPv6 address scanning is the likelihood that the attack would occur at all. Chown originally argued in [RFC5157] that address scans were impossible due to the sheer number of possibilities. However, in September 2010 a report was made to NANOG of an IPv6 address scan. Additionally, there are ways to limit the field; for example, one can observe that a company buys a certain kind of machine or network interface card (NIC), and


therefore its probable EUI-64 addresses are limited to a much smaller range than 2^64 -- more like 2^24 addresses on a given subnet -- or one can observe DNS, SMTP envelopes, Extensible Messaging and Presence Protocol (XMPP) messages, FTP, HTTP, etc., that carry IP addresses in other ways. Such attacks can be limited by the use of Privacy Addresses [RFC4941], which periodically change, rendering historical information less useful, but the fact is that such analytic methods exist.


2. Deploying Greynets
2. 部署Greynets

Corporate IT departments and other network operators frequently run collectors or other kinds of sensors. A collector is a computer 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 (honeypots).


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
2.1. 使用路由暗网进行部署

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 Sparse Address Space - Greynets
2.2. 使用稀疏地址空间的部署-Greynets

IPv4 subnets usually have some unallocated space in them, if only because Classless Inter-Domain Routing (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 an IP prefix.


Routers use IPv4 ARP [RFC0826] and IPv6 Neighbor Discovery [RFC4861] to determine the MAC (Media Access Control) address of a neighbor to which a datagram needs to be sent. Both specifications intend that when a datagram arrives at a router that serves the target prefix, but that doesn't know the MAC address of the intended destination, it should:

路由器使用IPv4 ARP[RFC0826]和IPv6邻居发现[RFC4861]来确定需要向其发送数据报的邻居的MAC(媒体访问控制)地址。这两个规范都打算,当数据报到达为目标前缀服务的路由器,但不知道目标的MAC地址时,它应该:

o Enqueue the datagram,

o 将数据报排队,

o Emit a Neighbor Solicitation or ARP Request,

o 发出邻居请求或ARP请求,

o Await a Neighbor Advertisement or ARP Response, and

o 等待邻居广告或ARP响应,以及

o On receipt, dequeue and forward the datagram.

o 收到数据报后,退出队列并转发数据报。

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 behavior 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, UDP, or other encapsulation, or in fact any place such a datagram could be handled. Depending on the requirements of the receiving collector, one could also imagine summarizing information in a form similar to IP Flow Information Export (IPFIX) [RFC5101] [RFC5610].


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 neighbor 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 choose 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.


One implication of this model is that distributed denial-of-service (DDoS) attacks terminate on router subnets within a network, as opposed to stopping on inter-router links.


2.3. Other Filters
2.3. 其他过滤器

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 that fail a unicast Reverse Path Forwarding (uRPF) check [RFC2827] to the collector via the same tunnel.


3. Implications for Router Design
3. 路由器设计的启示

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 to an analytic system the 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.

路由器设计的含义适用于IPv4 ARP和IPv6邻居发现算法。在配置控制下,将触发ARP请求或邻居请求的到达数据报转发给分析系统,然后无法接收到接口、电路、VLAN或隧道的预期响应,这可能很有趣。

4. Security Considerations
4. 安全考虑

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 selects (in a manner the operator deems appropriate) 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.


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? 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 Select all datagrams that trigger an ARP Request or Neighbor Solicit.

o 选择触发ARP请求或邻居请求的所有数据报。

o Select the subset of those that are not responded to within some stated interval and are therefore likely dark.

o 选择那些在规定的时间间隔内没有响应的,因此可能是黑暗的子集。

o Select the subset of those that are new; if the address is currently being solicited, forwarding redundant data may not be useful.

o 选择新的子集;如果当前正在请求地址,转发冗余数据可能没有用。

o Select all datagrams up to some rate.

o 选择高达某个速率的所有数据报。

o Select all datagrams matching (or not matching) a specified filter rule.

o 选择与指定筛选规则匹配(或不匹配)的所有数据报。

5. Acknowledgements
5. 致谢

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.

CAEDA,密歇根大学,团队CYMRU和其他人已经使用了通过观察反向散射业务来学习互联网攻击行为的算法。哈洛普在他的研究中扩展了它们。这一概念的表述起源于2005年作者之间的讨论。这张便条出自与Paul Vixie和Rhette Marsh关于互联网流量传感器的对话;他们还就此发表了有益的评论。Albert Manfredi评论了LAN(由IEEE 802定义)和IP子网之间的区别。

Tim Chown [RFC5157] has observed that, at least at the time of writing that RFC, address scanning attacks in IPv6 have not been reported in the wild. However, as mentioned in Section 1.1 above, a (partial) scanning attack was recently reported on the NANOG mailing list. Rhette Marsh has suggested the structure of such an attack, however, and Fred Baker has suggested approaches based on addressing

Tim Chown[RFC5157]观察到,至少在撰写本文时,IPv6中的RFC、地址扫描攻击尚未在野外报告。然而,如上文第1.1节所述,NANOG邮件列表最近报告了一次(部分)扫描攻击。然而,Rhette Marsh提出了这种攻击的结构,Fred Baker提出了基于寻址的方法

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.


Tim Chown and Owen Stephens tested the proposal, and made useful comments that have been incorporated in this text. His fundamental comment was, however, that "it works".

蒂姆·乔恩(Tim Chown)和欧文·斯蒂芬斯(Owen Stephens)对提案进行了测试,并提出了有用的意见,这些意见已纳入本文。然而,他的基本评论是“它有效”。

6. References
6. 工具书类
6.1. Normative References
6.1. 规范性引用文件

[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.

[Harrop]Harrop,W.和G.Armitage,“Greynets:人烟稀少的黑暗地带的定义和评估”,IEEE LCN IEEE第30届本地计算机网络会议,2005年。

[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981.

[RFC0791]Postel,J.,“互联网协议”,STD 5,RFC 7911981年9月。

[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.

[RFC0826]Plummer,D.,“以太网地址解析协议:或将网络协议地址转换为48位以太网地址,以便在以太网硬件上传输”,STD 37,RFC 826,1982年11月。

[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998.

[RFC2460]Deering,S.和R.Hinden,“互联网协议,第6版(IPv6)规范”,RFC 2460,1998年12月。

[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, February 2006.

[RFC4291]Hinden,R.和S.Deering,“IP版本6寻址体系结构”,RFC 42912006年2月。

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

[RFC4861]Narten,T.,Nordmark,E.,Simpson,W.,和H.Soliman,“IP版本6(IPv6)的邻居发现”,RFC 48612007年9月。

[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy Extensions for Stateless Address Autoconfiguration in IPv6", RFC 4941, September 2007.

[RFC4941]Narten,T.,Draves,R.,和S.Krishnan,“IPv6中无状态地址自动配置的隐私扩展”,RFC 49412007年9月。

6.2. Informative References
6.2. 资料性引用

[Armitage] Armitage, G., Harrop, W., Heyde, A., Parry, L., "Greynets: Passive Detection of Unsolicited Network Scans in Small ISP and Enterprise networks", CAIA, Swinburne University of Technology, December 2008,


[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.

[RFC2827]Ferguson,P.和D.Senie,“网络入口过滤:击败利用IP源地址欺骗的拒绝服务攻击”,BCP 38,RFC 2827,2000年5月。

[RFC5101] Claise, B., "Specification of the IP Flow Information Export (IPFIX) Protocol for the Exchange of IP Traffic Flow Information", RFC 5101, January 2008.

[RFC5101]Claise,B.,“用于交换IP流量信息的IP流量信息导出(IPFIX)协议规范”,RFC 5101,2008年1月。

[RFC5157] Chown, T., "IPv6 Implications for Network Scanning", RFC 5157, March 2008.

[RFC5157]Chown,T.,“IPv6对网络扫描的影响”,RFC 5157,2008年3月。

[RFC5610] Boschi, E., Trammell, B., Mark, L., and T. Zseby, "Exporting Type Information for IP Flow Information Export (IPFIX) Information Elements", RFC 5610, July 2009.

[RFC5610]Boschi,E.,Trammell,B.,Mark,L.,和T.Zseby,“为IP流信息导出(IPFIX)信息元素导出类型信息”,RFC 56102009年7月。

Authors' Addresses


Fred Baker Cisco Systems Santa Barbara, California 93117 USA



Warren Harrop Centre for Advanced Internet Architectures Swinburne University of Technology PO Box 218 John Street, Hawthorn, Victoria, 3122 Australia



Grenville Armitage Centre for Advanced Internet Architectures Swinburne University of Technology PO Box 218 John Street, Hawthorn, Victoria, 3122 Australia