OPSEC D. Dugal Internet-Draft Juniper Networks Intended status: Informational C. Pignataro Expires: December 31, 2010 R. Dunn Cisco Systems June 29, 2010 Protecting The Router Control Plane draft-ietf-opsec-protect-control-plane-00 Abstract This memo provides a method for protecting a router's control plane from undesired or malicious traffic. In this approach, all legitimate router control plane traffic is identified. Once legitimate traffic has been identified, a filter is deployed in the router's forwarding plane. That filter prevents traffic not specifically identified as legitimate from reaching the router's control plane or rate limited to an acceptable level. 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 December 31, 2010. Copyright Notice Copyright (c) 2010 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 Dugal, et al. Expires December 31, 2010 [Page 1] Internet-Draft Protect Router Control Plane June 2010 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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Applicability Statement . . . . . . . . . . . . . . . . . . . 4 3. Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.1. Legitimate Traffic . . . . . . . . . . . . . . . . . . . . 4 3.2. Filter Design . . . . . . . . . . . . . . . . . . . . . . 5 3.3. Design Trade-offs . . . . . . . . . . . . . . . . . . . . 6 4. Security Considerations . . . . . . . . . . . . . . . . . . . 8 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9 7. Informative References . . . . . . . . . . . . . . . . . . . . 9 Appendix A. Cisco Configuration . . . . . . . . . . . . . . . . . 10 Appendix B. Juniper Configuration . . . . . . . . . . . . . . . . 12 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16 Dugal, et al. Expires December 31, 2010 [Page 2] Internet-Draft Protect Router Control Plane June 2010 1. Introduction Modern router architecture design maintains a strict separation of forwarding and routing control plane hardware and software. The router control plane supports routing and management functions, and is generally described as router architecture hardware and software components for handling packets destined to the device itself as well as building and sending packets originated locally on the device. Forwarding plane is typically described as router architecture hardware and software components responsible for taking a packet coming in one interface, performing a lookup to identify the packet's IP next hop and determine the outgoing interface towards the destination, and forwarding the packet through the correct outgoing interface. Visually it can be represented as the router's control plane hardware sitting on top of and interfacing with the forwarding plane hardware, with interfaces connecting to other network devices. See Figure 1. +----------------+ | Router Control | | Plane | +------+ +-------+ | | Router Control Plane Protection | | +------+ +-------+ | Forwarding | Interface X ==[ Plane ]== Interface Y +----------------+ Figure 1: Router Control Plane Protection Typically, forwarding plane functionality is realized in high- performance Application Specific Integrated Circuits (ASICs) that are capable of handling very high packet rates. By contrast, the router control plane is generally realized in software on general purpose processors. While software instructions run on both planes, the router control plane software is usually not optimized for high speed packet handling. Given their differences in packet handling capabilities, the router's control plane hardware is more susceptible to be overwhelmed by a DoS attack than forwarding plane ASICs. It is imperative that the router control plane remain stable regardless of traffic load to and from the device because the router control plane is what drives the programming of the forwarding plane. The router control plane processes traffic destined to the router, Dugal, et al. Expires December 31, 2010 [Page 3] Internet-Draft Protect Router Control Plane June 2010 and because of the wider range of functionality is more susceptible to security vulnerabilities and a more likely target for a DoS attack than the forwarding plane. It is advisable to protect the router control plane by implementing mechanisms to filter completely or rate limit traffic not required at the control plane level (i.e., unwanted traffic). Router Control Plane Protection is the concept of filtering or rate limiting unwanted traffic which would be diverted out of the forwarding plane up to the router control plane. The closer to the forwarding plane and line-rate hardware the filters and rate-limiters are, the more effective the protection is and the more resistant the system is to DoS attacks. This memo demonstrates how to deploy an example policy filter that satisfies a set of example traffic matching, filtering and rate limiting criteria.. 2. Applicability Statement The method described in Section 3 and depicted in Figure 1 illustrates how to protect the router control plane from unwanted traffic. Recognizing that deployment scenarios will vary, the exact implementation is not generally applicable in all situations. The categorization of legitimate router control plane traffic is critically important in a successful implementation. The examples given in this memo are simplified and minimalistic, designed to illustrate the concept of protecting the router's control plane. From them, operators can extrapolate specifics based on their unique configuration and environment. This method is applicable for IPv4 as well as IPv6 address families. 3. Method In this memo, the authors demonstrate how a filter protecting the router control plane can be deployed. In Section 3.1, a sample router is introduced and all traffic that its control plane must process is identified. In Section 3.2, filter design concepts are discussed. Cisco (Cisco IOS software) and Juniper (JUNOS) implementations are provided in Appendices A and B, respectively. 3.1. Legitimate Traffic In this example, the router control plane must process traffic per the following criteria: Dugal, et al. Expires December 31, 2010 [Page 4] Internet-Draft Protect Router Control Plane June 2010 o Drop all IP packets that are fragments o Permit ICMP traffic from any source, rate-limited to 500 kbps o Permit OSPF traffic from routers within the local network (192.0.2.0/24) o Permit iBGP traffic from routers within the local network (192.0.2.0/24) o Permit eBGP traffic from known eBGP peers (198.51.100.25, 198.51.100.27, 198.51.100.29, and 198.51.100.31) o Permit DNS traffic from local DNS resolvers (198.51.100.0/30) o Permit NTP traffic from local NTP servers (198.51.100.4/30) o Permit SSH traffic from network management stations (198.51.100.128/25) o Permit SNMP traffic from network management stations (198.51.100.128/25) o Permit RADIUS authentication and accounting replies from RADIUS servers (198.51.100.9 and 198.51.100.10) that are listening on UDP ports 1645 and 1646. Note that this doesn't account for a server using Internet Assigned Numbers Authority (IANA) ports 1812 and 1813 for RADIUS. o Permit all other IP traffic that was not explicitly matched in a class above, rate-limited to 500 kbps, and drop above that rate o Permit non-IP traffic, rate-limited to rate of 250 kbps, and drop all remaining traffic above that rate The characteristics of legitimate traffic will vary from network to network. The list provided above is for example only. 3.2. Filter Design A filter is installed on the forwarding plane. This filter counts and applies the actions to the categories of traffic described in Section 3.1. Because the filter is enforced in the forwarding plane, it prevents traffic from consuming bandwidth on the interface that connects the forwarding plane to the router control plane. The counters serve as an important forensic tool for the analysis of potential attacks, and as an invaluable debugging and troubleshooting aid. By adjusting the granularity and order of the filters more Dugal, et al. Expires December 31, 2010 [Page 5] Internet-Draft Protect Router Control Plane June 2010 granular forensics can be performed (i.e., create a filter that matches only on traffic allowed from a group of IP addresses for a given protocol followed by a filter that denies all traffic for that protocol). This would allow for counters to be monitored for the allowed protocol filter as well as any traffic matching traffic for the specific protocol that didn't originate from the explicitly allowed hosts. In addition to the filters, rate-limiters for certain classes of traffic are also installed in the forwarding plane as defined in Section 3.1. These rate limiters help futher control the traffic that will reach the control plane for each filtered class as well as all traffic not matching an explicit class. The actual rates selected for various classes is network deployment specific and analysis of required rates for stability should be done periodically. Syntactically, these filters explicitly define "allowed" traffic (including IP addresses, protocols, and ports), define acceptable actions for these acceptable traffic profiles (e.g., rate-limit or simply permit the traffic), and then drop to the bit bucket all traffic destined to the router control plane that is not within the specifications of the policy definition. In an actual production environment, predicting a complete and exhaustive list of traffic necessary to reach the router's control plane for day-to-day operation may not be this obvious. One recommended method to gauge this set of traffic is to allow all traffic initially, and audit what hits the router control plane before applying any explicit filters or rate limits. See the Section 3.3 section below for more discussion of this topic. The filter design provided in this document is intentionally limited to attachment at the local router in question (e.g., a 'service- policy' attached to the 'control-plane' in Cisco IOS, or a firewall filter attached to the 'lo0' interface in JUNOS). While virtually all production environments utilize and rely heavily upon edge protection or interface filtering, these methods of router protection are beyond the intended scope of this document. Additionally, the protocols themselves that are allowed to reach the control plane (e.g., OSPF, RSVP, TCP, SNMP, DNS, NTP, and inherently, SSH, TLS, ESP, etc.) may have cryptographic security methods applied to them, and the method of router control plane protection herein provided is not a replacement for these cryptographic methods. 3.3. Design Trade-offs In designing the protection method, there are two independent parts to consider: the classification of traffic (i.e., which traffic is Dugal, et al. Expires December 31, 2010 [Page 6] Internet-Draft Protect Router Control Plane June 2010 matched by the filters), and the policy actions taken on the classified traffic. There are different levels of granularity utilized for traffic classification. For example, allowing all traffic from specific source IP addresses versus allowing only a specific set of protocols from those specific source IP addresses will each affect a different set of traffic. Similarly, the policy actions taken on the classified traffic have degrees of impact that may not become immediately obvious. For example, discarding all ICMP traffic may have a negative impact on the operational use of ICMP tools such as ping or traceroute to debug network issues or to test turn up of a new circuit. Expanding on this, in a real production network, an astute operator could define varying rate limits for ICMP such that internal traffic is granted uninhibited access to the router control plane, while traffic from external addresses is rate limited. It is important to note that both classification and policy action decisions are accompanied by respective trade-offs. Two examples of these trade-off decisions are, operational complexity at the expense of policy (and statistics gathering) detail, and tighter protection at the expense of network supportability and troubleshooting ability. Two types of traffic that need special consideration are IP fragments and IP optioned packets. For network deployments where IP fragmentation is necessary, a blanket policy of dropping all fragments may not be possible. However, many deployments allow network configurations such that the router control plane should never see a fragmented datagram. Since many attacks rely on ip fragmentation the example policy referenced here drops all fragments. Similarly, some deployments may chose to drop all IP Optioned Packets. Others may need to losen the constraint to allow for protocols that require IP Optioned packets such as RSVP. The goal of the method for protecting the router control plane is to minimize potential disruptions. The granularity of the filter design inversely correlates to the scope of the potential disruption. The finer the granularity of the filter design (e.g., isolating a more targeted subset of traffic from the rest of the policed traffic, or isolating valid source addresses into a different class or classes) the smaller the scope of disruption. Additionally, the baselining and monitoring of traffic flows to the router's control plane are critical in determining both the rates and granularity of the policies being applied. This is important to validate the existing policies and rules or update them as the Dugal, et al. Expires December 31, 2010 [Page 7] Internet-Draft Protect Router Control Plane June 2010 network evolves and its traffic dynamics change. Some possible ways to achieve this include individual policy counters that can be exported or retrieved for example via SNMP, and logging of filtering actions. Finally, the use of flow-based behavioral analysis or CLI functions to identify what client/server functions a given router's control plane handles would be very useful during initial policy development phases, and certainly for forensic analysis afterwards. 4. Security Considerations The filter above leaves the router susceptible to discovery from any host on the Internet. If network operators find this risk objectionable, they can mitigate it by restricting the sub-networks from which ICMP Echo requests or traceroute packets are accepted. Moreover, different rate-limiting policies may be defined for internally (e.g., from the NOC) versus externally sourced traffic. The filter above also leaves the router exposed to port scans from hosts spoofing the source addresses found in Section 3.1. Network operators can mitigate this risk by preventing source address spoofing with filters applied at the network edge. Refer to Section 5.3.8 of [RFC1812] for more information regarding source address validation. Other methods also exist for limiting exposure to packet spoofing such as the Generalized TTL Security Mechanism (GTSM) [RFC5082] and Ingress Filtering [RFC2827] [RFC3704]. The ICMP rate limiter specified in this filter protects the router from floods of ICMP traffic. However, during an ICMP flood, some legitimate ICMP traffic may be dropped. Because of this, when operators discover a flood of ICMP traffic, they are highly motivated to cut it off at its source. Additional considerations pertaining to the usage and handling of traffic that utilizes the IP Router Alert Options can be found at [I-D.ietf-intarea-router-alert-considerations], and additional IP Options filtering explanations can be found at [I-D.gont-opsec-ip-options-filtering]. The treatment of exception traffic in the forwarding plane, and the generation of specific messages by the router control plane also requires protection from a DoS attack. Specifically, the generation of ICMP Unreachable messages by the router control plane needs to be rate-limited, either implicitly within the router's architecture or explicitly through configuration. See Section 4.3.2.8 of [RFC1812]. Dugal, et al. Expires December 31, 2010 [Page 8] Internet-Draft Protect Router Control Plane June 2010 Additionally, the handling of TTL / Hop Limit expired traffic needs protection. This traffic is not necessarily addressed to the device, but it can get sent to the control plane to process the TTL / Hop Limit expiration. For example, rate limiting the TTL / Hop Limit expired traffic before sending the packets to the router control plane component that will generate the ICMP error, and distributing the sending of ICMP errors to Line Card CPUs are protection mechanisms that mitigate attacks before they can negatively affect a rate-limited router control plane component. 5. IANA Considerations [RFC Editor: please remove this section prior to publication.] This document has no IANA actions. 6. Acknowledgements The authors would like to thank Ron Bonica for providing initial and ongoing review, suggestions, and valuable input. Pekka Savola, Warren Kumari, and Xu Chen provided very thorough and useful feedback that improved the document. Many thanks to John Kristoff, Christopher Morrow, and Donald Smith for a fruitful discussion around the operational and manageability aspects of router control plane protection techniques. The authors would also like to thank Joel Jaeggli, Richard Graveman, Danny McPherson, Gregg Schudel, and Eddie Parra for providing thorough review, useful suggestions, and valuable input. 7. Informative References [I-D.gont-opsec-ip-options-filtering] Gont, F. and S. Fouant, "IP Options Filtering Recommendations", draft-gont-opsec-ip-options-filtering-00 (work in progress), March 2010. [I-D.ietf-intarea-router-alert-considerations] Faucheur, F., "IP Router Alert Considerations and Usage", draft-ietf-intarea-router-alert-considerations-00 (work in progress), March 2010. [RFC1812] Baker, F., "Requirements for IP Version 4 Routers", RFC 1812, June 1995. [RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering: Dugal, et al. Expires December 31, 2010 [Page 9] Internet-Draft Protect Router Control Plane June 2010 Defeating Denial of Service Attacks which employ IP Source Address Spoofing", BCP 38, RFC 2827, May 2000. [RFC3704] Baker, F. and P. Savola, "Ingress Filtering for Multihomed Networks", BCP 84, RFC 3704, March 2004. [RFC5082] Gill, V., Heasley, J., Meyer, D., Savola, P., and C. Pignataro, "The Generalized TTL Security Mechanism (GTSM)", RFC 5082, October 2007. Appendix A. Cisco Configuration !Start: Protecting The Router Control Plane ! !Policy-map Configuration ! !Access-list Definitions ip access-list extended ICMP permit icmp any any ip access-list extended OSPF permit ospf 192.0.2.0 0.0.0.255 any ip access-list extended IBGP permit tcp 192.0.2.0 0.0.0.255 eq bgp any permit tcp 192.0.2.0 0.0.0.255 any eq bgp ip access-list extended EBGP permit tcp host 198.51.100.25 eq bgp any permit tcp host 198.51.100.25 any eq bgp permit tcp host 198.51.100.27 eq bgp any permit tcp host 198.51.100.27 any eq bgp permit tcp host 198.51.100.29 eq bgp any permit tcp host 198.51.100.29 any eq bgp permit tcp host 198.51.100.31 eq bgp any permit tcp host 198.51.100.31 any eq bgp ip access-list extended DNS permit udp 198.51.100.0 0.0.0.252 eq domain any ip access-list extended NTP permit udp 198.51.100.4 255.255.255.252 any eq ntp ip access-list extended SSH permit tcp 198.51.100.0 0.0.0.128 any eq 22 ip access-list extended SNMP permit udp 198.51.100.128 0.0.0.125 any eq snmp ip access-list extended RADIUS permit udp host 198.51.100.9 eq 1645 any permit udp host 198.51.100.9 eq 1646 any permit udp host 198.51.100.10 eq 1645 any permit udp host 198.51.100.10 eq 1646 any Dugal, et al. Expires December 31, 2010 [Page 10] Internet-Draft Protect Router Control Plane June 2010 ip access-list extended FRAGMENTS permit ip any any fragments ip access-list extended ALLOTHERIP permit ip any any ! !Class Definitions ! class-map match-all ICMP match access-group name ICMP class-map match-all OSPF match access-group name OSPF class-map match-all IBGP match access-group name IBGP class-map match-all EBGP match access-group name EBGP class-map match-all DNS match access-group name DNS class-map match-all NTP match access-group name NTP class-map match-all SSH match access-group name SSH class-map match-all SNMP match access-group name SNMP class-map match-all RADIUS match access-group name RADIUS class-map match-all FRAGMENTS match access-group name FRAGMENTS class match-all ALLOTHERIP match access-group name ALLOTHERIP ! !Policy Definition ! policy-map COPP class FRAGMENTS drop class ICMP police 500000 class OSPF class IBGP class EBGP class DNS class NTP class SSH class SNMP class RADIUS class ALLOTHERIP police cir 500000 conform-action transmit Dugal, et al. Expires December 31, 2010 [Page 11] Internet-Draft Protect Router Control Plane June 2010 exceed-action drop violate-action drop class class-default police cir 250000 conform-action transmit exceed-action drop violate-action drop ! !Control Plane Configuration ! control-plane service-policy input COPP ! !End: Protecting The Router Control Plane Appendix B. Juniper Configuration policy-options { prefix-list IBGP-NEIGHBORS { 192.0.2.0/24; } prefix-list EBGP-NEIGHBORS { 198.51.100.25/32; 198.51.100.27/32; 198.51.100.29/32; 198.51.100.31/32; } prefix-list RADIUS-SERVERS { 198.51.100.9/32; 198.51.100.10/32; } } firewall { policer 500kbps { if-exceeding { bandwidth-limit 500k; burst-size-limit 1500; } then discard; } policer 250kbps { if-exceeding { bandwidth-limit 250k; burst-size-limit 1500; } then discard; Dugal, et al. Expires December 31, 2010 [Page 12] Internet-Draft Protect Router Control Plane June 2010 } family inet { filter protect-router-control-plane { term first-frag { from { first-fragment; } then { count frag-discards; log; discard; } } term next-frag { from { is-fragment; } then { count frag-discards; log; discard; } } term icmp { from { protocol icmp; } then { policer 500kbps; accept; } } term ospf { from { source-address { 192.0.2.0/24; } protocol ospf; } then accept; } term ibgp-connect { from { source-prefix-list { IBGP-NEIGHBORS; } protocol tcp; destination-port bgp; Dugal, et al. Expires December 31, 2010 [Page 13] Internet-Draft Protect Router Control Plane June 2010 } then accept; } term ibgp-reply { from { source-prefix-list { IBGP-NEIGHBORS; } protocol tcp; port bgp; } then accept; } term ebgp-connect { from { source-prefix-list { EBGP-NEIGHBORS; } protocol tcp; destination-port bgp; } then accept; } term ebgp-reply { from { source-prefix-list { EBGP-NEIGHBORS; } protocol tcp; port bgp; } then accept; } term dns { from { source-address { 198.51.100.0/30; } protocol udp; port domain; } then accept; } term ntp { from { source-address { 198.51.100.4/30; } Dugal, et al. Expires December 31, 2010 [Page 14] Internet-Draft Protect Router Control Plane June 2010 protocol udp; destination-port ntp; } then accept; } term ssh { from { source-address { 198.51.100.128/25; } protocol tcp; destination-port ssh; } then accept; } term snmp { from { source-address { 198.51.100.128/25; } protocol udp; destination-port snmp; } then accept; } term radius { from { source-prefix-list { RADIUS-SERVERS; } protocol udp; port [1645 1646]; } then accept; } term default-term { then { count copp-exceptions; log; policer 500kbps; accept; } } } } family any { filter protect-router-control-plane-non-ip { term rate-limit-non-ip { Dugal, et al. Expires December 31, 2010 [Page 15] Internet-Draft Protect Router Control Plane June 2010 then { policer 250kbps; accept; } } } } } interfaces { lo0 { unit 0 { family inet { filter input protect-router-control-plane; } family any { filter input protect-router-control-plane-non-ip; } } } } Authors' Addresses David Dugal Juniper Networks 10 Technology Park Drive Westford, MA 01886 US Email: ddugal@juniper.net Carlos Pignataro Cisco Systems 7200-12 Kit Creek Road Research Triangle Park, NC 27709 US Email: cpignata@cisco.com Dugal, et al. Expires December 31, 2010 [Page 16] Internet-Draft Protect Router Control Plane June 2010 Rodney Dunn Cisco Systems 7200-12 Kit Creek Road Research Triangle Park, NC 27709 US Email: rodunn@cisco.com Dugal, et al. Expires December 31, 2010 [Page 17]