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Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) No issues found here. Summary: 0 errors (**), 0 flaws (~~), 2 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 PCP working group S. Kiesel 3 Internet-Draft University of Stuttgart 4 Intended status: Standards Track R. Penno 5 Expires: April 8, 2016 Cisco Systems, Inc. 6 S. Cheshire 7 Apple 8 October 6, 2015 10 Port Control Protocol (PCP) Anycast Addresses 11 draft-ietf-pcp-anycast-08 13 Abstract 15 The Port Control Protocol (PCP) Anycast Addresses enable PCP clients 16 to transmit signaling messages to their closest PCP-aware on-path 17 NAT, Firewall, or other middlebox, without having to learn the IP 18 address of that middlebox via some external channel. This document 19 establishes one well-known IPv4 address and one well-known IPv6 20 address to be used as PCP Anycast Addresses. 22 Status of this Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current Internet- 30 Drafts is at http://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 This Internet-Draft will expire on April 8, 2016. 39 Copyright Notice 41 Copyright (c) 2015 IETF Trust and the persons identified as the 42 document authors. All rights reserved. 44 This document is subject to BCP 78 and the IETF Trust's Legal 45 Provisions Relating to IETF Documents 46 (http://trustee.ietf.org/license-info) in effect on the date of 47 publication of this document. Please review these documents 48 carefully, as they describe your rights and restrictions with respect 49 to this document. Code Components extracted from this document must 50 include Simplified BSD License text as described in Section 4.e of 51 the Trust Legal Provisions and are provided without warranty as 52 described in the Simplified BSD License. 54 Table of Contents 56 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 57 2. PCP Server Discovery based on well-known IP Address . . . . . 4 58 2.1. PCP Discovery Client behavior . . . . . . . . . . . . . . 4 59 2.2. PCP Discovery Server behavior . . . . . . . . . . . . . . 4 60 3. Deployment Considerations . . . . . . . . . . . . . . . . . . 5 61 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 62 4.1. Registration of IPv4 Special Purpose Address . . . . . . . 6 63 4.2. Registration of IPv6 Special Purpose Address . . . . . . . 6 64 5. Security Considerations . . . . . . . . . . . . . . . . . . . 7 65 5.1. Information Leakage through Anycast . . . . . . . . . . . 7 66 5.2. Hijacking of PCP Messages sent to Anycast Addresses . . . 7 67 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9 68 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 69 7.1. Normative References . . . . . . . . . . . . . . . . . . . 10 70 7.2. Informative References . . . . . . . . . . . . . . . . . . 10 71 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11 73 1. Introduction 75 The Port Control Protocol (PCP) [RFC6887] provides a mechanism to 76 control how incoming packets are forwarded by upstream devices such 77 as Network Address Translator IPv6/IPv4 (NAT64), Network Address 78 Translator IPv4/IPv4 (NAT44), and IPv6 and IPv4 firewall devices. 79 Furthermore, it provides a mechanism to reduce application keep alive 80 traffic [I-D.ietf-pcp-optimize-keepalives]. The PCP base protocol 81 document [RFC6887] specifies the message formats used, but the 82 address to which a client sends its request is either assumed to be 83 the default router (which is appropriate in a typical single-link 84 residential network) or has to be configured otherwise via some 85 external mechanism, such as a configuration file or a DHCP option 86 [RFC7291]. 88 This document follows a different approach: it establishes two well- 89 known anycast addresses for the PCP Server, one IPv4 address and one 90 IPv6 address. PCP clients usually send PCP requests to these well- 91 known addresses if no other PCP server addresses are known or after 92 communication attempts to such other addresses have failed. The 93 anycast addresses are allocated from pools of special-purpose IP 94 addresses (see Section 4), in accordance with Section 3.4 of 95 [RFC4085]. Yet, a means to disable or override these well-known 96 addresses (e. g., a configuration file option) should be available in 97 implementations. 99 Using an anycast address is particularly useful in larger network 100 topologies. For example, if the PCP-enabled NAT/firewall function is 101 not located on the client's default gateway, but further upstream in 102 a Carrier-grade NAT (CGN), sending PCP requests to the default 103 gateway's IP address will not have the desired effect. When using a 104 configuration file or the DHCP option to learn the PCP server's IP 105 address, this file or the DHCP server configuration must reflect the 106 network topology, and the router and CGN configuration. This may be 107 cumbersome to achieve and maintain. If there is more than one 108 upstream CGN and traffic is routed using a dynamic routing protocol 109 such as OSPF, this approach may not be feasible at all, as it cannot 110 provide timely information on which CGN to interact with. In 111 contrast, when using the PCP anycast address, the PCP request will 112 travel through the network like any other packet, without any special 113 support from DNS, DHCP, other routers, or anything else, until it 114 reaches the PCP-capable device, which receives it, handles it, and 115 sends back a reply. A further advantage of using an anycast address 116 instead of a DHCP option is, that the anycast address can be hard- 117 coded into the application. There is no need for an application 118 programming interface for passing the PCP server's address from the 119 operating system's DHCP client to the application. For further 120 discussion of deployment considerations see Section 3. 122 2. PCP Server Discovery based on well-known IP Address 124 2.1. PCP Discovery Client behavior 126 PCP clients can add the PCP anycast addresses, which are defined in 127 Sections 4.1 and 4.2, after the default router list (for IPv4 and 128 IPv6) to the list of PCP server(s) (see Section 8.1, step 2. of 129 [RFC6887]). This list is processed as specified in [RFC7488]. 131 Note: If, in some specific scenario, it was desirable to use only the 132 anycast address (and not the default router), this could be achieved 133 by putting the anycast address into the configuration file, or DHCP 134 option, etc. 136 2.2. PCP Discovery Server behavior 138 PCP Servers can be configured to listen on the anycast addresses for 139 incoming PCP requests. When a PCP server receives a PCP requests 140 destined for an anycast address it supports, it sends the 141 corresponding PCP replies using that same anycast address as the 142 source address (see Page 6 of [RFC1546] for further discussion). 144 3. Deployment Considerations 146 For general recommendations regarding operation of anycast services 147 see [RFC4786]. Architectural considerations of IP anycast are 148 discussed in [RFC7094]. 150 In some deployment scenarios, using PCP anycasting may have certain 151 limitations, which can be overcome by using additional mechanisms or 152 by using other PCP server discovery methods instead, such as DHCP 153 [RFC7291] or a configuration file. 155 One important example is a network topology, in which a network is 156 connected to one or more upstream network(s) via several parallel 157 firewalls, each individually controlled by its own PCP server. Even 158 if all of these PCP servers are configured for anycasting, only one 159 will receive the messages sent by a given client, depending on the 160 state of the routing tables. 162 As long as routing is always symmetric, i.e., all upstream and 163 downstream packets from/to that client are routed through this very 164 same firewall, communication will be possible as expected. If there 165 is a routing change, a PCP client using PCP anycasting might start 166 interacting with a different PCP server. From the PCP client's point 167 of view this would be the same as a PCP server reboot and the client 168 could detect it by examining the Epoch field during the next PCP 169 response or ANNOUNCE message. The client would re-establish the 170 firewall rules and packet flows could resume. 172 If, however, routing is asymmetric, upstream packets from a client 173 traverse a different firewall than the downstream packets to that 174 client. Establishing policy rules in only one of these two firewalls 175 by means of PCP anycasting will not have the desired result of 176 allowing bi-directional connectivity. One solution approach to 177 overcome this problem is an implementation-specific mechanism to 178 synchronize state between all firewalls at the border of a network, 179 i.e., a PEER message sent to any of these PCP servers would establish 180 rules in all firewalls. Another approach would be to use a different 181 discovery mechanism (e.g., DHCP or a configuration file) that allows 182 a PCP client to acquire a list of all PCP servers controlling the 183 parallel firewalls and configure each of them individually. 185 4. IANA Considerations 187 4.1. Registration of IPv4 Special Purpose Address 189 IANA is requested to assign a single IPv4 address from the 190 192.0.0.0/24 prefix and register it in the IANA IPv4 Special-Purpose 191 Address Registry [RFC6890]. 193 +----------------------+-------------------------------------------+ 194 | Attribute | Value | 195 +----------------------+-------------------------------------------+ 196 | Address Block | 192.0.0.???/32 (??? = TBD by IANA) | 197 | Name | Port Control Protocol Anycast | 198 | RFC | This document, if approved (TBD) | 199 | Allocation Date | Date of approval of this document (TBD) | 200 | Termination Date | N/A | 201 | Source | True | 202 | Destination | True | 203 | Forwardable | True | 204 | Global | True | 205 | Reserved-by-Protocol | False | 206 +----------------------+-------------------------------------------+ 208 4.2. Registration of IPv6 Special Purpose Address 210 IANA is requested to assign a single IPv6 address from the 2001: 211 0000::/23 prefix and register it in the IANA IPv6 Special-Purpose 212 Address Registry [RFC6890]. 214 +----------------------+-------------------------------------------+ 215 | Attribute | Value | 216 +----------------------+-------------------------------------------+ 217 | Address Block | 2001:0????????/128 (??? = TBD by IANA) | 218 | Name | Port Control Protocol Anycast | 219 | RFC | This document, if approved (TBD) | 220 | Allocation Date | Date of approval of this document (TBD) | 221 | Termination Date | N/A | 222 | Source | True | 223 | Destination | True | 224 | Forwardable | True | 225 | Global | True | 226 | Reserved-by-Protocol | False | 227 +----------------------+-------------------------------------------+ 229 5. Security Considerations 231 In addition to the security considerations in [RFC6887], [RFC4786], 232 and [RFC7094], two further security issues are considered here. 234 5.1. Information Leakage through Anycast 236 In a network without any border gateway, NAT or firewall that is 237 aware of the PCP anycast address, outgoing PCP requests could leak 238 out onto the external Internet, possibly revealing information about 239 internal devices. 241 Using an IANA-assigned well-known PCP anycast address enables border 242 gateways to block such outgoing packets. In the default-free zone, 243 routers should be configured to drop such packets. Such 244 configuration can occur naturally via BGP messages advertising that 245 no route exists to said address. 247 Sensitive clients that do not wish to leak information about their 248 presence can set an IP TTL on their PCP requests that limits how far 249 they can travel towards the public Internet. However, methods for 250 choosing an appropriate TTL value, e.g., based on the assumed radius 251 of the trusted network domain, is beyond the scope of this document. 253 Before sending PCP requests with possibly privacy-sensitive 254 parameters (e.g., IP addresses and port numbers) to the PCP anycast 255 addresses, PCP clients can send an ANNOUNCE request (without 256 parameters; see Section 14.1 of [RFC6887]), in order to probe whether 257 a PCP server consumes and processes PCP requests sent to that anycast 258 address. 260 5.2. Hijacking of PCP Messages sent to Anycast Addresses 262 The anycast addresses are treated by normal host operating systems 263 just as normal unicast addresses, i.e., packets destined for an 264 anycast address are sent to the default router for processing and 265 forwarding. Hijacking such packets in the first network segment 266 would effectively require the attacker to impersonate the default 267 router, e.g., by means of ARP spoofing in an Ethernet network. Once 268 an anycast message is forwarded closer to the core network, routing 269 will likely become subject to dynamic routing protocols such as OSPF 270 or BGP. Anycast messages could be hijacked by announcing 271 counterfeited messages in these routing protocols. When analyzing 272 the risk and possible consequences of such attacks in a given network 273 scenario, the probable impacts on PCP signaling need to be put into 274 proportion with probable impacts on other protocols such as the 275 actual application protocols. 277 In addition to following best current practices in first hop security 278 and routing protocol security, PCP authentication [RFC7652] may be 279 useful in some scenarios. However, the effort needed for a proper 280 setup of this authentication mechanism (e.g., installing the right 281 shared secrets or cryptograpic keys on all involved systems) may 282 thwart the goal of fully automatic configuration by using PCP 283 anycast. Therefore, this approach may be less suitable for scenarios 284 with high trust between the operator of the PCP-controlled middlebox 285 and all users (e.g., a residential gateway used only by family 286 members) or if there is anyway rather limited trust that the 287 middlebox will behave correctly (e.g., the Wifi in an airport 288 lounge). In contrast, this scheme may be highly useful in scenarios 289 with many users and a trusted network operator, such as a large 290 corporate network or a university campus network, which uses several 291 parallel NATs or firewalls to connect to the Internet. Therefore, a 292 thorough analysis of the benefits and costs of using PCP 293 authentication in a given network scenario is recommended. 295 6. Acknowledgments 297 The authors would like to thank the members of the PCP working group 298 for contributions and feedback, in particular Mohamed Boucadair, 299 Charles Eckel, Simon Perreault, Tirumaleswar Reddy, Markus Stenberg, 300 Dave Thaler, and Dan Wing. 302 7. References 304 7.1. Normative References 306 [RFC6887] Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P. 307 Selkirk, "Port Control Protocol (PCP)", RFC 6887, 308 April 2013. 310 [RFC6890] Cotton, M., Vegoda, L., Bonica, R., and B. Haberman, 311 "Special-Purpose IP Address Registries", BCP 153, 312 RFC 6890, April 2013. 314 [RFC7488] Boucadair, M., Penno, R., Wing, D., Patil, P., and T. 315 Reddy, "Port Control Protocol (PCP) Server Selection", 316 RFC 7488, March 2015. 318 7.2. Informative References 320 [I-D.ietf-pcp-optimize-keepalives] 321 Reddy, T., Patil, P., Isomaki, M., and D. Wing, 322 "Optimizing NAT and Firewall Keepalives Using Port Control 323 Protocol (PCP)", draft-ietf-pcp-optimize-keepalives-06 324 (work in progress), May 2015. 326 [RFC1546] Partridge, C., Mendez, T., and W. Milliken, "Host 327 Anycasting Service", RFC 1546, November 1993. 329 [RFC4085] Plonka, D., "Embedding Globally-Routable Internet 330 Addresses Considered Harmful", BCP 105, RFC 4085, 331 DOI 10.17487/RFC4085, June 2005, 332 . 334 [RFC4786] Abley, J. and K. Lindqvist, "Operation of Anycast 335 Services", BCP 126, RFC 4786, December 2006. 337 [RFC7094] McPherson, D., Oran, D., Thaler, D., and E. Osterweil, 338 "Architectural Considerations of IP Anycast", RFC 7094, 339 DOI 10.17487/RFC7094, January 2014, 340 . 342 [RFC7291] Boucadair, M., Penno, R., and D. Wing, "DHCP Options for 343 the Port Control Protocol (PCP)", RFC 7291, July 2014. 345 [RFC7652] Cullen, M., Hartman, S., Zhang, D., and T. Reddy, "Port 346 Control Protocol (PCP) Authentication Mechanism", 347 RFC 7652, DOI 10.17487/RFC7652, September 2015, 348 . 350 Authors' Addresses 352 Sebastian Kiesel 353 University of Stuttgart Information Center 354 Networks and Communication Systems Department 355 Allmandring 30 356 Stuttgart 70550 357 Germany 359 Email: ietf-pcp@skiesel.de 361 Reinaldo Penno 362 Cisco Systems, Inc. 363 170 West Tasman Drive 364 San Jose, California 95134 365 USA 367 Email: repenno@cisco.com 369 Stuart Cheshire 370 Apple Inc. 371 1 Infinite Loop 372 Cupertino, California 95014 373 USA 375 Phone: +1 408 974 3207 376 Email: cheshire@apple.com