PCP working group S. Kiesel Internet-Draft University of Stuttgart Intended status: Standards Track R. Penno Expires: August 18, 2014 Cisco Systems, Inc. S. Cheshire Apple February 14, 2014 PCP Anycast Address draft-ietf-pcp-anycast-01 Abstract The Port Control Protocol (PCP) Anycast Address enables PCP clients to transmit signaling messages to their closest on-path NAT, Firewall, or other middlebox, without having to learn the IP address of that middlebox via some external channel. This document establishes one well-known IPv4 address and one well-known IPv6 address to be used as PCP Anycast Address. 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 August 18, 2014. Copyright Notice Copyright (c) 2014 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 Kiesel, et al. Expires August 18, 2014 [Page 1] Internet-Draft PCP Anycast Address February 2014 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. PCP Server Discovery based on well-known IP Address . . . . . 4 2.1. PCP Discovery Client behavior . . . . . . . . . . . . . . 4 2.2. PCP Discovery Server behavior . . . . . . . . . . . . . . 4 3. Deployment Considerations . . . . . . . . . . . . . . . . . . 5 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 4.1. Registration of IPv4 Special Purpose Address . . . . . . . 6 4.2. Registration of IPv6 Special Purpose Address . . . . . . . 7 5. Security Considerations . . . . . . . . . . . . . . . . . . . 9 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 6.1. Normative References . . . . . . . . . . . . . . . . . . . 10 6.2. Informative References . . . . . . . . . . . . . . . . . . 10 Appendix A. Discussion of other PCP Discovery methods . . . . . . 11 A.1. Default Router . . . . . . . . . . . . . . . . . . . . . . 11 A.2. DHCP PCP Options . . . . . . . . . . . . . . . . . . . . . 11 A.3. User Input . . . . . . . . . . . . . . . . . . . . . . . . 12 A.4. Domain Name System Based . . . . . . . . . . . . . . . . . 12 A.5. Addressing only based on Destination Port . . . . . . . . 12 Appendix B. Discussion of IP Anycast Address usage for PCP . . . 14 B.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . . 14 B.2. Scenarios . . . . . . . . . . . . . . . . . . . . . . . . 14 B.3. Historical Objections to Anycast . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16 Kiesel, et al. Expires August 18, 2014 [Page 2] Internet-Draft PCP Anycast Address February 2014 1. Introduction The Port Control Protocol (PCP) [RFC6887] provides a mechanism to control how incoming packets are forwarded by upstream devices such as Network Address Translator IPv6/IPv4 (NAT64), Network Address Translator IPv4/IPv4 (NAT44), IPv6 and IPv4 firewall devices, and a mechanism to reduce application keep alive traffic. The PCP document [RFC6887] specifies the message formats used, but the address to which a client sends its request is either assumed to be the default router (which is appropriate in a typical single-link residential network) or has to be configured otherwise via some external mechanism, such as DHCP. The properties and drawbacks of various mechanisms are discussed in Appendix A. This document follows a different approach: it establishes a well- known anycast address for the PCP Server. PCP clients are expected to send requests to this address during the PCP Server discovery process. A PCP Server configured with the anycast address could optionally redirect or return a list of unicast PCP Servers to the client. For a more extensive discussion on anycasting see Appendix B. The benefit of using an anycast address is simplicity and reliability. In an example deployment scenario: 1. A network administrator installs a PCP-capable NAT. 2. An end user (who may be the same person) runs a PCP-enabled application. This application can implement PCP with purely user-level code -- no operating system support is required. 3. This PCP-enabled application sends its PCP request to the PCP anycast address. This packet travels through the network like any other, without any special support from DNS, DHCP, other routers, or anything else, until it reaches the PCP-capable NAT, which receives it, handles it, and sends back a reply. Using the PCP anycast address, the only two things that need to be deployed in the network are the two things that actually use PCP: The PCP-capable NAT, and the PCP-enabled application. Nothing else in the network needs to be changed or upgraded, and nothing needs to be configured, including the PCP client. Kiesel, et al. Expires August 18, 2014 [Page 3] Internet-Draft PCP Anycast Address February 2014 2. PCP Server Discovery based on well-known IP Address 2.1. PCP Discovery Client behavior PCP Clients that need to discover PCP servers SHOULD first send a PCP request to its default router. This is important because in the case of cascaded PCP Servers, all of them need to be discovered in order of hop distance from the client. The PCP client then SHOULD send a PCP request to the anycast address. PCP Clients must be prepared to receive an error and try other discovery methods. 2.2. PCP Discovery Server behavior PCP Server can be configured to listen on the anycast address for incoming PCP requests. PCP responses are sent from that same IANA-assigned address (see Page 5 of [RFC1546]). Kiesel, et al. Expires August 18, 2014 [Page 4] Internet-Draft PCP Anycast Address February 2014 3. Deployment Considerations There are known limitations when there is more than one PCP server and asymmetric routing, or similar scenarios. Mechanisms to deal with those situations, such as state synchronization between PCP servers, are beyond the scope of this document. Kiesel, et al. Expires August 18, 2014 [Page 5] Internet-Draft PCP Anycast Address February 2014 4. IANA Considerations 4.1. Registration of IPv4 Special Purpose Address IANA is requested to register a single IPv4 address in the IANA IPv4 Special Purpose Address Registry [RFC5736]. [RFC5736] itemizes some information to be recorded for all designations: 1. The designated address prefix. Prefix: TBD by IANA. Prefix length: /32 2. The RFC that called for the IANA address designation. This document. 3. The date the designation was made. TBD. 4. The date the use designation is to be terminated (if specified as a limited-use designation). Unlimited. No termination date. 5. The nature of the purpose of the designated address (e.g., unicast experiment or protocol service anycast). protocol service anycast. 6. For experimental unicast applications and otherwise as appropriate, the registry will also identify the entity and related contact details to whom the address designation has been made. N/A. 7. The registry will also note, for each designation, the intended routing scope of the address, indicating whether the address is intended to be routable only in scoped, local, or private contexts, or whether the address prefix is intended to be routed globally. Kiesel, et al. Expires August 18, 2014 [Page 6] Internet-Draft PCP Anycast Address February 2014 Typically used within a network operator's network domain, but in principle globally routable. 8. The date in the IANA registry is the date of the IANA action, i.e., the day IANA records the allocation. TBD. 4.2. Registration of IPv6 Special Purpose Address IANA is requested to register a single IPv6 address in the IANA IPv6 Special Purpose Address Block [RFC4773]. [RFC4773] itemizes some information to be recorded for all designations: 1. The designated address prefix. Prefix: TBD by IANA. Prefix length: /128 2. The RFC that called for the IANA address designation. This document. 3. The date the designation was made. TBD. 4. The date the use designation is to be terminated (if specified as a limited-use designation). Unlimited. No termination date. 5. The nature of the purpose of the designated address (e.g., unicast experiment or protocol service anycast). protocol service anycast. 6. For experimental unicast applications and otherwise as appropriate, the registry will also identify the entity and related contact details to whom the address designation has been made. N/A. Kiesel, et al. Expires August 18, 2014 [Page 7] Internet-Draft PCP Anycast Address February 2014 7. The registry will also note, for each designation, the intended routing scope of the address, indicating whether the address is intended to be routable only in scoped, local, or private contexts, or whether the address prefix is intended to be routed globally. Typically used within a network operator's network domain, but in principle globally routable. 8. The date in the IANA registry is the date of the IANA action, i.e., the day IANA records the allocation. TBD. Kiesel, et al. Expires August 18, 2014 [Page 8] Internet-Draft PCP Anycast Address February 2014 5. Security Considerations In a network without any border gateway, NAT or firewall that is aware of the PCP anycast address, outgoing PCP requests could leak out onto the external Internet, possibly revealing information about internal devices. Using an IANA-assigned well-known PCP anycast address enables border gateways to block such outgoing packets. In the default-free zone, routers should be configured to drop such packets. Such configuration can occur naturally via BGP messages advertising that no route exists to said address. Sensitive clients that do not wish to leak information about their presesence can set an IP TTL on their PCP requests that limits how far they can travel into the public Internet. Kiesel, et al. Expires August 18, 2014 [Page 9] Internet-Draft PCP Anycast Address February 2014 6. References 6.1. Normative References [RFC1546] Partridge, C., Mendez, T., and W. Milliken, "Host Anycasting Service", RFC 1546, November 1993. [RFC3958] Daigle, L. and A. Newton, "Domain-Based Application Service Location Using SRV RRs and the Dynamic Delegation Discovery Service (DDDS)", RFC 3958, January 2005. [RFC4773] Huston, G., "Administration of the IANA Special Purpose IPv6 Address Block", RFC 4773, December 2006. [RFC5736] Huston, G., Cotton, M., and L. Vegoda, "IANA IPv4 Special Purpose Address Registry", RFC 5736, January 2010. [RFC6887] Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P. Selkirk, "Port Control Protocol (PCP)", RFC 6887, April 2013. 6.2. Informative References [DNSDisc] Hagino, J. and D. Thaler, "Analysis of DNS Server Discovery Mechanisms for IPv6", draft-ietf-ipngwg-dns-discovery-01 (work in progress), November 2001. [DhcpRequestParams] OpenFlow, "OpenFlow Switch Specification", February 2011, . [I-D.chen-pcp-mobile-deployment] Chen, G., Cao, Z., Boucadair, M., Ales, V., and L. Thiebaut, "Analysis of Port Control Protocol in Mobile Network", draft-chen-pcp-mobile-deployment-04 (work in progress), July 2013. [I-D.ietf-dhc-container-opt] Droms, R. and R. Penno, "Container Option for Server Configuration", draft-ietf-dhc-container-opt-07 (work in progress), April 2013. [I-D.ietf-pcp-dhcp] Boucadair, M., Penno, R., and D. Wing, "DHCP Options for the Port Control Protocol (PCP)", draft-ietf-pcp-dhcp-09 (work in progress), November 2013. Kiesel, et al. Expires August 18, 2014 [Page 10] Internet-Draft PCP Anycast Address February 2014 Appendix A. Discussion of other PCP Discovery methods Several algorithms have been specified that allows PCP Client to discover the PCP Servers on a network . However, each of this approaches has technical or operational issues that will hinder the fast deployment of PCP. A.1. Default Router The PCP specification allows one mode of operation in which the PCP client sends its requests to the default router. This approach is appropriate in a typical single-link residential network but has limitations in more complex network topologies. If PCP server does not reside in first hop router, whether because subscriber has a existing home router or in the case of Wireless Networks (3G, LTE) [I-D.chen-pcp-mobile-deployment], trying to send a request to default router will not work. A.2. DHCP PCP Options One general drawback of relying on external configuration mechanisms, such as DHCP [I-D.ietf-pcp-dhcp], is that it creates an external dependency on another piece of network infrastructure which must be configured with the right address for PCP to work. In some environments the staff managing the DHCP servers may not be the same staff managing the NAT gateways, and in any case, constantly keeping the DHCP server address information up to date as NAT gateways are added, removed, or reconfigured, is burdensome. Another drawback of relying on DHCP for configuration is that at least one significant target deployment environments for PCP -- namely 3GPP for mobile telephones -- does not use DHCP. There are two problems with DHCP Options: DHCP Server on Home Gateways (HGW) and Operating Systems DHCP clients Currently what the HGW does with the options it receives from the ISP is not standardized in any general way. As a matter of practice, the HGW is most likely to use its own customer-LAN-facing IP address for the DNS server address. As for other options, it's free to offer the same values to the client, offer no value at all, or offer its own IP address if that makes sense, as it does (sort of) for DNS. In scenarios where PCP Server resides on ISP network and is intended to work with arbitrary home gateways that don't know they are being used in a PCP context, that won't work, because there's no reason to think that the HGW will even request the option from the DHCP server, Kiesel, et al. Expires August 18, 2014 [Page 11] Internet-Draft PCP Anycast Address February 2014 much less offer the value it gets from the server on the customer- facing LAN. There is work on the DHC WG to overcome some of these limitations [I-D.ietf-dhc-container-opt] but in terms of deployment it also needs HGW to be upgraded. The problems with Operating Systems is that even if DHCP PCP Option were made available to customer-facing LAN, host stack DHCP enhancements are required to process or request new DHCP PCP option. One exception is Windows [DhcpRequestParams] Finally, in the case of IPv6 there are networks where there is DHCPv6 infrastructure at all or some hosts do not have a DHCPv6 client. A.3. User Input A regular subscriber can not be expected to input IP address of PCP Server or network domain name. Moreover, user can be at a Wi-Fi hotspot, Hotel or related. Therefore relying on user input is not reliable. A.4. Domain Name System Based There are three separate category of problems with NAPTR [RFC3958] 1. End Points: It relies on PCP client determining the domain name and supporting certain DNS queries 2. DNS Servers: DNS server need to be provisioned with the necessary records 3. CPEs: CPEs might interfere with DNS queries and the DHCP domain name option conveyed by ISP that could be used to bootstrap NAPTR might not be relayed to home network. A.5. Addressing only based on Destination Port One design option that was considered for Apple's NAT gateways was to have the NAT gateway simply handle and respond to all packets addressed to UDP port 5351, regardless of the destination address in the packet. Since the device is a NAT gateway, it already examines every packet in order to rewrite port numbers, so also detecting packets addressed to UDP port 5351 is not a significant additional burden. Also, since this device is a NAT gateway which rewrites port numbers, any attempt by a client to talk *though* this first NAT gateway to create mappings in some second upstream NAT gateway is futile and pointless. Any mappings created in the second NAT gateway are useful to the client only if there are also corresponding mappings created in the first NAT gateway. Consequently, there is no Kiesel, et al. Expires August 18, 2014 [Page 12] Internet-Draft PCP Anycast Address February 2014 case where it is useful for PCP requests to pass transparently through the first PCP-aware NAT gateway on their way to the second PCP-aware NAT gateway. In all cases, for useful connectivity to be established, the PCP request must be handled by the first NAT gateway, and then the first NAT gateway generates a corresponding new upstream request to establish a mapping in the second NAT gateway. (This process can be repeated recursively for as many times as necessary for the depth of nesting of NAT gateways; this is transparent to the client device.) Kiesel, et al. Expires August 18, 2014 [Page 13] Internet-Draft PCP Anycast Address February 2014 Appendix B. Discussion of IP Anycast Address usage for PCP B.1. Motivation The two issues identified in Appendix A.5 result in the following related observations: the PCP client may not *know* what destination address to use in its PCP request packets; the PCP server doesn't *care* what destination address is in the PCP request packets. Given that the devices neither need to know nor care what destination address goes in the packet, all we need to do is pick one and use it. It's little more than a placeholder in the IP header. Any globally routable unicast address will do. Since this address is one that automatically routes its packet to the closest on-path device that implements the desired functionality, it is an anycast address. B.2. Scenarios In the simple case where the first-hop router is also the NAT gateway (as is common in a typical single-link residential network), sending to the PCP anycast address is equivalent to sending to the client's default router, as specified in the PCP base document [RFC6887]. In the case of a larger corporate network, where there may be several internal routed subnets and one or more border NAT gateway(s) connecting to the rest of the Internet, sending to the PCP anycast address has the interesting property that it magically finds the right border NAT gateway for that client. Since we posit that other network infrastructure does not need (and should not have) any special knowledge of PCP (or its anycast address) this means that to other non-NAT routers, the PCP anycast address will look like any other unicast destination address on the public Internet, and consequently the packet will be forwarded as for any other packet destined to the public Internet, until it reaches a NAT or firewall device that is aware of the PCP anycast address. This will result in the packet naturally arriving the NAT gateway that handles this client's outbound traffic destined to the public Internet, which is exactly the NAT gateway that the client wishes to communicate with when managing its port mappings. B.3. Historical Objections to Anycast In March 2001 a draft document entitled "Analysis of DNS Server Discovery Mechanisms for IPv6" [DNSDisc] proposed using anycast to discover DNS servers, a proposal that was subsequently abandoned in later revisions of that draft document. There are legitimate reasons why using anycast to discover DNS Kiesel, et al. Expires August 18, 2014 [Page 14] Internet-Draft PCP Anycast Address February 2014 servers is not compelling, mainly because it requires explicit configuration of routing tables to direct those anycast packets to the desired DNS server. However, DNS server discovery is very different to NAT gateway discovery. A DNS server is something a client explicitly talks to, via IP address. The DNS server may be literally anywhere on the Internet. Various reasons make anycast an uncompelling technique for DNS server discovery: o DNS is a pure application-layer protocol, running over UDP. o On an operating system without appropriate support for configuring anycast addresses, a DNS server would have to use something like Berkeley Packet Filter (BPF) to snoop on received packets to intercept DNS requests, which is inelegant and inefficient. o Without appropriate routing changes elsewhere in the network, there's no reason to assume that packets sent to that anycast address would even make it to the desired DNS server machine. This places an addition configuration burden on the network administrators, to install appropriate routing table entries to direct packets to the desired DNS server machine. In contrast, a NAT gateway is something a client's packets stumble across as they try to leave the local network and head out onto the public Internet. The NAT gateway has to be on the path those packets naturally take or it can't perform its NAT functions. As a result, the objections to using anycast for DNS server discovery do not apply to PCP: o No routing changes are needed (or desired) elsewhere in the local network, because the whole *point* of using anycast is that we want the client's PCP request packet to take the same forwarding path through the network as a TCP SYN to any other remote destination address, because we want the *same* NAT gateway that would have made a mapping in response to receiving an outbound TCP SYN packet from the client to be the the one that makes a mapping in response to receiving a PCP request packet from the client. o A NAT engine is already snooping on (and rewriting) every packet it forwards. As part of that snooping it could trivially look for packets addressed to the PCP UDP port and process them locally (just like the local processing it already does when it sees an outbound TCP SYN packet). Kiesel, et al. Expires August 18, 2014 [Page 15] Internet-Draft PCP Anycast Address February 2014 Authors' Addresses Sebastian Kiesel University of Stuttgart Computing Center Allmandring 30 Stuttgart 70550 Germany Email: ietf-pcp@skiesel.de URI: http://www.rus.uni-stuttgart.de/nks/ Reinaldo Penno Cisco Systems, Inc. San Jose, CA US Phone: Fax: Email: repenno@cisco.com URI: Stuart Cheshire Apple Inc. 1 Infinite Loop Cupertino, California 95014 USA Phone: +1 408 974 3207 Email: cheshire@apple.com Kiesel, et al. Expires August 18, 2014 [Page 16]