Internet Engineering Task Force T. Tsou, Ed. Internet-Draft Huawei Technologies (USA) Intended status: Informational March 5, 2012 Expires: September 7, 2012 BFD Support DS-Lite draft-tsou-softwire-bfd-ds-lite-00 Abstract In DS-Lite, there is no state information of the tunnel, which make it difficult to mange and diagnose. BFD can be used in this case to detect the state of the IPv4-in-IPv6 tunnel by creating BFD session between CPE and AFTR. 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 September 7, 2012. Copyright Notice Copyright (c) 2012 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 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. Tsou Expires September 7, 2012 [Page 1] Internet-Draft BFD DS-Lite March 2012 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. BFD for DS-Lite . . . . . . . . . . . . . . . . . . . . . . . . 3 3.1. DS-Lite Scenario . . . . . . . . . . . . . . . . . . . . . 4 3.2. Parameters for BFD . . . . . . . . . . . . . . . . . . . . 4 3.3. Procedures . . . . . . . . . . . . . . . . . . . . . . . . 5 3.4. Failover . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.5. Implementation Considerations . . . . . . . . . . . . . . . 7 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 7 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 6.1. Normative References . . . . . . . . . . . . . . . . . . . 7 6.2. Informative References . . . . . . . . . . . . . . . . . . 8 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 8 Tsou Expires September 7, 2012 [Page 2] Internet-Draft BFD DS-Lite March 2012 1. Introduction In DS-Lite [RFC6333], there is no status information about the IPv4- in-IPv6 tunnel, no keep-alive mechanism available, it is difficult to know whether the tunnle is up or down, which causes trouble to operation and maintenance. Although administor can use ping to test the connectivity, but that is not a commonly used keep-alive mechanism. BFD [RFC5880] is a mechanism intended to detect faults in the bidirectional path. It is uaually used in conjunction with applications like OSPF, IS-IS, etc, for fast fault recover -- fast re-route. BFD [RFC5880] can be used in DS-Lite, creating BFD session between CPE and AFTR, to provide tunnel status information. If a fault is detected CPE can try to create DS-Lite tunnel with another AFTR, and terminate the existing one, so as to continue network service. [I-D.vinokour-bfd-dhcp] proposes using DHCP option to distribute BFD parameters to CPE. But in case of DS-Lite, some of the key BFD parameters are already available, e.g. peer ip address is already available, and other parameters can be negotiated by BFD signaling, or statically configured, no extra DHCP option(s) need to be defined. 1.1. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. 2. Terminology BFD: Bidirectional Forwarding Detection. AFTR: Address Family Transition Router. CPE: Customer Premise Equipment. FQDN Fully Qualified Domain Name 3. BFD for DS-Lite Tsou Expires September 7, 2012 [Page 3] Internet-Draft BFD DS-Lite March 2012 3.1. DS-Lite Scenario In DS-Lite [RFC6333], BFD packet SHOULD be sent through IPv6 tunnel, as shown Figure 1. The IPv4 address of CPE and AFTR SHOULD be the endpoint of a BFD session. +--------------+ +--------------+ +-----+ | | +------+ | | | |-----+--------------+-----| | | | | CPE | IPv6 Tunnel | AFTR |-----| IPv4 Network | | |-----+--------------+-----| | | | +-----+ | IPv6 Network | +------+ | | 192.0.0.2 +--------------+ 192.0.0.1 +--------------+ Figure 1: DS-Lite Scenario 3.2. Parameters for BFD In order to setup a BFD session, the following parameters are needed, as shown in session 4.1 of [RFC5880]: o Peer IP address o My Discriminator o Your Discriminator o Desired Min TX Interval o Required Min RX Interval o Required Min Echo RX Interval In DS-Lite [RFC6334], CPE WAN port IPv4 address is a well known address 192.0.0.2, and AFTR's IPv4 address is 192.0.0.1, as defined in section 5.7 of [RFC6333]. Because all the CPEs and AFTRs are using well known IP address, IPv4 address is not suffient for setting up a BFD session. From the CPE's point of view, CPE needs to create an IPv6 tunnel to an AFTR so as to get network connectivity to the AFTR, and send IPv4 BFD packets through the tunnel. From the AFTR's point of view, a lot of CPEs with the same IPv4 address will setup BFD session with itself, in order to distinguish the CPEs, AFTR needs to combine both the IPv4 address and the IPv6 address of a CPE with a BFD session. When a CPE gets online, set up a tunnel with a AFTR, then it should iniitate a BFD session with the AFTR, generating a local discriminator, and send the first BFD packet to AFTR with peer Tsou Expires September 7, 2012 [Page 4] Internet-Draft BFD DS-Lite March 2012 discriminator set to zero; when receiving the first BFD packet from CPE, AFTR should get a local discriminator and put it in the response BFD packet to the CPE. Other parameters can be negotiated by BFD signaling; and initial values can be set on CPE and AFTR. 3.3. Procedures In DS-Lite [RFC6333], When a CPE gets online, it will be assigned an IPv6 prefix/address, and also the FQDN of the AFTR, as defined in [RFC6334]. The CPE will create an IPv6 tunnel to the AFTR, With which, and also the well know CPE IPv4 address 192.168.0.0.2 and AFTR IPv4 address 192.0.0.1, the CPE can initiate a BFD session to the AFTR. BFD packets will be sent through DS-Lite tunnel. When sending out the first BFD packet, the CPE can generate a unique local discriminator, and set the remote discriminator to zero. When the AFTR receive the first BFD packet from a CPE, the AFTR will also generate a corresponding local discriminator, and put it in the response packet to the CPE. This will finish the discriminator negotiation, without any manual configuration. When the AFTR receive the first packet from a CPE, AFTR will get the IPv6 address and discriminator of the CPE, then AFTR can BFD session of the other direction. The procedures of setting up a BFD session is shown below: Tsou Expires September 7, 2012 [Page 5] Internet-Draft BFD DS-Lite March 2012 CPE AFTR | (CPE get online) | | BFD DOWN | | -------------------------------------------------------> | | local discriminator = 1234 | | remote discriminator = 0 | | | | BFD INIT | | <------------------------------------------------------- | | local discriminator = 5678 | | remote discirminator = 1234 | | | | BFD UP | | -------------------------------------------------------> | | local discriminator = 1234 | | remote discriminator = 5678 | | | | (BFD session in one direction is finished) | | (Start BFD session in the other direction) | | | | BFD DOWN | | <------------------------------------------------------- | | local discriminator = 5678 | | remote discriminator = 1234 | | | | BFD INIT | | -------------------------------------------------------> | | local discriminator = 1234 | | remote discriminator = 5678 | | | | BFD UP | | <------------------------------------------------------- | | local discriminator = 5678 | | remote discriminator = 1234 | | | | (Bidirectional session created!) | | | Figure 2: BFD session setup procedures 3.4. Failover The FQDN of AFTR is sent to CPE via DHCP option, as defined in [RFC6334]. Multiple IP addresses can be configured for a FQDN on the DNS server. If BFD detect a fault on the link to an AFTR, CPE can choose another AFTR address, use a different AFTR to provide network sevice. Tsou Expires September 7, 2012 [Page 6] Internet-Draft BFD DS-Lite March 2012 If anycast is used for loadbalance and failover, there might be a ICMP error message problem, that is, when a packet is sent from AFTR to CPE, one of the routers between them may generate a error ICMP message, e.g. packet too big, and the error message is not sent back to the source AFTR, but sent to another AFTR. 3.5. Implementation Considerations BFD is usually used for quick fault detection, at a very small time scale, e.g. milliseconds. But in DS-Lite, it may not be necessary to detect fault in such a short time. On the other hand, an AFTR may need to tens of thousand CPEs, which means the AFTR will need to support the same number of BFD sessions. In order to performance requirement to the AFTR, it may be necessary to reduce the time period between BFD packets transmission to a longer time, e.g. 10s or 30s. 4. IANA Considerations This memo includes no request to IANA. 5. Security Considerations In DS-Lite [RFC6333], CPE may not be directly connected to AFTR, there may be other routers between them. Then there are potential spoofing problem, as described in [RFC5883], cryptographic authentication should be used. 6. References 6.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection (BFD)", RFC 5880, June 2010. [RFC5883] Katz, D. and D. Ward, "Bidirectional Forwarding Detection (BFD) for Multihop Paths", RFC 5883, June 2010. [RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual- Stack Lite Broadband Deployments Following IPv4 Exhaustion", RFC 6333, August 2011. Tsou Expires September 7, 2012 [Page 7] Internet-Draft BFD DS-Lite March 2012 [RFC6334] Hankins, D. and T. Mrugalski, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Option for Dual-Stack Lite", RFC 6334, August 2011. 6.2. Informative References [I-D.vinokour-bfd-dhcp] Vinokour, V., "Configuring BFD with DHCP and Other Musings", May 2008. Author's Address Tina Tsou (editor) Huawei Technologies (USA) 2330 Central Expressway Santa Clara CA 95050 USA Phone: +1 408 330 4424 Email: tina.tsou.zouting@huawei.com Tsou Expires September 7, 2012 [Page 8]