Internet Engineering Task Force T. Tsou, Ed. Internet-Draft Huawei Technologies (USA) Intended status: Informational March 5, 2012 Expires: September 5, 2012 BFD Support DS-Lite draft-tsou-bfd-ds-lite-00 Abstract In DS-Lite, the tunnel is not associated with any state information, which makes it difficult to manage and diagnose. Bidirectional Forwarding Detection (BFD) can be used in this case to detect the state of the IPv4-in-IPv6 tunnel by creating a BFD session between the DS-Lite CPE and the Address Family Transitional Router (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/. 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Tsou Expires August 30, 2012 [Page 1] Internet-Draft BFD DS-Lite February 2012 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. BFD for DS-Lite . . . . . . . . . . . . . . . . . . . . . . . . 4 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 August 30, 2012 [Page 2] Internet-Draft BFD DS-Lite February 2012 1. Introduction In DS-Lite [RFC6333], there is no status information about the IPv4- in-IPv6 tunnel; no keep-alive mechanism is available. It is difficult to know whether the tunnle is up or down, which creates a problem for operation and maintenance. Although administor can use ping to test the connectivity, that is not a commonly used keep-alive mechanism. BFD [RFC5880] is a mechanism intended to detect faults in the bidirectional path. It is usually used in conjunction with applications like OSPF, IS-IS, etc, for fast fault recovery/fast re- route. BFD [RFC5880] can be used in DS-Lite, by creating a BFD session between the CPE and the AFTR to provide tunnel status information. If a fault is detected the CPE can try to create a DS-Lite tunnel with another AFTR and terminate the existing one, so as to continue network service. [I-D.vinokour-bfd-dhcp] proposes using a DHCP option to distribute BFD parameters to the 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, so that 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 (i.e., the DS-Lite B4). FQDN Fully Qualified Domain Name Tsou Expires August 30, 2012 [Page 3] Internet-Draft BFD DS-Lite February 2012 3. BFD for DS-Lite 3.1. DS-Lite Scenario In DS-Lite [RFC6333], the BFD packet SHOULD be sent through an IPv4- in-IPv6 tunnel, as shown in Figure 1. The IPv4 addresses of the CPE and AFTR SHOULD be the endpoints 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 set up a BFD session, the following parameters are needed, as shown in Section 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], the CPE WAN-side IPv4 address is a well-known address 192.0.0.2, and the AFTR's IPv4 address is 192.0.0.1, as defined in section 5.7 of [RFC6333]. Because all the CPEs and AFTRs use the same well-known IP addresses, IPv4 addresses are not sufficient for setting up a BFD session. From the CPE's point of view, the 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 to manage it. From the AFTR's point of view, a lot of CPEs with the same IPv4 address will setup BFD sessions with it, so in order to distinguish the CPEs, the AFTR needs to take account of both the IPv4 address and the IPv6 address of the CPE that establishes a BFD session. [Editor's note - I think this isn't quite consistent with the following from Section 6 of RFC 5881: Tsou Expires August 30, 2012 [Page 4] Internet-Draft BFD DS-Lite February 2012 "On a point-to-point link, the source address of a BFD Control packet MUST NOT be used to identify the session. This means that the initial BFD packet MUST be accepted with any source address, and that subsequent BFD packets MUST be demultiplexed solely by the Your Discriminator field (as is always the case)."] [PTT - Should be a reference to RFC 5881 Section 3 here.] When a CPE goes online and sets up a tunnel with an AFTR, then it should initiate a BFD session with the AFTR, generating a local discriminator, and send the first BFD packet to AFTR with peer 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. The other parameters listed above can be negotiated by BFD signaling, and initial values can be configured on the 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, along with the well known CPE IPv4 address 192.0.0.2 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. [PTT- should refer to RFC 5881 Section 4 for source and destination port settings.] 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 in the CPE to AFTR direction, without any manual configuration. When the AFTR receives the first packet from a CPE, AFTR will get the IPv6 address and discriminator of the CPE, so that the AFTR can initiate the BFD session in the other direction and a similar discriminator negotiation can be carried out. The procedure to set up a BFD session is illustrated below: [Is this really necessary given that it is covered by RFC 5880?] Tsou Expires August 30, 2012 [Page 5] Internet-Draft BFD DS-Lite February 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 the AFTR is sent to CPE via a DHCP option, as defined in [RFC6334]. Multiple IP addresses can be configured for an FQDN on the DNS server. If BFD detects a fault on the link to an AFTR, the CPE can choose another AFTR address and use a different AFTR to provide network sevice. Tsou Expires August 30, 2012 [Page 6] Internet-Draft BFD DS-Lite February 2012 If anycast is used for load balancing and failover, there might be an ICMP error message problem, that is, when a packet is sent from AFTR to CPE, one of the routers along the path 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. [PTT - this has to do with DS-Lite, but not with BFD. Off topic!] 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 faults in such a short time. On the other hand, an AFTR may need to support tens of thousands of CPEs, which means the AFTR will need to support the same number of BFD sessions. In order to meet performance requirements on the AFTR, it may be necessary to extend the time period between BFD packet transmissions 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], the CPE may not be directly connected to the AFTR; there may be other routers between them. Then there are potential spoofing problems, as described in [RFC5883]. Hence cryptographic authentication should be used as described in [RFC5880]. 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. [RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881, June 2010. [RFC5882] Katz, D. and D. Ward, "Generic Application of Tsou Expires August 30, 2012 [Page 7] Internet-Draft BFD DS-Lite February 2012 Bidirectional Forwarding Detection (BFD)", RFC 5882, 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. [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 August 30, 2012 [Page 8]