INTERNET-DRAFT DCCP-NAT Encapsulation February 14, 2008 DCCP-NAT Encapsulation Internet Draft T. Phelan Document: draft-phelan-dccp-natencap-00.txt Sonus Networks Expires: August 2008 February 14, 2008 Intended status: Proposed Standard Datagram Congestion Control Protocol (DCCP) Encapsulation for NAT Traversal (DCCP-NAT) Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on August 14, 2008. Abstract This document specifies an alternative encapsulation of the Datagram Congestion Control Protocol (DCCP), referred to as DCCP-NAT. This encapsulation will allow DCCP to be carried through the current generation of Network Address Translation (NAT) middleboxes without modification of those middleboxes. Phelan Expires - August 2008 [Page 1] INTERNET-DRAFT DCCP-NAT Encapsulation February 14, 2008 Table of Contents 1. Introduction...................................................3 2. Terminology....................................................3 3. DCCP-NAT.......................................................3 3.1 UDP Header.................................................4 3.2 DCCP-NAT Generic Header....................................5 3.2.1 DCCP-RAW Checksum and CsCov Fields....................5 3.3 Other DCCP Headers and Options.............................6 3.4 Service Codes and the DCCP Port Registry...................6 4. Security Considerations........................................6 5. IANA Considerations............................................7 6. References.....................................................7 6.1 Normative References.......................................7 6.2 Informative References.....................................7 7. Author's Address...............................................7 Phelan Expires - August 2008 [Page 2] INTERNET-DRAFT DCCP-NAT Encapsulation February 14, 2008 1. Introduction The Datagram Congestion Control Protocol (DCCP), specified in [RFC4340], is a transport-layer protocol that provides upper layers with the capability of using unreliable but congestion controlled flows. According to [RFC4340], DCCP packets are directly encapsulated in IPv4 or IPv6 packets. In order for the [RFC4340] encapsulation to pass through Network Address Translation (NAT) devices, these devices must be updated to recognize and properly modify DCCP. This is the long-term objective for DCCP, and work is underway to specify the necessary operations. However, in the short term it would be useful to have an encapsulation for DCCP that would be compatible with NAT devices conforming to [RFC4787]. This document specifies that encapsulation, which is referred to as DCCP-NAT. For convenience, the [RFC4340] encapsulation is referred to as DCCP-RAW. 2. Terminology 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 [RFC2119]. 3. DCCP-NAT The basic approach here is to insert a UDP ([RFC768]) "shim" layer between the IP header and a DCCP packet with a modified generic header (modified to eliminate redundancies between UDP and DCCP). Note that this is not strictly a tunneling approach. The IP addresses of the communicating end systems are carried in the IP header (which could be modified by NAT devices) and there are no other IP addresses embedded. Devices offering or using DCCP services via DCCP-NAT encapsulation listen on a UDP port (normally 2210) for incoming packets and pass received packets along to the DCCP protocol. DCCP implementations MAY allow services to be simultaneously offered over all combinations of DCCP-RAW and DCCP-NAT encapsulations with IPv4 and IPv6. Phelan Expires - August 2008 [Page 3] INTERNET-DRAFT DCCP-NAT Encapsulation February 14, 2008 The basic format of a DCCP-NAT packet is: +-----------------------------------+ | IP Header (IPv4 or IPv6) | Variable length +-----------------------------------+ | UDP Header | 8 bytes +-----------------------------------+ | DCCP-NAT Generic Header | 12 bytes +-----------------------------------+ | Additional (type-specific) Fields | Variable length (could be 0) +--------------------------------------+ | DCCP Options | Variable length (could be 0) +-----------------------------------+ | Application Data Area | Variable length (could be 0) +-----------------------------------+ 3.1 UDP Header The format of the UDP header is taken from [RFC768]: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Port | Dest Port | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ For DCCP-NAT, the fields are interpreted as follows: Source and Dest(ination) Ports: 16 bits each These fields identify the UDP ports on which the source and destination (respectively) of the packet are listening for incoming DCCP-NAT packets (normally both are port 2210). Note that they do not identify the DCCP source and destination ports. Length: 16 bits This field is the length of the UDP datagram, including the UDP header and the payload (which for DCCP-NAT is the DCCP-NAT datagram). For DCCP-NAT, it MUST be at least the size of the UDP header (8 bytes) plus the minimum size of a DCCP-NAT header (12 bytes), for a total minimum value of 20 bytes. Received packets with a UDP Length of less than 20 bytes MUST be ignored. Checksum: 16 bits This field is the Internet checksum of a network-layer pseudoheader and the entire UDP packet. For DCCP-NAT, a packet with a checksum field equal to 0 MUST be ignored as incorrect checksum. Phelan Expires - August 2008 [Page 4] INTERNET-DRAFT DCCP-NAT Encapsulation February 14, 2008 3.2 DCCP-NAT Generic Header Unlike the DCCP-RAW generic header, the DCCP-NAT generic header takes only one form; it does not support short sequence numbers. Its format is as follows: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Port | Dest Port | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Data Offset | CCVal | Type | Sequence Number (high bits) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . Sequence Number (low bits) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ All DCCP-NAT generic header fields function as specified in [RFC4340]. 3.2.1 DCCP-RAW Checksum and CsCov Fields For DCCP-NAT, the function of the DCCP-RAW generic header field Checksum is performed by the UDP Checksum field. If the UDP Checksum field in a received packet is invalid or has a value of 0, that packet MUST be ignored as per the invalid checksum procedures of DCCP-RAW (i.e., the options in the packet MUST NOT be processed). If the UDP Length field in a received packet is less than the length of the UDP header plus the entire DCCP-NAT header (including the generic header, type-specific fields and options), or the UDP Length field is greater than the length of the packet from the beginning of the UDP header to the end of the packet, that packet MUST also be ignored as per the invalid checksum procedures. Since the UDP Checksum can only cover the entire packet, there is no ability to apply checksum coverage to only part of the user data as with DCCP-RAW, and therefore there is no need for the CsCov (Checksum Coverage) field in DCCP-NAT. DCCP-NAT implementations SHOULD include the ability to negotiate the DCCP Minimum Checksum Coverage feature, but SHOULD NOT accept any value other than 0 for this field. Note that if UDP-Lite ([RFC3828]) were used as the shim layer it would be possible to provide functionality equivalent to the DCCP partial checksum coverage. However, UDP-Lite uses a different protocol number than UDP and would therefore defeat the purpose of DCCP-NAT in passing through NAT devices. Phelan Expires - August 2008 [Page 5] INTERNET-DRAFT DCCP-NAT Encapsulation February 14, 2008 3.3 Other DCCP Headers and Options All type-specific DCCP headers are as in DCCP-RAW, except that the short sequence number version of the acknowledgement header is not supported. All option and feature encodings are as in DCCP-RAW. 3.4 Service Codes and the DCCP Port Registry There is one Service Code registry and one DCCP port registry and they apply to all combinations of encapsulation and IP version. A DCCP Service Code specifies an application using DCCP regardless of the combination of DCCP encapsulation and IP version. An application MAY choose not to support some combinations of encapsulation and IP version, but its Service Code will remain registered for those combinations and MUST NOT be used by other applications. An application SHOULD NOT register different Service Codes for different combinations of encapsulation and IP version. Similarly, a port registration is applicable to all combinations of encapsulation and IP version. Again, an application MAY choose not to support some combinations of encapsulation and IP version on its registered port, although the port will remain registered for those combinations. Applications SHOULD NOT register different ports just for the purpose of using different encapsulation combinations. Since the port registry supports multiple applications registering the same port (as long as the Service Codes are different), other applications MAY register on the same port, but those registrations are also applicable to all combinations of encapsulation and IP version. 4. Security Considerations DCCP-NAT provides all of the security risk-mitigation measures present in DCCP-RAW, and also all of the security risks, except those associated with short sequence numbers and partial checksum coverage (since DCCP-NAT does not support those features). The purpose of DCCP-NAT is to allow DCCP to pass through NAT devices, and therefore it exposes DCCP to the risks associated with passing through NAT devices. It does not create any new risks with regard to NAT devices. DCCP-NAT may also allow DCCP applications to pass through existing firewall devices, if the administrators of the devices so choose. The option is a binary one however, either allow all DCCP applications or allow none. Proper control of DCCP application-by- application will require enhancements to firewalls. Phelan Expires - August 2008 [Page 6] INTERNET-DRAFT DCCP-NAT Encapsulation February 14, 2008 5. IANA Considerations This document requests allocation of UDP port 2210 for the DCCP-NAT service. The allocation should have the form of: dccp-nat 2210/udp DCCP-NAT Encapsulation 6. References 6.1 Normative References [RFC4340] Kohler, E., Handley, M., Floyd, S., "Datagram Congestion Control Protocol (DCCP)", RFC 4340, March 2006. [RFC768] Postel, J., "User Datagram Protocol", RFC 768, August 1980. [RFC4787] Audet, F., Jennings, C., "Network Address Translation (NAT) Behavioral Requirements for Unicast UDP", RFC 4787, January 2007. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997. 6.2 Informative References [RFC3828] Larzon, L-A., Degermark, M., Pink, S., Jonsson, L-E., Fairhurst, G., "The Lightweight User Datagram Protocol (UDP-Lite)", RFC 3828, July 2004. 7. Author's Address Tom Phelan Sonus Networks 7 Technology Park Dr. Westford, MA USA 01886 Phone: 978-614-8456 Email: tphelan@sonusnet.com Phelan Expires - August 2008 [Page 7] INTERNET-DRAFT DCCP-NAT Encapsulation February 14, 2008 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. 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