Internet Engineering Task Force T. Tsou Internet-Draft C. Zhou Intended status: Standards Track Huawei Technologies Expires: September 5, 2011 Q. Sun China Telecom Beijing Research Institute T. Taylor Huawei Technologies March 4, 2011 Using PCP To Coordinate Between the CGN and Home Gateway Via Port Allocation draft-tsou-pcp-natcoord-00 Abstract Consider a situation where a subscriber's packets are subject to two levels of NAT, with both NATs operating under the control of the ISP. An example of this would be a NATing Home Gateway forwarding packets to a Large Scale NAT. This memo proposes that advantage be taken of the presence of the second NAT, to offload the burden on the Large Scale NAT by delegation to the Home Gateway. Enhancements to the Port Control Protocol are specified to achieve this. 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 5, 2011. Copyright Notice Copyright (c) 2011 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 Tsou, et al. Expires September 5, 2011 [Page 1] Internet-Draft NAT Coordination Using Port Allocation March 2011 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. Table of Contents 1. Application Scenario . . . . . . . . . . . . . . . . . . . . . 3 2. Proposed Solution . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Delegation of Port Ranges . . . . . . . . . . . . . . . . . 3 2.2. Packet Processing At the Home Gateway and LSN . . . . . . . 4 2.3. Proposed Enhancements To and Usage Of the Port Control Protocol . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Port Range Options . . . . . . . . . . . . . . . . . . . . . . 6 4. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 6.1. Normative References . . . . . . . . . . . . . . . . . . . 7 6.2. informative References . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7 Tsou, et al. Expires September 5, 2011 [Page 2] Internet-Draft NAT Coordination Using Port Allocation March 2011 1. Application Scenario A Large Scale NAT (LSN) is responsible for translating source addresses and ports for packets passing into and out of the provider network. Especially for large scale service providers, one LSN may need to support at least tens of thousands of customers, resulting in heavy processing requirements for the LSN. In some broadband scenarios an additional NAT is present at the edge of the customer network. For convenience we will call this the Home Gateway. The load on the LSN could be reduced if address and port translation were actually done at the Home Gateway. Achieving such an outcome would require coordination between the two devices. This memo makes a detailed proposal for the required coordination mechanism. 2. Proposed Solution 2.1. Delegation of Port Ranges The basic proposal made in this memo is to provide the means for the Home Gateway to request that the LSN delegate to it a set of ports and optionally an external address that will be associated with those ports. It is proposed to use the Port Control Protocol (PCP) [ID.port-control-protocol] to achieve this. The procedure is illustrated in Figure 1. The LSN allocation of port sets MAY take into account the advice given in [ID.behave-natx4-log-reduction]. [Open Issue: if we want to make the port sets discontinuous, we must either allow negotiation of the algorithm or parameters of that algorithm for determining the complete set from a given starting point, or specify it here. Specifying it all here is probably counter-productive, given that this is a security measure to make port guessing harder.] Tsou, et al. Expires September 5, 2011 [Page 3] Internet-Draft NAT Coordination Using Port Allocation March 2011 Home Gateway CG-NAT | | | | |------(1)Pinhole Request---->| | | | +----+----+ | | Create | | |NAT entry| | +----+----+ | | |<-----(2)Pinhole Response----| | (Port Set) | | | Figure 1: Acquiring a Delegated Port Set If the Home Gateway allocates all of the ports that have been delegated to it for a given protocol, it MAY send a request to the LSN for another delegated set of ports. If the LSN satisfies that request, the Home Gateway MUST release the additional set as soon as possible. To achieve this, the Home Gateway May follow a policy for allocation of additional ports to flows, that has the same effect as searching for "free" ports in the port sets in the order in which they were delegated to the Home Gateway. A port SHOULD be considered "free" if no traffic has been observed through it for the timeout interval specified for the protocol concerned, as discussed in [ID.behave-natx4-log-reduction], or if the Home Gateway knows through other means (e.g., host reboot) that it is no longer in use. 2.2. Packet Processing At the Home Gateway and LSN The Home Gateway maps outgoing flows to the delegated ports. If an external address was received it uses that for the source address; otherwise it retains the private address of the Home Gateway as the source address. The procedures are more complicated, of course, if the IP version running externally to the LSN is different from the IP version running between the Home Gateway and the LSN, since the destination address also has to be translated. The details depend on the particular transition mechanism in use, and are left as an exercise for the reader. If the private address is retained, the LSN recognizes it from the original delegation request and changes the source address but not the port before forwarding the packet. If the external public address was used, the LSN is not useful and another device may be needed to allocate the port range. Tsou, et al. Expires September 5, 2011 [Page 4] Internet-Draft NAT Coordination Using Port Allocation March 2011 In the reverse direction, the LSN recognizes the public destination address and port of an incoming packet as belonging to a delegated set for the Home Gateway. It translates the destination address, if necessary, leaving the destination port unchanged. The Home Gateway translates the destination port and address to the corresponding values in the customer network and forwards the packet in turn. 2.3. Proposed Enhancements To and Usage Of the Port Control Protocol This document proposes the following new option for PIN opcodes: PORT_SET_REQUESTED. option number: to be allocated is valid for OpCodes: PIN44, PIN64, PIN46, or PIN66 is included in responses: MUST has length: 0 in requests, 4 in successful responses. [As mentioned above, if non-consecutive sets of ports are allocated, we may want to add parameters of the algorithm for deriving the complete set from the initial value provided in the "assigned external port" field of the response.] may appear more than once: no When constructing a PIN request with the PORT_SET_REQUESTED option, the client MUST set the "internal port" field of the request to zero. If requesting a new set of delegated ports, the client MAY set the "requested external port" field to a non-zero value. If releasing a set of delegated ports (i.e., by setting the "Requested lifetime" field to zero), the client MUST set the "requested external port" field to the value of the "assigned external port" field of the earlier response from the server. The remaining fields of the PIN request MUST be set as directed by [ID.port-control-protocol] [Open issue: for a release, should the PORT_SET_REQUESTED option have the same contents as it had in the earlier response?] Upon receiving a PIN request with the PORT_SET_REQUESTED option, the server MAY reject it using return codes 151 - NOT_AUTHORIZED, or 152 - USER_EX_QUOTA. In this case, the PORT_SET_REQUESTED option in the response MUST have zero length (no data). If the server chooses to honour the request, it MUST place the value of the first port in the assigned set in the "assigned external port" field of the response. It MUST set the length of the PORT_SET_REQUESTED option in the response to 4, and MUST provide the number of ports in the delegated set as the value of the option. Tsou, et al. Expires September 5, 2011 [Page 5] Internet-Draft NAT Coordination Using Port Allocation March 2011 3. Port Range Options The Port Range option is used to specify one range of ports (contiguous or not contiguous) pertaining to a given IP address. The starting point of the ports and the number of delegated ports are used to infer a set of allowed port values. This section provides only one method to request the port range values. Other ways and Optcode can be proposed in later versions. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Protocol | Reserved (24 bits) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Starting point 1 | Number of delegated ports 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | : | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Starting point n | Number of delegated ports n | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: Port_Range_Option These fields are described as below: o Starting Port: A 16 bit value used as an input to the specified function. o Number of delegated ports: A 16 bit value specifying the number of ports delegated to the client for use as source port values. o The value "n" indicates that the port range is not contiguous. 4. Security Considerations Will do later. Trust issues between the client and server, plus the port randomization issues discussed in [ID.behave-natx4-log-reduction]. 5. IANA Considerations Will register the new option if this draft goes through as a standalone document rather than being incorporated into the base protocol. Tsou, et al. Expires September 5, 2011 [Page 6] Internet-Draft NAT Coordination Using Port Allocation March 2011 6. References 6.1. Normative References [ID.port-control-protocol] Wing, D., "Port Control Protocol (PCP)", January 2011. 6.2. informative References [ID.behave-natx4-log-reduction] Tsou, T., Li, W., and T. Taylor, "Port Management To Reduce Logging In Large-Scale NATs", September 2010. Authors' Addresses Tina Tsou Huawei Technologies Bantian, Longgang District Shenzhen 518129 P.R. China Phone: Email: tena@huawei.com Cathy Zhou Huawei Technologies Bantian, Longgang District Shenzhen 518129 P.R. China Phone: Email: cathyzhou@huawei.com Qiong Sun China Telecom Beijing Research Institute Room 708 No.118, Xizhimenneidajie Beijing, xicheng District 100035 China Phone: +86 10 58552923 Email: sunqiong@ctbri.com.cn Tsou, et al. Expires September 5, 2011 [Page 7] Internet-Draft NAT Coordination Using Port Allocation March 2011 Tom Taylor Huawei Technologies 1852 Lorraine Ave.t Ottawa, Ontario K1H 6Z8 Canada Phone: Email: tom111.taylor@bell.net Tsou, et al. Expires September 5, 2011 [Page 8]