INTERNET DRAFT C. Huitema <draft-ietf-midcom-scenarios-01.txt> Microsoft Expires November 3, 2001 May 3, 2001 MIDCOM Scenarios Status of this memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. This document is an Internet-Draft. 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. Abstract As trusted third parties are increasingly being asked to make policy decisions on behalf of the various entities participating in an application's operation, a need has developed for applications to be able to communicate their needs to the devices in the network that provide transport policy enforcement. Examples of these devices include firewalls, network address translators (both within and between address families), signature management for intrusion detection systems, and multimedia buffer management. These devices are a subset of what can be referred to as 'middle boxes.' This document describes traversal scenarios that a 'middle box traversal protocol' should enable. 1 Introduction In order to delineate the requirement of the MIDCOM protocol, we present here a set of scenarios that should be enabled by this protocol. The scenarios include running a server behind a NAT/Firewall, enabling direct connection between peers that exchange addresses in an ad-hoc way, e.g. through an instant messaging service, and enabling peer-to-peer communication with explicit signaling, e.g. using SIP or H.323. These scenarios may include several variants that we will present. We also present the evolution of these scenarios when IPv6 provides global addresses, and introduce the "6to4 router" scenario required for IPv6 transition, Huitema [Page 1]
INTERNET DRAFT MIDCOM Scenarios and the IPSEC scenario enabled by IPv6. This memo uses the definitions introduced in [MIDBOXFRAME], in particular the definition of a Firewall/NAT. 2 Scenarios 2.1 TCP server behind a firewall/NAT An internal server wants to receive TCP-IP connections requests from the outside (where outside is some place outside a domain). An example is, running a web server in a domain protected by a firewall. __________ _________ | |-----[DNS Query]-------->| | ___________ | external |<---[DNS Response]------<| N.S. | | | | host | |_________| | Internal | |__________| | Host | v |___________| v __________ v ^ v | |<--midcom -----/ ^ v | firewall | ^ \>>>Connection Attempt>>>>| / NAT |>>>>>>>>>>>>>>>>>>^ |__________| In this scenario, the internal host publishes the IP address and TCP port number at which it can be joined in a name server, using for example SRV and A records in the DNS. The IP address that is published must be valid in the "external" domain; if this external domain is the current Internet, the published IP address must be valid in the global Internet. The scenario implies that the following operations happen in sequence: 1) The internal host interacts with the firewall/NAT, using the midcom protocol. As a result of the interaction, the internal host learns the IP address and TCP port that it may advertise to external parties. 2) The internal host publishes the information in a name server. 3) The external host obtains the information from the name server. 4) The external host issues a TCP connection request, and sends a TCP SYN packet. 5) The firewall/NAT receives the packet, performs address translations and port mapping if necessary, and relays the TCP SYN packet to the internal host. Huitema [Page 2]
INTERNET DRAFT MIDCOM Scenarios 6) After that point, the TCP connection proceeds. In the diagram, we depict only one external host, but this is an example, not a limitation. Once the address and ports are published in the name server, an unlimited number of external hosts may attempt to connect to the internal server. It is quite clear that the interaction between the internal host and the firewall/NAT described in the first step of the scenario may require some form of access control. The specific form of access control will depend of the internal domain's policies. In practical examples, these policies varies from allowing all internal hosts to run services, in un-managed domains, to allowing only a specific set of services on a specific set of hosts. There are two interesting variants of that scenario: the use of UDP instead of TCP, and the control of the firewall/NAT by a third party instead of the internal host. 2.1.1 UDP Server behind a firewall/NAT This scenario is exactly the same as the TCP server scenario, with the difference that the external host issues unsolicited UDP packets, instead of TCP/SYN packets. An example of this scenario is, running a SIP server or a DNS server behind a NAT/Firewall. 2.1.2 TCP/UDP server authorized by a third party This scenario differs from the base scenario in a simple way: the midcom protocol is exercised by a third party instead of the host itself. In the diagram, we call this third party a management server: __________ _________ ___________ | |-----[DNS Query]-------->| | | | | external |<---[DNS Response]------<| N.S. | | Management| | host | |_________| | Server | |__________| |___________| v __________ v v | |<--midcom -----/ v | firewall | ___________ \>>>Connection Attempt>>>>| / NAT |>>>>>>>| Internal | |__________| | Host | |___________| The management server will interact with the firewall/NAT, using the midcom protocol, as in the step 1 of the main scenario. The other steps will be unchanged. A key point of this scenario is that the internal host is unaware of the midcom protocol; in practical deployment, the internal host can be an unmodified server, such as a web server responding to HTTP requests on incoming TCP connections, Huitema [Page 3]
INTERNET DRAFT MIDCOM Scenarios or a DNS server responding to name requests on incoming UDP packets. 2.2 Peer-to-peer communication with ad-hoc rendezvous The mediated peer-to-peer communication scenario describes hosts that communicate through some external third party, such as an instant messaging service, and then establish a direct communication channel, such as a TCP connection. An example of this scenario is, starting the exchange of files from an IM service. __________ ___________ | | | | | external |<-- Messaging --> | IM Server | <-- Messaging -. | host | |___________| __v________ |__________| | | v | internal | v | host | v |___________| v __________ v ^ v | |<--midcom -----/ ^ v | firewall | ^ \>>>Connection Attempt>>>>| / NAT |>>>>>>>>>>>>>>>>>>^ |__________| This scenario does not involve any particular cooperation between the firewall/NAT and the IM server. The connection between the internal host and the IM system can use any protocol, in particular combinations of TCP, HTTP and TLS. The scenario implies that the following operations happen in sequence: 1) The internal and external hosts communicate through some form of instant messaging service or chat room. At some point, they decide to establish a direct channel, e.g. to exchange files. 2) The internal host interacts with the firewall/NAT, using the midcom protocol. As a result of the interaction, the internal host learns the IP address and TCP port that it may advertise to the external host. 3) The internal host sends the IP address and the TCP port to the external host. 4) The external host issues a TCP connection request, and sends a TCP SYN packet. 5) The firewall/NAT receives the packet, performs address translations and port mapping if necessary, and relays the TCP SYN packet to the internal host. 6) After that point, the TCP connection proceeds. Huitema [Page 4]
INTERNET DRAFT MIDCOM Scenarios 7) After the application has finished using the connection, the internal host may interact with the firewall/NAT and close the hole. In this scenario, the NAT firewall only has to authorize the communication between a single internal host and a well identified external host; the authorization is typically valid for only a single TCP connection. In any case, the authorization is only valid for a limited duration. There are two variants of that scenario, when the dialog occurs over UDP and when both hosts are hidden behind a firewall/NAT. 2.2.1 Peer-to-peer communication using UDP This scenario is exactly the same as the TCP scenario, with the difference that the external host issues UDP packets, instead of TCP/SYN packets. An example of this scenario is, streaming audio or video between two peers. 2.2.2 Both peers behind firewalls When both peers are behind firewalls, it is hard to predict the IP address that will be used by the host initiating the TCP connection. In this situation, there are two options: 1) Allow the internal host to accept TCP connections from any external address. 2) Let the "external" host use the midcom protocol to predict the "external" IP address that it will use for the incoming connection. The first option may look insecure, but the possible insecurity of accepting connections from multiple source is often mitigated by application level protections, such as security tokens exchanged through the IM channel. A variation of this option is to accept connections from multiple sources, but restrict the hole to exactly one source once the connection has been established. 2.3 Peer-to-peer communication with explicit signaling In this scenario, two peers that want to communicate use a standard signaling protocol such as SIP or H.323. The communication requests for internal host arrive to an internal server, e.g. the "sip proxy" for the internal domain. In the diagram, we call this agent the "internal server". The following description assumes the use of SIP; scenarios that use an H.323 gatekeeper will use a different message flow, but will involve similar interactions between the gatekeeper and the firewall/NAT. Huitema [Page 5]
INTERNET DRAFT MIDCOM Scenarios The scenario implies that the internal server can receive signaling packets from external hosts and servers. This is an application of the previously describe scenarios: TCP or UDP server behind a firewall/NAT. There are really two scenarios to consider, depending on whether the call initiates from an internal host or from an external host. These two scenarios assume that the firewall/NAT interacts with the internal server. We will then consider a variant, in which the interactions with the firewall/Nat are directly performed by the internal host. 2.3.1 Explicit call from an internal host In this scenario, an internal host calls a third party through the internal server. __________ _________ __________ | |<--[Invite]---<| |<----------| |<--. | external |---[response]->| Server |---------->| Internal |--.| | host | |_________| | Server | || |__________| |__________| || ^v __________ v || ^v | |<--midcom-/ || ^v | firewall | ______v|___ ^\>>> Media over UDP >>>>>>| / NAT |>>>>>>>| Internal | \<<<<<<<<<<<<<<<<<<<<<<<<<<|__________|<<<<<<<| Host | |___________| The scenario implies that the following operations happen in sequence: 1) The internal host who want to start the call sends an invite message to its preferred internal server. The invite message carries the name of the invited user, and the IP address and UDP ports through which the internal host intends to receive the media, e.g. voice or video. 2) The internal server determines that the target of the invite is located outside the internal domain. If the firewall/NAT performs address and port mapping, the internal server must interact with the firewall/NAT and learn the "external mappings" corresponding to the IP address and UDP ports used by the internal host. 3) The internal server updates the address and port information in the invite message, and relays the call to the "external server." 4) The external server determines that the target of the invite is located in a specific external host. It relays the call to this Huitema [Page 6]
INTERNET DRAFT MIDCOM Scenarios host. 5) The external host responds to the call. The response provides the IP address and UDP port at which the external host will be expecting to receive the media. 6) The response message is relayed by the external server to the internal server. 7) The internal server receives the response. At this point, it knows the IP addresses and ports used by both the internal and the external host. The internal server interacts with the firewall/NAT using the midcom protocol, to guarantee that the exchange between the internal and external host will be authorized. 8) The response message is relayed by the internal server to the internal host. 9) The external and internal hosts send media packets to the addresses and ports mentioned in the invite and response message; these packets pass through the Firewall/NAT and reach their destination. We should note that, at step 2, the internal server must learn the external mappings of the internal address and ports; at this stage, it does no know the IP address and ports of the third party. There is a potential race condition between the signaling message that "responds to the call" and the first media packets sent by the called party. Should the signaling loose the race, the early media packets will bang against a closed firewall and be clipped. It is in theory possible to design signaling exchange that include a three ways handshake before media transmission can start, followed by a message asking to start ringing only after the availability of all necessary resource has been verified. However, this is not compatible with existing implementations of SIP or H.323, and would require a serious revisiting of the gatewaying between SIP or H.323 and the telephone network. The description assumes that the hosts use the same UDP ports in both direction of the media communication. This is not necessarily the case. The source IP address may be unpredictable in the case of multi-homed hosts; the source port may be systematically different from the receive port in some implementation, e.g. parallel processing of the send and receive channels by different software or hardware components. The scenario does not necessarily require a strict control by the firewall/NAT of the source address and port authorized to send data. Many implementations already support exchange of media level Huitema [Page 7]
INTERNET DRAFT MIDCOM Scenarios authentication and encryption keys during the call set-up. This provides a level of security that is at least as good as any control of the source address and port: if attackers can manage to read the signaling exchange and get the keys, they can just as well discover the IP addresses and ports, and send forged packets. 2.3.2 Explicit call to an internal host In this scenario, a third party host calls an internal through the internal server. __________ _________ __________ | |---[Invite]--->| |---------->| |---. | external |<--[response]-<| Server |<----------| Internal |<-.| | host | |_________| | Server | || |__________| |__________| || ^v __________ v || ^v | |<--midcom-/ || ^v | firewall | ______|v___ ^\>>> Media over UDP >>>>>>| / NAT |>>>>>>>| Internal | \<<<<<<<<<<<<<<<<<<<<<<<<<<|__________|<<<<<<<| Host | |___________| The scenario implies that the following operations happen in sequence: 1) The external host who want to start the call sends an invite message to its preferred external server. The invite message carries the name of the invited user, and the IP address and UDP ports through which the external host intends to receive the media, e.g. voice or video. 2) The external server determines that the target of the invite is located in the internal domain. It relays the call to the "internal server." 3) The internal server determines that the target of the invite is located in a specific internal host. It relays the call to this host. 4) The internal host responds to the call. The response provides the "internal" IP address and UDP port at which the internal host will be expecting to receive the media, e.g. voice and video. 5) The internal server receives the host's response. At this point, it knows the IP addresses and ports used by both the internal and the external host. 6) The internal server interacts with the firewall/NAT using the midcom protocol. If the firewall/NAT performs address mapping, Huitema [Page 8]
INTERNET DRAFT MIDCOM Scenarios the internal server retrieves the mapping of the IP address(es) and port(s) used by the internal host. 7) The internal server prepares an updated response message that reflects the mapping of the internal addresses. It sends the response message to the external server. 8) The response message is relayed to the external host by the external server. 9) The external and internal hosts send media packets to the addresses and ports mentioned in the invite and response message; these packets pass through the Firewall/NAT and reach their destination. We note that in this sequence the interaction with the firewall only occurs after the internal host has accepted the call. This can create an annoying effect if the interaction with the firewall fails, equivalent to hearing a void telephone line after picking an incoming call. To avoid this effect, the internal server will have to somehow guarantee that the Firewall/NAT interaction will be successful before relaying the call to the internal host. Just like scenario 2.3.1, it may not be possible or desirable to predict or check the source IP address and UDP ports used by the internal and external hosts. 2.3.3 Firewall interaction by the internal host It is possible to update the previous two scenarios so that the internal host interacts directly with the Firewall/NAT, rather than relying on the internal server. This set-up has the advantage of avoiding the "void telephone line" effect mentioned in the previous scenario: the internal host that receives the invite can pick the UDP ports used for audio and video and interact with the firewall/NAT before "ringing" the user; if the interaction fails, the call can be rejected without bothering the user. This set-up however has the disadvantage that all internal hosts must become able to interact with the Firewall/NAT, which in many cases may not be practical. The direct interaction between the internal host and the NAT/Firewall is already described in the "peer-to-peer" scenarios of the previous section. The only difference between these scenarios is the possibility for the internal server to pass some form of "authorization token" to the internal host. 2.3.4 Early media The "early media" scenario is an important variations of the scenario 2.3.1. Early media designates media transmission sent Huitema [Page 9]
INTERNET DRAFT MIDCOM Scenarios before the actual completion of the call. Examples are ringing tones and voice messages describing particular network conditions, such as "we are trying to locate your correspondent." In the early media scenario, the following interactions will happen in sequence: 1) The internal host who want to start the call sends an invite message to its preferred internal server, as in 2.3.1, 2) The internal server determines that the target of the invite is located outside the internal domain. If the firewall/NAT performs address and port mapping, the internal server must interact with the firewall/NAT and learn the "external mappings" corresponding to the IP address and UDP ports used by the internal host, as in 2.3.1. In addition, the internal server requests the authorization to receive packets from a yet unspecified external source. 3) The internal server updates the address and port information in the invite message, and relays the call to the "external server." 4) The external server, or a secondary server acting on its behalf, sends a stream of voice packets towards the "external mappings" of the IP address and UDP ports used by the internal host, 5) The firewall/NAT receives these packets and forwards them to the internal host, 6) The call proceeds as in 2.3.1. There is a common telephony practice of sending recorded announcements during call set-up; the source IP address of these announcements is not likely to be the same as the source IP address used after call set-up is complete. It is theoretically possible to use the equivalent of call transfer to switch between multiple source in a controlled fashion, but this introduce a lot of signaling complexity, and is incompatible with currently deployed hardware and software. In practice, this scenario requires that the firewall/NAT "opens a hole" without knowing the IP address and port of the external peer. 2.3.5 Mobility of the external host The mobility scenario can be thought as a complication of scenarios 2.3.1 or 2.3.2, in which the IP address of one of the peers is allowed to change during a call, due to either mobility or network renumbering. The scenario involves the following exchanges: 1) The external host receives a new IP address, and sends a signaling packet to the "internal server" mentioning the new IP address, 2) The internal server programs the firewall/NAT to start Huitema [Page 10]
INTERNET DRAFT MIDCOM Scenarios authorizing packets between this new address and the internal host, 3) In parallel with 2, the internal server relays the signaling message to the internal host, 4) The internal and external hosts exchange packets with the new address; the firewall/NAT authorizes these packets to proceed. SIP supports that through the re-invite mechanism, but we should note that there is either a gap in the call or a race condition between media packets with the new source address and the signaling message. The external host is likely to source packets with its new address immediately after the address change; if the packets arrive before the firewall/NAT has been programmed to accept them, the packets will bang against the closed firewall/NAT and be dropped. 2.4 IPv6 Scenarios All of the scenarios mentioned above can be modified if the domains have been upgraded to run IPv6. The main difference between the IPv6 and IPv4 scenarios is that the internal hosts use global addresses. The "Firewall/NAT" combination becomes strictly a "Firewall"; however, in many domains, there will still be the need to perform explicit authorizations. In order to start the IPv6 transition, we will have to introduce relay routers, as specified in [RFC3056]. In addition, the global addressing allows the introduction of another scenario, the use of IPSEC between an internal and an external host. 2.4.1 IPv6 TCP or UDP server behind a firewall In this scenario, the internal host publishes the IP address and TCP port number at which it can be joined in a name server, using for example SRV and A6 records in the DNS. The sequence of operation is the same as in the IPv4 case, but each of the step has a different emphasis: 1) The internal host interacts with the firewall, using the midcom protocol. As a result of the interaction, the firewall learns the IP address and TCP port that the host will use. 2) The internal host publishes the information in a name server. 3) The external host obtains the information from the name server. 4) The external host issues a TCP connection request, and sends a TCP SYN packet. 5) The firewall receives the packet, checks that the destination address and port are authorized, and relays the TCP SYN packet to the internal host. Huitema [Page 11]
INTERNET DRAFT MIDCOM Scenarios 6) After that point, the TCP connection proceeds. The only reason for the first step in the scenario is access control. If the domain's policy is to authorize all hosts to receive all traffic, there is no need for this step - indeed, the firewall becomes mostly a transparent IPv6 router. The impact of IPv6 on the two variants of that scenario is obvious: the use of UDP will have to be authorized if needed, and there may be a need to let a third party perform the authorizations. 2.4.2 Peer-to-peer communication with ad-hoc rendezvous and IPv6 With IPv6, both peers have a global address. They will only have to interact with a firewall if the domain's manager insists on having a firewall control all incoming traffic; there will not be a need for a NAT functionality. The internal host may still need to interact with the firewall in order to "open a hole" for the packets coming from the remote peer, but it will always be able to specify the complete "five tuple" of protocol type, IP addresses and UDP ports; the problem exposed in the case when both hosts were being firewalls disappears. 2.4.3 Peer-to-peer communication with explicit signaling and IPv6 This scenario is also made simpler by the availability of global addresses. In the case of a call from an internal host, the internal server will not have to rewrite the addresses in the outgoing "invite"; it will only have to interact with the firewall to open a hole after the reception of the response. In the case of a call to an internal host, the internal server may still have to interact with a firewall if the domain managers insist on requiring this type of protection; it will do so with an explicit knowledge of the IPv6 addresses and UDP ports used by both ends of the connection. 2.4.4 IPv6 transition service behind a firewall/NAT A typical IPv6 transition scenario is described in [RFC3056]. In this scenario, IPv6 is progressively made available by installing in each site a "6to4" router, which receives IPv6 packets through automatic tunnels and forwards them to internal IPv6 hosts. __________ _________ | |-----[DNS Query]--->| | ___________ | external |<---[DNS Response]-<| N.S. | | | | host | |_________| | 6to4 | |__________| | Router | ^ |___________| | __________ v ^ ^ | | |<--midcom -/ | | | | firewall | | \-> IPv6 \--- IPv6/IPv4 -->| / NAT |<-- IPv6/IPv4 -/ |__________| Huitema [Page 12]
INTERNET DRAFT MIDCOM Scenarios In this scenario, the 6to4 router provides the internal IPv6 hosts with IPv6 addresses; the IPv6 prefix in these addresses is based on a "global" IPv4 address of the domain. The IPv6 hosts will publish their IPv6 addresses in the DNS. The external hosts will send IPv6 packets encapsulated in IPv4 headers, whose destination will be the internal 6to4 router; the 6to4 router will receive the packets sent by internal hosts to external hosts, and will encapsulate them with adequate IPv4 headers. The scenario implies that the following operations happen in sequence: 1) The 6to4 router interacts with the firewall/NAT, using the midcom protocol. As a result of the interaction, the 6to4 router learns a global IPv4 address that it can use to build a 6to4 prefix. 2) The internal hosts publish IPv6 addresses based on this prefix in a name server. 3) The external host obtains the information from the name server. 4) The external host sends IPv6 packets towards this address. 5) The firewall/NAT receives the packet, notes that these are IPv6 packets carried in IPv4 (protocol type = 41), translates the destination address if necessary and relays the packet to the 6to4 router. 6) The 6to4 router removes the IPv4 header and forwards the IPv6 packet to the internal host. 7) When the 6to4 router receives an IPv6 packet, it determines the adequate IPv4 destination, and uses it to build an encapsulation IPv4 header. 8) The firewall/NAT receives the encapsulated packet. It may perform translation of the source address if needed. It forwards the packet to the IPv4 destination. In the diagram, we depict only one external host, but this is an example, not a limitation. It is quite clear that, if firewalling function are desired for the IPv6 traffic, these functions will have to be provided by the 6to4 router. 2.4.5 Enabling an IPSEC connection between IPv6 hosts Once IPv6 provides global addresses to internal hosts, it becomes possible to establish IPSEC associations between an internal host Huitema [Page 13]
INTERNET DRAFT MIDCOM Scenarios and an external host. The establishment of the association will start by a key exchange, and will continue with the exchange of encrypted traffic. __________ | | | external | | host | ___________ |__________| | | ^ | internal | | | host | | |___________| | __________ v ^ | | |<--midcom -----/ | \-- Key exchange, IPSEC ->| firewall |<-----------------/ |__________| The scenario implies that the following operations happen in sequence: 1) The internal and external hosts decide to communicate, e.g. after the internal host finds the address of the external host in the DNS. 2) The internal host and the external host exchange key negotiation packets (IKE). The firewall passes these packets. 3) The internal host uses the midcom protocol to signal to the firewall that it is going to exchange encrypted traffic with an external host, and obtains the authorization to proceed. 4) IPSEC packets are exchanged. 5) After the hosts have finished using the IPSEC association, the internal host may interact with the firewall and close the hole. We should note that this scenario requires that the firewall delegates some of its control functions to the internal host: encrypted traffic cannot be inspected. 3 Security Considerations Firewalls are used by domain managers to control the traffic that can be exchanged between their domain and the Internet. In the scenarios that we described, this control is relaxed in order to enable certain applications. Relaxing the control has to be a conscious decision of the domain manager. 4 IANA Considerations The purpose of this memo is to document the allocation by IANA of an IPv4 prefix dedicated to the 6to4 gateways to the native v6 Huitema [Page 14]
INTERNET DRAFT MIDCOM Scenarios Internet; there is no need for any recurring assignment. 5 Copyright The following copyright notice is copied from RFC 2026 [Bradner, 1996], Section 10.4, and describes the applicable copyright for this document. Copyright (C) The Internet Society March 23, 2001. All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assignees. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 6 Intellectual Property The following notice is copied from RFC 2026 [Bradner, 1996], Section 10.4, and describes the position of the IETF concerning intellectual property claims made against this document. The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use other technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. Copies of claims of rights made available for publication and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such Huitema [Page 15]
INTERNET DRAFT MIDCOM Scenarios proprietary rights by implementers or users of this specification can be obtained from the IETF Secretariat. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights which may cover technology that may be required to practice this standard. Please address the information to the IETF Executive Director. 7 Acknowledgements The discussion presented here was triggered by the meeting of the MIDCOM working group in Minneapolis. An initial description of the "TCP server" scenario was sent to the group's e-mail list by Eliot Lear. 8 References [RFC3056] B. Carpenter, K. Moore. Connection of IPv6 Domains via IPv4 Clouds. RFC 3056, February 2001. [MIDBOXFRAME] Middlebox Communication Architecture and Framework. Work in progress. 9 Author's Addresses Christian Huitema Microsoft Corporation One Microsoft Way Redmond, WA 98052-6399 Email: huitema@exchange.microsoft.com INTERNET-DRAFT Midcom Scenarios March 29, 2001 Huitema [Page 16]
