Internet Draft Kaouthar Sethom INT-France Hossam Afifi Document: draft-sethom-adhoc-gateway- INT-France selection-01.txt Frank Y. Li Expires: June 2006 UniK, Norway Andreas Hafslund Thales,Norway January 2006 Gateway Selection in Multi-homed Ad Hoc Networks 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. Sethom Expires - June 2006 [Page 1] Gateway Selection in Multi-homed Ad Hoc Networks January 2006 Abstract When an ad hoc network is connected to the Internet, it is important for the mobile nodes to detect available gateways providing access to the Internet. Therefore, a gateway discovery and selection mechanism is required. Current ad hoc routing protocols have been extended to support gateway discovery. However, the selection process is based on the default gateway configuration. We here describe an extension to MANET protocols to enable the gateway selection according to users’ requirements, especially in the case where multiple gateways co- exist. Conventions used in this document 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. Table of Contents 1. Introduction...................................................2 2. Terminology ...................................................4 3. Protocol overview..............................................4 3.1 GNA Message Format.........................................5 4. Addressing and auto-configuration considerations .............7 5. IPv6 Considerations............................................8 6.Security Considerations.........................................8 References........................................................8 Authors’ Addresses................................................9 1. Introduction An ad hoc network is a highly dynamical wireless network without the use of any existing network infrastructure or centralised administration. An ad hoc network can operate either in a stand-alone mode or as a subnetwork to the global Internet. In the latter case, an ad hoc user does not only demand for Internet connectivity but also a certain level of QoS. To provide this connectivity, some ad hoc nodes act as “gateways” which can be used by mobile terminals to seamlessly communicate with other nodes in external networks. Sethom Expires - June 2006 [Page 2] Gateway Selection in Multi-homed Ad Hoc Networks January 2006 Therefore, a user – even inside an ad hoc network - must be able to discover the gateway, and/or to select an optimal gateway in the presence of multiple gateways, according to its application requirements. In a simpler case where there is only one gateway available, the problem is simply how to discover the gateway and configure a globally valid address to the mobile node for incoming and outgoing traffic. In a more complicated case where several gateways co-exist, i.e., for multi-homed ad hoc networks, the availability of multiple gateways provides the network with higher robustness and more flexibility for global Internet connectivity. Therefore, it is important, especially for a multi-homed network, to discover and select a gateway that is the ‘optimal’ one among all available gateways, according to certain criteria. Methods for Internet gateway discovery include reactive [1], proactive [2], or hybrid [3] approach. For multi-homed ad hoc networks, one specific problem is related to which gateway(s) a node should use. The challenge stems from the need to inform ad hoc nodes about available gateways and their associated capabilities in an infrastructure-less and extremely dynamic environment. A straightforward solution for gateway selection is to select the gateway that has the shortest number of hops to the mobile node as the ‘working’ gateway. This means that when a mobile node is closer to a new gateway than the previous one, the mobile node will usually switch to the second gateway for the global connectivity. If the mobile node already has a data connection up and running, this can impose problems. This is especially true when the gateways have deployed NAT or some specific security mechanisms. Mechanisms for gateway connection in multi-homed proactive ad hoc networks were discussed in [4]. Generally speaking, selecting a gateway based on only the shortest number of hops does not appear to be good enough. Another alternative is to consider both the distance in number of hops between mobile nodes and gateways and the traffic load of available gateways. The one that has the minimum weighted sum of Euclidean distance for these two factors will be selected as the gateway [5]. Other considerations for gateway selecting include load and congestion status in the gateways, delay for certain types of traffic flow, session continuity when shifting gateways etc. In this draft, we present a gateway selection protocol for multi- homed ad hoc networks. Other issues related to multi-homing for a MANET, such as addressing and auto-configuration, NAT deployed on the gateways, the use of Mobile IP, and security mechanisms, are not addressed in this draft. Sethom Expires - June 2006 [Page 3] Gateway Selection in Multi-homed Ad Hoc Networks January 2006 2. Terminology Multi-homed ad hoc network An ad-hoc network which has more than one gateway connecting it to the global Internet. 3. Protocol overview When a node wishes to offer Internet connectivity to other nodes in a MANET, it sends (or disseminates) Gateway and Network Association (GNA) messages. In the case of a proactive routing protocol this is done periodically. A selected set of nodes that received a GNA packet shall forward it to their neighbours. GNA message is in this way flooded onto the entire ad hoc network. Duplicate retransmissions will be eliminated locally (i.e., each node maintains a duplicate table to prevent transmitting the same message twice). However, in the case of a reactive protocol the generation of GNA message is generally in response to some previous gateway discovery request message. The GNA message follows then down the reverse path of the associated request to reach the querying node. At each node in the network, all received GNA packets are registered in the gateway table. This information repository is re-freshed periodically. This means that entries are deleted as soon as their validity time expires. GNA routing is done hop-by-hop. This means that when A (Figure 1) receives from B a GNA announcing connectivity to the Internet. It adds a route in its gateway table with the next-hop on the route to the gateway i.e B as the actual gateway and a route metric equal to 2. A --- B --- G ------ Internet Figure 1: GNA routing When a GNA message is received, the node updates its gateway table either by updating an existing entry, or if no entry exists for the gateway address, creating a new entry. All nodes in the ad hoc network must support GNA processing and route calculation for the actual GNA routing to work. If a node routes Sethom Expires - June 2006 [Page 4] Gateway Selection in Multi-homed Ad Hoc Networks January 2006 Internet traffic to an intermediate neighbor based on GNA information, the intermediate neighbor must also have set up an Internet route for the traffic to be routed. Therefore, in the general case, the neighbor must support GNA functioning. The present document is presented with IPv4 addresses. Considerations regarding IPv6 are given in section 5. 3.1 GNA Message Format A GNA message contains triplets of (router interface characteristic, network address, netmask). The proposed format of an GNA-message is (omitting IP and UDP headers): 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length | Message Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message Type | Vtime | Time To Live | Hop Count | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Originator Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Interface Type| Cost | Throughput | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Network Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Netmask | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Interface Type| Cost | Throughput | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Network Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Netmask | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Fields: Sethom Expires - June 2006 [Page 5] Gateway Selection in Multi-homed Ad Hoc Networks January 2006 Length The length (in bytes) of the packet Sequence Number The Message Sequence Number MUST be incremented by one each time a new GNA message is transmitted. A separate Packet Sequence Number is maintained for each interface such that packets transmitted over an interface are sequentially enumerated. Message Type Set to GNA_MESSAGE Vtime This field indicates for how long time after reception a node MUST consider the information contained in the message as valid, unless a more recent update to the information is received. TTL field May be set from 1 to 255. Hop Count This field contains the number of hops a message has attained. It’s particularly interesting to have this information in the case of an adhoc network; to know how far the gateway is. Initially, this is set to '0' by the originator of the message Originator Address This field contains the address of the node, which has originally generated the GNA message i.e the gateway. This field SHOULD NOT be confused with the source address from the IP header, which is changed each time to the address of the intermediate interface which is re-transmitting this message. The Originator Sethom Expires - June 2006 [Page 6] Gateway Selection in Multi-homed Ad Hoc Networks January 2006 Address field MUST *NEVER* be changed in retransmissions Interface Type This field indicates the technology used by the gateway Egress interface. Example Bluetooth, 802.11, Ethernet, UMTS … Type values can be encoded as follows: 0x00 Ethernet (default) 0x01 Bluetooth 0x10 UMTS 0x11 802.16 … Cost This field indicates the communication cost associated with the use of the interface described in the interface Type field. This parameter can be a combination of different metrics such as offered QoS, security issues, price and possibly other preferences. Throughput This field indicates the throughput associated with the gateway egress interface i.e. nominal bandwidth/capacity/datarate. Network Address The network address associated with the egress interface described in the interface Type field. Netmask The netmask, corresponding to the network address immediately above. 4. Addressing and auto-configuration considerations Sethom Expires - June 2006 [Page 7] Gateway Selection in Multi-homed Ad Hoc Networks January 2006 When a mobile node has discovered a gateway, it will need to configure an address related to this gateway. Many suggestions assume that the mobile node will need to configure an address from the gateway’s network prefix. In this way, the node will be in an address subnetwork of that gateway. This new address must then be inserted into the ad hoc routing so the node is reachable on this address. The mobile node should also be reachable on other temporary addresses, and its home address. This imposes several more problems for the ad hoc routing. There exist several Internet-Drafts, e.g., [6][7], on addressing and auto-configuration in MANETs. Therefore, these issues, although closely associated with the gateway selection problems, are not discussed in this draft. 5. IPv6 Considerations All the operations and parameters described in this document used by GNA for IP version 4 are the same as those used by GNA for IP version 6. To operate with IP version 6, the only required change is to replace the IPv4 addresses with IPv6 addresses. 6. Security Considerations This memo does not specify any security considerations. References [1] J. Jonsson, F. Alriksson, T. Larsson, P. Johansson, and G. Maguire, “MIPMANET – Mobile IP for Mobile Ad Hoc Networks”, Proceedings of the first ACM Annual Workshop on Mobile Ad Hoc Networking and Computing (MobiHoc), 2000. [2] T. Clausen, and P. Jacquet, “Optimized Link State Routing Protocol”, RFC 3626, IETF, October 2003. [3] P. Ratanchandani, and R. Kravets, “A Hybrid Approach to Internet Connectivity for Mobile Ad Hoc Networks”, Proceedings of IEEE Wireless Communications and Networking Conference (WCNC), March 2003. Sethom Expires - June 2006 [Page 8] Gateway Selection in Multi-homed Ad Hoc Networks January 2006 [4] P. Engelstad, A. Tønnesen, A. Hafslund, and G. Egeland, ”Internet Connectivity for Multi-Homed Proactive Ad Hoc Networks”, Proceedings of the IEEE Int. Conf. on Communications (ICC), June 2004. [5] H. Ammari and H. El-Rewini, “Using Hybrid Selection Schemes to Support QoS when Providing Multihop Wireless Internet Access to Mobile Ad Hoc Networks”, Proceedings of the First IEEE Int. Conf.on Quality of Service in Heterogeneous Wired/Wireless Networks (QSHINE), Oct. 2004. [6] C. Adjih, S. Boudjit, P. Jacquet, A. Laouiti, and P. Muhlethaler, “Address autoconfiguration in Optimized Link State Routing Protocol”, Internet-Draft (draft-laouiti-manet- olsr-address-autoconf-00.txt), work-in-progress, Feb. 2005. [7] T. Clausen, and E. Baccelli, “Simple MANET Address Autoconfiguration”, Internet-Draft (draft-clausen-manet- address-autoconf-00.txt), work-in-progress, Jan. 2005. Authors’ Addresses Kaouthar Sethom INT-France 9 rue charles fourrier 91011 evry cedex France Email: kaouthar.sethom@int-evry.fr Hossam Afifi INT-France 9 rue charles fourrier 91011 evry cedex France Email: hossam.afifi@int-evry.fr Frank Y. Li UniK – University Graduate Center N-2027 Kjeller Norway Email: frank.li@unik.no Andreas Hafslund Thales Norway AS P.O Box 22 Økern N-0508 Oslo, Norway Sethom Expires - June 2006 [Page 9] Gateway Selection in Multi-homed Ad Hoc Networks January 2006 Email: andreha@unik.no Copyright (C) The Internet Society (2006) This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights." This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM 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. Sethom Expires - June 2006 [Page 10]