Design and Implementation of Wireless OSPF for Mobile Ad Hoc Networks Kenneth Holter * , Andreas Hafslund † , Frank Y. Li * , and Knut Øvsthus * * UniK - University Graduate Center, P. O. Box 70, N-2007 Kjeller, Norway † Thales Norway AS, N-0609 Oslo, Norway Email: {kenneho, fli, knuto}@unik.no, Andreas.Hafslund@no.thalesgroup.com Abstract— OSPF is the standard interior routing protocol widely deployed in the fixed Internet. Wireless OSPF is targeted at extending OSPF in a mobile ad hoc environment in which reducing protocol overhead is of paramount importance. So far two proposals have received most attention and are currently under active investigation within the IETF. In this paper, we present the design and implementation of one of them, referred to as WOSPF-OR in the context, that uses overlapping relays for reliable and efficient flooding. We adopt a plugin module concept in our implementation design and our implementation is developed based on the Quagga routing software platform. I. I NTRODUCTION Several routing protocols have been standardized by the IETF Mobile Ad-hoc Network (MANET) [1] working group during the past few years, where a typical category is de- veloped based on traditional link state routing protocols. Optimized Link State Routing (OLSR) [8], for example, is the most representative routing protocol of this kind, where protocol overhead minimization is achieved through unreliable flooding of network topology messages via Multipoint Relays (MPRs). On the other hand, another link state routing protocol, Open Shortest Path First (OSPF), which is the current Internet standard for interior routing, has been extensively studied and widely deployed in the wired Internet. A natural question that has recently received much attention with the IETF is: Why not adopt OSPF in MANETs? The motivation for adopting OSPF in a MANET environ- ment is twofold: Interoperability and familiarity. With both wired and wireless support, a MANET-capable OSPF router could operate properly when plugged into a wired OSPF network. By extending and building an OSPF framework, the transition and interoperability between wired and wireless net- works would become seamless. Furthermore, OSPF is already a mature routing protocol. Experience and lessons learned from OSPF can be of great help when extending OSPF to wireless networks. However, adopting OSPF in MANETs is not an easy task since OSPF was originally designed for more or less static, wired networks. There are several reasons that the OSPF pro- tocol cannot be deployed directly in a MANET environment. First of all, OSPF does not have a suitable interface type for a wireless broadcast environment which is characterized by a multicast-capable transmission medium and where routers do not necessarily form a full mesh. Moreover, to adapt to the unpredictable behavior of mobile nodes, OSPF will have to increase the amount of topology dissemination messages, leading to a prohibitively high routing overhead when adopted in MANETs. Consequently, OSPF does not scale well even for a quite small MANET [17]. Furthermore, since links in a wireless environment cannot be assumed to be bi-directional, the Designated Router (DR) mechanism, a common OSPF flooding optimization mechanism, will not perform correctly in MANETs as this mechanism assumes a true multi-access network. The first proposal for wireless extension of OSPF [17] employed an unacknowledged flooding technique based on the principles of OLSR. Later in 2004, the IETF OSPF working group decided to focus on protocols using acknowl- edged flooding to keep consistency of OSPF which relies on reliable flooding. So far, two proposals, [2] and [4], have received most attention. In this study we have designed and implemented wireless extensions to the OSPF for IPv6 (usually referred to as OSPFv3) routing protocol, based on the mechanisms described in [2], referred to as WOSPF-OR in this context. This proposal is aimed at reducing the routing overhead on the network by optimizing flooding of Link State Advertisements (LSAs) using Overlapping Relays (ORs), incremental Hellos, and reducing the size of Hello messages. These mechanisms may have significant impact on OSPF performance in MANETs. The optimized flooding scheme minimizes the number of retransmissions needed to diffuse topology information throughout the network. A decrease in size of a message type that is to be transmitted quite frequently will over time benefit the network performance. The rest of the paper is organized as follows. Section 2 gives an overview of OSPF, WOSPF-OR, and discusses some related works. The designed and implementation of WOSPF- OR are presented in Section 3, followed by discussions on other related issues in Section 4. The paper is concluded in Section 5. II. OSPF AND WOSPF-OR FUNCTIONALITY This section outlines the functionality of OSPF and WOSPF-OR. First we provide a high-level overview of OSPF, whereas details are further discussed when comparing OSPF with WOSPF-OR.