......................................................................................................................................4 Table of Contents .....................................................................................................................5 Introduction ..............................................................................................................................6 Overview and Weaknesses of Traditional IP Routing.................................................8 Overview of QoS .................................................................................................................... 11 History and Downfalls of Packet-Based Service: ATM ............................................. 13 What is Flow-Based Routing? ........................................................................................... 15 Flow-Based Routing and Resource Reservation ...................................................................17 Characteristics of a Flow .................................................................................................... 19 Storing Flow State Information ..................................................................................................20 Hardware Requirements for Flow-Based Router ...................................................... 21 Software Requirements for Flow-Based Router ........................................................ 23 Distributed Routing Algorithms.................................................................................................24 Flow Routing Table .........................................................................................................................24 Flow-based Routing in IPv6 .........................................................................................................24 Benefits of Flow-Based Routing....................................................................................... 26 Cisco Express Forwarding vs. Flow Based Switching ..........................................................27 Security Considerations for Flow-Based Routing ...................................................... 29 OPNET Modeler 16.0 Simulation ..................................................................................... 30 Configuration of Testing Environment ....................................................................................33 Project 1: Flow-based Routing ....................................................................................................33 Scenario 1: IP Routing with OSPF...............................................................................................36 Scenario 2: IP Routing with OSPF and QoS..............................................................................42 Scenario 3: Flow-based Routing .................................................................................................45 Roadblocks ........................................................................................................................................55 OPNET Modeler 16.0 Simulation Analysis/Results................................................... 57 CPU Utilization .................................................................................................................................58 Traffic Dropped (packets/sec) ...................................................................................................63 Background Traffic Delay.............................................................................................................64 Processing Delay..............................................................................................................................65 IP Processor: Forwarding Memory Free Size.........................................................................67 Survivability Analysis ....................................................................................................................68 Conclusion............................................................................................................................... 71 Future Direction.................................................................................................................... 72 References............................................................................................................................... 74 An Analysis of Flow-Based Routing Jennifer Casella 6 Introduction Current services such as voice and video require high amounts of bandwidth and Quality of Service for reliable delivery of time-sensitive traffic. It is primitive that the delivery method, bandwidth consumption, and control of latency/delay in packet transport are improved upon from routers’ current capabilities. “All these problems can be solved with no change to TCP/IP by routing flows rather than packets” [2]. A new method to avoid the redundant inspections that routers perform on packets travelling to the same destination is the first step in changing the way packets are routed across networks. A flow-based solution is capable of recognizing flows – state information is stored about the initial packet, which is then used to switch the remaining packets in the flow. “The unique level of data obtained in flowbased routing, such as flow length, rate, delay variation and other parameters, enable a number of new network benefits” [4]. State information is created on-the-fly and is capable of being deleted without any additional signaling intervention [3]. The ability to route incoming packets based on pre-determined information provides a certain level of predictability. For this reason, networking devices are able to route several different flows simultaneously. “Leveraging flow state information allows the design of novel congestion control schemes that are more efficient at improving network-level behavior” [3]. The benefits of this design from a QoS standpoint are huge. Ensuring that packets are not dropped randomly would improve the quality of applications and services that cannot tolerate loss. It would also enable the routing protocol to reach its maximum transmission rate more quickly. Traffic is controlled in TCP with An Analysis of Flow-Based Routing Jennifer Casella 7 the concept of windowing, which requires that a sending device slow down if it is transmitting too much data or if a packet was lost; however, if packets were never lost, the speed of transmission of a flow would increase. Many different approaches to a flow-based technique have been experimented with in the field, each introducing their own methods and benefits. It would be a great advancement if routers could inspect packets and store routing information from only the first packet in a flow; then route all packets that follow based on that criteria. Router resources would be more efficiently used; time would be saved in link failure recoveries by storing a primary and alternate route in the router’s memory; we would save on power bills, because routers’ energy consumption would decrease; and most importantly network devices would be able to support the service needs of increasing application demands. An Analysis of Flow-Based Routing Jennifer Casella 8 Overview and Weaknesses of Traditional IP Routing The primary function of the Internet Protocol (IP) is to route packets from source to destination. Routers are responsible for the processing and forwarding of traffic through various paths, pre-determined by routing protocols (i.e. EIGRP, OSPF, BGP). In order to maintain information about directly connected and remote networks and make forwarding decisions, a router maintains a routing table, which is populated with network information learned by neighboring devices. The routing table will typically contain routes to different destinations, making note of their associated metrics. The routing table entries are highly aggregated with today’s BGP backbone routers have upwards of 350,000 routing table entries. Although this does provide some advantages such as reduced router memory and less updates to neighbors, it does have a cost – “to look up a packet’s next hop, we need to find the longest prefix matching the header, which is a more complicated operation than a simple index into a table” [5]. When a router needs to forward a packet, it will compare information found in the IP header with entries in its routing table. “This simple model allows IP routers to be stateless: a router does not need to know anything about the potentially large number of individual connections passing through it; it simply forwards each IP packet based on the destination address contained in the packet header. [5]” Once the appropriate route is found, the packet will be transmitted out the associated interface to reach the destination network (a default route or default gateway will be used if no route exists for a particular