Chapter 5 – TCP/IP: Part 4 Dr. V.T. Raja Oregon State University

TCP/IP – Part 4 - Routing Outline Part 4a: Introduction Different Types of Routing Part 4b : Routing Protocols Routing Tables

TCP/IP-Part 4a: Routing Routing : Path taken by message from sender to final destination Routing Table : Devices that perform routing have a routing table that specifies route to different destinations. The routing tables are constructed/updated using different types of routing technique(s). Different Types of Routing –Centralized –Decentralized Static Dynamic Routing (Distance Vector and Link State Dynamic Routing) – Connectionless and Connection-Oriented Routing – QoS Routing

Centralized and Decentralized Routing Different Types of Routing Centralized and Decentralized Routing Centralized Routing –All routing decisions are made by one central computer –Example: Decentralized Routing –Computers/routers in network make their own routing decisions following a formal routing protocol, which could be capable of self-adjusting, and adapting to changes in the network configurations

Static Routing Different types of Routing Decentralized Routing: Static Routing Static –Routing table is developed by the network manager –Changes are made to the routing table only when computers are added or removed from network –Example:

Dynamic (Adaptive) Routing Different types of Routing Decentralized Routing: Dynamic (Adaptive) Routing Dynamic Routing –Used when there are multiple routes and it is important to select the best (or fastest) route, in order to route messages away from traffic on busy circuits –An initial routing table is developed by the network manager, but is continuously updated by the computers themselves (with the help of routing protocols) to reflect changing network conditions, such as network traffic

Distance Vector Dynamic Routing Different types of Routing Decentralized Routing – Dynamic (Adaptive) Routing Distance Vector Dynamic Routing Distance Vector Dynamic Routing –Routing decisions are made based on # of hops along a route –What is a hop? Examples: –A - C (via B): »# of hops = –A – C (via D, E & F): »# of hops = –Computers periodically (could be as often as every 1-2 minutes) exchange information on the hop count and sometimes the relative speed of the circuits in route with their neighbor

Link State Dynamic Routing Different types of Routing Decentralized Routing – Dynamic (Adaptive) Routing Link State Dynamic Routing Link State Dynamic Routing –Routing decisions are based on several factors: Number of hops in each route Speed of circuits in each route Traffic conditions on each route (How busy the route is?) Reliability of each route

Disadvantages of Dynamic Routing Requires more processing effort from each computer on the network compared to centralized or static routing “Compromises” on network capacity during transmission of route status information

Connectionless and Connection-Oriented Routing Different Types of Routing Connectionless and Connection-Oriented Routing A message may be segmented into several packets Connectionless Routing –Different packets of the same message could take different routes Connection-Oriented Routing –A virtual circuit (VC) is set up between sender and receiver –A VC is one that appears to be a point-to-point circuit –All packets follow the same VC route; –Overhead involved in establishing and closing VC before and after transmission of all packets

Quality of Service (QoS) Routing Different Types of Routing Quality of Service (QoS) Routing Quality of Service (QoS) Routing –Special type of connection- oriented dynamic routing protocol –Different messages or packets are assigned different priorities Applications: –Different classes of service are defined for different priorities Example:

Routing Protocols Used to exchange route status information among computers to enable them to build and maintain their routing tables As network grows large, knowing all possible routes become impractical Even at some modest # of computers, routing protocols become impractical due to the amount of traffic they generate autonomous system For this reason, networks are often subdivided into autonomous system of networks

Autonomous System of Networks Routing Protocols Autonomous System of Networks Each large organizational network connected to Internet (e.g., AT&T, IBM, OSU) can be viewed as a separate autonomous system Computers within each autonomous system usually exchange routing information among themselves Routing protocols used inside an autonomous system are called interior routing protocols Routing protocols used between autonomous systems are called exterior routing protocols

Routing Protocols Internet Control Message Protocol (ICMP) –Echo cycles Example: Ping command – Determine if destination is reachable before a connection is established to transmit packets –Error advisement Example: Ping command – Host (Destination) unreachable –Flow control Requesting a device to reduce the rate at which it transmits

Routing Protocols Routing Information Protocol (RIP) –Dynamic distance vector routing protocol –Scalability: 15-hop limit –Good for smaller networks –Broadcast interruptions (entire routing table transmitted very often) –Slower convergence – Takes a longer time for routing tables to be transmitted very often

Routing Protocols Open Shortest Path First (OSPF) –Link State Dynamic Routing Protocol –Faster convergence Designated router updated on changes in route status Border Gateway Protocol (BGP) –Distance Vector Dynamic Routing Protocol –Used between autonomous systems –Changes in route status info transmitted

Comparison of Routing Protocols RIPOSPFBGP Interior/Exterior? Interior Exterior Type (Distance Vector/ Link State?) Distance VectorLink StateDistance Vector Routing update content (Routing Table/Updates?) Routing TableUpdates only Routing update frequency Very often (e.g., every 30 seconds) Updates only Convergence (Slow/Fast/Complex?) SlowFastComplex Scalability PoorVery Good

TCP/IP and Routing TCP/IP can use RIP, ICMP, OSPF, BGP It is compatible with distance vector and link state protocols Can operate either as connectionless or connection oriented routing Can support QoS routing (a new version of OSPF called QOSPF)

Routing Tables Routing Table for B DestinationRouteAC DAE FE GC DefaultA

Routing Table (Continued) Network Destination NetmaskGatewayInterfaceMetric (Cost) Default route: Loop back (Self) Network Route Local Host Subnet broadcast Multicast: Broadcast

Introduction Router Forwarding Table Destination AddressPrefix (Mask)Metric (Cost)InterfaceNext-Hop Router ( )472G H F H Local H

Unicast/Broadcast/Multicast Unicast –Most common type of message transmitted (from one sender to one final destination) –Example: Broadcast –Subnet broadcast Example –LAN broadcast Example Multicast –Message sent to different destinations, each of which could belong to different subnets or different networks –Use (IGMP) Internet Group Management Protocol for routing –Each multicast group is temporarily assigned a special Class D IP address to identify the group, thus allowing a restricted multicast to the group members only –Examples: