Chapter 22 Delivery, Forwarding, and Routing
Chapter 22 of Data Communications and Networking by Behrouz A. Forouzan focuses on Delivery, Forwarding, and Routing in the Network Layer. Here are the detailed notes:
22.1 Delivery
The delivery of a packet involves getting the data from the source to the destination. There are two types:
Direct Delivery: Occurs when the destination is on the same network as the source. The packet is delivered without passing through intermediate routers.
Indirect Delivery: Happens when the destination is on a different network, requiring the packet to be routed through one or more intermediate routers.
22.2 Forwarding
Forwarding refers to the process of moving a packet from one router to another along the path to the destination. Each router uses a routing table to determine the next hop based on the destination address.
Forwarding Techniques:
Next-Hop Method: The routing table contains only the next hop information instead of the complete route.
Network-Specific Method: Instead of storing individual host routes, routers store the route for the entire network, significantly reducing the size of the routing table.
Default Method: Routers can have a default route used when no specific route to the destination is found.
The Forwarding Process uses the routing table to match the destination IP with a network prefix, determining the next hop based on the longest mask match.
22.3 Unicast Routing Protocols
Routing protocols help create routing tables and enable efficient delivery. These are categorized based on their scope:
Intrdomain Routing: Used within an autonomous system (AS).
Interdomain Routing: Used between autonomous systems.
Key Unicast Routing Protocols:
Distance Vector Routing: Each router shares its knowledge of the entire network with its neighbors periodically. The routers use this information to calculate the shortest paths to all destinations based on the number of hops.
The Routing Information Protocol (RIP) is based on this model.
Link-State Routing: Each router shares information about its neighbors with the entire network. Routers then independently compute the shortest paths using algorithms like Dijkstra's algorithm.
Open Shortest Path First (OSPF) is an example of link-state routing.
Path Vector Routing: Routers maintain the AS paths that data must traverse. The Border Gateway Protocol (BGP) uses this method to determine the best path between different autonomous systems.
22.4 Multicast Routing Protocols
Multicast routing enables the transmission of data from one sender to multiple receivers. Two primary approaches are:
Source-Based Tree: A unique shortest-path tree is built from the source to all recipients for each multicast group.
Group-Shared Tree: A single tree is constructed that connects all the members of a group, regardless of the source. A core or rendezvous router is responsible for forwarding multicast packets to all group members.
Examples of Multicast Protocols:
DVMRP (Distance Vector Multicast Routing Protocol): Extends distance vector routing for multicast by using techniques like Reverse Path Forwarding (RPF) to prevent loops.
MOSPF (Multicast OSPF): An extension of OSPF for multicast, creating source-based trees using link-state routing.
PIM (Protocol Independent Multicast): Available in two modes:
PIM-Dense Mode (PIM-DM): Used for dense networks where most routers are involved in multicast.
PIM-Sparse Mode (PIM-SM): Used in sparse networks where fewer routers are involved in multicast.
Key Terms:
Routing Table: Contains information used by routers to decide where to forward packets.
Metric: A cost assigned to a route, used by routing protocols to determine the best path.
Autonomous System (AS): A collection of IP networks and routers under the control of a single organization.
RIP, OSPF, BGP: Key routing protocols for managing unicast and interdomain routing.
Summary:
Direct and Indirect Delivery depend on whether the destination is on the same or a different network.
Routing Tables may use next-hop, network-specific, or default methods to optimize the routing process.
Unicast Routing Protocols such as RIP, OSPF, and BGP are used to update routing tables dynamically.
Multicast Routing Protocols support the transmission of data to multiple recipients and include protocols like DVMRP, MOSPF, and PIM.
This chapter outlines the process of ensuring packets reach their destinations efficiently, focusing on different routing techniques and protocols that manage both unicast and multicast traffic.
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