1 © 2004, Cisco Systems, Inc. All rights reserved. CCNA 1 Module 10 Routing Fundamentals and Subnets

Objectives

IP Address

IP Address Grouping

Routed and Routing Protocols Consider that a packet needs to be sent from node A to node F. How would it decide which path to take?

Routing Protocol vs Routed Protocol A routed protocol 1.defines the end to end addressing and the packet format of a packet that is forwarded between nodes on different networks. Internet Protocol (IP) is a routed protocol A routing protocol 1.e xchanges topology information with adjacent routers to update and maintain their routing tables. 2.selects the best path through a network RIP is a routing protocol

Routed Protocol A protocol is a set of rules A routed protocol is a set of rules that determines how computers at the source and destination communicate with each other across networks – packet format – end to end addressing In order for a protocol to be routable, it must provide the ability to assign both a network number and a host number for each individual device.

Internet Protocol IP IP is a connectionless, unreliable, best-effort delivery protocol As information flows down the layers of the OSI model, the data is processed at each layer. IP accepts whatever data is passed down to it from the upper layers.

IP Packet Header

Network Layer Devices in Data Flow As a frame is received at a router interface. The MAC address is checked to see if the frame is directly addressed to the router interface, or a broadcast. The frame header and trailer are removed and the packet is passed up to Layer 3. The destination IP address is compared to the routing table to find a match. The packet (datagram) is placed in a new frame with the MAC address of the next hop interface. The frame is then transmitted. If a match is found or there is a default route, the packet will be sent to the interface specified in the matched routing table statement otherwise packet is discarded

Packets Travel Across Links in a Frame Packets NEVER travel through the network – they are carried within frames A new frame MUST be created to carry the packet over each individual link Routers provide the IP address of the next hop interface (router or host) The ARP table provides the MAC address of this IP address for the frame destination

Connectionless vs. Connection-Oriented In a connection oriented system is established between the sender and the recipient before any data is transferred. – example: Telephone In a connectionless system, the destination is not contacted before a packet is sent. – example: Postal system TCP is connection oriented IP is connectionless

Connectionless Network Services The Internet is a huge network where packets are routed according to their IP addresses. IP is unreliable and best-effort as IP does not verify that the data reached its destination and therefore does not resend missing packets. Reliability and resending of packets is handled by the upper layer protocols. IP may be used in conjunction with TCP to add a Layer 4, connection- oriented service that checks for missing segments and resends them to provide reliability.

The IPv4 Packet Header Time-to-live (TTL) Count Decreases with every hop This prevents packets from looping endlessly.

Routing

The Network Layer

Routing Routing is an OSI Layer 3 function. Routers connect networks (or subnetworks) Routing is the process of finding the most efficient path from one device to another (router) Routers must maintain routing tables and make sure other routers know of changes in the network topology. This function is performed using a routing protocol to communicate network information with other routers

Routing Through a Network A router is a network layer device that uses one or more routing metrics to determine the optimal path through the network

Routing Metrics

Data Encapsulation

Layer 3 Routing and Layer 2 Switching

Routers Reduce the Size of Broadcast Domains Routers block LAN broadcasts, so a broadcast storm only affects the broadcast domain from which it originated Switched networks do not block broadcasts

Routing and Switching in a Network

ARP Tables and Routing Tables

The difference between a routed and routing protocol – revisited

Routed Protocol

Routing Protocol

Routed Vs Routing protocols A Routed Protocol: – A network protocol suite that provides enough information in its network layer address to allow a router to forward it to the next device and ultimately to its destination. – Defines the format and use of the fields within a packet. – The Internet Protocol (IP) and Novell's Internetwork Packet Exchange (IPX), DECnet, AppleTalk, Banyan VINES, and Xerox Network Systems (XNS) A Routing Protocol: – Provides processes for sharing route information. Exchange topology info. To determining the best routing paths and transporting packets through an internetwork – Also allows routers to communicate with other routers to update and maintain the routing tables. – Routing Information Protocol (RIP), Interior Gateway Routing Protocol (IGRP), Open Shortest Path First (OSPF), Border Gateway Protocol (BGP), and Enhanced IGRP (EIGRP).

Back to Routing

Path Determination

Routing Tables Routing tables contain the best routes to all known networks. These routes can be either – Static routes, which are entered manually by the system administrator – Or dynamic routes, which are constructed from information passed between adjacent routers. A routing table entry contains: – Each Destination – The next hop IP address to reach that destination – The metric for the route via that next hop – Outbound router interface for the next hop

Routing Tables

Routing Algorithms and Metrics Routing protocols have one or more of the following design goals: Optimization Simplicity and low overhead Robustness and stability Flexibility Rapid convergence

Routing Algorithms and Metrics

Interior and Exterior Gateway Protocols

IGPs route data within an autonomous system. RIP, RIPv2, IGRP, EIGRP, OSPF, IS-IS EGPs route data between autonomous systems Border Gateway Protocol (BGP)

Interior Gateway Routing Protocols Link State and Distance Vector Routing Protocols Examples of distance-vector protocols: Routing Information Protocol (RIP) Interior Gateway Routing Protocol (IGRP) Enhanced IGRP (EIGRP) Examples of link-state protocols: Open Shortest Path First (OSPF) Intermediate System-to-Intermediate System (IS-IS)

Mechanics of Subnetting

Subnetting Reasons for subnetting –Provides addressing flexibility for the network administrator. Each LAN must have its own network or subnetwork address. –Provides broadcast containment and low-level security on the LAN. –Provides some security since access to other subnets is only available through the services of a router.

IP Address Bit Patterns

Introduction to Subnetting Host bits must are reassigned (or “borrowed”) as network bits. The starting point is always the leftmost host bit. 3 bits borrowed allows or 6 subnets 5 bits borrowed allows or 30 subnets 12 bits borrowed allows or 4094 subnets

Subnetting Chart (Bit Position and Value)

Subnetting Chart (Subnet Mask Identifier)

Subnetting

Subnetting Chart

Subnetting Example This is an example of subnetting the class C network into 8 subnets with 32 host addresses per subnet Note that the first and last subnets are not used (the first can be) Also the first and last host address in each subnet are not used

Example Host IP Address from Subnet 2 Packet Address Subnet Mask Subnet Address The subnet mask is ANDed with the packet address to determine the subnet address - as shown in the next slides

The Logical ANDing Process

Calculating the Subnet ID

Subnet Mask Defines the Number of Subnets

Summary