1 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 1 v3.0 Module 10 Routing Fundamentals and Subnets

222 © 2003, Cisco Systems, Inc. All rights reserved. Objectives Routed protocol IP routing protocols The mechanics of subnetting

3 © 2003, Cisco Systems, Inc. All rights reserved. Routed Protocol

444 © 2003, Cisco Systems, Inc. All rights reserved. Routable and Routed Protocols A routed protocol allows the router to forward data between nodes on different networks. In order for a protocol to be routable, it must provide the ability to assign a network number and a host number to each individual device. These protocols also require a network mask in order to differentiate the two numbers. The reason that a network mask is used is to allow groups of sequential IP addresses to be treated as a single unit.

555 © 2003, Cisco Systems, Inc. All rights reserved. Routed Protocols Versus Routing Protocols Routing protocols determine the path that routed protocols follow to their destinations.

666 © 2003, Cisco Systems, Inc. All rights reserved. Characteristics of a Routable Protocol

777 © 2003, Cisco Systems, Inc. All rights reserved. IP as a Routed Protocol 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.

888 © 2003, Cisco Systems, Inc. All rights reserved. Packet Propagation Each router provides its services to support upper-layer functions.

999 © 2003, Cisco Systems, Inc. All rights reserved. Packet Propagation and Switching Within a Router 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 is switched to the outgoing interface and given the proper frame header. The frame is then transmitted.

10 © 2003, Cisco Systems, Inc. All rights reserved. Internet Protocol (IP): Connectionless The Internet is a gigantic, connectionless network in which all packet deliveries are handled by IP. TCP adds Layer 4, connection-oriented reliability services to IP.

11 © 2003, Cisco Systems, Inc. All rights reserved. A connection is established between the sender and the recipient before any data is transferred. Telephone Calls: Connection-oriented

12 © 2003, Cisco Systems, Inc. All rights reserved. A connection is established between the sender and the recipient before any data is transferred. Connection-Oriented Network Services

13 © 2003, Cisco Systems, Inc. All rights reserved. Anatomy of an IP Packet While the IP source and destination addresses are important, the other header fields have made IP very flexible. The header fields are the information that is provided to the upper layer protocols defining the data in the packet.

14 © 2003, Cisco Systems, Inc. All rights reserved. IP Routing Protocols

15 © 2003, Cisco Systems, Inc. All rights reserved. Routing Overview A router is a network layer device that uses one or more routing metrics to determine the optimal path. Routing metrics are values used in determining the advantage of one route over another. Routing protocols use various combinations of metrics for determining the best path for data.

16 © 2003, Cisco Systems, Inc. All rights reserved. Routing Versus Switching This distinction is routing and switching use different information in the process of moving data from source to destination.

17 © 2003, Cisco Systems, Inc. All rights reserved. Routing Versus Switching

18 © 2003, Cisco Systems, Inc. All rights reserved. Routed Versus Routing A routed protocol: Includes any 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. A routing protocol: Provides processes for sharing route information. Allows routers to communicate with other routers to update and maintain the routing tables.

19 © 2003, Cisco Systems, Inc. All rights reserved. Path Determination Path determination enables a router to compare the destination address to the available routes in its routing table, and to select the best path.

20 © 2003, Cisco Systems, Inc. All rights reserved. Routing Tables Routers keep track of the following: Protocol type Destination/next-hop associations Routing metric Outbound interfaces

21 © 2003, Cisco Systems, Inc. All rights reserved. Routing Table Example

22 © 2003, Cisco Systems, Inc. All rights reserved. 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

23 © 2003, Cisco Systems, Inc. All rights reserved. IGP and EGP IGPs route data within an autonomous system. RIP, RIPv2, IGRP, EIGRP, OSPF, IS-IS EGPs route data between autonomous systems Border Gateway Protocol (BGP)

24 © 2003, Cisco Systems, Inc. All rights reserved. Link State and Distance Vector 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)

25 © 2003, Cisco Systems, Inc. All rights reserved. Routing Protocols RIP RIP v2 IGRP EIGRP OSPF IS-IS BGP

26 © 2003, Cisco Systems, Inc. All rights reserved. Mechanics of Subnetting

27 © 2003, Cisco Systems, Inc. All rights reserved. Classes of Network IP Addresses

28 © 2003, Cisco Systems, Inc. All rights reserved. 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

29 © 2003, Cisco Systems, Inc. All rights reserved. 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.

30 © 2003, Cisco Systems, Inc. All rights reserved. Establishing the Subnet Mask Address Determines which part of an IP address is the network field and which part is the host field. Follow these steps to determine the subnet mask: 1. Express the subnetwork IP address in binary form. 2. Replace the network and subnet portion of the address with all 1s. 3. Replace the host portion of the address with all 0s. 4. Convert the binary expression back to dotted- decimal notation.

31 © 2003, Cisco Systems, Inc. All rights reserved. Subnet mask in decimal = Subnet Mask

32 © 2003, Cisco Systems, Inc. All rights reserved. Subnet Addresses

33 © 2003, Cisco Systems, Inc. All rights reserved. Class B address with 8 bits borrowed for the subnet (8 bits borrowed for subnetting) routes to subnet rather than just to network Determining Subnet Mask Size

34 © 2003, Cisco Systems, Inc. All rights reserved. The address would be on the subnet Network FieldSN Host Field Class C address with a subnet mask of (3 bits borrowed) Determining Subnet Mask Size

35 © 2003, Cisco Systems, Inc. All rights reserved. Establishing the Subnet Mask Address To determine the number of bits to be used, the network designer needs to calculate how many hosts the largest subnetwork requires and the number of subnetworks needed. The “slash format” is a shorter way of representing the subnet mask: /25 represents the 25 one bits in the subnet mask

36 © 2003, Cisco Systems, Inc. All rights reserved. Establishing the Subnet Mask Address

37 © 2003, Cisco Systems, Inc. All rights reserved. Subnetting Class A and B Networks The available bits for assignment to the subnet field in a Class A address is 22 bits while a Class B address has 14 bits.

38 © 2003, Cisco Systems, Inc. All rights reserved. Calculating the Subnetwork With ANDing ANDing is a binary process by which the router calculates the subnetwork ID for an incoming packet. 1 AND 1 = 1; 1 AND 0 = 0; 0 AND 0 = 0 The router then uses that information to forward the packet across the correct interface. Packet Address Subnet Mask Subnetwork Address