Routing Fundamentals and Subnets CCNA 1 v 3

Routing Fundamentals and Subnets CCNA 1 v 3 – Module 10 NESCOT CATC 1

Routed and Routing Protocols Routing protocols should not be confused with routed protocols: Routing protocols determine the paths that routed protocols follow to their destinations. n Examples: RIP, OSPF, IGRP, EIGRP, IS-IS, BGP Routed protocols provide addressing and support at the network layer. n Examples: IP, IPX, Appletalk, DECnet There are protocols that do not support Layer 3, and these are classed as nonroutable protocols n Example: NETBEUI NESCOT CATC 2

IP IP is the most widely used implementation of a hierarchical network-addressing scheme. n Connectionless n Unreliable n Best-effort delivery These terms do not imply that the system does not work well, but that IP leaves verification to upper layer protocols. Routing protocols work with IP to find the most efficient route for data. IP determines the contents of the IP packet header, which includes addressing and other control information. NESCOT CATC 3

Two types of delivery services: 1. Connectionless 2. Connection-oriented Most network services use a connectionless delivery system: Destination is not contacted before a packet is sent. n Packets can switch to different paths, and possibly arrive out of order. n Referred to as packet-switched processes. n Comparison: the postal system. n In connection-oriented systems: n Connection is established between the sender and the recipient before any data is transferred. n All packets travel sequentially across the same physical or virtual circuit. n Referred to as circuit-switched processes. n Example: telephone system. The Internet is a connectionless network in which all packet deliveries are handled by IP. TCP adds Layer 4, connection-oriented reliability services.

Anatomy of an IP Packet Header length - total length of all header information, two variablelength header fields Version – IP version used; must match receiving device Sequence number Specifies no. of hops a packet may travel Supports options such as security, variable length Indicates upperlayer protocol: TCP or UDP Specifies level of importance assigned by a particular upperlayer protocol Length of packet, including data and header Control fragmentation Helps ensure IP header integrity 5

IP Routing Protocols n n 3 Routing is an OSI Layer ___ function. most efficient path Routing is the process of finding the _________ from one device to another router The primary device that performs routing is the _______. Two key functions of a router: 1. Routers must maintain routing tables using a routing protocol to communicate network information with other routers. The router switches the packets to the appropriate interface, adds the necessary framing information for the interface, and then transmits the frame. Routing metrics are values used in determining the advantage 2. of one route over another. The encapsulation and de-encapsulation process occurs each time a packet transfers through a router. NESCOT CATC 6

Packet Propagation and Switching within a Router NESCOT CATC 7

Routing vs. Switching § Routing and switching use different information in the process of moving data from source to destination. § Each computer and router interface maintains an ARP table for Layer 2 communication. The ARP table is only effective for the broadcast domain (or LAN) that it is connected to. § The router also maintains a routing table that allows it to route data outside of the broadcast domain. NESCOT CATC 8

ARP Tables and Routing Tables NESCOT CATC 9

IGP and EGP IGPs can be further categorized as Distance-Vector or Link State. Examples of Distance-Vector protocols: RIP, RIPv 2, IGRP, (EIGRP) Examples of Link-State protocols: OSPF, IS-IS NESCOT CATC 10

NESCOT CATC 11

Subnetting Why use Subnetting? n Reduce network traffic n Optimise network performance n Simplify management n Facilitate spanning of large geographical areas The 32 bits of an IP address can be divided into three parts: NETWORK-SUBNET-HOST Example 1: 172. 16. 10. 5 255. 128 Can also be written: 172. 16. 10. 5/25 Binary: 10101100. 000100001010. 10000101 Class B Network address Subnet Host 12

Values in a Subnet Mask 128 64 32 16 8 4 2 1 The Subnet is represented by an unbroken series of ‘ 1’s in the mask. Only possible values (other than 0) for each octet in a subnet mask are: 128 192 224 240 248 252 254 255 Mechanics of Subnetting - ANDing is a binary process by which the router calculates the subnetwork ID for an incoming packet. The IP address and the subnetwork address are ANDed with the result being the subnetwork ID. NESCOT CATC 13

Determining Subnet, Broadcast Address and Valid Host Range Example: Host: 172. 16. 10. 33 Subnet Mask: 255. 224 Is this a Class A, Class B or Class C address? Class B Therefore how many bits make up the Network portion? 16 How many bits are in the Subnet Mask? 11111111. 11100000 = 27 How many bits are left for Host addresses? 5 How many separate addresses in each subnet? 32 Which address represents the whole subnet? 172. 16. 10. 32 Which address is used to broadcast to the subnet? 172. 16. 10. 63 Which addresses are left in the valid host range? First Valid: 172. 16. 10. 33 Last Valid: 172. 16. 10. 62 NESCOT CATC 14

Determining Subnet, Broadcast Address and Valid Host Range Example 2: Host: 192. 168. 100. 25 Subnet Mask: 255. 252 Is this a Class A, Class B or Class C address? Therefore how many bits make up the Network portion? How many bits are in the Subnet Mask? How many bits are left for Host addresses? How many separate addresses in each subnet? Which address represents the whole subnet? Which address is used to broadcast to the subnet? Which addresses are left in the valid host range? NESCOT CATC 15