cisco ccna module 10

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Module 10 Routing Fundamentals and

Subnets

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www.pnj.ac.idObjectives

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www.pnj.ac.idIP Address

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www.pnj.ac.idIP Address Grouping

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www.pnj.ac.idRouted 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?

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www.pnj.ac.idRouting 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. exchanges 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

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www.pnj.ac.idRouted 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.

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www.pnj.ac.idInternet 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.

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www.pnj.ac.idIP Packet Header

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www.pnj.ac.idNetwork 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

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www.pnj.ac.idPackets 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

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www.pnj.ac.idConnectionless 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

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www.pnj.ac.idConnectionless 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.

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www.pnj.ac.idThe IPv4 Packet Header

Time-to-live (TTL)

Count Decreases with every hop This prevents packets from looping endlessly.

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Routing

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www.pnj.ac.idThe Network Layer

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www.pnj.ac.idRouting

• 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

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www.pnj.ac.idRouting 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

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www.pnj.ac.idRouting Metrics

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www.pnj.ac.idData Encapsulation

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www.pnj.ac.idLayer 3 Routing and Layer 2 Switching

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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

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www.pnj.ac.idRouting and Switching in a Network

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www.pnj.ac.idARP Tables and Routing Tables

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The difference between a routed and routing protocol – revisited

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www.pnj.ac.idRouted Protocol

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www.pnj.ac.idRouting Protocol

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www.pnj.ac.idRouted 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).

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Back to Routing

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www.pnj.ac.idPath Determination

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www.pnj.ac.idPath Determination

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www.pnj.ac.idRouting 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

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www.pnj.ac.idRouting Tables

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www.pnj.ac.idRouting 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

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www.pnj.ac.idRouting Algorithms and Metrics

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www.pnj.ac.idInterior and Exterior Gateway Protocols

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www.pnj.ac.idInterior 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)

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www.pnj.ac.idInterior 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)

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Mechanics of Subnetting

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www.pnj.ac.idSubnetting

• 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.

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www.pnj.ac.idIP Address Bit Patterns

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www.pnj.ac.idIntroduction 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 23-2 or 6 subnets

5 bits borrowed allows 25-2 or 30 subnets

12 bits borrowed allows 212-2 or 4094 subnets

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www.pnj.ac.idSubnetting Chart (Bit Position and Value)

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www.pnj.ac.idSubnetting Chart (Subnet Mask Identifier)

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www.pnj.ac.idSubnetting

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www.pnj.ac.idSubnetting Chart

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www.pnj.ac.idSubnetting Example

• This is an example of subnetting the 192.168.10.0 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

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www.pnj.ac.idExample Host IP Address from Subnet 2

Packet Address 192.168.10.65 11000000.10101000.00001010.010 00001

Subnet Mask 255.255.255.224 11111111.11111111.11111111.111 00000

Subnet Address 192.168.10.64 11000000.10101000.00001010.010 00000

• The subnet mask is ANDed with the packet address to determine the subnet address - as shown in the next slides

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www.pnj.ac.idThe Logical ANDing Process

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www.pnj.ac.idCalculating the Subnet ID

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www.pnj.ac.idSubnet Mask Defines the Number of Subnets

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www.pnj.ac.idSummary