cisco ccna module 10
DESCRIPTION
TRANSCRIPT
1© 2004, Cisco Systems, Inc. All rights reserved.
Module 10 Routing Fundamentals and
Subnets
222© 2004, Cisco Systems, Inc. All rights reserved.
www.pnj.ac.idObjectives
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www.pnj.ac.idIP Address
444© 2004, Cisco Systems, Inc. All rights reserved.
www.pnj.ac.idIP Address Grouping
555© 2004, Cisco Systems, Inc. All rights reserved.
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?
666© 2004, Cisco Systems, Inc. All rights reserved.
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
777© 2004, Cisco Systems, Inc. All rights reserved.
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.
888© 2004, Cisco Systems, Inc. All rights reserved.
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
111111© 2004, Cisco Systems, Inc. All rights reserved.
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
121212© 2004, Cisco Systems, Inc. All rights reserved.
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
131313© 2004, Cisco Systems, Inc. All rights reserved.
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.
141414© 2004, Cisco Systems, Inc. All rights reserved.
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
171717© 2004, Cisco Systems, Inc. All rights reserved.
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
181818© 2004, Cisco Systems, Inc. All rights reserved.
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
191919© 2004, Cisco Systems, Inc. All rights reserved.
www.pnj.ac.idRouting Metrics
202020© 2004, Cisco Systems, Inc. All rights reserved.
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
242424© 2004, Cisco Systems, Inc. All rights reserved.
www.pnj.ac.idARP Tables and Routing Tables
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The difference between a routed and routing protocol – revisited
262626© 2004, Cisco Systems, Inc. All rights reserved.
www.pnj.ac.idRouted Protocol
272727© 2004, Cisco Systems, Inc. All rights reserved.
www.pnj.ac.idRouting Protocol
282828© 2004, Cisco Systems, Inc. All rights reserved.
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
323232© 2004, Cisco Systems, Inc. All rights reserved.
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
333333© 2004, Cisco Systems, Inc. All rights reserved.
www.pnj.ac.idRouting Tables
343434© 2004, Cisco Systems, Inc. All rights reserved.
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
353535© 2004, Cisco Systems, Inc. All rights reserved.
www.pnj.ac.idRouting Algorithms and Metrics
363636© 2004, Cisco Systems, Inc. All rights reserved.
www.pnj.ac.idInterior and Exterior Gateway Protocols
373737© 2004, Cisco Systems, Inc. All rights reserved.
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)
383838© 2004, Cisco Systems, Inc. All rights reserved.
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
404040© 2004, Cisco Systems, Inc. All rights reserved.
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.
414141© 2004, Cisco Systems, Inc. All rights reserved.
www.pnj.ac.idIP Address Bit Patterns
424242© 2004, Cisco Systems, Inc. All rights reserved.
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
434343© 2004, Cisco Systems, Inc. All rights reserved.
www.pnj.ac.idSubnetting Chart (Bit Position and Value)
444444© 2004, Cisco Systems, Inc. All rights reserved.
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
484848© 2004, Cisco Systems, Inc. All rights reserved.
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
515151© 2004, Cisco Systems, Inc. All rights reserved.
www.pnj.ac.idSubnet Mask Defines the Number of Subnets
525252© 2004, Cisco Systems, Inc. All rights reserved.
www.pnj.ac.idSummary