Transcript CCNA 1 Module 10 Routing Fundamentals and Subnets - CIC-CBU
CCNA 1 Module 10 Routing Fundamentals and Subnets
© 2004, Cisco Systems, Inc. All rights reserved.
1
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 layer address to allow a to its destination. suite that provides enough information in its network router to forward it to the next device and ultimately
–
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 maintain the routing tables.
update and
–
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
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
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 2 3 -2 or 6 subnets 5 bits borrowed allows 2 5 -2 or 30 subnets 12 bits borrowed allows 2 12 -2 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 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
Example Host IP Address from Subnet 2 Packet Address Subnet Mask Subnet Address 192.168.10.65
11000000.10101000.00001010.010
00001 255.255.255.224
11111111.11111111.11111111.111
192.168.10.64
11000000.10101000.00001010.010
00000 00000
• 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