chap 10 routing and addressing andres, wen-yuan liao department of computer science and engineering...
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Chap 10 Routing and Addressing
Andres, Wen-Yuan Liao
Department of Computer Science and Engineering
De Lin Institute of Technology
http://www.cse.dlit.edu.tw/~andres
Importance of a Network Layer
Identifiers
Segmentation and autonomous systems
Communication between separate networks
Layer 3 network devices
Identifiers Move data through a set of networks (internetwork)
Network layer: hierarchical addressing Unique addresses across network b
oundariesA method for finding a path
MAC addresses: flat addressing
Segmentation and autonomous systems
Multiple networks are necessary The growth in size of each networkThe growth in the number of
networks
Network segments (or just segments)
Communication between separate networks
Internet is a collection of network segments
Internet service providers (ISPs) offering services that tie together multiple network segment
Layer 3 network devices
Routers are internetworking devices which operate at OSI Layer 3
Tie together, or interconnect, network segments or entire networks
Layer 3 network devices
Routers make logical decisions regarding the best path on an internetwork and then direct packets
Routing is sometimes referred to as Layer 3 switching
Path Determination
Path determination Network layer addressing Layer 3 and computer mobility Comparing flat and hierarchical addressing
Path determination
Routing the packetThe process that the router uses
to choose the next hop in the path for the packet to travel to its destination
Make their decisions based on the traffic density and the speed of the link
Network layer addressing
Network addressThe router uses the network a
ddress to identify the destination network of a packet within an internetwork.
Host address
Layer 3 and computer mobility
A MAC address can be compared to your name
The network address to your mailing address
Comparing flat and hierarchical addressing
A flat addressing scheme Assigns a device the next
available address
The postal system ZIP codes are a good example of hierarchical addressing
IP Addresses within the IP Header
Network layer datagrams
Network layer fields
IP header source and destination fields
IP address as a 32-bit binary number
IP address component fields
IP address component fields
The network number of an IP address identifies the network to which a device is attached
The host portion of an IP address identifies the specific device on that network
IP Address Classes
IP address classes
IP addresses as decimal numbers
The first (leftmost) bit is always 0
First octet of its IP address: 0-126
A Class A IP address can have assigned up to 224 - 2 or 16,777,214, possible IP addresses
Class A
Class B
The first 2 bits: 10
First octet of its IP address:128 to 191
A Class B IP address can have assigned up to 216 - 2, or 65,534, possible IP addresses
Class C
The first 3 bits: 110
First octet of its IP address:192 to 223
A Class C IP address can have assigned up to 28 - 2, or 254, possible IP addresses
Reserved Address Space Purposes for network IDs and broadcast addresses Network ID Network ID analogy Broadcast address analogy Hosts for classes of IP addresses
Purposes for network IDs and broadcast addresses
An IP address that ends with binary 0s in all host bits is reserved for the network address The wire address
Class A network: 113.0.0.0 Contain the host 113.1.2.3
Network & Host ID A network IDEnable a router to put a packet onto
the appropriate network segment
The host IDHelp the router address the Layer 2
frame to the specific host on that network
Basics of Subnetting Classical IP Addressing
Subnetwork
Purpose for subnetting
Subnet mask
Boolean operations: AND, OR, and NOT
Performing the AND function
Classical IP Addressing
Network administrators sometimes need to divide networks into smaller networks
SubnetworksProvide addressing flexibilityBe simply referred to as subnet
Subnetwork Subnet addresses includeThe Class A, Class B, or Class C
network portionA subnet fieldA host field
To create a subnet addressBorrows bits from the original host
portion
Subnetwork
The minimum number of bits that can be borrowed is 2
The maximum number of bits that can be borrowed can be any number that leaves at least 2 bits remaining, for the host number
Purpose for subnetting
A primary reason for using subnets is to reduce the size of a broadcast domain
Subnet mask
The subnet mask determines which part of an IP address is the network field and which part is the host field
SubnetRouters determine the destination network/subnet addressPerform a logical AND using the
destination host's IP address and the subnet mask
The result will be the network/subnet address
Creating a Subnet
Range of bits needed to create subnets
Determining subnet mask size
Computing subnet mask and IP address
Computing hosts per subnetwork
Boolean AND operation
IP configuration on a network diagram
Host/subnet schemes
Private addresses
The subnet field always follows immediately after the network number The subnet field always follows immediately after the network number The subnet field always follows immediately after the network number
Example
Class C address 197.15.22.131
Subnet mask of 255.255.255.224
224:11100000
Been extended by 3 bits: 27 bits
The 131: the third usable host address in the subnet 197.15.22.128
ExampleThe routers in the Internet (that don't know the subnet mask) will only worry about routing to the Class C network 197.15.22.0The routers inside that network, knowing the subnet mask, will be looking at 27 bits to make a routing decision
Example
Class B network:subnet mask of 255.255.240.0
The number 240 decimal is 11110000
4 bits for the subnet field.
Example
Number - 0000 ~ 1111 (15)Sixteen subnetsCannot use subnet 0 (network
address), and subnet 15 (1111) (broadcast address)
Fourteen usable subnets (1-14)
Computing hosts per subnetwork
Borrow 2 bits from the default 8 bit host field
The total number of possible hosts: 64 (26)
The number of usable host numbers would be reduced to 62
IP configuration on a network diagram
When you configure routers, you must connect each interface to a different network segment
Then each of these segments will become a separate subnet
Private addresses
There are certain addresses in each class of IP address that are not assignedPrivate addresses might be used by hosts that use network address translation (NAT), or a proxy server, to connect to a public network
Summary
Network addressing and best path selection Flat and hierarchical. Three classes of IP addresses Subnetworks or subnets Subnet masks