Addressing & Subneting

Addressing & Subnettingfor Exploration-S1

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Addressing

• …to identify and locate each host. We call it “addressing”.

• Identification: hostname, address (MAC, IP)– IP address ? MAC add ?

• MAC address: local• IP address: internetwork

• An address generally represents the connection to the network

Addressing

unique address: letter (network address) and number (host address)

IP Address (IPv4)

• IP address is 32-bit long.• It is often writen in dotted decimal format.

IP Addressing Structure

• IP add has 2 parts: net-id & host-id• Two different networks must have different network

address (net-id).• 2 different hosts in the same network must have different

host address (host-id). • Hosts in the same network have the same network

address.• Broadcast domain: one network address• Network address= IP address AND Subnet mask

IP Addressing Structure

• 32-bit address is expressed in Dotted decimal

• Network portion

• Host portion

• Octet

Subnet Mask

• The subnet mask is 32-bit pattern and created by – placing a binary 1 in each bit position that represents the network

portion and – placing a binary 0 in each bit position that represents the host

portion. • The prefix and the subnet mask are different ways of representing the

same thing - the network portion of an address. – The number of bits of an address used as the network portion is

called the prefix length.• In 8-bit pattern, there are:

00000000 = 0 11110000 = 24010000000 = 128 11111000 = 24811000000 = 192 11111100 = 25211100000 = 224 11111110 = 254

11111111 = 255

Defining the Network and Host Portions

Example 1:

SM : 255.255.255.0Net/host id: N.N.N.HNet E1 (Net-ID): 192.168.11.0Net E2 : 192.168.10.0Net E3 : 192.168.12.0

Number of broadcast domain ?

Example 2:

SM: 255.255.255.0Net address: 192.168.10.0Net/host id: N.N.N.H

H: hhhhhhhh0000000000000001000000100000001100000100…

1111111011111111

Example 3:

• IP address: 192.168.100.1• Subnet mask: 255.255.255.0• Net address: 192.168.100.0• Net/Host ID: N.N.N.H

• IP address : 11000000.10101000.01100100.00000001

• SM : 11111111.11111111.11111111.00000000

• Net address : 11000000.10101000.01100100.00000000

Example 4:

• IP address: 96.168.100.1• Subnet mask: 255.255.224.0• Net address: ?

• IP address : 01100000.10101000.01100100.00000001

• SM : 11111111.11111111.11100000.00000000

• Net address : 01100000.10101000.01100000.00000000

Hierachical addressing scheme

As a hierachical addressing scheme, IP addresses are divided into “classes”.

Classes of IP Addresses

• Class A addresses are assigned to larger networks.

• Class B addresses are used for medium-sized networks

• Class C for small networks.

• First octet order bits:– Class A: 00000000 (0)

00000001 (1)…01111110 (126)01111111 (127)

• First octet order bits:– Class B: 10000000 (128)

10000001 (129)…10111110 (190)10111111 (191)

• First octet order bits:– Class C: 11000000 (192)

11000001 (193)…11011110 (222)11011111 (223)

• First octet order bits:– Class D: 11100000 (224)

11100001 (225)…11101110 (238)11101111 (239)

Type of Address in an IPv4 Network

• Three types of addresses:– Network address - The address by which we refer

to the network. All hosts in a network will have the same network bits.

– Broadcast address - A special address used to send data to all hosts in the network. The broadcast address uses the highest address in the network range. This is the address in which the bits in the host portion are all 1s. This address is also referred to as the directed broadcast.

– Host addresses - The addresses assigned to the end devices in the network

Network Address

• When all host-bits are zeros (0), we have a number that represents network address. This address is reserved, namely it cannot be assigned to any host.

Network Address

Broadcast Address

• When host-bits are all one (1), we have a number that represents broadcast address. This address is also reserved, namely it cannot be assigned to any host.

• Exp: – ping 10.0.6.255– Ping 255.255.255.255

Broadcast Address

Extra: Broadcast Address

• The router supports the following kinds of broadcast types: – Limited broadcast - A packet is sent to a specific network or series of

networks. In a limited broadcast packet destined for a local network, the network identifier portion and host identifier portion of the destination address is either all 1s (255.255.255.255) or all 0s (0.0.0.0).

– Directed broadcast - A packet is sent to a specific destination address where only the host portion of the IP address is either all 1s or all 0s (such as 192.20.255.255 or 190.20.0.0).

Host address

Calculating Network, Hosts & Broadcast Addresses

• Practice 6.2.2

Type of Communication

• Three types: Unicast, Broadcast, Multicast

Unicast

• Is used for the normal host-to-host communication in both a client/server and a peer-to-peer network.

• Uses the host address of the destination device as the destination address and can be routed through an internetwork.

Broadcast

• The process of sending a packet from one host to all hosts in the network

• Host processes a broadcast address destination packet like unicast address. – A directed broadcast is sent to all hosts on a specific network. – The limited broadcast is used for communication that is limited to

the hosts on the local network.

Multicast

• The process of sending a packet from one host to a selected group of hosts.

• Multicast transmission is designed to conserve the bandwidth of the IPv4 network.

• The multicast clients use services initiated by a client program to subscribe to the multicast group.

Reserved IPv4 Address Ranges

Public and Private addresses

Public IP Addresses

• Public Addresses: are designed to be used in the hosts that are publicly accessible from the Internet.•Public IP addresses are unique.

•No two machines that connect to a public network can have the same IP address. (X#Y#Z )

• Public IP addresses must be obtained from an Internet service provider (ISP) or a registry at some expense.• With the rapid growth of the Internet, public IP addresses were beginning to run out(IP address depletion).

Private IP Addresses

• Private Addresses: are set aside for use in private networks.• Network Address Translation (NAT): is used to translate private addresses to public addresses, be implemented on a device at the edge of the private network.

Private IP Addresses

• RFC 1918 sets aside three blocks of IP addresses for private, internal use. These three blocks consist of one Class A, a range of Class B addresses, and a range of Class C addresses.• Addresses that fall within these ranges are not routed on the Internet backbone. Internet routers immediately discard private addresses.

10.0.0.0 /8172.16.0.0 /12192.168.0.0 /16

Using Private Addresses

• When addressing a nonpublic intranet, a test lab, or a home network, we normally use private addresses instead of globally unique addresses.

• Private addresses can be used to address point-to-point serial links without wasting real IP addresses.

Special IPv4 Addresses

• TEST-NET Addresses– The address block 192.0.2.0 to 192.0.2.255 (192.0.2.0 /24) is set aside for

teaching and learning purposes. These addresses can be used in documentation and network examples. Unlike the experimental addresses, network devices will accept these addresses in their configurations

• Network Addresses• Broadcast Addresses• Default Route

– 0.0.0.0/0• Loopback: 127.0.0.0/8• Link-Local Addresses

– 169.254.0.0 to 169.254.255.255 (169.254.0.0 /16)

– These addresses can be automatically assigned

– APIPA ( Automatic Private IP Addressing )

Extra: Reserved IP Address

• all 0s -This host, exp: 0.0.0.0• all 0s.host - Host on this net, exp:0.x.x.x• all 1s - Limitted broadcast (local net),exp: 255.255.255.255• Net.all 1s - Directed broadcast for net, exp: 192.168.100.255• Net.all 0s – Network address, exp: 192.168.1.0• 127.anything (often 1) - Loopback, exp: 127.0.0.1• Exp: ping 0.0.0.0

0.0.6.156255.255.255.25510.0.6.255

Legacy IPv4 Addressing

• Classful addressing: A company or organization was assigned an entire class A, class B, or class C address block.– Limits to the Class-based System

• Classful allocation of address space often wasted many addresses, which exhausted the availability of IPv4 addresses.

• Classless Addressing– Address blocks appropriate to the number of hosts

are assigned to companies or organizations without regard to the unicast class.

IP addressing crisis

• Address Depletion• Internet Routing Table Explosion

Subnetting

• Exp:• Net address: 192.168.100.0; SM: 255.255.255.0; usable host addresses:2^8-2=254• If hosts per network is 60 à used: 6 host bits: xxhhhhhh, 2^6-2=62 hosts;

unused: 2 host bitsxxhhhhhhxx000000 (0)xx000001xx000010…xx111110xx111111 (63)

• IP addresses for poin-to-point link (router – router): 2 hosts à 2 IP

• Net 1: 172.16.0.0• Net 2: 172.17.0.0• Net 3: 172.18.0.0• Net 4: 172.19.0.0• Usable hosts per network : 2^16-2= 65534 !!!

Subnetting

• Subnetting is another method of managing IP addresses. This method of dividing full network address classes into smaller pieces has prevented complete IP address exhaustion.• The network is no longer limited to the default Class A, B, or C network masks and there is more flexibility in the network design.• Subnet addresses include the network (N) portion, plus a subnet (sN) field and a host (H) field.

To create a subnet address, a network administrator borrows bits from the host field and designates them as the subnet field.

Subnetting

• Host bit must be reassigned as network bit.The starting “borrow” bit is the leftmost hosting bit.

• Providing broadcast contentment and low level security.

Subnetting

• 1 net address: 192.168.10.0; SM: 255.255.255.0; 254 hosts• hosts per network: 30; networks: 6 ?

– Borrows bits: 3 à 2^3-2= 6 subnets– Host bits: 5 à 2^5-2=30 hosts– SM: 255.255.255.224– Subnets:

192.168.10.0192.168.10.32192.168.10.64192.168.10.96

.128…192.168.10.192192.168.10.224

xxxhhhhh

000 (0)

001 (32)

010 (64)

011 (96)

100 (128)

101 (160)

110 (192)

111 (224)

Establishing SM address

• The number of bits in the subnet will depend on the maximum number of hosts required per subnet.

• The subnet mask: using binary ones in the host octet(s)

• (2 power of borrowed bits) – 2 = usable subnets (previous !)

• (2 power of remaining host bits)–2= usable hosts

Applying the Subnet Mask

• Exp: subnet 192.168.10.32/27

• Host Range ???

• 192.168.10.001hhhhh • .00100000• .00100001 (33)• .00100010• .00100011• …• 192.168.10.00111110 (62)• .00111111

Other: Basic subnetting

Example 5:

• Primary network 192.168.10.0/24• Number of hosts per network: 60• Number of subnets: 4• Borrows bits ?• Subnetwork address ?• Subnet Mask ?• Host Range ?• Broadcast address ?

Calculating subnets with VLSM

4 subnets of 62 hosts4 links of 2 hosts

172.16.0010xxxx.xxhhhhhh/26

172.16.0010hhhh.hhhhhhhh/20

• 4 subnets of 62 hosts: – 172.16.32.0/26– 172.16.32.64/26– 172.16.32.128/26– 172.16.32.192/26

• 4 links of 2 hosts:– 172.16.33.0/26 is further subnetted with a prefix of

• 172.16.33.0/26 is further subnetted:– 172.16.33.00xxxxhh/30– 172.16.33.000000hh à 172.16.33.0/30– 172.16.33.000001hh à 172.16.33.4/30– 172.16.33.000010hh à 172.16.33.8/30– 172.16.33.000011hh à 172.16.33.12/30

Example 2

• Your company has been given the network address 172.16.32.0/19. After careful planning, looking at current needs and expansion, you realize you need a maximum of three subnets of 1000 hosts, three subnets of 250 hosts, and several subnets for serial point-to-point links.

Example 2

• 172.16.32.0/19• 172.16.00100000.00000000• Subnets of 1000 hosts: need 10 host bits

– 172.16.001xxxhh.hhhhhhhh/22– 172.16.001000hh.hhhhhhhhà172.16.32.0– 172.16.001001hh.hhhhhhhhà172.16.36.0– 172.16.001010hh.hhhhhhhhà172.16.40.0– 172.16.001011hh.hhhhhhhhà172.16.44.0– 172.16.001100hh.hhhhhhhhà172.16.48.0– 172.16.001101hh.hhhhhhhhà172.16.52.0– 172.16.001110hh.hhhhhhhhà172.16.56.0– 172.16.001111hh.hhhhhhhhà172.16.60.0

Example 2

• 3 subnets of 1000 hosts:– 172.16.32.0/22– 172.16.36.0/22– 172.16.40.0/22

• Subnets of 250 hosts: need 8 host bits• To sub-subnet the subnet 172.16.44.0/22

Example 2

• 172.16.44.0/22• 172.16.001011xx.hhhhhhhh/24• 172.16.00101100.hhhhhhhhà172.16.44.0• 172.16.00101101.hhhhhhhhà172.16.45.0• 172.16.00101110.hhhhhhhhà172.16.46.0• 172.16.00101111.hhhhhhhhà172.16.47.0

Example 2

• 3 subnets of 250 hosts:– 172.16.44.0/24– 172.16.45.0/24– 172.16.46.0/24

• Links of 2 hosts: need 2 host bits• To sub-subnet the subnet 172.16.47.0/24

Example 2

• 172.16.47.0/24• 172.16.47.xxxxxxhh/30• 172.16.47.000000hhà172.16.47.0/30• 172.16.47.000001hhà172.16.47.4• 172.16.47.000010hhà172.16.47.8• 172.16.47.000011hhà172.16.47.12• …

Other: Subnetting a Subnet

• Practice 6.5.4-6

Addressing & Subneting

hierachical

octet order

ip addressing

legacy ipv4

public ip

private ip

ip addresses

ip address

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