Addressing & Sub Netting

Addressing & Subnetting

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Addressing • …to identify and locate each host. We call it “addressing”. • Identification: hostname, address (MAC, IP) • IP add ? MAC add ? • MAC add: local • IP add: internetwork • An address generally represents the connection to the network

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Addressing

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

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IP Address (IPv4)

• IP address is 32-bit long.

• It is often writen in dotted decimal format.

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Addressing • IP add has two parts: net-id & host-id • Two different networks must have different network address (net-id). • Two 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 add • Network address= IP address AND Subnet mask

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Example 1:

SM : 255.255.255.0 Net/host id: N.N.N.H Net E1 (Net-ID): 192.168.11.0 Net E2 : 192.168.10.0 Net E3 : 192.168.12.0 PDF created with pdfFactory Pro trial version www.pdffactory.com

Number broadcast domain ?

Example 2:

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

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H: hhhhhhhh 00000000 00000001 00000010 00000011 00000100 … 11111110 11111111

Example 3: • • • •

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

• IP add : 11000000.10101000.01100100.00000001 • SM : 11111111.11111111.11111111.00000000 • Net add : 11000000.10101000.01100100.00000000

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Example 4: • IP add: 96.168.100.1 • Subnet mask: 255.255.224.0 • Net add: ? • IP add : 01100000.10101000.01100100.00000001 • SM : 11111111.11111111.11100000.00000000 • Net add : 01100000.10101000.01100000.00000000 • Note: subnetmask

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Hierachical addressing scheme

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

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Classes of IP Addresses •

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Class A addresses are assigned to larger networks. Class B addresses are used for mediumsized networks Class C for small networks.

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Classes of IP Addresses

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First octet order bits: – Class A: 00000000 00000001 … 01111110 01111111 First octet order bits: – Class C: 11000000 11000001 … 11011110 11011111

• (0) (1) (126) (127) • (192) (193) (222) (223)

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First octet order bits: – Class B: 10000000 10000001 … 10111110 10111111 First octet order bits: – Class D: 11100000 11100001 … 11101110 11101111

(128) (129) (190) (191)

(224) (225) (238) (239)

Classes of IP Addresses

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Network Address

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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.

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Broadcast Address

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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

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Reference: 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 ones (255.255.255.255) or all zeros (0.0.0.0). – Flooded broadcast - A packet is sent to every network. – Directed broadcast - A packet is sent to a specific destination address where only the host portion of the IP address is either all ones or all zeros (such as 192.20.255.255 or 190.20.0.0).

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Unicast and Broadcast Transmission

Unicast transmission

Broadcast transmission

• The concept of unicast and broadcast transmission exist in both layer 2 and layer 3 protocols. There are refelections in the addressing scheme.

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Reserved IP Address

Host-bits = all zeros (network address); exp: 176.10.0.0 Host-bits = all ones (broadcast address); exp: 176.10.255.255 Network-bits = all ones; exp: 01111111.x.x.x Network-bits = all zeros; exp: 00000000.x.x.x 127.x.x.x (loopback address = 127.0.0.1).

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Reference: 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 • 127.anything (often 1) - Loopback, (127.0.0.1) • Exp: ping 0.0.0.0 0.0.6.156 255.255.255.255 10.0.6.255

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Public IP Addresses

• 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). • New addressing schemes, such as classless interdomain routing (CIDR) and IPv6 were developed to help solve the problem. Private IP addresses are another solution.

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Private IP Addresses

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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.

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Using Private Addresses

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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. Connecting a network using private addresses to the Internet requires translation of the private addresses to public addresses. This translation process is referred to as Network Address Translation (NAT).

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Subnetting • Net 1: 172.16.0.0 • Net 2: 172.17.0.0 • Net 3: 172.18.0.0 • Net 4: 172.19.0.0 • Hosts per network (usable): 2^16-2= 65534 !!! • IP add for poin-to-point link (router – router): 2 hosts à 2 IP add • Waste !!! • Exp: • Net add: 192.168.100.0; SM: 255.255.255.0; Number hosts usable: 2^8-2=254 • If hosts per network is 60 à used: 6 bits host: xxhhhhhh, 2^6-2=62 hosts; unused: 2 bits host xxhhhhhh xx000000 (0) xx000001 xx000010 … xx111110 xx111111 (63)

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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.

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Subnetting •

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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 add: 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: 192.168.10.32 192.168.10.64 192.168.10.96 .128 … 192.168.10.192

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Exp: xxxhhhhh 000 (0) 001 (32) 010 (64) 011 (96) 100 (128) 101 (160) 110 (192) 111 (224)

Establishing SM address •

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

Applying the Subnet Mask

• Exp: subnet

192.168.10.32/27 • Host Range ???

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

Example 5:

• Primary network 192.168.10.0/24 • Hosts per network: 30 • Number subnets: 4 • Borrows bits ? • Subnets ? • IP add for hosts ? PDF created with pdfFactory Pro trial version www.pdffactory.com