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Subnetting

ITEC 370

George Vaughan

Franklin University

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Sources for Slides

• Material in these slides comes primarily from course text, Guide to Networking Essentials,Tomsho, Tittel, Johnson (2007).

• Other sources are cited in line and listed in reference section.

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TCP/IP and OSI ModelsTCP/IP and OSI Models (OSI-Model, n.d.) and (Tomsho, 2007)

TCP/IP Layers

PDU OSI Layers Function Devices - Apps Standards

7 Application Network process to application, Initiates or accepts a request to transfer data

Browsers, servers, Gateways

HTTP, SNMP, FTP, Telnet

6 Presentation Adds formatting, display, and encryption of information

Gateways ASCII, MPEG

Application Data

5 Session Adds communication session control information, Login/Logout

DNS, Gateways

NetBIOS

Transport Segments 4 Transport Adds End-to-end connections and reliability, re-sequencing, flow control

Gateways TCP, UDP

Network Packets 3 Network Path determination and logical addressing (IP), translates MAC address to logical address

Routers IP, ICMP, ARP, NetBEUI

LLC Frames 2 Data Link

MAC

Adds error checking and physical addressing (MAC & LLC)

Switches, Bridges, NICs

802.3, 802.11, FDDI

Link

Bits 1 Physical Media, signal and binary transmission, sends data as a bit stream

Hubs, Repeaters

10Base-T, T1, E1

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Some Simple Binary Arithmetic Tomsho, Tittel, Johnson (2007)

• Four kinds of binary calculations:– Converting between binary and decimal– Converting between decimal and binary– Understanding how setting high-order bits to

the value of 1 in 8-bit binary numbers corresponds to specific decimal numbers

– Recognizing the decimal values for numbers that correspond to low-order bits when set to 1

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Converting Decimal to Binary Tomsho, Tittel, Johnson (2007)

• 125 is converted to binary as follows:– 125 divided by 2 equals 62, remainder 1– 62 divided by 2 equals 31, remainder 0– 31 divided by 2 equals 15, remainder 1– 15 divided by 2 equals 7, remainder 1– 7 divided by 2 equals 3, remainder 1– 3 divided by 2 equals 1, remainder 1– 1 divided by 2 equals 0, remainder 1

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Converting Binary to Decimal Tomsho, Tittel, Johnson (2007)

To convert 11010011 to decimal:

1. Count the total number of digits in the number (8)

2. Subtract one from the total (8 - 1 = 7)

3. That number (7) is the power of 2 to associate with the highest exponent for two in the number

4. Convert to exponential notation, using all the digits as multipliers

5. 11010011, therefore, converts to:

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High-Order Bit Patterns Tomsho, Tittel, Johnson (2007)

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Low-Order Bit Patterns Tomsho, Tittel, Johnson (2007)

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Types of IP Addressing

• The demarcation point in the 32 bit address between network ID and host ID depends on addressing scheme:– Class Based Addressing generally uses a

byte boundary as the dividing point– Classless Based Addressing uses a bit

boundary.

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Class Based IP Addressing

(Cisco – IP Addressing, n.d.).

Used less frequently now, CIDR preferred

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Special IP Addresses• Information on this slide from http://www.iana.org/faqs/abuse-faq.htm• "Private Use" IP addresses:

– 10.0.0.0 - 10.255.255.255 – 172.16.0.0 - 172.31.255.255 – 192.168.0.0 - 192.168.255.255

• "Autoconfiguration" IP Addresses:– 169.254.0.0 - 169.254.255.255 – used automatically by some PCs and Macs when

• They are configured to use IP• Do not have a static IP Address assigned• And are unable to obtain an IP address using DHCP.

• "Loopback" IP addresses:– 127.0.0.0 - 127.255.255.255 – Each computer on the Internet uses 127.0.0.0/8 to identify itself, to itself.– 127.0.0.0 to 127.255.255.255 is earmarked for what is called "loopback". – This construct allows a computer to establish/validate its IP stack. – Most software only uses 127.0.0.1 for loopback purposes

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Classless Interdomain Routing (CIDR)

• Division between Network and Host ID is at bit level.• Example: 192.203.187.0/27

– IP address is: 192.203.187.0– ‘/27’ indicates that:

• First 27 bits define Network ID• Last 5 bits define Host ID (defines size of subnet)• Subnet Mask =

– (binary) 11111111 11111111 11111111 11100000– (decimal) 255.255.255.224

• Subnet Mask defines Host ID size– 1’s used to define which bits belong to Network ID– 0’s used to define which bits belong to Host ID

• Subnet Mask is assigned to host at same time that IP address is assigned.

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CIDR (Cont.)

• Mapping class based IP addressing to CIDR:– Class A submask = 255.0.0.0– Class B submask = 255.255.0.0– Class C submask = 255.255.255.0

• All hosts in same network must use same subnet mask.

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Subnetting with Classless IP Addressing: Example 1

• Background • Assume you have the network address: 194.10.3.0 • Assume you want to create 5 subnets.

• You have a class C network. Default Mask = • 1111 1111 . 1111 1111 . 1111 1111. 0000 0000 • or 255.255.255.0

• 23 = 8, which is >= 5; therefore n = 3 • Therefore the new submask is:

• 1111 1111 . 1111 1111 . 1111 1111. 1110 0000 • or 255.255.255.128+64+32 • or 255.255.255.224

• We have 5 bits left for host ID • Each subnet can support 25-2 or 30 hosts

• Subnet Interval = 256 – 224 = 32 • IP address using CIDR Notation: 194.10.3.0/27

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Subnetting with Classless IP Addressing: Example 1 (Continued)

Subnet Subnet Address

First Usable IP Address

Last Usable IP Address

Broadcast Address

0 194.10.3.0 194.10.3.1 194.10.3.30 194.10.3.31 1 194.10.3.32 194.10.3.33 194.10.3.62 194.10.3.63 2 194.10.3.64 194.10.3.65 194.10.3.94 194.10.3.95 3 194.10.3.96 194.10.3.97 194.10.3.126 194.10.3.127 4 194.10.3.128 194.10.3.129 194.10.3.158 194.10.3.159 5 194.10.3.160 194.10.3.161 194.10.3.190 194.10.3.191 6 194.10.3.192 194.10.3.193 194.10.3.222 194.10.3.223 7 194.10.3.224 194.10.3.225 194.10.3.254 194.10.3.255

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Network Diagram of Subnets

Subnet 7 194.10.3.224 - 194.10.3.255

Subnet 3 194.10.3.96 - 194.10.3.127

Subnet 6 194.10.3.192 - 194.10.3.223

Subnet 2 194.10.3.64 - 194.10.3.95

Subnet 5 194.10.3.160 - 194.10.3.191

Subnet 1 194.10.3.32 - 194.10.3.63

Subnet 4 194.10.3.128 - 194.10.3.159

Subnet 0 194.10.3.0 - 194.10.3.31

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Subnetting with Classless IP Addressing: Example 2

• Background • Assume you have the network address:

132.132.0.0 • Assume you want to create 15 subnets.

• You have a class B network. Default Mask = • 1111 1111 . 1111 1111 . 0000 0000. 0000 0000 • or 255.255.255.0

• 24 = 16, which is >= 15; therefore n = 4 • Therefore the new submask is:

• 1111 1111 . 1111 1111 . 1111 0000. 0000 0000 • or 255.255.128+64+32+16.0 • or 255.255.240.0

• We have 5 bits left for host ID • Each subnet can support 212-2 or 4,094 hosts

• Subnet Interval = 256 – 240 = 16 • IP address using CIDR Notation: 132.132.0.0/20

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Subnetting with Classless IP Addressing: Example 2 (Continued)

Subnet Subnet Address

First Usable IP Address

Last Usable IP Address

Broadcast Address

0 132.132.0.0 132.132.0.1 132.132.15.254 132.132.15.255 1 132.132.16.0 132.132.16.1 132.132.31.254 132.132.31.255 2 132.132.32.0 132.132.32.1 132.132.47.254 132.132.47.255 3 132.132.48.0 132.132.48.1 132.132.63.254 132.132.63.255

… and so on… 13 132.132.208.0 132.132.208.1 132.132.223.254 132.132.223.255 14 132.132.224.0 132.132.224.1 132.132.239.254 132.132.239.255 15 132.132.240.0 132.132.240.1 132.132.255.254 132.132.255.255

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References

Tomsho, Tittel, Johnson (2007). Guide to Networking Essentials. Boston: Thompson Course Technology.

Odom, Knott (2006). Networking Basics: CCNA 1 Companion Guide. Indianapolis: Cisco Press

Wikipedia (n.d.). OSI Model. Retrieved 09/12/2006 from http://en.wikipedia.org/wiki/OSI_Model

Cisco – IP Addressing (n.d.). IP Addressing. Retrieved 09/27/2006 from http://cco.cisco.com/warp/public/701/3.html#figone

IANA (n.d.) Abuse Issues and IP Addresses . Retrieved 11/11/06 from http://www.iana.org/faqs/abuse-faq.htm