Ip Subnet Address Worksheet

							Subnetting and Variable
 Length Subnet Masks
Topics
  Planning & Designing
  • Design a simple LAN
  • Design an IP addressing scheme to meet design
    requirements
  • Design a simple internetwork
  Technology
  • Evaluate TCP/IP communication process and its
    associated protocols
   Troubleshooting
  •   Perform LAN and VLAN troubleshooting
  •   Troubleshoot routing protocols
  •   Troubleshoot IP addressing and host configuration
  •   Troubleshoot a device as part of a working network
Benefits of Subnetting
• Reduced network traffic
  – as a result of segmenting the network
  – reducing broadcast traffic
• Optimized network performance
• Simplified management
• Facilitated spanning of large geographical
 distances
  – by connecting smaller networks together
Subnet Masks

• A 32-bit value that separates the network
  ID of the IP address from the host ID
• Identifies that part of the host address
  used for the subnet
Subnetting Basics

• An IP address can be separated into
  network and host portions by its class or
  subnet mask
• Bits are “borrowed” from the host portion
  of the IP address to create the
  subnetworks
Creating Subnets
• Determine the number of network IDs needed, typically
   – 1 ID per subnet
   – 1 ID per WAN connection
• Determine how many hosts IDs per subnet are needed,
  typically
   – 1 ID per host
   – 1 ID per router
• Create
   – a subnet mask for the entire network
   – a subnet ID for each physical subnet
   – A range of host IDs for each subnet
Class Subnet Masks
Classless Inter-Domain Routing
(CIDR)
  • Does not use class boundaries for distinguishing
    network and hosts portions of IP address
  • Allocates an amount of IP address space to a
    company, home, or customer, based upon customer
    requirements
  • Uses the slash notation (/) to indicate how many bits
    are used for the network portion of the IP address;
    also indicates subnet mask value
CIDR Values
Subnetting Class C Addresses
   • Class C addresses use 24 bits for identifying
     network IDs
   • Bits are borrowed from the host portion to
     subnet, yielding the following subnet masks:
                 Binary Decimal CIDR
                 10000000 = 128         /25
                 11000000 = 192         /26
                 11100000 = 224         /27
                 11110000 = 240         /28
                 11111000 = 248         /29
                 11111100 = 252         /30
   /31 and /32 provide fewer than 2 host IDs
Binary Subnetting
• Determine number of bits used for subnet
   – Example 1000 0000 (1 bit used for subnet)
   – Example 1100 0000 (2 bits for subnet)
• Determine all possible subnet values for that number of
  bits
   – 00, 01, 10, and 11 are subnets for
     1100 0000
• Determine number of hosts per subnet
   – for 1100 0000, six bits define 2 6 – 2 hosts/subnet
• Determine broadcast address and host ID range
   – Broadcast address has all 1s in host portion
Subnets 00 and 01
 Subnet    Host           Meaning

 00        000000 = 0     The network (do this first)
 00        000001 = 1     The first valid host
 00        111110 = 62    The last valid host
 00        111111 = 63    The broadcast address (do
                          this second)



Subnet    Host           Meaning


01        000000 = 64    The network
01        000001 = 65    The first valid host
01        111110 = 126   The last valid host
01        111111 = 127   The broadcast address
Subnets 10, 11
             Host            Meaning
   Subnet
   10        000000 = 128    The subnet address
   10        000001 = 129    The first valid host
   10        111110 = 190    The last valid host
   10        111111 = 191    The broadcast address



            Host            Meaning
   Subnet
   11       000000 = 192    The subnet address
   11       000001 = 193    The first valid host
   11       111110 = 254    The last valid host
   11       111111 = 255    The broadcast address
Subnetting Class C Addresses –
Fast Method
      Answer Five Simple Questions:
How Many Subnets?
  2x = number of subnets
     x is the number of masked bits (1s)
     For example, if 2 bits are used to identify
      the subnet (1100 00002 = 19210), there are
      22 or 4 subnets
How Many Hosts Per Subnet?

2y - 2 = number of hosts per subnet
  • y is the number of unmasked bits (0s)
  • For example, if 2 bits are used for the
    network ID, then 6 bits are left for host IDs
  • Thus the number of hosts per subnet is 2 6-2
    or 62.
What Are The Valid Subnets?
• 256 - subnet mask = block size and subnet base
    value (Critical values; know these and
    everything else is simple)
•   For example 256 - 192=64. 64 is the first
    subnet.
•   The next subnet would be the base value plus
    the block size or 64 + 64 = 128, the second
    subnet
Subnet Broadcast Addresses

• The broadcast address is determined
  by setting all host bits to 1
• This is the number immediately
  preceding the next subnet
Valid Host IDs

• Valid hosts are the values
 between the subnets, omitting all
 0s and all 1s IDs
Variable Length Subnet Masks
(VLSM)
• Some segments do not need as many IDs
  as do other segments
• VLSM conserves address space by allotting
  the minimum number of IDs to each
  segment
• Like the name implies this is accomplished
  by using masks of different lengths
Routing Protocols that Support
VLSM
• RIPv2, EIGRP, and OSPF accommodate VLSM by
    including a field for subnet information
•   RIPv1 and IGRP do not
•   Protocols that support VLSM are said to be
    classless
• Protocols that do not support VLSM are called
    classful
Same Mask Subnetting
Applying VLSM
Implementing VLSM

• Relate number of hosts needed to block
  sizes
• Create VLSM table using VLSM Worksheet
  to avoid overlap
VLSM Worksheet
VSLM, Example 1
VLSM Worksheet for Example 1
VLSM, Example 2
VLSM Worksheet for Example 2
What are the IP addresses for the Fast
Ethernet and Serial Interfaces?
Answer
Summarization or Route
Aggregation
  • Advertises many networks as one
  • Reduces size of routing tables
  • Determine block size and summary mask
Troubleshooting
• The following examples provide practice at
    troubleshooting subnet addressing problems
•   General trouble shooting steps
    –   ping localhost
    –   ping local IP address
    –   ping default gateway
    –   ping remote server
    –   Consider DNS (ping host names and IP addresses)
Why Can’t the Sales LAN Contact
Server A?
Why Can’t Hosts in the Sales LAN
Contact Server B?
What is the Host Address?
Which Addresses Can Be Assigned
to the Hosts?
Which IP Addresses Can Be
Assigned?
Which Class C Mask Should Be
Used?