Day 08 / 63 · Network foundations
IPv4 Addressing (pt 2)
Study notes based primarily on Jeremy’s IT Lab CCNA learning videos. Credit to Jeremy’s IT Lab for the source lessons and diagrams.
IPv4 Addressing (pt 2)
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Day 8 - IPv4 Addressing (pt 2) Saturday, August 22, 2026 2:50 PM 8. IPv4 ADDRESSING : PART 2 MAXIMUM HOSTS PER NETWORK Let's take a Class C Network: 192.168.1.0/24 (gives a range of 0 ---> 255) Said another way, the HOST portion (the .0) is equal to 8 bits so... Host portion = 8 bits = 2^8 = 256 HOWEVER, since the Network Address (Network ID) 192.168.1.0 is Reserved AND 192.168.1.255 (BROADCAST ADDRESS) is ALSO reserved. The MAXIMUM Hosts per Network = 2^8-2 = 254 hosts What about a Class B Network ? 172.16.0.0/16 ----> 172.16.255.255/16 Host portion = 16 bits = 2^16 = 65,536 Maximum hosts per network = 2^16-2 = 65,534 hosts What about a Class A Network ? 10.0.0.0/8 -------------> 10.255.255.255/8 Host portion = 24 bits = 2^24 = 16,777,216 Maximum hosts per network = 2^24-2 = 16,777,214 hosts THEREFORE: The formula for calculating the number of HOSTS on a network is: 2 ^ N - 2 (2 to the power of N - 2) where N = number of HOST bits FIRST / LAST USABLE ADDRESSES Class C Network 192.168.1.0/24 (NETWORK ADDRESS) Add 1 so the Host Portion = 00000001 192.168.1.1/24 = FIRST USABLE ADDRESS 192.168.1.255/24 (BROADCAST ADDRESS) Subtract 1 from the BROADCAST ADDRESS = 11111110 192.168.1.254/24 = LAST USABLE ADDRESS Class B Network 172.16.0.0/16 (NETWORK ADDRESS) Add 1 to Host portion so 0000 0000 0000 0001 172.16.0.1/16 is the FIRST USABLE ADDRESS 172.16.255.255/16 (BROADCAST ADDRESS) Subtract 1 to Broadcast Address so 1111 1111 1111 1110 172.16.255.254/16 is the LAST USABLE ADDRESS Class A Network 10.0.0.0/8 (NETWORK ADDRESS) Add 1 to Host portion so 00000000 00000000 00000001 10.0.0.1/8 is the FIRST USABLE ADDRESS 10.255.255.255/8 (BROADCAST ADDRESS) Subtract 1 to Broadcast Address so 1111 1111 1111 1110 10.255.255.254/16 is the LAST USABLE ADDRESS CISCO CLI DEVICE CONFIGURATION R1> enable R1# show ip interface brief Lists the Interfaces, IP Addresses, Method, Status, and Protocol. Interfaces: • What port interfaces are available/connected IP Addresses • Self explanatory. What IP Address is assigned. Method • What method was the IP address assigned? Status (Layer 1 Status) • Current status of interface • 'administratively down' = Interface has been disabled with the 'shutdown' command Administratively down is the DEFAULT status of Cisco Router interfaces. Cisco Switch interfaces are NOT administratively down by DEFAULT. Protocol (Layer 2 Status) • Cannot operate if Status (Layer 1) is down // configure terminal cmd R1# conf t // This enters interface configuration mode R1(config)# interface gigabitethernet 0/0 This can be shortened to 'g0/0' like they are listed in physical network maps. // This sets the IP ADDRESS and SUBNET MASK of device R1(config-if) #ip address 10.255.255.254 255.0.0.0 // This enables the device R1(config-if) #no shutdown Two messages should appear showing the state has changed to 'up' (Status). Second message should show line protocol is now 'up' (Protocol). // 'do' allows you to run a Privileged EXEC command from outside the mode. R1(config-if) #do show ip interface brief Good to confirm that the device/interface you have configured is up and running. More 'show' CLI Commands 'show interfaces ' • Shows Layer 1 and Layer 2 information about the interface and some Layer 3. • Shows MAC Address (or BIA address) • IP Address • ... and so much more 'show interfaces description' • show description for interface. Example: // Configure mode for interface Gigabyte Interface 0/0 R1(config) #int g0/0 R1(config) #description ## to SW1 ## This sets the 'Description' column to display: Interface Description Gi0/0 ## to SW1 ## Day 8 - IPv4 Addressing (pt 2) Saturday, August 22, 2026 2:50 PM 8. IPv4 ADDRESSING : PART 2 MAXIMUM HOSTS PER NETWORK Let's take a Class C Network: 192.168.1.0/24 (gives a range of 0 ---> 255) Said another way, the HOST portion (the .0) is equal to 8 bits so... Host portion = 8 bits = 2^8 = 256 HOWEVER, since the Network Address (Network ID) 192.168.1.0 is Reserved AND 192.168.1.255 (BROADCAST ADDRESS) is ALSO reserved. The MAXIMUM Hosts per Network = 2^8-2 = 254 hosts What about a Class B Network ? 172.16.0.0/16 ----> 172.16.255.255/16 Host portion = 16 bits = 2^16 = 65,536 Maximum hosts per network = 2^16-2 = 65,534 hosts What about a Class A Network ? 10.0.0.0/8 -------------> 10.255.255.255/8 Host portion = 24 bits = 2^24 = 16,777,216 Maximum hosts per network = 2^24-2 = 16,777,214 hosts THEREFORE: The formula for calculating the number of HOSTS on a network is: 2 ^ N - 2 (2 to the power of N - 2) where N = number of HOST bits FIRST / LAST USABLE ADDRESSES Class C Network 192.168.1.0/24 (NETWORK ADDRESS) Add 1 so the Host Portion = 00000001 192.168.1.1/24 = FIRST USABLE ADDRESS 192.168.1.255/24 (BROADCAST ADDRESS) Subtract 1 from the BROADCAST ADDRESS = 11111110 192.168.1.254/24 = LAST USABLE ADDRESS Class B Network 172.16.0.0/16 (NETWORK ADDRESS) Add 1 to Host portion so 0000 0000 0000 0001 172.16.0.1/16 is the FIRST USABLE ADDRESS 172.16.255.255/16 (BROADCAST ADDRESS) Subtract 1 to Broadcast Address so 1111 1111 1111 1110 172.16.255.254/16 is the LAST USABLE ADDRESS Class A Network 10.0.0.0/8 (NETWORK ADDRESS) Add 1 to Host portion so 00000000 00000000 00000001 10.0.0.1/8 is the FIRST USABLE ADDRESS 10.255.255.255/8 (BROADCAST ADDRESS) Subtract 1 to Broadcast Address so 1111 1111 1111 1110 10.255.255.254/16 is the LAST USABLE ADDRESS CISCO CLI DEVICE CONFIGURATION R1> enable R1# show ip interface brief Lists the Interfaces, IP Addresses, Method, Status, and Protocol. Interfaces: • What port interfaces are available/connected IP Addresses • Self explanatory. What IP Address is assigned. Method • What method was the IP address assigned? Status (Layer 1 Status) • Current status of interface • 'administratively down' = Interface has been disabled with the 'shutdown' command Administratively down is the DEFAULT status of Cisco Router interfaces. Cisco Switch interfaces are NOT administratively down by DEFAULT. Protocol (Layer 2 Status) • Cannot operate if Status (Layer 1) is down // configure terminal cmd R1# conf t // This enters interface configuration mode R1(config)# interface gigabitethernet 0/0 This can be shortened to 'g0/0' like they are listed in physical network maps. // This sets the IP ADDRESS and SUBNET MASK of device R1(config-if) #ip address 10.255.255.254 255.0.0.0 // This enables the device R1(config-if) #no shutdown Two messages should appear showing the state has changed to 'up' (Status). Second message should show line protocol is now 'up' (Protocol). // 'do' allows you to run a Privileged EXEC command from outside the mode. R1(config-if) #do show ip interface brief Good to confirm that the device/interface you have configured is up and running. More 'show' CLI Commands 'show interfaces ' • Shows Layer 1 and Layer 2 information about the interface and some Layer 3. • Shows MAC Address (or BIA address) • IP Address • ... and so much more 'show interfaces description' • show description for interface. Example: // Configure mode for interface Gigabyte Interface 0/0 R1(config) #int g0/0 R1(config) #description ## to SW1 ## This sets the 'Description' column to display: Interface Description Gi0/0 ## to SW1 ## Day 8 - IPv4 Addressing (pt 2) Saturday, August 22, 2026 2:50 PM 8. IPv4 ADDRESSING : PART 2 MAXIMUM HOSTS PER NETWORK Let's take a Class C Network: 192.168.1.0/24 (gives a range of 0 ---> 255) Said another way, the HOST portion (the .0) is equal to 8 bits so... Host portion = 8 bits = 2^8 = 256 HOWEVER, since the Network Address (Network ID) 192.168.1.0 is Reserved AND 192.168.1.255 (BROADCAST ADDRESS) is ALSO reserved. The MAXIMUM Hosts per Network = 2^8-2 = 254 hosts What about a Class B Network ? 172.16.0.0/16 ----> 172.16.255.255/16 Host portion = 16 bits = 2^16 = 65,536 Maximum hosts per network = 2^16-2 = 65,534 hosts What about a Class A Network ? 10.0.0.0/8 -------------> 10.255.255.255/8 Host portion = 24 bits = 2^24 = 16,777,216 Maximum hosts per network = 2^24-2 = 16,777,214 hosts THEREFORE: The formula for calculating the number of HOSTS on a network is: 2 ^ N - 2 (2 to the power of N - 2) where N = number of HOST bits FIRST / LAST USABLE ADDRESSES Class C Network 192.168.1.0/24 (NETWORK ADDRESS) Add 1 so the Host Portion = 00000001 192.168.1.1/24 = FIRST USABLE ADDRESS 192.168.1.255/24 (BROADCAST ADDRESS) Subtract 1 from the BROADCAST ADDRESS = 11111110 192.168.1.254/24 = LAST USABLE ADDRESS Class B Network 172.16.0.0/16 (NETWORK ADDRESS) Add 1 to Host portion so 0000 0000 0000 0001 172.16.0.1/16 is the FIRST USABLE ADDRESS 172.16.255.255/16 (BROADCAST ADDRESS) Subtract 1 to Broadcast Address so 1111 1111 1111 1110 172.16.255.254/16 is the LAST USABLE ADDRESS Class A Network 10.0.0.0/8 (NETWORK ADDRESS) Add 1 to Host portion so 00000000 00000000 00000001 10.0.0.1/8 is the FIRST USABLE ADDRESS 10.255.255.255/8 (BROADCAST ADDRESS) Subtract 1 to Broadcast Address so 1111 1111 1111 1110 10.255.255.254/16 is the LAST USABLE ADDRESS CISCO CLI DEVICE CONFIGURATION R1> enable R1# show ip interface brief Lists the Interfaces, IP Addresses, Method, Status, and Protocol. Interfaces: • What port interfaces are available/connected IP Addresses • Self explanatory. What IP Address is assigned. Method • What method was the IP address assigned? Status (Layer 1 Status) • Current status of interface • 'administratively down' = Interface has been disabled with the 'shutdown' command Administratively down is the DEFAULT status of Cisco Router interfaces. Cisco Switch interfaces are NOT administratively down by DEFAULT. Protocol (Layer 2 Status) • Cannot operate if Status (Layer 1) is down // configure terminal cmd R1# conf t // This enters interface configuration mode R1(config)# interface gigabitethernet 0/0 This can be shortened to 'g0/0' like they are listed in physical network maps. // This sets the IP ADDRESS and SUBNET MASK of device R1(config-if) #ip address 10.255.255.254 255.0.0.0 // This enables the device R1(config-if) #no shutdown Two messages should appear showing the state has changed to 'up' (Status). Second message should show line protocol is now 'up' (Protocol). // 'do' allows you to run a Privileged EXEC command from outside the mode. R1(config-if) #do show ip interface brief Good to confirm that the device/interface you have configured is up and running. More 'show' CLI Commands 'show interfaces ' • Shows Layer 1 and Layer 2 information about the interface and some Layer 3. • Shows MAC Address (or BIA address) • IP Address • ... and so much more 'show interfaces description' • show description for interface. Example: // Configure mode for interface Gigabyte Interface 0/0 R1(config) #int g0/0 R1(config) #description ## to SW1 ## This sets the 'Description' column to display: Interface Description Gi0/0 ## to SW1 ## Day 8 - IPv4 Addressing (pt 2) Saturday, August 22, 2026 2:50 PM 8. IPv4 ADDRESSING : PART 2 MAXIMUM HOSTS PER NETWORK Let's take a Class C Network: 192.168.1.0/24 (gives a range of 0 ---> 255) Said another way, the HOST portion (the .0) is equal to 8 bits so... Host portion = 8 bits = 2^8 = 256 HOWEVER, since the Network Address (Network ID) 192.168.1.0 is Reserved AND 192.168.1.255 (BROADCAST ADDRESS) is ALSO reserved. The MAXIMUM Hosts per Network = 2^8-2 = 254 hosts What about a Class B Network ? 172.16.0.0/16 ----> 172.16.255.255/16 Host portion = 16 bits = 2^16 = 65,536 Maximum hosts per network = 2^16-2 = 65,534 hosts What about a Class A Network ? 10.0.0.0/8 -------------> 10.255.255.255/8 Host portion = 24 bits = 2^24 = 16,777,216 Maximum hosts per network = 2^24-2 = 16,777,214 hosts THEREFORE: The formula for calculating the number of HOSTS on a network is: 2 ^ N - 2 (2 to the power of N - 2) where N = number of HOST bits FIRST / LAST USABLE ADDRESSES Class C Network 192.168.1.0/24 (NETWORK ADDRESS) Add 1 so the Host Portion = 00000001 192.168.1.1/24 = FIRST USABLE ADDRESS 192.168.1.255/24 (BROADCAST ADDRESS) Subtract 1 from the BROADCAST ADDRESS = 11111110 192.168.1.254/24 = LAST USABLE ADDRESS Class B Network 172.16.0.0/16 (NETWORK ADDRESS) Add 1 to Host portion so 0000 0000 0000 0001 172.16.0.1/16 is the FIRST USABLE ADDRESS 172.16.255.255/16 (BROADCAST ADDRESS) Subtract 1 to Broadcast Address so 1111 1111 1111 1110 172.16.255.254/16 is the LAST USABLE ADDRESS Class A Network 10.0.0.0/8 (NETWORK ADDRESS) Add 1 to Host portion so 00000000 00000000 00000001 10.0.0.1/8 is the FIRST USABLE ADDRESS 10.255.255.255/8 (BROADCAST ADDRESS) Subtract 1 to Broadcast Address so 1111 1111 1111 1110 10.255.255.254/16 is the LAST USABLE ADDRESS CISCO CLI DEVICE CONFIGURATION R1> enable R1# show ip interface brief Lists the Interfaces, IP Addresses, Method, Status, and Protocol. Interfaces: • What port interfaces are available/connected IP Addresses • Self explanatory. What IP Address is assigned. Method • What method was the IP address assigned? Status (Layer 1 Status) • Current status of interface • 'administratively down' = Interface has been disabled with the 'shutdown' command Administratively down is the DEFAULT status of Cisco Router interfaces. Cisco Switch interfaces are NOT administratively down by DEFAULT. Protocol (Layer 2 Status) • Cannot operate if Status (Layer 1) is down // configure terminal cmd R1# conf t // This enters interface configuration mode R1(config)# interface gigabitethernet 0/0 This can be shortened to 'g0/0' like they are listed in physical network maps. // This sets the IP ADDRESS and SUBNET MASK of device R1(config-if) #ip address 10.255.255.254 255.0.0.0 // This enables the device R1(config-if) #no shutdown Two messages should appear showing the state has changed to 'up' (Status). Second message should show line protocol is now 'up' (Protocol). // 'do' allows you to run a Privileged EXEC command from outside the mode. R1(config-if) #do show ip interface brief Good to confirm that the device/interface you have configured is up and running. More 'show' CLI Commands 'show interfaces ' • Shows Layer 1 and Layer 2 information about the interface and some Layer 3. • Shows MAC Address (or BIA address) • IP Address • ... and so much more 'show interfaces description' • show description for interface. Example: // Configure mode for interface Gigabyte Interface 0/0 R1(config) #int g0/0 R1(config) #description ## to SW1 ## This sets the 'Description' column to display: Interface Description Gi0/0 ## to SW1 ## Day 8 - IPv4 Addressing (pt 2) Saturday, August 22, 2026 2:50 PM 8. IPv4 ADDRESSING : PART 2 MAXIMUM HOSTS PER NETWORK Let's take a Class C Network: 192.168.1.0/24 (gives a range of 0 ---> 255) Said another way, the HOST portion (the .0) is equal to 8 bits so... Host portion = 8 bits = 2^8 = 256 HOWEVER, since the Network Address (Network ID) 192.168.1.0 is Reserved AND 192.168.1.255 (BROADCAST ADDRESS) is ALSO reserved. The MAXIMUM Hosts per Network = 2^8-2 = 254 hosts What about a Class B Network ? 172.16.0.0/16 ----> 172.16.255.255/16 Host portion = 16 bits = 2^16 = 65,536 Maximum hosts per network = 2^16-2 = 65,534 hosts What about a Class A Network ? 10.0.0.0/8 -------------> 10.255.255.255/8 Host portion = 24 bits = 2^24 = 16,777,216 Maximum hosts per network = 2^24-2 = 16,777,214 hosts THEREFORE: The formula for calculating the number of HOSTS on a network is: 2 ^ N - 2 (2 to the power of N - 2) where N = number of HOST bits FIRST / LAST USABLE ADDRESSES Class C Network 192.168.1.0/24 (NETWORK ADDRESS) Add 1 so the Host Portion = 00000001 192.168.1.1/24 = FIRST USABLE ADDRESS 192.168.1.255/24 (BROADCAST ADDRESS) Subtract 1 from the BROADCAST ADDRESS = 11111110 192.168.1.254/24 = LAST USABLE ADDRESS Class B Network 172.16.0.0/16 (NETWORK ADDRESS) Add 1 to Host portion so 0000 0000 0000 0001 172.16.0.1/16 is the FIRST USABLE ADDRESS 172.16.255.255/16 (BROADCAST ADDRESS) Subtract 1 to Broadcast Address so 1111 1111 1111 1110 172.16.255.254/16 is the LAST USABLE ADDRESS Class A Network 10.0.0.0/8 (NETWORK ADDRESS) Add 1 to Host portion so 00000000 00000000 00000001 10.0.0.1/8 is the FIRST USABLE ADDRESS 10.255.255.255/8 (BROADCAST ADDRESS) Subtract 1 to Broadcast Address so 1111 1111 1111 1110 10.255.255.254/16 is the LAST USABLE ADDRESS CISCO CLI DEVICE CONFIGURATION R1> enable R1# show ip interface brief Lists the Interfaces, IP Addresses, Method, Status, and Protocol. Interfaces: • What port interfaces are available/connected IP Addresses • Self explanatory. What IP Address is assigned. Method • What method was the IP address assigned? Status (Layer 1 Status) • Current status of interface • 'administratively down' = Interface has been disabled with the 'shutdown' command Administratively down is the DEFAULT status of Cisco Router interfaces. Cisco Switch interfaces are NOT administratively down by DEFAULT. Protocol (Layer 2 Status) • Cannot operate if Status (Layer 1) is down // configure terminal cmd R1# conf t // This enters interface configuration mode R1(config)# interface gigabitethernet 0/0 This can be shortened to 'g0/0' like they are listed in physical network maps. // This sets the IP ADDRESS and SUBNET MASK of device R1(config-if) #ip address 10.255.255.254 255.0.0.0 // This enables the device R1(config-if) #no shutdown Two messages should appear showing the state has changed to 'up' (Status). Second message should show line protocol is now 'up' (Protocol). // 'do' allows you to run a Privileged EXEC command from outside the mode. R1(config-if) #do show ip interface brief Good to confirm that the device/interface you have configured is up and running. More 'show' CLI Commands 'show interfaces ' • Shows Layer 1 and Layer 2 information about the interface and some Layer 3. • Shows MAC Address (or BIA address) • IP Address • ... and so much more 'show interfaces description' • show description for interface. Example: // Configure mode for interface Gigabyte Interface 0/0 R1(config) #int g0/0 R1(config) #description ## to SW1 ## This sets the 'Description' column to display: Interface Description Gi0/0 ## to SW1 ##