Week 6 - Subnetting and VLSM

Subnet basics

• most networks fall between Class C (/24) and /30
• the host ID can't be all 0s - that's the network address itself
• the host ID can't be all 1s - that's the broadcast address

usable hosts 2^(hosts bits) - 2 (subtracting network and broadcast addresses)

Patterns for finding network addresses

• /23 - 3rd octet is always even (increments of 2)
• /22 - 3rd octet increments of 4
• /21 - 3rd octet increments of 8

Week 6 - IPav4 Exhaustion, Private IPs, and NAT

IPv4 exhaustion

• all IPv4 addresses have been assigned
• organizations get a limited number of public IPs
• private IP ranges are used for internal/private LANs - they are not routable on the Internet

Private Ranges

• 10.0.0.0 - 10.255.255.255 (10.0.0.0/8)
• 172.16.0.0 - 172.31.255.255 (172.16.0.0/12)
• 192.168.0.0 - 192.168.255.255 (192.168.0.0/26)

Example: Champlain

• Champlain's public block: 216.93.144.0/20
• used on some subnets, the labs use private ranges

NAT (Network Address Translation)

• maps private IPs to public IPs so a limited set of public addresses can be shared efficiently