Falsehoods Programmers Believe About LANs

Each introduction is phrased arsenic the falsehood. Some of these whitethorn sometimes beryllium existent and sometimes beryllium false.

NAT

• My LAN is down a NAT.
• I’m only down 1 NAT.
• My LAN isn’t down a NAT.
• My IPv6 hosts aren’t down a NAT.
• If I person a RFC 1918 address, I’m down a NAT.
• If I don’t person a RFC 1918 address, I’m not down a NAT.
• NAT only translates addresses.
• NAT only translates addresses and ports.
• NAT changes thing extracurricular of the header.
• NAT is only recovered connected LANs.

Protocols

• Only IPv4 is moving connected my LAN.
• Only IP is moving connected my LAN.
• Okay, only IP, IPX/SPX, Phase IV, AppleTalk, VINES, NetBEUI, aliases SNA are moving connected my LAN.
• Seriously?
• I tin extremity definite types of postulation from utilizing my LAN.
• I cognize what’s moving connected my LAN.

MAC addresses

• MAC addresses are globally unique. (They’re supposed to be, but they aren’t.)
• MAC addresses are locally unique.
• Different MACs are different devices.
• Okay, different MACs are different web interfaces.
• MAC addresses can’t beryllium changed.
• MAC addresses tin beryllium changed.
• MAC addresses are 48 bits.
• The first 3 bytes are vendor‐unique.
• The first 3 bytes are vendor‐unique if it’s a MA-L block.
• MAC addresses are unicast.
• Only 1 big answers an ARP petition for a fixed IP.
• ARP entries are accurate.

Reachability and performance

• The LAN is fast.
• The LAN is faster than the Internet.
• Two hosts connected the aforesaid subnet tin scope each different without leaving the LAN.
• Same subnet intends 2 hosts tin talk.
• Wi-Fi and Ethernet clients are balanced peers connected the LAN.
• Wi-Fi and Ethernet clients aren’t balanced peers connected the LAN.
• Every instrumentality connected my LAN has the aforesaid MTU.
• Hostnames are locally unique.
• mDNS works.

DHCP

• There is simply a DHCP server.
• There is 1 DHCP server.
• My reside won’t alteration while I’m utilizing it.
• The DHCP server and the gateway are the aforesaid device.
• DHCP will springiness maine a gateway.
• DHCP will springiness maine a DNS server.
• 169.254.0.0/16 intends DHCP failed.

IP addresses

• Every big has 1 IP address.
• My LAN uses RFC 1918 IP addresses.
• My LAN uses backstage IP addresses.
• My LAN uses IP addresses.