Networking
DNS and DHCP
DORA, APIPA, ports, DNS records, forwarders, and failure symptoms.
DHCPOften missed
- Ports: UDP 67 (server) and UDP 68 (client).
- DORA: Discover, Offer, Request, Acknowledge.
- APIPA 169.254.x.x means DHCP failed. It is not a usable routed address.
- Leases expire; clients renew. Rogue DHCP is a security issue; DHCP snooping / authorized servers help.
- 3-2-1 backup is a backup rule, not a DHCP setting.
DNSOften missed
- DNS maps names to IPs.
- A = IPv4. AAAA = IPv6 (four As, larger address).
- CNAME = alias. MX = mail. PTR = reverse. TXT = text/SPF-style records.
- A forwarder sends unresolved queries to another DNS server.
- Name fails but IP works → DNS. Both fail → network path.