DNS
DNS uses TCP and UDP.
UDP is usually tried first.
TC — TrunCation
- Message was truncated due to length greater than permitted
RFC 2181 says “try again with TCP”
DNS resource records
| RR | Description |
|---|---|
| A | v4 IP Address |
| AAAA | v6 IP Address |
| CNAME | Alias or nickname. Secondary Name |
| MX | Email server |
| NS | DNS Server |
| PTR | Reverse Mapping of an IP. Used to find the host that “owns” the IP |
| SOA | Start of Authority. Which DNS server is authoritative for the zone. |
DHCP & DNS placement
Always in groups of at least two, this is a HA service.
Each module should have its own set of DHCP and DNS nodes.
| Location | DHCP | DNS |
|---|---|---|
| Enterprise / Campus / DC | Yes | Internal DNS |
| Enterprise / Remote / Branch | Yes | Internal DNS |
| Enterprise / Remote / DC | — | Internal and External DNS |
| Enterprise / Edge / DMZ | — | External DNS |
| Enterprise / Edge / WAN | — | — |
| Enterprise / Edge / VPN | — | — |
| SP / Edge | — | External DNS |
References
DNS and UDP truncation | APNIC Blog
RFC 1035: STD 13: Domain names - implementation and specification
RFC 2181: Clarifications to the DNS Specification | RFC Editor