samoshkin / dns-server-examples

Show common setups of various DNS servers

DNS servers configuration examples

This is a demo project to show most common configurations of various DNS server implementations.

NOTE: This is WIP and unstable project.

Overview

DNS servers implementations:

• BIND9
• dnsmasq
• unbound (TBD)
• NSD (TBD)

Server configurations/roles:

• caching and resolving server
• forwarding server
• authoritative only server (master or slave), no caching and forwarding
• master and slave for a given zone
• delegate a subdomain (like gTLD servers do)
• both authoritative and forwarding server on private LAN
• stealth server, two servers: internal behind firewall and external server for public and private queries
• split horizon, different zone files used to serve single zone depending on client address/location (geographical)
• single name server, which uses BIND "views" feature to serves both internal/private and external/public queries/clients

Combinations of different roles within single name server deployment are also shown.

Various tricks and features covered:

• DNS load balancing (several A records for single name)
• disable caching (server would always go thru query resolve process)
• single name server, which acts as master for zone A and as slave for zone B
• wildcard records
• "glue" A record for delegated subdomain NS record
• virtual subdomains (subdomains declared within single zone, without delegation to another name server)
• reverse lookup zone files
• using BIND "rndc" to manage name server remotely (clear cache, reload zone files, trigger zone transfer)
• using ~/.digrc to make dig output prettier
• using BIND named-checkconf and named-checkzone to validate conf and zone file before starting server

Install and run

Every name server deployment runs inside unique Docker container. For BIND9 server, I'm using resystit/bind9 base Docker image, which runs BIND9 server on top of Linux Alpine.

Use Docker Compose to start all available name servers. Dedicated user-defined network is created: subnet: 172.20.0.0/16. Each name server runs inside individual container, joined to that network.

git clone <url> <path>
cd <path>
docker-compose up --build

There is a dedicated client container, which includes BIND server (rndc), bind-tools (dig) and nano. Use it to test various name server configurations:

docker-compose run client
/ # dig sun.galaxy @master
/ # dig asia.earth.sun.galaxy @delegated_subzone
/ # dig -x 172.20.0.22 @slave

Once you're done, just clean up everything (containers/networks/images):

docker-compose down --rmi all -v

Domain name hierarchy

I use somewhat fictitious domain name from a space realm: sun.galaxy. It's good to reason about hierarhy. For example, 3-level domains: earth.sun.galaxy, moon.sun.galaxy, mars.sun.galaxy. 4-level subdomains can be created easy as well: europe.earth.sun.galaxy, even 5-level domains possible: ua.europe.earth.sun.galaxy.