DNS

Local BIND9 Caching DNS Server

This tutorial will show you how to configure a caching BIND9 server on your local network, and configure an OpenWrt router to use it. This should result in slightly quicker DNS lookups, but to be honest, you may not notice a huge difference (my DNS lookups now take 30% less time, but I don't think this has made page loading noticeably faster). Here are a few situations where it could be particularly worthwhile:

  • You have a large LAN with lots of clients, and you want to take some load off your router
  • You are using something like modsecurity's real time RBL lookups and you want to reduce latency
  • Your ISP's nameservers are slow but you would still like to use them
  • You are a curious soul and you want to learn about DNS ;)

DNS Basics for Websites and Email Servers

DNS-signpost.jpg

This article aims to explain what various DNS records are and how to use them. It is aimed at people hosting websites and email servers on a home server such as a raspberry pi.

How DNS Works

DNS stands for Domain Name System. In a nutshell, it's the system that we use to translate human readable domain names (e.g. samhobbs.co.uk) into the Internet Protocol (IP) addresses for those services (e.g. 195.166.151.235).

The DNS system has a strict hierarchy, and lookups are performed recursively using a client/server model. This means that when your computer asks for the IP address for "subdomain.example.com", the DNS resolver you are using starts at the top and works backwards to find the address. The servers at the top of the pyramid (root name servers) direct clients to the name servers reponsibe for Top Level Domains (TLD, e.g. .com), and that server in turn is able to tell the client which name server is authoritative for the second level domain (e.g. example.com), and so on. Usually for small sites, the DNS records for your domain are managed by your Domain Name Registrar.

The DNS resolver doesn't have to perform all these lookups every time, because each record has a Time To Live (TTL) in seconds, which tells the client how long they can cache the information for until it should be refreshed. That's Time To Live (live free), not Live (live electrical circuit), which is how I first read it!

There are loads of different types of DNS record, so I've picked the most important ones you might need or want to use. These are:

  1. DNS A - used to map a host name to an IP address
  2. Mail Exchanger (MX) - used to tell clients which hostnames are used for email services
  3. Sender Policy Framework (SPF) - used to define which servers are allowed to send email from your domain name
  4. Pointer (PTR) - the opposite of DNS A, this record maps an IP address to the hostname

For a website, you only need a DNS A record. For an email server, you need at least a DNS A record and an MX record; PTR and SPF records will help you get your email through spam filters.

I'll be illustrating how to set up the different types of record using Namecheap, my Domain Name Registrar, as an example. If you haven't registered a domain name yet, I'd recommend Namecheap -avoid GoDaddy if you can, since they have some pretty horrible pricing practices and consistently back the wrong side when it comes to internet censorship acts like SOPA and PIPA.

Dynamic DNS with ddclient on Raspberry Pi and Ubuntu

This tutorial will show you how to configure ddclient on Raspbian and Ubuntu. Many tutorials don't explain what to do if your server is behind a router, but this one will.

I recently set up a backup server on an internet connection that has a dynamic IP address. So far, I've been spoiled at home because my ISP (PlusNet) makes switching to a static IP address easy and cheap, so obviously I did that. This time though, I didn't have that option, and I didn't want to configure a dynamic dns client on that router either, so I had to set it up on the server itself.

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