Difference between revisions of "DNS"

Revision as of 08:30, 26 August 2015

What is DNS?

Overview

DNS (Domain Name System) is a protocol which handles how computers exchange data on the Internet. Simply put, it translates a recognizable name like xmission.com into an IP address like 198.60.22.4. In the background your computer connects to a DNS Server (i.e., Name Server) which manages a database that maps domain names to IP addresses.

When you connect your computer to the Internet, it automatically assigns an IP address that comes from a DHCP (Dynamic Host Configuration Protocol) server on your network. The job of this DHCP server is to make sure your computer has a IP address and other network configurations it needs to give you access online. Under normal circumstances, XMission connectivity customers will use XMission's DNS. This is handled automatically when you connect. You can refer to this as your Primary DNS.

If you run a business we know that having a reliable connection to the internet is essential since downtime can cause a loss of sales and unhappy customers. In a perfect world we would never have an outage; however outages can and do occur. Therefore, configuring your network for redundancy can be important to mitigate the risk of an outage. DNS resilience is determined by the steps you take to ensure your business, or home network is available to the Internet should your primary DNS service with XMission experience any interruption. Setting up both primary and secondary DNS servers can help keep you online.

Many alternative DNS providers, like OpenDNS and Google's Public DNS, allow you to use their free service as a primary or secondary DNS. Setting them up will take a little configuration on your side but help mitigate issues during an outage: if your primary DNS is unavailable then your secondary name service can be available for redundancy.

XMission DNS

Overview

XMission provides basic and advanced name service options, depending on customer needs.

Basic DNS Setup

XMissions DNS: 198.60.22.2, 198.60.22.22.

All XMission connectivity customers should automatically obtain these two IP addresses when connecting to the Internet. If you need assistance adding these to your connection, feel free to contact support.

Advanced DNS Configuration Options

While XMission's name service is very reliable we encourage businesses and individuals who prioritize always being online to consider some advanced configuration options including DNS caching and configuring additional offsite service like OpenDNS and Googles Public DNS for redundancy.

What is XMission's Primary DNS Server? XMissions Primary DNS server is 198.60.22.2. This server is responsible for any new entries and updates from DNS zones. It holds the "Master Copy" of all DNS records and is XMission's authoritative name server.

What is XMission's Secondary DNS Server? XMissions Secondary DNS server is 198.60.22.22. This server is mainly for redundancy. It will simulate what is on the Primary DNS server and relatively act the same as our Primary DNS server.

What are tertiary, quaternary, quinary, etc. DNS Servers? Additional name servers are for pure redundancy. You can have many other DNS servers for your connections. Often these servers are located offsite, whereas primary DNS servers are onsite. If both of XMission's Primary and Secondary DNS servers go down, additional DNS servers can help mitigate some aspects of an outage (i.e., ns2.xmission.com and ns3.xmission.com are located on the East and West coasts of the US for this purpose).

DNS Caching

Overview

A DNS cache is a local database copy of all domain names translated to IP addresses which runs on server software at your office, for instance. As such, it can temporarily mitigate most issues related to a DNS outage. Note that DNS caching software requires some expertise and maintenance. Popular open source software BIND is often used for DNS caching. An on site caching server can also speed up DNS queries for other software like mail servers.

Occasionally, there may be issues with a DNS server caching information that is no longer valid. A DNS flush on your server software will update the information to be valid.

Sometimes, the DNS cache on your computer might also need to be flushed.

DNS Flushing Your Computer

Windows DNS FLush

Windows Vista/7

Click the start button on the bottom left of your screen and navigate to the command prompt (Start > All Programs > Accessories > Command Prompt)

Make sure that you right click on the command prompt application and choose "Run as Administrator"

Type in the command ipconfig /flushdns

Windows 8/8.1

Ensure that you're on the Windows 8 Start Screen.

Simply type cmd and the Windows search bar will appear on the right hand side with search results.

Right click on Command Prompt and click Run as administrator.

Type in the command ipconfig /flushdns

Windows 10

Click the start buttom on the bottom left of your screen, and type in "cmd".

Right click on the command prompt application and choose "Run as Administrator"

type in the command ipconfig /flushdns

Mac OSX DNS Flush

Yosemite

Mac OS X 10.10, you need to do the following:

Open up the command terminal.

Run the command sudo discoveryutil udnsflushcaches

Lion, Mountain Lion, Mavericks

Mac OS X 10.7, 10.8 or 10.9, you need to do the following:

Open up the command terminal.

Run the command sudo killall -HUP mDNSResponder

Snow Leopard

Mac OS X 10.6, you need to do the following:

Open up a command terminal.

Run the command sudo dscacheutil -flushcache

Leopard and below

Mac OS X 10.5.1 or below, you need to do the following:

Open a command terminal.

Run the command sudo lookupd -flushcache

Linux DNS Flush

Open up a command terminal

Run the command sudo /etc/init.d/nscd restart

Third Party DNS Options

Overview

Relying on a third party for redundant name service is by far the simplest option to add redundancy and hence resiliency for your office and any hosting services your business relies upon (PBX, Colocation, etc). The instructions below can be used to add one or more of these alternative name servers to the configuration for your server, network router, or workstation.

Note that XMission recommends you continue to use at least our primary name server but then augment that with one or more off site options for redundancy.

OpenDNS

Probably the oldest public DNS service still around. They offer a variety of free and paid services. Their IP address are 208.67.222.222 and 208.67.220.220

OpenDNS configuration guide

Google Public DNS

You may have see these number or heard of them and didn't know what they were. Well now you know Google Public DNS IP address are 8.8.8.8 and 8.8.4.4

Google Public DNS configuration guide