Testing DNS
Rejoice. Google announces a public DNS offering that we can use for testing when deploying Internet connections, or troubleshooting proxy servers.
Greg-Ferros-MacBook-Pro:~ gregferro$ dig @8.8.8.8 etherealmind.com
; < <>> DiG 9.6.0-APPLE-P2 < <>> @8.8.8.8 etherealmind.com
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER< <- opcode: QUERY, status: NOERROR, id: 6418
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;etherealmind.com. IN A
;; ANSWER SECTION:
etherealmind.com. 300 IN A 70.32.114.237
;; Query time: 594 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Thu Dec 3 19:50:18 2009
;; MSG SIZE rcvd: 50
Greg-Ferros-MacBook-Pro:~ gregferro$
Testing your Internet connection using ICMP
Also, both of these IP addresses respond to ICMP so if you need to test your Internet connection you can easily remember to type
ping 8.8.8.8
The engineers have clearly chosen easy to remember IP addresses so that all Network Engineers can rejoice at this most useful, most ordinary of tools. It’s so simple, so elegant. An engineer must have thought of it.
SLA Monitors for Internet connectivity
Many people uses IOS SLA monitors to test for Internet connectivty. It’s always been difficult to know what to test that is reliable measure of application availability. The Google Public DNS is a good choice to poll when using these monitors.
What is Google Public DNS?
Google Public DNS is a free, global Domain Name System (DNS) resolution service, that you can use as an alternative to your current DNS provider.
To try it out:
* Configure your network settings to use the IP addresses 8.8.8.8 and 8.8.4.4 as your DNS servers
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About Greg Ferro
as far as i can see, the performance sucks, l3′s anycasted 4.2.2.2 are better for now
I’ve heard that L3 are moving away from a public DNS service. They forced a company I worked for to stop using it because of volume.
I always used DNS server like 4.2.2.1 and 4.2.2.3 for simple DNS queries and testing purposes. I guess I will add 8.8.8.8 to that list.
I cannot imagine a company running the Google DNS servers as their primary DNS forwarders. I am thinking about performance reasons and technical support, so I will just keep using the providers DNS servers and add Google DNS as third or fourth.
Why not ? Many companies use OpenDNS for the same reason. If you have a small to medium sized company, with two internet connections you need a DNS server that is independent of your ISP. Most ISPs block access to their DNS from outside their network.
In this case Google’s DNS is much better. It will not recursively look up domain names and present an advertising result which is much nicer.