How can I check my DNS server perfomance on my network?

Products

• ProxySG Software - SGOS

Issue/Introduction

Here are some useful DNS testing commands. Execute these commands from the client PC running Windows.

Firstly run the command nslookup domainname on the command prompt. Next run command ping -a hostname.

Example of slow DNS response:

C:\>nslookup bluecoat.com
Server:  cookie.bluecoat.com
Address:  10.2.2.100 <- Internal DNS server being used possible reason for slow response

Non-authoritative answer:
Name:    bluecoat.com
Address:  199.91.133.25

C:\>ping -a bluecoat.com

Pinging bluecoat.com [199.91.133.25] with 32 bytes of data:

Reply from 199.91.133.25: bytes=32 time=149ms TTL=57
Reply from 199.91.133.25: bytes=32 time=149ms TTL=57
Reply from 199.91.133.25: bytes=32 time=150ms TTL=57
Reply from 199.91.133.25: bytes=32 time=154ms TTL=57

Ping statistics for 199.91.133.25:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 149ms, Maximum = 154ms, Average = 150ms <- Slow DNS response

As can be seen the round trip time is quite long. In this scenario further investigation is required using resources available at the bottom of this document.

 

Example of fast DNS response:

 C:\>nslookup bbc.co.uk
Server:  resolver2.opendns.com
Address:  208.67.220.220 <- external DNS server being used possible reason for fast response

Non-authoritative answer:
Name:    bbc.co.uk.internal.cacheflow.com
Address:  67.215.77.132

C:\>ping -a bbc.co.uk

Pinging bbc.co.uk [212.58.241.131] with 32 bytes of data:

Reply from 212.58.241.131: bytes=32 time=18ms TTL=246
Reply from 212.58.241.131: bytes=32 time=18ms TTL=246
Reply from 212.58.241.131: bytes=32 time=18ms TTL=246
Reply from 212.58.241.131: bytes=32 time=18ms TTL=246

Ping statistics for 212.58.241.131:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 18ms, Maximum = 18ms, Average = 18ms <- Fast DNS response

C:\>

Resources that can used to further investigate DNS issues:-

Wireshark - perform unfilitered PCAP on both client PC and proxy. Analyse the results checking especially for DNS response times

Other free resources on the web {Remember use these resources at your own discretion}

 http://www.dnsstuff.com/

http://www.dnsqueries.com/en/domain_check.php

https://www.grc.com/dns/benchmark.htm

http://dnscheck.pingdom.com/

Resolution

Here are some useful DNS testing commands. Execute these commands from the client PC running Windows.