33dots

Modern webpages reference resources from many domains. So time for DNS lookups can cause significant delay in browsing.

These days i was having slow internet speeds, and i suspect its due to bad performance by my ISP’s DNS server.

The speed of DNS lookup can be determined by the dig command combined with a time command,

[root@localhost ~]# time dig @10.0.0.1 www.yahoo.co.in
......
rc.a07.yahoodns.net.    148     IN      A       87.248.120.14
.....
real    0m0.607s
.....

replace 10.0.0.1 with your DNS server’s IP address.

you could also use nslookup instead of dig

[root@localhost ~]# time nslookup www.yahoo.co.in 8.8.8.8
.....
Address: 87.248.120.148
.....
real    0m0.366s
.....

Here i am checking the resolution time taken from GoogleDNS

You could compare the performance of your DNS server with some of the free open DNS servers like, GoogleDNS(8.8.8.8), OpenDNS(208.67.222.222)

Make sure you test with less commonly used domains as the common ones will be already cached in the DNS server’s cache.

I just wanted to extract the USB boot image from the .iso of the CentOS DVD image that i downloaded.

Now i mounted it by

[root@localhost ~]# mkdir /mnt/iso
[root@localhost ~]# mount /home/dloads/CentOS-5.2-i386-bin-DVD.iso /mnt/iso/ -t iso9660 -o loop,ro

ro mounts it read only so that we dont accidentally make no changes.
loop is required to mount it as a loop device (so as to access the file as a block device).