Category Archives: General

“Ping Hostname” Returning an IPv6 Address Instead of IPv4? (Windows)

On Windows based PCs and Servers, and where IPv6 is enabled on one of the network adapters, you may find that when you do a:

ping name-of-host

… you get an IPv6 address returned in the results.  But what if you want to test IPv4 connectivity?  You can add a -4 switch to the ping command to force it to use IPv4 as follows:

ping -4 name-of-host

Ping will now ping the IPv4 address as opposed to the IPv6.

It’s worth noting, that if you do want to test for IPv6 connectivity, you can add a -6 switch to force that:

ping -6 name-of-host

Using grep and Ignoring Case (Case Insensitive grep)

grep is a great way to find phrases, words, and characters in text.  One of the biggest stumbling blocks is case – is the word “Hello”, “hello”, “HELLO”, or even “HeLLo”?  All of these are different, and a “grep “Hello”” would only find lines containing the first “Hello” example.

You can, however, exclude case from a grep to make it not case sensitive – simply add -i:

grep -i “Hello” textfile.txt

Alternatively, you could use it in conjunction with cat and tac (Reverse Cat)

cat textfile.txt | grep -i “Hello”

The above will find all lines containing “Hello” in textfile.txt, whether it’s “Hello”, “HELLO”, HElLO”, etc, making it much easier to find instances of “Hello” if you don’t really need to care about case.

 

(Read the article on Wikipedia about Case Sensitivity..)

CIDR, Subnet Masks, and Usable IP Addresses Quick Reference Guide (Cheat Sheet)

A quick reference Subnet and CIDR guide.

What’s a /28?  How many IPs do I get to use with a /26?  Well, see the table below!
Usable IPs is the Total IPs minus the Network and Broadcast IPs.

 

CIDR

Subnet Mask

Total IPs

Usable IPs

/32 255.255.255.255 1 1
/31 255.255.255.254 2 0
/30 255.255.255.252 4 2
/29 255.255.255.248 8 6
/28 255.255.255.240 16 14
/27 255.255.255.224 32 30
/26 255.255.255.192 64 62
/25 255.255.255.128 128 126
/24 255.255.255.0 256 254
/23 255.255.254.0 512 510
/22 255.255.252.0 1024 1022
/21 255.255.248.0 2048 2046
/20 255.255.240.0 4096 4094
/19 255.255.224.0 8192 8190
/18 255.255.192.0 16,384 16,382
/17 255.255.128.0 32,768 32,766
/16 255.255.0.0 65,536 65,534
/15 255.254.0.0 131,072 131,070
/14 255.252.0.0 262,144 262,142
/13 255.248.0.0 524,288 524,286
/12 255.240.0.0 1,048,576 1,048,574
/11 255.224.0.0 2,097,152 2,097,150
/10 255.192.0.0 4,194,304 4,194,302
/9 255.128.0.0 8,388,608 8,388,606
/8 255.0.0.0 16,777,216 16,777,214
/7 254.0.0.0 33,554,432 33,554,430
/6 252.0.0.0 67,108,864 67,108,862
/5 248.0.0.0 134,217,728 134,217,726
/4 240.0.0.0 268,435,456 268,435,454
/3 224.0.0.0 536,870,912 536,870,910
/2 192.0.0.0 1,073,741,824 1,073,741,822
/1 128.0.0.0 2,147,483,648 2,147,483,646
/0 0.0.0.0 4,294,967,296 4,294,967,294