In this lecture, we are going to learn to write and apply the basic CAPTCHA filters.
CAPTCHA filters are different from display filters in terms of syntax.
A few filters are same for both display and CAPTCHA filters, but most of the CAPTCHA filters are completely
different from display filters.
So let's get started.
Now, there are two places where you can write your CAPTCHA filters.
One is the welcome window here.
As you can see, we have the CAPTCHA filter box, which is saying enter a gap filter.
Here, you can write your CAPTCHA filters and other is the CAPTCHA options a window.
We will get back to capture options later in the video.
Now, before writing the CAPTCHA filter, we have to select a network interface where you want to capture
the packets from.
Then the filter gets applied to the selected interface.
So let me select, let's say wi fi now or type a capture filter.
Now this filter will be applied to the selected interface wi fi or wireless card.
Now let me select Ethernet.
And now as you can see, filter has disappeared.
So guys, you have to write separate filters for each interface.
So back to the wi fi.
Now, just like the display filter bar, the background color of capture filter bar also turns green
when you type a valid filter.
Right now, this filter is only going to capture or save the TCP traffic.
It will not capture any other traffic.
It will only capture the TCP traffic.
So double click on wi fi.
And under the protocol column, as you can see, we only have the TCP traffic.
Now, let me stop the session.
Like I mentioned earlier, another place to write the capture filters is the caption options windows.
So go to the CAPTCHA options.
And down here we have the box for writing CAPTCHA filters as you can see.
And this is the last gap filter that I used or applied, and this is a better and recommended place
to write the CAPTCHA filters because it offers you some additional features.
Now click on the button, which is at the beginning of a CAPTCHA filter box, manage saved bookmark.
These are some in-built CAPTCHA filters that you can use, right?
These are most commonly used CAPTCHA filters from this list.
You can select the filter that you want to use.
Now let me select, let's say UDP.
Now this filter is going to capture only the UDP traffic to start capturing packets from CAPTCHA options
window here.
Also, you have to select the network interface first, then type your filter, then click on start
continue without saving.
As you can see under the protocol column, it is only capturing the UDP traffic or protocols that use
UDP for delivering packets.
Now back to the CAPTCHA options.
Now I want to capture both UDP and TCP traffic.
So to combine multiple filters, we have to use our operator logical operators and or not, they are
same for both display and capture filters.
So UDP or TCP, this filter is going to capture both UDP and TCP packets right here.
As you can see, we have both UDP and TCP traffic.
In the same way, guys, you can combine as many filters as you like with or operator like let's say
ah, or ICMP.
LTC And let's use a note.
Operator if I type not UDP and this filter will not capture the UDP traffic.