November 23, at 1:
Data Link layer Physical layer A packet that is sent by us, goes from the top and to the bottom of this list, each layer adding its own set of headers to the packet in what we call the encapsulation phase.
When the packet finally reaches it's destination the packet goes backwards through the list and the headers are stripped out of the packet, one by one, each header giving the destination host all of the needed information for the packet data to finally reach the application or program that it was destined for.
However, it is generally considered that there are 3 through 5 layers available, and in most pictures and explanations, there will be 4 layers discussed. We will, for simplicities sake, only consider those four layers that are generally discussed. Just the same as with the OSI Reference Model, we add and subtract headers for each layer that we enter or leave.
For example, lets use one of the most common analogies to modern computer networking, the snail-mail letter. You want to send a letter to someone asking how they are, and what they are doing. To do this, you must first create the data, or questions. The actual data would be located inside the Application layer.
After this we would put the data written on a sheet of paper inside an envelope and write on it to whom the letter is destined for within a specific company or household. Perhaps something like the example below: In the Transport layer, if we were dealing with TCP, this would have been equivalent to some port e.
At this point we write the address on the envelope of the recipient, such as this: Andersgardsgatan 2 Gothenburg This would in the analogy be the same as the Internet layer.
Just the same way as the recipient on an envelope. This would be the equivalent of the IP address in other words e.
The final step is to put the whole letter in a postbox. Doing this would approximately equal to putting a packet into the Network Access Layer.
The network access layer contains the functions and routines for accessing the actual physical network that the packet should be transported over.
When the receiver finally receives the letter, he will open the whole letter from the envelope and address etc decapsulate it. The letter he receives may either require a reply or not. In either case, the letter may be replied upon by the receiver, by reversing the receiver and transmitter addresses on the original letter he received, so that receiver becomes transmitter, and transmitter becomes receiver.
It is very important to understand that iptables was and is specifically built to work on the headers of the Internet and the Transport layers. It is possible to do some very basic filtering with iptables in the Application and Network access layers as well, but it was not designed for this, nor is it very suitable for those purposes.
However, if the packet size is very small, it will not. The reason is that iptables is built to work on a per packet basis, which means that if the string is split into several separate packets, iptables will not see that whole string.
For this reason, you are much, much better off using a proxy of some sort for filtering in the application layer.Apache's rewrite engine is very powerful and often misunderstood. It can be fairly cryptic to work with and given that a mistake can take down your site it can be costly to debug.
While I've tested the following rules thoroughly I'd recommend testing them yourself on a non-live site prior to putting into production.
Join GitHub today. GitHub is home to over 28 million developers working together to host and review code, manage projects, and build software together. Laura P May 29, at am. I’m 41; my mum hasn’t worked FT since and worked briefly as a secretary in a recruitment office in the early 70s.
I’m a software engineer, a job that barely existed last time my mum worked. Google classes many types of pages as doorway pages. Doorway pages can be thought of as lots of pages on a website designed to rank for very specific keywords using minimal original text content e.g.
location pages often end up looking like doorway pages. At the risk of sounding like Captain Obvious here, I just feel like I need to state I am absolutely aghast (which is a word I have never used in a sentence before now) at what the death toll is shaping up to be from the Camp Fire.
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