Networking | Routing And Switching | Tutorial 4 | 2018
Welcome to my 4th new tutorial of the series of networking. In this blog you'll the content about network switches. You'll learn about how to make a communication successful and secure in the same network (LAN) by using STP. As Spanning tree protocol (STP) we used in multi-switched networks. Why we use this protocol in multi-switched network etc.
What is Switch?
A switch is an intelligent device used to connect multiple devices within the same network. The intelligence of is that it requires Media Access Control (MAC) address for communication and doesn't allow broadcast. Let's understand the whole thing by a little example, consider there is a network having 3 end devices name Device-A, Device-B,Device-C connected with each other respectively with the help of switch. When a Device-A sends data to Device-C so that data will only forwarded by switch to Device-C not to Device-B.What is Media Access Control (MAC) address?
A Media Access Control (MAC) address is 48-bit unique physical address given to network interface controller (NIC) or network adapter, for communication within the same network which is given by its manufacturer. It is made up of hexadecimal numbers like a1:b1:cc:ac:2e:f1.What is STP?
STP stands for Spanning tree protocol which is basically used in bridge and switches to prevent loops when you have a redundant links in the Ethernet networks. If the loop is present in the Ethernet network so the whole network will suffer because there will MAC instability in the MAC table, duplicate frames generation and so on. Let's move to the video for further detail.
More information
Reversing Some C++ Io Operations
In general decompilers are not friendly with c++ let's analyse a simple program to get familiar with it.
Let's implement a simple code that loads a file into a vector and then save the vector with following functions:
Lets identify the typical way in C++ to print to stdout with the operator "<<"
The basic_ostream is initialized writing the word "error" to the cout, and then the operator<< again to add the endl.
The Main function simply calls "vec = load(filename)" but the compiler modified it and passed the vector pointer as a parámeter. Then it bulds and prints "loaded " << size << " users".
And finally saves the vector to /tmp/pwd and print "saved".
Most of the mess is basically the operator "<<" to concat and print values.
Also note that the vectors and strings are automatically deallocated when exit the function.
And here is the code:
Let's take a look to the load function, which iterates the ifs.getline() and push to the vector.
First of all there is a mess on the function definition, __return_storage_ptr is the vector.
the ifstream object ifs is initialized as a basic_ifstream and then operator! checks if it wasn't possible to open the file and in that case calls err()
We see the memset and a loop, getline read a cstr like line from the file, and then is converted to a string before pushing it to the vector. lVar1 is the stack canary value.
In this situations dont obfuscate with the vector pointer vec initialization at the begining, in this case the logic is quite clear.
The function save is a bit more tricky, but it's no more than a vector iteration and ofs writing.
Looping a simple "for (auto s : *vec)" in the decompiler is quite dense, but we can see clearly two write, the second write DAT_0010400b is a "\n"
As we see, save implememtation is quite straightforward.
Related posts
Let's implement a simple code that loads a file into a vector and then save the vector with following functions:
- err
- load
- save
- main
Lets identify the typical way in C++ to print to stdout with the operator "<<"
The basic_ostream is initialized writing the word "error" to the cout, and then the operator<< again to add the endl.
The Main function simply calls "vec = load(filename)" but the compiler modified it and passed the vector pointer as a parámeter. Then it bulds and prints "loaded " << size << " users".
And finally saves the vector to /tmp/pwd and print "saved".
Most of the mess is basically the operator "<<" to concat and print values.
Also note that the vectors and strings are automatically deallocated when exit the function.
And here is the code:
Let's take a look to the load function, which iterates the ifs.getline() and push to the vector.
First of all there is a mess on the function definition, __return_storage_ptr is the vector.
the ifstream object ifs is initialized as a basic_ifstream and then operator! checks if it wasn't possible to open the file and in that case calls err()
We see the memset and a loop, getline read a cstr like line from the file, and then is converted to a string before pushing it to the vector. lVar1 is the stack canary value.
In this situations dont obfuscate with the vector pointer vec initialization at the begining, in this case the logic is quite clear.
The function save is a bit more tricky, but it's no more than a vector iteration and ofs writing.
Looping a simple "for (auto s : *vec)" in the decompiler is quite dense, but we can see clearly two write, the second write DAT_0010400b is a "\n"
As we see, save implememtation is quite straightforward.
Related posts
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