The Ethernet header contains the physical address of the source and destination, or the MAC address and protocol of the receiving packet. Later, we will consider the next header as the IP header. Note 2: We can also direct the output to a file for better understanding. The IP layer gives various pieces of information like the source and destination IP address, the transport layer protocol, etc. The structure of the IP header is defined in the ip.
Now, to get this information, you need to increment your buffer pointer by the size of the Ethernet header because the IP header comes after the Ethernet header:. There are various transport layer protocols. These structures provide the port number of the source and destination. With the help of the port number, the system gives data to a particular application see Figures 7 and 8. The size of the IP header varies from 20 bytes to 60 bytes. So we have to multiply the IHL by 4 to get the size of the header in bytes:.
Note: If your machine is little endian, you have to use ntohs because the network uses the big endian scheme. After the transport layer header, there is data payload remaining. For this, we will move the pointer to the data, and then print. To send a packet, we first have to know the source and destination IP addresses as well as the MAC address. The second way is more efficient and will make your program machine-independent, which means you should not enter ifconfig in each machine.
Linux supports some standard ioctls to configure network devices. They pass an ifreq structure, which means that if you want to know some information about the network, like the interface index or interface name, you can use ioctl and it will fill the value of the ifreq structure passed as a third argument. In short, the ifreq structure is a way to get and set the network configuration.
It is defined in the if. There may be various interfaces in your machine like loopback, wired interface and wireless interface. So you have to decide the interface through which we can send our packet. After deciding on the interface, you have to get the index of that interface. First, take a buffer in which you will place all information like the Ethernet header, IP header, UDP header and data.
Because I use the above technique with good success. Good luck. No they have different subnets — Jul3k. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. Podcast Helping communities build their own LTE networks. Podcast Making Agile work for data science. Featured on Meta. New post summary designs on greatest hits now, everywhere else eventually.
Visit chat. Linked 1. The IP source address for any outgoing UDP datagram must exist on a network interface or the datagram is dropped. Other Winsock providers may not support the use of raw sockets. For example, all applications listening for a specific protocol will receive all packets received for this protocol.
This may not be what is desired for multiple applications using a protocol. This is also not suitable for high-performance applications. To get around these issues, it may be required to write a Windows network protocol driver device driver for the specific network protocol.
The network protocol would then be added to the Winsock catalog as a supported protocol. This allows multiple applications to open sockets for this specific protocol and the device driver can keep track of which socket receives specific packets and errors. Applications also need to be aware of the impact that firewall settings may have on sending and receiving packets using raw sockets.
Skip to main content. Sockets are automatically closed when they are garbage-collected, but it is recommended to close them explicitly, or to use a with statement around them. If you want to close the connection in a timely fashion, call shutdown before close. Connect to a remote socket at address. For non-blocking sockets, the method raises an InterruptedError exception if the connection is interrupted by a signal or the exception raised by the signal handler.
The error indicator is 0 if the operation succeeded, otherwise the value of the errno variable. This is useful to support, for example, asynchronous connects. Put the socket object into closed state without actually closing the underlying file descriptor. The file descriptor is returned, and can be reused for other purposes. This is useful with select. Under Windows the small integer returned by this method cannot be used where a file descriptor can be used such as os.
Unix does not have this limitation. Return the remote address to which the socket is connected. The format of the address returned depends on the address family — see above. On some systems this function is not supported. Return the value of the given socket option see the Unix man page getsockopt 2.
If buflen is absent, an integer option is assumed and its integer value is returned by the function. If buflen is present, it specifies the maximum length of the buffer used to receive the option in, and this buffer is returned as a bytes object. It is up to the caller to decode the contents of the buffer see the optional built-in module struct for a way to decode C structures encoded as byte strings.
Return True if socket is in blocking mode, False if in non-blocking. This is equivalent to checking socket. Return the timeout in seconds float associated with socket operations, or None if no timeout is set. This reflects the last call to setblocking or settimeout. The ioctl method is a limited interface to the WSAIoctl system interface. Please refer to the Win32 documentation for more information.
On other platforms, the generic fcntl. Enable a server to accept connections. If backlog is specified, it must be at least 0 if it is lower, it is set to 0 ; it specifies the number of unaccepted connections that the system will allow before refusing new connections. If not specified, a default reasonable value is chosen.
Return a file object associated with the socket. The exact returned type depends on the arguments given to makefile. These arguments are interpreted the same way as by the built-in open function, except the only supported mode values are 'r' default , 'w' and 'b'. On Windows, the file-like object created by makefile cannot be used where a file object with a file descriptor is expected, such as the stream arguments of subprocess. Receive data from the socket.
The return value is a bytes object representing the data received. The maximum amount of data to be received at once is specified by bufsize. See the Unix manual page recv 2 for the meaning of the optional argument flags ; it defaults to zero. For best match with hardware and network realities, the value of bufsize should be a relatively small power of 2, for example, The return value is a pair bytes, address where bytes is a bytes object representing the data received and address is the address of the socket sending the data.
In order to get full IPv6 address use getnameinfo. Receive normal data up to bufsize bytes and ancillary data from the socket. The ancbufsize argument sets the size in bytes of the internal buffer used to receive the ancillary data; it defaults to 0, meaning that no ancillary data will be received.
The flags argument defaults to 0 and has the same meaning as for recv. The data item is a bytes object holding the non-ancillary data received. If the receiving socket is unconnected, address is the address of the sending socket, if available; otherwise, its value is unspecified.
If recvmsg raises an exception after the system call returns, it will first attempt to close any file descriptors received via this mechanism. Some systems do not indicate the truncated length of ancillary data items which have been only partially received. If an item appears to extend beyond the end of the buffer, recvmsg will issue a RuntimeWarning , and will return the part of it which is inside the buffer provided it has not been truncated before the start of its associated data.
See also sendmsg. Receive normal data and ancillary data from the socket, behaving as recvmsg would, but scatter the non-ancillary data into a series of buffers instead of returning a new bytes object. The buffers argument must be an iterable of objects that export writable buffers e. The ancbufsize and flags arguments have the same meaning as for recvmsg. Receive data from the socket, writing it into buffer instead of creating a new bytestring.
The return value is a pair nbytes, address where nbytes is the number of bytes received and address is the address of the socket sending the data. Receive up to nbytes bytes from the socket, storing the data into a buffer rather than creating a new bytestring. If nbytes is not specified or 0 , receive up to the size available in the given buffer. Returns the number of bytes received. Send data to the socket. The socket must be connected to a remote socket. The optional flags argument has the same meaning as for recv above.
Returns the number of bytes sent. Applications are responsible for checking that all data has been sent; if only some of the data was transmitted, the application needs to attempt delivery of the remaining data. Unlike send , this method continues to send data from bytes until either all data has been sent or an error occurs. None is returned on success. On error, an exception is raised, and there is no way to determine how much data, if any, was successfully sent.
The socket timeout is now the maximum total duration to send all data. The socket should not be connected to a remote socket, since the destination socket is specified by address.
Return the number of bytes sent. Send normal and ancillary data to the socket, gathering the non-ancillary data from a series of buffers and concatenating it into a single message. The buffers argument specifies the non-ancillary data as an iterable of bytes-like objects e.
The flags argument defaults to 0 and has the same meaning as for send. If address is supplied and not None , it sets a destination address for the message.
The return value is the number of bytes of non-ancillary data sent.
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