Difference Between SO_REUSEADDR and SO_REUSEPORT

Processes use sockets as endpoints of a two-way channel to transfer data. The socket options SO_REUSEADDR and SO_REUSEPORT have different man pages and programmer documentation for various operating systems, which can be very confusing. The option SO_REUSEPORT is not even available on some operating systems. To perform socket operations, such as connecting to a socket address or listening for a new connection, processes use a variety of socket-layer functions.

Understanding Socket Implementation

Pipes and sockets are comparable. To the programs that use them, both appear to be filed. Both aid in the communication between processes. Sockets interact with a remote program; pipes interact with a local program. As you mentioned, sockets also provide bidirectional communication (much like a pair of properly connected pipes could). The values of a socket are the protocol, source IP address, source port, destination IP address, and port. A socket is a five-tuple. In order to maintain a connection between the two endpoints, no two sockets can have the same five values. A call to the socket() function is used to initially create a socket. A socket’s unique identifier, or socket descriptor, is what this function returns. We can give the socket a source IP address and a source port with the bind() function. The connect() function sets the destination IP address and destination port. At last, it is normal for programs on a solitary machine to convey utilizing standard organization conventions, like TCP; it would be inefficient to go the whole way to the organization equipment (if any!) and compute checksums. 

The protocol, source IP address, source port, destination IP address, and port are the values of a socket, which is a five-tuple. In order to maintain a connection between the two endpoints, no two sockets can have the same five values. Connecting to www.geeksforgeeks.org in our web browser will allow us to verify this.

nslookup www.geeksforgeeks.org 

A collection of IPV4 and IPV6 addresses are retrieved. Then, when we use the ss command, we’ll search for any of these IP addresses. This command aids in our ongoing investigation of the socket:

ss- t

Output

We can see that the socket we have has a working connection. The source IP address in this instance is 180.149.59.201, and the source port is 52984. Additionally, the destination IP address (180.149.59.203) and port (192 for HTTPS) are both those of the youtube server.

What Are Socket Options?

A network socket’s identifier is a socket file descriptor. It is essential to keep in mind that while all file descriptors are sockets, not all sockets are file descriptors. This is due to the fact that file descriptors can serve as identifiers for pipes, sockets, and files. The option name, such as SO_BROADCAST, indicates that the property is set. There are various options for various protocol levels. The protocol level is a necessary parameter because of this. When examining the socket level, the protocol level to use is SOL SOCKET. By looking at the option name’s prefix, we can tell the options for a level apart. For example, we can perceive that SO_DEBUG is on the attachment level just from the initial two letters of the chchosenoice name. IP_DONTFRAG operates at the IP protocol level, whereas TCP_NODELAY operates at the TCP protocol level. Socket management must be possible for processes. For instance, a process might need to enable the recording of debugging information or broadcast messages. The values of SO BROADCAST and SO DEBUG would change in this situation. This is accomplished by a process using the setsockopt() function. The setsockopt function needs the following five inputs: Name of the socket, file descriptor, Protocol level, value, and length.

What Is SO_REUSEADDR?

Local addresses and ports can be reused with the SO_REUSEADDR socket option. Your server can bind to an address that is in the TIME-WAIT state using SO REUSEADDR. It prevents multiple servers from binding to the same address. The fact that another server can bind to the same port by binding to a specific address rather than INADDR_ANY poses a security risk when this flag is used. Starting with the Linux kernel version 2.4 and later, SO REUSEADDR is used. Different operating systems have different ways of implementing this socket option.

The same address/port combination will be used every time the process stops and starts over. We would need to explicitly request this behavior by activating the SO_REUSEADDR socket option with setsockopt() in order for this to take place. Before calling the bind() function, the setsockopt() function needs to be called. Additionally, the restarted process will fail if the SO_REUSEADDR socket option is not enabled. The way wildcard addresses are handled changes when the SO REUSEADDR socket option is set.  Because more than one socket needs to bind to the UDP port, SO_REUSEADDR is required. This guarantees that the source IP will send a message to each socket that is connected to the UDP port.

Additionally, wildcard addresses can bind to the same port with this socket option. A socket binding to 0.0.0.0:80 and another socket b attempting to bind to 10.1.0.1:40 will fail without SO_REUSEADDR. Since 0.0.0.0 also includes 10.1.0.1, there would be a conflict because it lists all possible local addresses. This is interpreted by the kernel as a pair of sockets sharing the same local address and port. The way wildcard addresses are handled changes when the SO REUSEADDR socket option is set. There won’t be a conflict between a socket bound to 0.0.0.0:40 and a socket bound to 10.1.0.1:40 if SO REUSEADDR is enabled. This is due to the fact that the IP address 0.0.0.0:40 is treated as a wildcard address and isn’t the same as the precise local address of 10.1.0.1.

What Is SO_REUSEPORT?

Multiple sockets can bind to the same address and port combination when SO REUSEPORT is enabled, just like SO REUSEADDR does. If all of the processes use the SO_REUSEPORT option, the SO_REUSEPORT flag allows them to bind to the same address. The rule stipulates that the socket option SO_REUSEPORT must be enabled for each socket binding to the address and port. Before binding to a specific local IP and port combination, for instance, no socket can bind to socket A if SO_REUSEPORT is not enabled.

As previously mentioned, a socket enters the synchronized state known as TIME WAIT when it closes. Unless both sockets have the SO REUSEPORT option, another socket won’t be able to use the IP address and port combination of the socket in the TIME-WAIT state. The SO_REUSEPORT socket option behaves similarly to SO_REUSEADDR when it comes to multicasting. The user’s restriction is what differentiates SO_REUSEPORT from the others. With SO_REUSEPORT, one compelling userID ought to achieve all attachments that share a similar IP and port. In point of fact, this holds true for both TCP and UDP.

Difference Between SO_REUSEADDR and SO_REUSEPORT

SO_REUSEADDR	SO_REUSEPORT
Local addresses and ports may be reused with the SO REUSEADDR socket option.	Multiple sockets may bind to the same address and port combination with SO REUSEPORT enabled.
Starting with Linux kernel version 2.4 and up, SO_REUSEADDR can be used.	This socket option was only implemented in Linux kernel version 3.9, making it relatively recent.
Different operating systems have different ways of implementing this socket option.	Different operating systems have the same ways of implementing this socket option.
In a multicast, packets are sent in a group communication to multiple destination IPs at once.	The SO REUSEPORT socket option functions similarly to SO REUSEADDR when multicasting.
Using setsockopt(), set the SO_REUSEADDR socket option.	unless both sockets have the SO_REUSEPORT option, the TIME_WAIT state.
this holds true for only UDP.	this holds true for both TCP and UDP.
For example, SO REUSEADDR doesn’t examine whether any of the different sockets tying to the IP/port combination have a particular socket option set.	For example,  Before binding to a particular local IP and port combination, no socket can do so if socket A does not have SO_REUSEPORT enabled.

Conclusion

We started this article by learning about socket options and their implementation. The differences between and effects of the socket options SO REUSEADDR and SO REUSEPORT on TCP and UDP communication were then thoroughly discussed.