DIFFERENCE BETWEEN TCP AND UDP | NETSCOUT
TCP (Transmission Control Protocol) is connection oriented, whereas UDP (User Datagram Protocol) is connection-less. Learn why this matters here. You've probably seen references to TCP and UDP when setting up In other words, whether you're sending a packet via TCP or UDP, that packet is sent to an IP address. If you lose your connection for a few seconds, the video may freeze or get jumpy for a moment pc-game-team-fortressusing-udp. That information is sent most often via two methods, UDP and TCP. higher load on the computer as it has to monitor the connection and the data going across it. the devices in between the sending computer and the receiving computer to get the data where it is supposed to go properly. 0, 1, 2, 3, 4, 5.
TCP provides apps a way to deliver and receive an ordered and error-checked stream of information packets over the network. The User Datagram Protocol UDP is used by apps to deliver a faster stream of information by doing away with error-checking.
When configuring some network hardware or software, you may need to know the difference. Both protocols build on top of the IP protocol. However, they are the most widely used. The web server responds by sending a stream of TCP packets, which your web browser stitches together to form the web page.
When you click a link, sign in, post a comment, or do anything else, your web browser sends TCP packets to the server and the server sends TCP packets back. This sender chooses the sequence number to minimize the risk of using the already used sequence number. The client sends the packet with that sequence number and data along with the packet length field.
The server on receiving the packet sends ACK of the next expected sequence number. Thus, the sequence number are established between the Client and Server. Now, they are ready for the data transfer. Even while sending the data, same concept of the sequence number is followed.
For example, suppose the receiver has a byte buffer, as shown in Figure below. If the sender transmits a byte segment that is correctly received, the receiver will acknowledge the segment. However, since it now has only bytes of buffer space until the application removes some data from the bufferit will advertise a window of starting at the next byte expected. Now the sender transmits another bytes, which are acknowledged, but the advertised window is 0. The sender must stop until the application process on the receiving host has removed some data from the buffer, at which time TCP can advertise a larger window.
4. Packets and Protocols - Building Internet Firewalls, 2nd Edition [Book]
When the window is 0, the sender may not normally send segments, with two exceptions. First, urgent data may be sent, for example, to allow the user to kill the process running on the remote machine.
Second, the sender may send a 1-byte segment to make the receiver reannounce the next byte expected and window size. The TCP standard explicitly provides this option to prevent deadlock if a window announcement ever gets lost.
Building Internet Firewalls, 2nd Edition by D. Brent Chapman, Simon Cooper, Elizabeth D. Zwicky
Senders are not required to transmit data as soon as they come in from the application. Neither are receivers required to send acknowledgements as soon as possible.
When the first 2 KB of data came in, TCP, knowing that it had a 4-KB window available, would have been completely correct in just buffering the data until another 2 KB came in, to be able to transmit a segment with a 4-KB payload. This freedom can be exploited to improve performance. Consider a telnet connection to an interactive editor that reacts on every keystroke. Later, when the editor has read the byte, TCP sends a window update, moving the window 1 byte to the right.
This packet is also 40 bytes. Finally, when the editor has processed the character, it echoes the character as a byte packet.
In all, bytes of bandwidth are used and four segments are sent for each character typed. When bandwidth is scarce, this method of doing business is not desirable. One approach that many TCP implementations use to optimize this situation is to delay acknowledgments and window updates for msec in the hope of acquiring some data on which to hitch a free ride.
Assuming the editor echoes within msec, only one byte packet now need be sent back to the remote user, cutting the packet count and bandwidth usage in half. Although this rule reduces the load placed on the network by the receiver, the sender is still operating inefficiently by sending byte packets containing 1 byte of data.
A way to reduce this usage is known as Nagle's algorithm Nagle, What Nagle suggested is simple: Then send all the buffered characters in one TCP segment and start buffering again until they are all acknowledged. If the user is typing quickly and the network is slow, a substantial number of characters may go in each segment, greatly reducing the bandwidth used. The algorithm additionally allows a new packet to be sent if enough data have trickled in to fill half the window or a maximum segment.
Nagle's algorithm is widely used by TCP implementations, but there are times when it is better to disable it. In particular, when an X Windows application is being run over the Internet, mouse movements have to be sent to the remote computer. Gathering them up to send in bursts makes the mouse cursor move erratically, which makes for unhappy users. Another problem that can degrade TCP performance is the silly window syndrome.
This problem occurs when data are passed to the sending TCP entity in large blocks, but an interactive application on the receiving side reads data 1 byte at a time.
To see the problem, look at the figure below. Initially, the TCP buffer on the receiving side is full and the sender knows this i.
Then the interactive application reads one character from the TCP stream. This action makes the receiving TCP happy, so it sends a window update to the sender saying that it is all right to send 1 byte.
The sender obliges and sends 1 byte. The buffer is now full, so the receiver acknowledges the 1-byte segment but sets the window to 0. This behavior can go on forever. Clark's solution is to prevent the receiver from sending a window update for 1 byte. Instead it is forced to wait until it has a decent amount of space available and advertise that instead.
Specifically, the receiver should not send a window update until it can handle the maximum segment size it advertised when the connection was established or until its buffer is half empty, whichever is smaller. Furthermore, the sender can also help by not sending tiny segments. Instead, it should try to wait until it has accumulated enough space in the window to send a full segment or at least one containing half of the receiver's buffer size which it must estimate from the pattern of window updates it has received in the past.
Nagle's algorithm and Clark's solution to the silly window syndrome are complementary. Nagle was trying to solve the problem caused by the sending application delivering data to TCP a byte at a time. Clark was trying to solve the problem of the receiving application sucking the data up from TCP a byte at a time.
Both solutions are valid and can work together. The goal is for the sender not to send small segments and the receiver not to ask for them. The receiving TCP can go further in improving performance than just doing window updates in large units. Like the sending TCP, it can also buffer data, so it can block a READ request from the application until it has a large chunk of data to provide.
Doing this reduces the number of calls to TCP, and hence the overhead. Of course, it also increases the response time, but for noninteractive applications like file transfer, efficiency may be more important than response time to individual requests.
Another receiver issue is what to do with out-of-order segments. They can be kept or discarded, at the receiver's discretion. Of course, acknowledgments can be sent only when all the data up to the byte acknowledged have been received. If the receiver gets segments 0, 1, 2, 4, 5, 6, and 7, it can acknowledge everything up to and including the last byte in segment 2. When the sender times out, it then retransmits segment 3.
If the receiver has buffered segments 4 through 7, upon receipt of segment 3 it can acknowledge all bytes up to the end of segment 7.
Connection Establishment and Termination[ edit ] Establishing a Connection A connection can be established between two machines only if a connection between the two sockets does not exist, both machines agree to the connection, and both machines have adequate TCP resources to service the connection.
If any of these conditions are not met, the connection cannot be made. The acceptance of connections can be triggered by an application or a system administration routine. When a connection is established, it is given certain properties that are valid until the connection is closed. Typically, these will be a precedence value and a security value.
These settings are agreed upon by the two applications when the connection is in the process of being established. In most cases, a connection is expected by two applications, so they issue either active or passive open requests. Figure below shows a flow diagram for a TCP open. Address-based filtering will also be affected, to some extent, by the new autoconfiguration mechanisms.
While this is the intent of the standard mechanisms, one needs to be careful about proprietary schemes, dial-up servers, etc. Also, high-order address bits can change, to accommodate the combination of provider-based addressing and easy switching among carriers.
But they can also be used for firewalls, given appropriate authentication: This, by the way, is a vague idea of mine; there are no standards for how this should be done. But a firewall traversal header might do the job.
As you can see, IPv6 could have a major impact on firewalls, especially with respect to packet filtering. However, IPv6 is not being deployed rapidly. On the other hand, the problem of converting networks from IPv4 to IPv6 has turned out to be worse.
Most packet filtering implementations support IP filtering only and simply drop non-IP packets. The Internet is, by definition, a network of IP networks. If you are putting a firewall between parts of your network, you may find that you need to pass non-IP protocols. In this situation, you should be careful to evaluate what level of security you are actually getting from the filtering. Many packages that claim to support packet filtering on non-IP protocols simply mean that they can recognize non-IP packets as legal packets and allow them through, with minimal logging.
Products that were designed as IP routers but claim to support five or six other protocols are probably just trying to meet purchasing requirements, not to actually meet operational requirements well.
In most cases, you will be limited to permitting or denying encapsulated protocols in their entirety; you can accept all AppleTalk-in-UDP connections, or reject them all. A few packages that support non-IP protocols can recognize these connections when encapsulated and filter on fields in them.
You will often see attacks discussed using the names given to them by the people who wrote the original exploit programs, which are eye-catching but not informative. Port Scanning Port scanning is the process of looking for open ports on a machine, in order to figure out what might be attackable. Straightforward port scanning is quite easy to detect, so attackers use a number of methods to disguise port scans.
This is often called a SYN scan or a half open scan. Attackers may also send other packets, counting a port as closed if they get a RST and open if they get no response, or any other error. Almost any combination of flags other than SYN by itself can be used for this purpose, although the most common options are FIN by itself, all options on, and all options off.
For instance, teardrop and its relatives send overlapping fragments; there are also attacks that send invalid combinations of options, set invalid length fields, or mark data as urgent when no application would winnuke. When this happens, replies will be sent to the apparent source address, not to the attacker.
The attacker can intercept the reply. The attacker can intercept the reply If an attacker is somewhere on the network between the destination and the forged source, the attacker may be able to see the reply and carry on a conversation indefinitely. This is the basis of hijacking attacks, which are discussed in more detail later. This attack has a number of variants using different protocols and methods for multiplying the replies.
The most common method of multiplying the replies is to use a broadcast address as the source address. Attacker using forged packets to attack a third party The land attack sends a packet with a source identical to the destination, which causes many machines to lock up.
Attacker using looped forged packets Packet Interception Reading packets as they go by, frequently called packet sniffing, is a frequent way of gathering information. In order to read a packet, the attacker needs to get the packet somehow.
The easiest way to do that is to control some machine that the traffic is supposed to go through anyway a router or a firewall, for instance. An Ethernet network that uses a bus topology, or that uses base T cabling with unintelligent hubs, will send every packet on the network to every machine.
Token-ring networks, including FDDI rings, will send most or all packets to all machines. Using a network switch to connect machines is supposed to avoid this problem.
A network switch, by definition, is a network device that has multiple ports and sends traffic only to those ports that are supposed to get it. Unfortunately, switches are not an absolute guarantee.
Most switches have an administrative function that will allow a port to receive all traffic. Furthermore, switches have to keep track of which addresses belong to which ports, and they only have a finite amount of space to store this information. If that space is exhausted for instance, because an attacker is sending fake packets from many different addressesthe switch will fail. Some of them will stop sending packets anywhere; others will simply send all packets to all ports; and others provide a configuration parameter to allow you to choose a failure mode.
On a normal switch, all the ports are part of the same network. A switch that supports VLANs will be able to treat different ports as parts of different networks.