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61 votes
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Does UDP do anything at all?

Interesting perspective and question! Yes, most of what UDP does is supply a standard means for multiple applications to co-exist using the same IP address, by defining the concept of UDP ports. The ...
Jeff Wheeler's user avatar
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48 votes

Does UDP do anything at all?

UDP is a transport protocol, like TCP. That means it provides a protocol for an application to use IP. Like TCP, UDP has addressing (ports) to which applications bind so that datagrams destined to ...
Ron Maupin's user avatar
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35 votes
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Is a TCP server limited to 65535 clients?

The short answer is no, that's not the limit. A TCP Port field is 2x bytes and holds a quantity of 65536. This number limits the amount of addresses a server can have. But this doesn't limit the ...
Kind Contributor's user avatar
29 votes
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How can a TCP window size be allowed to be larger than the maximum size of an ethernet packet?

The TCP window size is generally independent of the maximum segment size which depends on the maximum transfer unit which in turn depends on the maximum frame size. Let's start low. The maximum frame ...
Zac67's user avatar
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25 votes
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acknowledgment by TCP does not guarantee that the data has been delivered

This part of the RFC is about passing responsibility over to the operating system or whatever is the next stage of the process. It's fundamentally concerned with the separation of layers. An ...
jonathanjo's user avatar
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23 votes
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Does TCP open a new connection for every packet that is sent?

One of my buddies is saying that TCP will be a problem for this gateway because it is going to establish a new connection for every message it sends (not kafka but the underlying transportation ...
Kevin's user avatar
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20 votes
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What does TCP DUP ACK mean?

There can be several things going on - the most common would be the use of TCP Fast Retransmission which is a mechanism by which a receiver can indicate that it has seen a gap in the received sequence ...
rnxrx's user avatar
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15 votes

Does UDP do anything at all?

I would encourage you to look at how higher level protocols that utilize UDP actually use it. Classic and well documented examples are DNS (in most cases at least, it's possible to do DNS over TCP but ...
Austin Hemmelgarn's user avatar
14 votes
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Why do FTP and SMTP not use IP?

TCP and UDP are layer 4 (transport) protocols. They always use IP as the layer 3 (network) protocol. The text you quote is just plain wrong. You may notice that the page you reference was marked ...
Ron Trunk's user avatar
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14 votes

Does the destination port change during TCP three-way handshake?

No, a TCP connection is uniquely identified by both source and destination IP and TCP (port) addresses. Changing any one of those will break the TCP connection (or prevent it from forming in the ...
Ron Maupin's user avatar
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13 votes
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Do these 2 packets belong to the same tcp socket?

First, TCP does not care about single packets. If these are just data packets without any previous connection establishment than they will be simply dropped, no sockets involved. So I'm assuming that ...
Steffen Ullrich's user avatar
12 votes
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Is rerouting possible in UDP?

This is not the hosts that decide which route a packet will follow, each router in the path make it's own decision. (Actually, the originating host could use the IP strict source option to try to ...
JFL's user avatar
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11 votes
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Port Numbers related doubt

User applications use random ephemeral ports for outgoing connections. TCP port 80 is only the server side's default port for WWW. A TCP socket connection consists of source IP, source port, ...
Zac67's user avatar
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11 votes

Can anyone explain to me the difference between the PSH and URG flags in TCP segment?

Jeremy Stretch has a good article on this. This is where the PSH flag comes in. The socket that TCP makes available at the session level can be written to by the application with the option of "...
Ron Trunk's user avatar
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11 votes

Does the destination port change during TCP three-way handshake?

We know that port 80 is just a welcoming port, when the web server reveives a http request, it create a new connection port(let's say 5000) That's not correct for the HTTP protocol. Some protocols, ...
Josh's user avatar
  • 211
10 votes

Does TCP open a new connection for every packet that is sent?

My understanding is that when you establish a TCP connection, that connection remains open until it is timed out by the application or forcibly closed by either the server or client. From the ...
Ron Maupin's user avatar
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10 votes

acknowledgment by TCP does not guarantee that the data has been delivered

From the RFC perspective, the "end user" is the application. There's no guarantee that the application got the data, just that the TCP process received it. From your NOC perspective, the network is ...
Ron Trunk's user avatar
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10 votes
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Where are 0 TCP/UDP ports banned?

IANA has reserved both TCP and UDP port 0. See the IANA Service Name and Transport Protocol Port Number Registry. IANA is the Internet Assigned Numbers Authority, so all internet numbers, including ...
Ron Maupin's user avatar
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9 votes
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How does NAT decide which connections are inbound, and which are outbound?

TCP is a connection-oriented protocol, and it can only communicate through connections. Before you start programming using TCP, it would be helpful to first understand how TCP works, and you should ...
Ron Maupin's user avatar
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9 votes
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TCP's three-way handshake and Denial of Service attack

why attackers just do the first step of 3-way handshake? why don't they just complete all three steps of 3-way handshake to be fully connected with the server just like normal users so it is going to ...
Steffen Ullrich's user avatar
9 votes

Can anyone explain to me the difference between the PSH and URG flags in TCP segment?

Suppose the receiving buffer has already some data to be processed by the application. A segment with the PSH flag set to 1 is sent now. The sending buffer will not wait to be filled, instead, it will ...
avistein's user avatar
9 votes

Where are 0 TCP/UDP ports banned?

TL;DR: RFC870 Port zero has been included in the "Network Wide Standard Functions" range since RFC433 in 1972, but has never been assigned. https://www.rfc-editor.org/rfc/rfc433.html Here ...
Ben's user avatar
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8 votes
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What is the transport protocol used in wget?

By default, wget uses HTTP to retrieve files. Which means wget uses TCP/80... unless you specify HTTPS, in which case it uses TCP/443.
Eddie's user avatar
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8 votes
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How do data packets travel without merging?

You are describing a problem called collision. There are different network media and protocols that are subject to collision, and the protocols must have a method to detect when that happens. Your ...
Ron Maupin's user avatar
  • 99.9k
8 votes

Why is a TCP Socket identified by a 4 tuple?

In the UDP protocol, a socket is uniquely identified by the source IP and the source port. In the TCP protocol, the socket is uniquely identified by the source IP, source port, destination IP, and ...
jonathanjo's user avatar
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8 votes
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Which one is right, UDP has 508 or 512 bytes payload limits?

You are confusing a couple of things. MTU is Maximum Transmission Unit, and it is a value of the data-link (layer-2) protocol on a specific medium. IP, neither IPv4 nor IPv6 has an MTU. They both have ...
Ron Maupin's user avatar
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7 votes
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Is UDP used in every TCP/IP connection?

UDP and TCP are completely separate Transport Layer (Layer 4 in the OSI model) protocols. There are also other layer-4 protocols, but TCP and UDP are the most commonly used. UDP was first, and it is a ...
Ron Maupin's user avatar
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7 votes
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Why does source port and destination port differ, in my network communications?

Source ports are randomly generated from the unregistered port range. The source/destination port works similar to your IP. The port you send from, is the port the service will reply too. For ...
PacketLoss's user avatar
7 votes

Port Numbers related doubt

Every TCP packet has two port fields; one is the Source Port, and the other is the Destination Port. The youtube.com server is listening on Port 80. This means that any packet travelling to youtube....
mere3ortal's user avatar
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