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Questions tagged [tcp]

For questions about Transmission Control Protocol (TCP), a transport protocol used to encapsulate data across a network for reliable communication.

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syn flooding attack on a telnet server that listens on multiple ports [on hold]

I want to implement a telnet server which listens on different ports for different applications. How to do it in a clean and efficient way? Suppose I am able to do it, i.e my telnet server listens ...
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Can anyone Explain me difference Between PSH and URG flag in TCP segment

According to me when PSH flag is set , it indicates that data will have to be sent immediately to the wire and on receiving side the data has to be pushed to the application immediately . When URG ...
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Acknowledgment number (Go back n) vs Sequence number (Selective repeat) [on hold]

An acknowledgment number in the Go-Back-N protocol defines the next packet expected, but an acknowledgment number in the Selective-Repeat protocol defines the sequence number of the packet to be ...
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What do the multiple occurencies mean in a packet trace file?

I have a trace file and I used tshark to find out the number of duplicate ACKs, with the following command: tshark -r file.pcap -T fields -e frame.number -e tcp.analysis.duplicate_ack After some ...
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Is a TCP segment with FIN but not ACK ever encountered today?

A fin-scan involves sending a TCP segment with FIN and no other flags other than (possibly) PSH and/or URG. Are such packets ever legitimately encountered in 2019? Note that in Is a FIN only segment ...
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why can't we use the sequence number to distinguish them since every packet has a different sequence number? [closed]

It is a question from Networking stanford course. A server typically listens for TCP connections on a particular port (e.g. 80 for HTTP or 22 for SSH). Which fields can the server use to ...
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Which fields can the server use to distinguish packets for a particular client connection? [duplicate]

A server typically listens for TCP connections on a particular port (e.g. 80 for HTTP or 22 for SSH). Which fields can the server use to distinguish packets for a particular client connection?It is a ...
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How CUBIC TCP behaves when the sender doesn't use all the available bandwidth?

While I was reading about CUBIC TCP (https://en.wikipedia.org/wiki/CUBIC_TCP) I asked myself one question, what happens to the congestion window if the sender doesn't send much data (enough to trigger ...
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Is an RST only segment ever legitimate?

Is a TCP segment with RST but no ACK ever legitimately encountered today? While some kernels emit such an RST when a SYN segment is sent "illegitimately" from themselves (e.g., nmap half-syn, scapy, ...
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How is SampleRTT measured once every RTT, without measuring every segment?

According to the RFC, SampleRTT is measured once every RTT. My text: Computer Networking: A top-down approach (6ed By: Kurose & Ross) also states, that: Instead of measuring a SampleRTT for ...
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Is it correct to assume that ordering of frames at switch level is not important?

My understanding is that if the payload of the frame contains any data that needs to be reassembled, at least for TCP payload, it can be done at the OS level, once all the packets are received and ...
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Is WRED configured for TCP traffic only?

I am looking out for a practical usage of WRED. After reading/searching I found that it is more suitable for TCP traffic. When the queue is full, all the TCP session at that time will start with slow ...
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TCP - correlation between ACKs and receive window

EDIT: I think i get it now. So a simple sliding window mechanism basically assumes the correctly received data is processed immediately. Therefore an acknowledgement implies the data was received AND ...
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1answer
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TCP or UDP for Stop & Wait / Go Back N

I'm creating server/client classes for "Stop & Wait" and "Go Back N" (variant of sliding window) protocols, though I'm unsure on whether I should pursue TCP or UDP. From my current understanding I ...
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Can throughput exceed the bandwidth of a network

I took an introductory course to networking this semester and I was wondering: looking at things at the layer 4 level using TCP can the throughput on the network exceed its bandwidth? According to the ...
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sequence number layer 4 vs sequence number LLC layer 2

I had read about TCP in layer 4 where sequence number and acknowledgment numbers were assigned to each segment so that each side of the connection could keep track of the process of sending/receiving ...
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Message formatting and encapsulation

I've gotten confused when reading about encapsulation and the OSI and TCP/IP models. I first read about message formatting and encapsulation and the diagram I read showed: Destination | Source and ...
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OSI Model vs Network Model: Does It Matter Which One You Use?

The OSI (Open Systems Interconnection) model is comprised of the following layers: 7. Application Layer 6. Presentation Layer 5. Session Layer 4. Transport Layer 3. Network Layer 2. Data Link ...
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Why maximum length of IP, TCP, UDP packet is not suit?

From many tutorials, I get follow knowledge(maybe I'm misunderstood) : maximum of an Ethernet packet is about 1500 bytes. maximum of an IP packet is about 65535 bytes. maximum of a UDP packet is ...
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Why maximum length of IP、TCP、UDP packet is not suit? [duplicate]

From many tutorials, I get follow knowledge(maybe I'm misunderstood) : maximum of an Ethernet packet is about 1500bytes. maximum of an IP packet is about 65535bytes. maximum of a UDP packet is 65515 ...
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1answer
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ACL and ACEs Query

So i'm configuring a basic network and I need to create a couple of Extended ACLs. Now my question is, does this ACE permit any TCP connection to the following subnet? permit tcp 192.168.10.0 0.0.0....
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How are connections in TCP recorded for sending messages one after another?

In transport layer, TCP is connection oriented and UDP are connectionless. What is "connection" as in TCP then? In network layer, is it correct that there should be no distinction between TCP and ...
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How can TCP be used in order to implement DHCP and under which circumstances is this preferable?

I am pretty new to the computer networking studies and was learning about the DHCP protocol. It is implemented based on UDP, as I've gathered, but is there a way for it to be implemented over TCP? ...
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Why do TCP/IP stacks send individual ACK packets?

I've been reading more about TCP and found out that since multiple flags can be set at once, basically every packet after the initial SYN has the ACK flag set, and serves as an acknowledgment of all ...
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What is the Acknowledgement number in connection synchronisation between client and server?

I came across this article in an attempt to understand sequence and acknowledgment numbers better. Here is the excerpt: Connection set-up uses the SYN flags. They are not used except for ...
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Role of TCP window header field [duplicate]

What is the role of that field in the header of a TCP segment? From what i understand,after the end hosts tell each other how much data they can send until the "buffer" fills up (what is the buffer?),...
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How do TCP connections work?

The TCP establishes a connection between the source and the destination. My questions are: What do we mean by end-to-end communication? What is the role of that connection?Couldn't reliability be ...
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Data Transmission Rate Video Stream

Given a web-server with an sd-card (storing 720p (7.2 Mbit/s) videos and 800 Mbit/s read-speed) and a wireless interface with 1200 Mbit/s transmission speed. I have to know how many clients can ...
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How do TCP/IP packets manifest in the RJ45 electric pinout?

Sorry if this is a stupid question. Given you could observe signals going through RJ45 pins, would you see single TCP packets or their fragments?
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How does the transport layer tell UDP apart from TCP?

So I'm reading Computer Networking: A top down approach (where these images are from) and I was looking at the Transport layer. A generic segment in the transport layer has a pretty simple structure: ...
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1answer
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How MPTCP closed connection?

how MPTCP connection with more than one subflow closed? what would happen to MPTCP connection if a client decide to close one of the subflows? it would be very kind of you if you explain it step by ...
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Understanding acknowledgement mechanism in sliding window protocol

I came across following problem: Node A sends packets to B through router R. The link A-R is instantaneous , but the R->B link transmits only 1 packet each second , one at a time . Assume A sends ...
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How are websites accessed without port numbers?

I am confused on how requests to websites are received. If I type in 172.217.5.110 to my browser, google.com sends me its home page. I didn't have to specify the port number. How does that work? I ...
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Can a ACK or SEQ Number exceed a range and crash the NIC?

I was watching the TCP Stream out of pure curiosity of my FTP Server and saw that the ACK and SEQ number increases by one with each sequence being transmitted successfully. I am not sure, but ...
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acknowledgment by TCP does not guarantee that the data has been delivered

In RFC 793 there is a part about the acknowledgment of TCP segments: When the TCP transmits a segment containing data, it puts a copy on a retransmission queue and starts a timer; when the ...
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TCP errors explain

Could anyone explain these errors: TCP ACKed unseen segment TCP Dup ACK TCP Previous segment not captured TCP Out-Of-Order TCP Retransmission
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tcp connection and stream flow question

Could anyone explain the main principe of tcp flow when making a session ? I have take a tcp dump when i'm trying to browse a site. when I analyse the packet by wireshark, i have found many Three way ...
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Is it possible to make a TCP connection connect back to the destination port? [closed]

I'm new in this forum, I thought I could ask a question here. I've set up a proxy by using nginx and Openresty, which supports LUA scripts, that changes the body of a HTTP SOAP POST request. The ...
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Is there any video streaming online service that actually uses UDP?

We usually hear that UDP is used with data with which a few packets loss/out-of-order can be tolerated like video streaming. And the instructor typically goes on saying "so if you lose a few ...
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AWS tunnel TCP retransmissions and DUP ACKs

I have a IPsec tunnel from my firewall towards AWS, the tunnel is up in both phases. If I run traffic sniffer in the firewall, I can see interesting traffic going through, but there are MANY TCP ...
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Gather the BGP data by using TCP connection on port 179

In order to gather the information shared between BGP peers, what port number should be used to connect using TCP (I am using 179, and don't see the connection being established)? Will I be able to ...
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When TCP SACK is already enabled, it is lost again

Because the No. 4245 packet loss, a new segment block is generated, but why the original 3040050-3048810 segment block will disappear. Can anyone help me to explain this situation?
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Why is retransmission delayed when the RTO is long?

I am new to networking and learning about TCP Timer Management and read this in my textbook: "If the value of time-out (RTO) is too small then unnecessary re-transmission will take place. If time-out ...
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How common are low MTU links (<1492) in the public internet?

Are there any kind of statistics how common are low MTU links (MTU is below 1492) in the common Internet?
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Initial TCP congestion window sizes

I have tried to look for this information on Google, but I haven't been able to find a good source for this information. So, I am interested in what are the initial TCP congestion windows on ...
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2answers
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Calculating the throughput of a given TCP connection

Given a TCP session, is there a way to determine the throughput of the sender? I have a wireshark sniff, and I see that to calculate the throughput of the sender I can use the TCP-Window-Size-in-bits /...
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How does the Transport Layer construct the Pseudo-Header for TCP checksum?

THE TCP Psuedo Header needs sender and destination IP Address and protocol type. All of this informations is present in the network layer/IP header. Since the transport layer cannot access the data ...
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How could a response be sent to the requestor without requestor's address?

I'm reading this talking about the differences between two fire-and-forget message (for example, under UDP) and a request-response communication (for example, under TCP). I came across this: The ...
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Processing received SACK information in case of reordering

I would like to understand how TCP receiver in established state should treat SACK information of out-of-order and fully within receive window segments, where rcv_nxt < seq_no < rvc_nxt + ...
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How many TCP connections are required to download a file though ftp?

Regardless of which mode is used (active or passive mode), the initial connection is done on port 21 (command port). Then a second channel starts (data port) for exchanging the files/data. Each of ...