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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Why in the TCP/IP model the link & physical are one?

I'm currently learning about the OSI model and the TCP/IP models, and I was wondering: Why in the TCP/IP model the physical layer and the data link layer are combined? I'll state how I understand the ...
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Why the pseudo-header is not transmitted with the UDP datagram?

I have read from E. Comer - Internetworking with TCP/IP 4th edition that "The purpose of using a pseudo-header is to verify that the UDP datagram has reached its correct destination. The key to ...
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UDP checksum calculation for checksum results in the value zero

I read UDP checksum from Wikipedia that "If the checksum calculation results in the value zero (all 16 bits 0) it should be sent as the one's complement (all 1s) as a zero-value checksum ...
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How UDP checksum get IP address to make pseudo header in transport layer?

We know that UDP checksum's pseudo header contains the most important parts of the IP header, that is, source and destination address, protocol number and data length. I hope that the concept of IP ...
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Why router can't be used for converting different model of network but gateway can do this?

We know that Router can't be used for converting different model (e.g OSI model to TCP/IP or TCP/IP model to OSI) of network. It isn't a multiprotocol converter. But gateway is a highly sophisticated ...
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Maximum value of file that can be sent [closed]

this is the following question I have encountered in school. There is a file of X bytes that needs to be transferred from Host A to Host B. The MSS is 10 bytes. What is the maximum value of X such ...
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How is UDP used in multimedia system inspite of being connectionless

We know that UDP does not care about segment (packet) in-order and their arrival on the destination.Then how on YouTube or VoIP (skype) are we able to stream videos? If a packets is lost (doesn't ...
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Is it possible for TCP can accept out of order segments?

TCP is connection-oriented protocol whereas IP isn't connection-oriented protocol. Any packets before sending into transport layer sorted operation must have been done in network layer. That's why we ...
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Why is bandwith-delay product the maximum in-flight datas in TCP? [duplicate]

I have often read, for example https://en.wikipedia.org/wiki/Bandwidth-delay_product that: The result, an amount of data measured in bits (or bytes), is equivalent to the maximum amount of data on ...
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Are duplicate sequence numbers from different TCP-connections possible?

While learning about Sequence and Acknowledgment numbers one thing bugged me. I wasn't able to rule out for myself if the following scenario in which Host A sends data to Host B by using some ...
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Definition of a socket [duplicate]

I wanted to confirm whether the definition of a socket I've understood in a computer network context is true. A socket is file who is unique and named by local IP,Local port, Foreign IP and foreign ...
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What would happen if SYN and ACK are in the initial request?

I understand that a three-way handshake is used to form a TCP connection and that the basic outline of a handshake is: A sends a packet to B with a SYN bit B sends a packet to A with a SYN bit and an ...
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Congestion control behaviour of TCP Reno

Which behaviour of TCP Reno after 3 DUP ACK is correct: The one described in the Italian Wikipedia (https://it.wikipedia.org/wiki/Controllo_della_congestione_in_TCP#TCP_Reno). It says the new cwnd is:...
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Are NAT external:internal mapping types the same for UDP and TCP

Suppose I use a STUN server (UDP) to determine that a client's NAT randomly assigns external port values. Does this imply that the client's NAT will also assign random external port values when using ...
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Is it possible to move a persistent TCP connection?

Context: Say I have a global cloud service. In each datacenter, I have numerous persistent TCP connections to various client devices. The TCP connections are distributed across various nodes in the ...
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Is the distinction between ports under and above port 1024 exists only in TCP and UDP protocols?

Is the distinction between ports under and above port 1024 exists only in TCP and UDP protocols? I want to know if in other protocols (i.e. not TCP and UDP) such a distinction between "root" ...
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Does UDP can be exposed to stateful analysis?

From protocol theory we know that TCP is stateful protocol. Different stateful packet filters do filtration based on connection state. I.e. it can distinguish responses and replies. It's obviously for ...
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What does it mean for a website to return syn:false ack:true to my connect attempt? [closed]

I'm using a userspace TCP stack and I send a syn:true, ack:false to a website: [2021-06-20T19:30:24Z DEBUG async_smoltcp::packet_log] PHY >>>> [2021-06-20T19:30:24Z DEBUG async_smoltcp::...
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How to create a mapping between TCP segments or IP packets or fragments and TCP Windows? [closed]

I am searching for a method how I practically can determine the segments within a TCP window both when sending and receiving them? I want to modify IP packets per TCP window. I already looked into the ...
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Why large queueing delays are experienced as a packet arrival rate nears the link's capacity? [duplicate]

From the book "Computer Networks A top Down Approach": It says if hosts A and B both are sending at rate R/2 and router's outgoing link has a capacity of R. There will be delays experienced ...
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Why does the Transport layer break data into packets? How does that make things reliable? Isn't the Network layer doing the same thing?

I'm new to CNs and there is something that I can't yet grasp. Why doesn't the Transport layer let the Network layer do all the splitting up? How does segmentation make things reliable? Also, I ...
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In TCP, when a receiver starts sending duplicate ACKs to the sender, does it also send ACKs for packets it has received past the hole?

I know that if a receiver sees holes in the packets it receives, it starts sending duplicate ACKs containing seq numbers of missing packets. At this time, the receiver is also receiving packets that ...
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nmap correct TCP traceroute [closed]

Why is only hop 1 & 6 displayed? Note: I can't use ICMP, due to firewall. The target is an educational website in the AWS cloud.
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What is the difference in reliability of sending a pure ACK packet (without any data), as opposed to a data packet in TCP?

I was going through the book TCP/IP Illustrated and in the zero windows section, I noticed the use of a TCP persist timer - which is used to avoid losing a window update message from a receiver after ...
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Difficulty in understanding the concept of "artificial inflate" and "deflate" in the fast recovery phase of TCP

I was going through the text Computer Networking- A Top-Down Approach by Kurose and Ross, there I found subtleties with the TCP congestion control FSM which is shown below: Mainly I am having ...
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Tearing down the FSM description of congestion control

I was going through the text Computer Networking- A Top-Down Approach by Kurose and Ross, there I found subtleties with the TCP congestion control FSM which is shown below: Mainly I am having ...
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1 vote
1 answer
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Who should reset TCP connection after VIP has moved onto another host? [closed]

Imagine such a situation - TCP connection(NFS4 or database) between client(Linux) and virtual IP hosted on a server(Linux). Server fails and VIP is taken over by another server(using ARP). The client ...
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Port 8080 closed over VPN (Linux, OpenVPN, webpack, Node.js application). How to troubleshoot? [closed]

I am running a node application that uses webpack. The application starts and automatically selects the port 8080 on localhost: The website works correctly on the browser on my machine. I want now to ...
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Some random client requests fails with unexpected TCP [RST] packets [duplicate]

I have a service doing listen that serves clients over a TCP sockets connection with a raw binary protocol. The principle is basic: the connection is established, the client sends a request with data, ...
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Is OSI model merely used for troubleshooting purpose? [duplicate]

I'm a student and recently started understanding OSI model, from what I understand is that OSI model is just theoretical and not really used in real world. It's mainly for troubleshooting purpose. I'...
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TCP ACK confusion

When a packet is being sent after the SYN ACK connection has been established between a host and a server, packets can now be sent between the hosts and a server. Sometimes, there’s a window size ...
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2 answers
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Slow SMB transfer rates with client direct to Cisco switch, normal when connected to a downstream Netgear switch

I have encountered a rather unusual problem that I'm having difficulty getting to the bottom of... Here is the configuration: SMB server ->(2x10Gb SFP+ LAG) Cisco SG500X-24 switch ->(1x10Gb SFP+)...
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How TCP sequence numbers work in bidirectional communication/sliding window?

I was trying to understand how TCP works (not in detail of course). I was surfing the web for easy-to-understand flow diagrams and a question arose and couldn't find a straight answer. Let's suppose ...
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3 answers
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Why does one say IP fragmentation is bad and to be avoided when in reality data always needs to be fragmented for MTU compatibility?

Why does one say fragmentation is bad and must be avoided due to performance issues when in reality fragmentation intrinsically occurs within the communication ? Example: User1 wants to send 100 000 ...
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Is packet transfer still possible, if the routers don't have the updated link cost information in the Bellman-Ford Algorithm?

In the Bellman-Ford Algorithm, the principle of "Good news travels fast but bad news travels slow" is implemented. So if the cost of the link between two routers is increased, then the ...
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Regarding TCP Packets [duplicate]

On a VSat link with 800ms RTT latency and 10mbps bandwidth, that means 1MB bandwidth-delay product (data in flight). According to this useful (but closed) Q/A, packets are injected on both sides of ...
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Options for establishing a secure TCP connection to an IoT edge device over the internet

I have an IoT edge device which is currently configured as a TCP server; the device gathers and processes some data, and then passes it to the connected clients. This works as intended when the server ...
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Resegment incoming TCP/UDP packet [closed]

The question is as follows: what is the algorithm to resegment an incoming TCP/UDP packet? So, for example, I have a TCP packet, which size is more than some number, and I want to split this packet ...
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Tail Loss Probing Timer of TCP

I've been wrapping my head around how TLP timer works that helps in faster loss recovery especially when packets are lost at end of transmission thus saving RTO(Retransmit Time Out) time. In normal ...
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Does the delayed ACK packet have to be retransmitted?

Node A sends 2 packets to node B (node B has 2 available buffer size), if node A has sent 2 packets, and the 2 packets were successfully received by node B. Node B sent the acknowledgement to A but ...
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What happens to the packets in the sender buffer when "eventually a timeout would be reached" for a **delayed ACK** in a AIMD TCP connection?

In a AIMD TCP connection, What happens to the packets in the sender buffer when "eventually a timeout would be reached" for a delayed ACK for a specific packet at the sender side? Suppose ...
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2 votes
2 answers
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How exactly does Path-MTU Blackhole Detection work?

I'm currently trying to understand how the Path-MTU Blackhole Detection really works. From what I understand: You send rather big packets, starting at like 1460 Bytes (TCP example) and wait for ...
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IP flow interpretation on Logrhythm Netmon

We have a Logrhythm freemium network monitoring solution depending on port mirroring using span ports on switches to receive all traffic and analyze it. But I cannot understand the output. If I am ...
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Retransmission timer: one per segment or one global timer?

TCP uses various mechanisms to detect packet loss and decide when to retransmit segments. In this question, I am asking about the timeout-based retransmission, wherein a TCP retransmits certain ...
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Can SMALL TCP segments slow the TCP transfer rate?

Hello everybody and thanks for reading me, I have a datacenter switch connected to 10 25G servers and running some sort of storage application (nsdperf), the problem is that we are seeing a very slow ...
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3 answers
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What would happen if TCP flow control is turned off hypothetically? [closed]

I understand that TCP flow control provides a way for the receiver to backpressure the sender. But what if we eliminated this from the protocol. Of course, the receiver would still ACK everything ...
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5 votes
2 answers
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Can a client-side outbound TCP port be reused concurrently for multiple destinations?

Can a client-side outbound TCP port be reused concurrently for multiple destinations? If it's possible, this would let NAT gateways milk an IP Address much more, and make it practically impossible to ...
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1 vote
1 answer
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How are TCP segments discarded after Maximum Segment Lifetime expires?

From RFC 793: To be sure that a TCP does not create a segment that carries a sequence number which may be duplicated by an old segment remaining in the network, the TCP must keep quiet for a maximum ...
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1 vote
1 answer
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I have issue with MSS and window size [duplicate]

I made a short example because I have tried understanding the difference between MSS and window size in tcp header when we consider a sender and a receiver. So let's say sender and receiver use the ...
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Nature of TCP Timeouts

Are timeouts in TCPs inherently part of sequence numbers, or is it an entirely different component of a TCP packet? I understand that timeouts provide some level of reliabilty to a data stream, in ...
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