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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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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Difficulty in understanding the action “transmit new segment(s), as allowed” in TCP 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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1answer
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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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1answer
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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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1answer
85 views

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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2answers
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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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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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42 views

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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2answers
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Resegment incoming TCP/UDP packet

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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1answer
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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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TCP Windows increasing on server [duplicate]

I am confused and looking for answers :) I am sending a text file to a server. During handshake the client advertise a windows size of 17600, and in next SYN/ACK message the server a 5480 byte windows ...
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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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1answer
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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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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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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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1answer
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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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1answer
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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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1answer
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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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Learning wireshark RST frames [duplicate]

I recently got into Wireshark and I'm just trying to grasp the basics. I've watched a few videos and they say to look out for reset frames on your WiFi, so I saw a few. They are an exchange between my ...
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Data sent with the “three way handshake” ack , but it is not TCP fast open

Hello guys this is my first question here. For my customer i was analyzing this ( anonymized ) capture because a SSL Handshake issue but i noted at first that TCP three way handshake is not as ...
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Is the TCP Reno Fast Recovery algorithm really linear?

I'm reading through Computer Networking, 8th Edition by Kurose & Ross, and I came upon this figure(Figure 3.52 pictured below), which graphs the operation of TCP Tahoe & TCP Reno. The graph ...
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Does the destination port change during TCP three-way handshake?

I'm learning networking programming in C and there is a question bothers me a lot, does the destination port change during TCP three-way handshake? Let's say I have a cilent application running on ...
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Do these 2 packets belong to the same tcp socket?

Let's say we have two packets A and B. A: Has source-IP S1 , destination-IP D1 , source-port SP1 , destination-port DP1 B: Has source-IP S2 , destination-IP D1 , source-port SP2 , destination-port DP1 ...
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tcp how the receiver behaves if it received an incomplete window

Suppose, for example, that the window has a size of 5 MSS, the sender sends 5 segments to the network, the fifth is lost. Actually the question: how does the recipient behave? It just doesn't ...
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1answer
386 views

What is “TIME_WAIT” connection in a TCP connection and what is it's purpose?

I am requesting a webpage running on local server port 8080 and was expecting one connection to be established between the server (port 8080) and client (random port). But one additional port is also ...
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Would a bidirectional exchange of data between two hosts, one using TCP Reno and the other using TCP Tahoe, be possible?

I know Reno and Tahoe are TCP congestion control algorithms and one recovers much faster than the other when a packet is lost, but would they affect how data are exchanged between the hosts? ...
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TCP Congestion Window

Looking at example of congestion window graph pasted below and wanted to confirm my understanding. Looking at the red bar would that be the timeout happening here due to ACK being lost? and the b1 ...
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1answer
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How to connect to a machine which is sitting behind NAT router?

I have a server that needs to push a message to a client from which it received a request a few days ago. Now request which was received has the IP address of the NAT router behind which the client ...
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Can Cumulative ACK number be higher than Selective ACK left edge number

I had recently been reading about selective ACK in TCP and had a question: Can Cumulative ACK's number be higher than Selective ACK's left edge number ? A hypothetical example: Receiver advertised ACK ...
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70 views

Does the first TCP FIN packet (active close) goes with just only FIN bit set?

Suppose we have established TCP connection. The active close process assumes the FIN packet been sent to trigger TCP connection closing. But I can't figure out, is this first (active close) FIN packet ...
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1answer
62 views

Is there any other network protocol than tcp/udp that works with ports?

Do you know at least one protocol (any OSI layer) that, like tcp and udp, works with ports ? Thank you
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what is happening when a host receives a datagram with its MAC address as a destination but different destination IP

In a specific network say the host receives this datagram what is happening ?
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Why is delayed segment prevention (TIME_WAIT) in TCP only done for one side?

One of the reasons for TIME_WAIT is to prevent old packets/duplicates, coming in late, to screw up subsequent connections on the same (src ip, src port, dst ip, dst port) quadruplet. That makes sense, ...
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How does a device get a response from a HTTP request without an open port on the router?

I don't know much about how TCP/IP works, so please bear with me here. I was wondering how, when your computer makes an HTTP request from a random port(on that device) to port 80 on a server, it gets ...

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