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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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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Failure from PLC/HMI to AWS [closed]

i can ping the device and wireshark is showing me a RST line. can anyone help me interpret the data?
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How does websockets works? [closed]

In normal TCP/IP protocol when a client has to send data to the server, it uses the public IP of the server. But as WebSockets is a bidirectional protocol how does the server know where to send data ...
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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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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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2answers
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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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1answer
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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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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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2answers
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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
26 views

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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2answers
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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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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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3answers
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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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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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1answer
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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
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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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2answers
104 views

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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1answer
129 views

How to use the TCP traceroute in Juniper?

How to use the TCP traceroute in Juniper? In Juniper OS I only know traceroute ip_address I don't know how to traceroute a destination with TCP protocol. is it possible to implement it?
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How to find the client's application port during communication [closed]

After reading firewall rules about inbound and outbount I have some questions and the most sources focus on the server's ports. What happens to the client side when is trying to make a connection to ...
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1answer
109 views

IPv4 and UDP/TCP packets inside of ICMP packet?

A week ago, after opening wireshark, i was surprised by seing a storm of ICMP packets from different IP addresses. While deep analysing of thoses packets, i noticed that those ICMP packets contains ...
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1answer
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RFC 6298 application

I got this? How many Fragments that are going to be sent are: 10800 / 1200 = 9 segments to Host B. And the full time is: (9*1200) / 1600000 = 6.75 ms According to RFC 6298 [1]: (2.2) When the first ...
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how data are fragmented based on MTU and MSS?

just to be clear.. if a sender wants to send a data of 1800bytes ( assuming MTU be 1500bytes so MSS = 1500-40 (taking min ip and tcp header) = 1460bytes) Then there will be three segments 750 + 750 + ...
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Does UDP do anything at all?

It's my understanding that TCP has logic for ensuring reliable communication, but UDP just naively sends information along the channel set up for it using IP and things in lower layers. Does UDP ...
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1answer
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What flow control mechanism does ethernet uses?

Datalink layer is basically responsible for 3 major functions - Error detection/correction - CRC is used by ethernet Collision detection - CSMA/CD is used by ethernet But I couldn't find what flow ...
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48 views

What if receiver changes its IP address during the transmission process?

Suppose I am sending data to a laptop with IP address say x but before data could reach its destination the laptop is moved to another network and now its IP address becomes Y. Will the receiver still ...
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Congestion control in transport and network layers in TCP/IP

Why do we need congestion control in BOTH the transport layer and network layer in TCP/IP model. Cant we be good enough with control in just one of the layers only? And how do they differ?
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Suspect MTR showing incorrect packet loss through router; other tools are not showing loss

Using MTR (sending TCP with or without SYN), I'm consistently seeing packet loss on one intermediate router in the path. UDP does the same. I'm use TCP to avoid the ICMP packet flood limits set. I ...
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1answer
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Propogation delay vs time required to send out a complete frame on channel

I was reading Data Communications and Networking by Behrouz A. Forouzan in which for simple Aloha protocol the vulnerable time given was T(fr) (time required to send out a complete frame on the ...

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