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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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Can an L4 Load Balancer shift an existing SCTP/TCP Connection from One Backend Server to another without requiring client to make a new Connection?

I'm currently working on a network setup that uses an L4 load balancer to manage traffic for our services. The L4 load balancer effectively distributes new client connections to various backend ...
The Average Developer's user avatar
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11 views

ARP request is successful, but TCP SYN is not visible in output of Wireshark [closed]

I have a TCP server, its properties are the following: It runs within a virtual machine (VMware). The host OS is Windows 10. The guest OS is Debian 9. The TCP server listens on a port on the IP of ...
user94749's user avatar
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8 views

Linux netfilter: How can i capture and modify packets going to a specific ip? [closed]

I am trying to write a linux service that captures the packets that go to a specific destination and performs necessary changes to them. More specifically, i want to find all of the tcp segments that ...
abe_carmgl's user avatar
1 vote
1 answer
48 views

Acknowledgment numbers in Wireshark do not match sequence numbers

Recently, I conducted an experiment involving uploading a file to a server. I noticed that the acknowledgment numbers I received did not align with the sequence numbers. Please refer to the attached ...
nsrdn's user avatar
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1 vote
1 answer
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What happens if the first segment after a 3-way handshake in a TCP connection is dropped

If I have a scenario with two hosts. Host A and Host B. Let's say that Host A initiates a TCP connection to host B. Let's say a connection has been established after a 3-way handshake. What happens if ...
CanadianBeaver's user avatar
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14 views

Clarification of relation between IPv6 and TCP [duplicate]

I thought IPv6 and TCP could be used independently, but IP does not need TCP at all, whereas TCP usually needs IP to function. Is my understanding correct? Does IPv6 need TCP to function? Looking at ...
Niklas Rosencrantz's user avatar
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1 answer
80 views

In wireshark, why following a TCP or UDP stream does not remove ICMP packets?

In Wireshark, when I follow a TCP or UDP stream using right click -> Follow -> UDP Stream, if there are some ICMP packets from same endpoints, wireshark will keep them in the stream. Why? Since ...
Sourav Kannantha B's user avatar
4 votes
4 answers
1k views

TCP/IP and data cut

I would like to clarify my understand about TCP/IP model and packet cutting. I think it's done by layer 3 (Transport, eg. TCP) but I'm note sure about layer 2 (Network, eg. IP) or even layer 1 (...
PanCho's user avatar
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2 answers
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How to connect TCP server behind NAT

I need to establish TCP connection with a server located behind the NAT. The simple solution is to reverse the connection and ask the server to connect to the client, but then I am unable to use ...
Grzegorz Ka's user avatar
1 vote
2 answers
109 views

How to calculate sampleRTT?

I'm working on a TCP implementation with UDP socket in C, and I'm trying to make the timeout variable with this algorithm estimatedRTT = (1-a)*EstimatedRTT + alpha*SampleRTT devRTT = (1-beta)*devRTT + ...
Matteo's user avatar
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End to end delay over N link including the (simplified) propagation delay

It is well know (see this question) and easily verifiable that end-to-end delay in case of trasmission of P packets of size L over N equal links (same transmission rate R) with zero propagation delay ...
frhack's user avatar
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TCP Multiple Segment Acknolegdement

Let's take example where in the example i will use the Independent acknowledgment. Host A has send segment 1,2,3 to the host B, after host b receive each segment it will send a Acknolegdement for each ...
Apabila X Terkadang's user avatar
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1 answer
87 views

TCP Duplicate Acknowledgement

Host A and Host B has establish the connection, Host A will send a segment 1,2,3,4,5,6 but segment number 2 and 5 is lost. Then the receiver will sending an duplicate ACK to sender, so whenever sender ...
Apabila X Terkadang's user avatar
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1 answer
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Reset Connection With RST Flag TCP

When a connection has been established between Host A and Host b, Then there is data exchange between host A and host b,Let's say host A already has 3 segments, segments 1 and 2 have been sent and ...
Apabila X Terkadang's user avatar
1 vote
1 answer
34 views

TCP Header Data Field

In TCP header there was a field called a data field which stores data, but does this field store the IPv4 header + datagram or just the datagram?
Darevil294's user avatar
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1 answer
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What happens when the sender sends more data then the advertised window by the receiver?

I am relatively new to networking. I am doubting what happens when the sender sends more data than the advertised window by the receiver. I mean that the receiver advertises the window size based of ...
Ayush Gupta's user avatar
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TCP blocked until the acknowledgment received

I am currently facing an issue in my application where the TCP messages seem to be blocked until an acknowledgment received. Specifically, the subsequent messages wait for the acknowledgment of the ...
myprogramistoobusywitherrors's user avatar
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1 answer
111 views

Why is this RST during handshake [closed]

This finally turns out to be a Linux kernel bug which is not fixed yet by 2023/12/18. (See https://lore.kernel.org/lkml/[email protected]) ---------------------------...
Milimili's user avatar
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1 answer
420 views

Wireshark filter for specific SYN packet which never received a SYN/ACK

Is there a way in wireshark to find out a single SYN that does not get answered by SYN/ACK?
fsociety's user avatar
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2 votes
2 answers
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Can TCP seq number increment after sending a FIN?

I have an embedded device connecting to a server (on AWS Application ELB if that matters). Both the server and the client are instructed to close the connection after one request. I noticed that the ...
xxljob's user avatar
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Why MTU setting change not showing any meaning change in file transfer via tcp?

I performed a test in which I transferred a file of 1GB by opening a tcp port on destination server with MTU 1000. then I tried to change the MTU from 1000 to 9000 and the total time duration of 1GB ...
Vipin Kumar's user avatar
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1 answer
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Are TCP connections within a host aware of one another? [closed]

I was wondering how a typical TCP/IP stack of a Windows or a Linux machine works in terms of congestion control. So, are active TCP connections within the OS aware of one another? I mean, the actual ...
Elias Bats's user avatar
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1 answer
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How does cumulative acknowledgement mechanism allows for straight-forward duplicate detection in case of retransmission?

I'm reading the RFC 793. https://www.ietf.org/rfc/rfc793.txt The acknowledgment mechanism employed is cumulative so that an acknowledgment of sequence number X indicates that all octets up to but ...
zeeshanseikh's user avatar
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How to determine which TCP payloads should be combined to form a complete PDU?

I understand that the TCP itself provides a byte stream connection, but has no idea nor does it care what its payload is and how it is segmented to fit into individual packets that travel on the wire. ...
miran80's user avatar
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What is the maximum size of an application-layer message for UDP?

TCP is capable of segmentation, i.e. even if the application layer creates an arbitrarily large message, the transport layer under TCP will split it into segments. Now, as per this answer, UDP doesn't ...
Kushagr Jaiswal's user avatar
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2 answers
80 views

How does leaving a TCP connection half-open makes SYN and SYN+ACK stealth and absent from the logs?

I was studying about TCP SYN (stealth) scan which involves carrying out port scan while avoiding detection. I also read that it is similar to TCP connect scan except that the last ACK packet is ...
user12137152's user avatar
13 votes
1 answer
3k views

Why in TCP the first data packet is sent with "sequence number = initial sequence number + 1" instead of "sequence number = initial sequence number"?

In the 3-way handshake, the initial sequence number of both endpoints of the TCP connection is synchronized. Here is an example: Endpoint A randomly generates an initial sequence number: 123. ...
ilBarra's user avatar
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1 answer
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What does "Configure kernels to not follow the RFC 5681 SHOULD" mean?

Netflix documentary The Playlist about Spotify, they present one of the technical breakthroughs that they created their own TCP implementation to reduce the latency from first click to playing the ...
zirkelc's user avatar
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1 vote
2 answers
146 views

BGP and Multi-Hop Adjacencies Using TCP

I am studying the basics of BGP and my book states the following: "BGP sessions use TCP port 179. TCP allows for adjacencies that are multiple hops away" I understand that this allows ...
Mitrixsen's user avatar
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Does TCP CUBIC reduce window size for an idle connection?

Does the TCP CUBIC congestion control algorithm reduce window size for a connection that has been idle for a time but has not yet timed out? For example, if an application starts sending data and ...
Cube Goldberg's user avatar
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1 answer
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What is the RFC 791 64 octet header?

I'm trying to understand the PDU sizes as it traverse the TCP/IP model. RFC 791 says the IP protocol is required to accept datagrams of 576 octets. ( 512 octets, plus up to 64 header octets). I know ...
Buster Poindexter's user avatar
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2 answers
113 views

Why does I2P use UDP? [closed]

UDP is unreliable, why does I2P (garlic routing, an alternative to Tor) use UDP instead of reliable alternative: TCP? Won't I2P become unreliable due to UDP?
Flan1335's user avatar
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2 votes
2 answers
1k views

How is TCP Segmentation/Reassembly Identified?

There might be something simple that I'm missing, but I just can't understand how related TCP segments are identified. So let's say I want to send 2000 bytes using TCP with an MSS of 1500 bytes. I ...
Etchy's user avatar
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-1 votes
2 answers
276 views

TCP / IP Payload 65535 is mtu restricting to 1500?

If the TCP Payload and IP Payload can be up to 65515 Bytes (-40 for ip and tcp hdr), is the MTU size of 1500(Ethernet) restricting what can be sent on the wire(i.e. is it because of Ethernet limit of ...
JoelP's user avatar
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0 votes
2 answers
79 views

Question about TCP data segments

I have been reading the book "High Performance Browser Networking" by Ilya Grigorik about the slow-start algorithm, which is used for congestion avoidance. While I do understand its concepts,...
John Pham's user avatar
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1 answer
140 views

How does a client end the TCP connection when SYN+ACK is not received after multiple retransmissions? [closed]

I am trying to establish a TCP connection with a server. I added a firewall rule in the server to drop the TCP packets in order to check how the TCP client terminates. Client retransmits SYN multiple ...
Vijaykumar Ainapur's user avatar
0 votes
1 answer
217 views

What is the unit and the behaviour of the congestion window?

I've learned that the congestion window is the maximum amount of packets that can be sent in one transmission round. Now TCP seems to acknowledge the packets in bytes, so wouldn't it make more sense ...
Felix's user avatar
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0 votes
2 answers
74 views

Why is congestion collapse from undelivered packets not possible when there's 1 congested link?

rfc 2914 says this: The avoidance of congestion collapse from undelivered packets requires that flows avoid a scenario of a high sending rate, multiple congested links, and a persistent high packet ...
user86942's user avatar
0 votes
2 answers
104 views

Why does the TCP rfc say that there shouldnt be an ACK for the left window edge sequence number?

From rfc 9293: A TCP implementation MAY send an ACK segment acknowledging RCV.NXT when a valid segment arrives that is in the window but not at the left window edge (MAY-13). But isn't RCV.NXT the ...
user86942's user avatar
0 votes
2 answers
851 views

Why are TCP keep-alive messages sent with an already ACKd sequence number?

This is what the TCP rfc says about keep-alive messages: Implementers MAY include "keep-alives" in their TCP implementations (MAY-5), although this practice is not universally accepted. ...
user86942's user avatar
0 votes
0 answers
12 views

How does the client verify its own SYN? [duplicate]

The TCP rfc 9293 says this: A 3WHS is necessary because sequence numbers are not tied to a global clock in the network, and TCP implementations may have different mechanisms for picking the ISNs. The ...
user86942's user avatar
0 votes
2 answers
124 views

Customized IPv6 packet with multiple inner data fragments for multiple destinations

I am studying the possibilities of using IPv6 potentialities to design a customized IPv6 data packet that has the following features: 1. Combines many fragments of different data in one packet. For ...
Lee's user avatar
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0 votes
1 answer
107 views

Is TCP used for data transfer after building the routing tables (using OSPF protocol)

I am trying to understand how Data (video, image, ...) is sent over the network, and what are the protocols and different processes involved. We know that OSPF (L3 protocol) does not use TCP or UDP, ...
Lee's user avatar
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0 votes
1 answer
38 views

Can anyone explain what the numbers at the top of this IP Header diagram represent?

… and what is the significance of the grouping? many thanks!
TimPowders's user avatar
1 vote
1 answer
71 views

TCP and Data field

Need clarification on TCP/UDP DATA field.. Does the Application Layer "Data" go inside the TCP [DATA FIELD] and all of TCP Layer with its Headers sit inside the IP [DATA FIELD], finally the ...
JoelP's user avatar
  • 29
1 vote
1 answer
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Running 2 or more applications PPP

I had a doubt regarding point-to-point protocol. Is it possible for a single PPP link to enable running of 2 or more simultaneous applications between two hosts? Thanks!
ikben's user avatar
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0 votes
1 answer
162 views

Where are the characters in Wireshark's Packet Bytes pane?

I've just updated my Wireshark to version 4.0.1, and now, while investigating a TCP communication, I don't see any textual information anymore in the Packet Bytes pane, as you can see from this ...
Dominique's user avatar
  • 131
0 votes
1 answer
79 views

Pushing Data in TCP and flow control

When TCP uses PUSH to send packets one after the other, is flow control required?
Majid Mohammadpanah's user avatar
0 votes
1 answer
61 views

How does an app initiate the process of packet construction? [closed]

Considering the example of an application or process that needs to send a particular request to a given server. How does the application initiate the process of creating the packet containing the ...
Mehdi Charife's user avatar
1 vote
1 answer
376 views

What stategy use TCP Cubic in Fast Recovery?

I want to do some simulations with different TCP algorithms I was reading one of the earliest papers for TCP CUBIC and I don't see explicitly the strategy of Fast Recovery after a loss of the packet. ...
Giannis Aggelis's user avatar

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