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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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 ...
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Unable to preserve HTTP/2 headers list when extracting frame using editcap. Hex Dump Matches [closed]
When I used editcap to extract a HTTP/2 Frame from a Captured PCAP using tcpdump, the HTTP/2 headers don't show up in extracted frame, but the Hex dump matches.
I am using the below editcap command to ...
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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 ...
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Why is this RST during handshake
Hi,
We are suffering from very rare case, where the server send unexpected RST during 3 way handshake. There are two things i don't understand.
(1) 238 is a PUSH and ACK sequence, while 240 is a pure ...
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Banking/some of websites are not opening in ILL VSAT connectivity [closed]
We are doing lab testing in which ILL has been connected to VSAT. while doing application testing some of websites like icici bank ,bank of baroda, passport seva kendra is not opening. web pages pf ...
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Advice needed. Connecting to a web server on a private network; STUN/TURN, WebRTC or something else?
The problem:
The company I work for offers a hardware solution that is managed from a web interface that runs on a local network on a dedicated machine that we built.
Because of low-level constraints, ...
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92
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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?
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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 ...
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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 ...
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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 ...
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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 ...
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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.
...
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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 ...
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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 ...
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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.
...
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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 ...
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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 ...
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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 ...
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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 ...
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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?
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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 ...
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How does each OSI layer get to know the information [duplicate]
This might sound dumb but how do each layer get the information?
To give a context,
Lets say I enter www.google.com, the browser sends a request to the Application layer and then the HTTPs request is ...
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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 ...
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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,...
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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 ...
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Why would TCP ever allow a SYN for a connection in the TIME-WAIT state?
RFC 1122 says this:
When a connection is closed actively, it MUST linger in
TIME-WAIT state for a time 2xMSL (Maximum Segment Lifetime).
However, it MAY accept a new SYN from ...
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How is window retraction a "general" problem when segment length is less than the window scale factor?
In the RFC 7323 there is an example about window retraction:
https://datatracker.ietf.org/doc/html/rfc7323#appendix-F
The text also says this:
This is a general problem and can happen any time the ...
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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 ...
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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 ...
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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 ...
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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. ...
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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 ...
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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 ...
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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, ...
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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!
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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 ...
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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!
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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 ...
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Pushing Data in TCP and flow control
When TCP uses PUSH to send packets one after the other, is flow control required?
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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 ...
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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.
...
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Are there protocols which utilize TCP shutdown for writing (a.k.a half-close, SHUT_WR)? [closed]
In TCP socket programming, there is a feature that allows to shutdown socket only one way, where data cannot be read from the socket, but it can still be written to. I've seen it referred as "...
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Does packet sent to myself using LAN IP leave current device?
I was somehow unable to google this.
When i send TCP packet to my own LAN IP, for example, 192.168.50.50, does this packet goes to switch and back, or is this transfer entirely handled by OS? If it ...
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Is application protocol a subset of TCP?
My question is related to a concept that really confused me while reading an introduction to network related topics. What is the distinction between application protocol and TCP, exactly?
What I don't ...
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Differences between TCP congestion and TCP flow control
From my understanding, flow control essentially how much the receiver can process.
Suppose I can send packets at 100mb/s but the receiver can only process information at 10mb/s, flow control would ...
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Queuing and TCP Global Synchronization
About TCP global synchronization.
If we have several hosts having TCP connections with some other hosts (over the internet, for example) and our network is congested, if there was a burst of traffic, ...
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"Expected" packet loss under heavy network load in TCP cubic
context
We have two machines that receive a lot of data, and mirror each other's content with rsync. When monitoring these boxes via ICMP echo requests (using the mtr tool), we see up to a couple % of ...
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Why does TCP sender drop rate 50% on lost-packets?
Why is the standard TCP sender response to packet-loss (congestion), to drop 50% of the sending rate and then start working back up ?
If packet-loss was 20%, why not just drop 20% or maybe 25% to be ...
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TCP MSS - Dynamic Adjustment
I've seen most of TCP flows having DF bit set. So, can any additional overheads like VXLAN cause TCP packet to be dropped (since DF bit set)? How will the TCP MSS be adjusted dynamically (in absence ...
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Is the SYN packet the only packet that have the ACK flag not set?
Is the SYN packet the only packet that have the ACK flag not set, or are there other packets that have the ACK flag not set?
