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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IP over LoRa: TCP timeout [closed]
I am trying to tunnel IP packets via LoRa. For this I use two devices running Meshtastic.
Using ICMP I was able to determine that there is a packet loss of about 30% of the packets and a latency of ...
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How to calculate maximum achievable throughput [closed]
Hey I've been given an assignment, that is,
TCP Throughput Calculation: Given a TCP connection with a round-trip time (RTT)
of 50 ms, a receiver window size of 8 KB, and a maximum segment size (MSS) ...
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2
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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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How to know whether a protocol uses TCP or UDP
Well I know that might sound a stupid question and I believe that the most proper answer will be like I will be able to tell as my experience builds up and I learn more and more about the protocols.
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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 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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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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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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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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How can I configure a Cisco router 4300 to allow internal server ip:80 to be accessed on public ip:4500
I have an internal web server on port 80. I need help commands maybe to configure port forwarding to access the server on my private network from a public IP
Current running config
interface ...
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Redundant IP link aggregation for failover operation without route failure detection
I am looking for a technology to achieve TCP connection fault tolerance with the help of two links between hosts and without time delays for route failure detection. Something like this:
...
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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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Sequence numbers of segments in three way handshakes of TCP connection establishment or termination
I was trying to understand TCP connection establishment and termination steps from Forouzan's book.
In third step of three way handshake of connection establishment, it says following
The client ...
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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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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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Why does FTP passive mode use a range of ephemeral ports as opposed to a single well known port? [closed]
In FTP passive mode, I read that the server sends a random port number to the client where it can establish a data channel.
Then client establishes a data channel from its random port number to this ...
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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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What's the use of an acknowledgement number without the ACK flag set?
Isn't it redundant if the ACK flag in the header isn't also on?
Do you ever mix an acknowledgement with a normal message - send data and acknowledge a message in the same TCP segment?
I feel like ...
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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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Does physical distance affect download speed?
I just had an argument with a colleague of mine and thought I'd just reach out to the experts on this. Here's the scenario. We were using a website that measures your connection's speed. We tested ...
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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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Ping port number?
Yesterday interviewer asked me what is the port number for ping and which protocol ping uses: TCP or UDP.
After interview, I searched on the Internet and found different results: someone says ICMP ...
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Wifi TCP iperf throughput: 1 stream vs multiple streams?
In a WLAN iperf TCP throughput test, multiple parallel streams will give me higher throughput than 1 stream. I tried increasing the TCP window size, but I still cannot achieve the max throughput with ...
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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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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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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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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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Wireshark capture showing a TCP packet with no flags [closed]
In our network, I captured a TCP packet by Wireshark that has no flag set.
What is the meaning of such packet ? Here is the dissection in text format :
Frame 1: 54 bytes on wire (432 bits), 54 bytes ...
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Maximum packet size Ethernet Frame and IP packet
I am a little bit confused about one fact. According to the specification, the ethernet frame maximum size is 1518 bytes, and the IPv4 packet size Length field in an IPv4 header can be up to 65535 ...
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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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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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Why does a pure ACK increment the sequence number?
I cannot figure out why a pure ACK will increment the sequence number of the sending host by 1 when the TCP segment contains only a header, such as in the third segment in a three-way handshake for ...
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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 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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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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