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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Understanding TCP congestion control

Why is the congestion avoidance here [6,14] and [18,25]. Why not [6-10] and [18-22]? Other examples I have seen online suggest otherwise: For example here: https://www.researchgate.net/figure/TCP-...
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24 views

Is there a difference between SYN-ACK and SEQ-ACK?

I've been trying to understand if there's a difference between the two, if any. Wireshark mentions SEQ-ACK under their TCP information of a packet, but I've typically heard this referred to as SYN-ACK....
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TCP Naive Question regarding client and server sending request and replies [closed]

I am debugging and application between server and client that talks through TCP, without having a great knowledge on the subject. The servers seems to reset quite often the connection and I don't ...
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15 views

Multiple TCP dup ACK with spurious retransmission [closed]

I have a cellular IoT-device connected to a MQTT broker with a keep alive of 15 sec. It happens once a day that the device gets disconnected from the server (server log shows: client stopped due to ...
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Why there is a statement of FIN packet is easy to discard in the networking?

In Nmap port scan there is a Covert scanning which use FIN for scanning, but it is not accurate, because the FIN packet easy be discard in transmission. Why there is a statement of FIN packet is ...
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Best ports to use for proprietary protocols that might get inspected/blocked by firewalls

We use software from Genesys that uses its own proprietary protocols (all TCP) and we often run into issues with customers firewalls. The ports we are using are 2000, 2200 and 3010 - I'm not sure ...
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TCP connection closes instantly (without timeout) when I change my IP address through the windows network and sharing center [closed]

I have tcp connection to some tcp server on internet. Tcp client is a simple application that I have created which works on my computer. The problem is that when I change my ip address through the ...
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Finding file transfer overhead [closed]

If this is not the right thread for this question, please bear with me and suggest the better one. So basically I'm trying to setup an experiment to estimate a data transfer overhead through an ...
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TCP throughtput [closed]

Suppose I am asked to send data segments 1-12. The 4th Data segment gets lost. How the throughput is calculated consider Round Trip Time is 10ms and Maximum Segment Size=512B
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TCP data reconstruction with Python? [closed]

Maybe that question has already been asked but I'm not finding any related topic. I'd like to sniff network packets on-the-go for a specific need. Much like Wireshark does with its "Packet reassembly"...
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Whether every TCP segment of Data Transmission Stage have ACK flag and ack number?

In classic TCP lifecycle, there shows every TCP segment have a flag(SYN, ACK and so on). In 3-times handshake and 4-times wave-leave, there must be flag in every TCP segment, I can understand. But ...
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Which of TCP flags will use a timer, and what Timer will use?

When I study the TCP protocol life cycle, There are 3 stages: Establish Connection Data Transmission Connection Removal TCP have 6 Flag types: SYN, ACK, PSH, FIN, RST, URG. TCP has 4 Timer: ...
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How do ACK packets get matched to SYN numbers? [duplicate]

I'm a newbie at networking, learning TCP for fun. I've been looking at packets on Wireshark, and I was wondering: How do the two sides know that an ACK packet was in response to a specific SYN packet?...
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335 views

Is TCP slow start supposed to be enabled for VoIP SIP?

TCP slow start mechanism generally is pretty useful in most cases. But it is not so good and reasonable for short-lived TCP connections. Hence the question: Should TCP slow start be used with SIP-over-...
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69 views

Confusion about TCP/IP data flow in layers

I'm confused about how the data flows through the layers of the TCP/IP model, so I'll just tell what I think it happens (using an email example) and I'd appreciate if you can point my mistakes. ...
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What type of address is this?

As the title says I'm curious as to the type of address this is as its clearly not IPv4 or v6, yet it is using TCP.
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61 views

TCP Checksum Calculation

I recently started with networking and tcp/ip. The RFC 793 document tells the checksum is made of: pseudo header+tcp header+tcp payload+zeroes(if not divisible by 16). So I have to take 16bit ...
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What if ACK FLAG is not set? [duplicate]

I read the RFC 793 section 3.1 , which says Acknowledgment Number: 32 bits If the ACK control bit is set this field contains the value of the next sequence number the sender of the ...
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What is the value of the Acknowledgement Field in TCP header when ACK flag is not set? [duplicate]

I am interested in knowing that what would be the value in the acknowledgement field of a TCP segment in case the ACK flag is not set? I read the RFC 793 section 3.1 , which says Acknowledgment ...
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2answers
52 views

Why can some people use public ip address to access a server from an internal network with the client device within the internal network

As the title suggests. I find it mind breaking to think how network architecture can differ to allow/not allow using public IP address to access a server within internal network from within the ...
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1answer
57 views

Which exact bytes are transmitted while TCP zero window probing?

I read the post about TCP zero window probe and it seems that such a probing segments transmit some payload. But I can't figure out which exactly bytes are sent in probing segments? Is it one (or more)...
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How does loopback address check if TCP/IP stack is correctly working or not? [duplicate]

I have been reading about loopback addresses and most of the online material says that it is used for testing purposes and it validates if TCP/IP stack is installed and working correctly. How does ...
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2answers
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Best way to Fast Reconnect TCP with dynamic IP

I am aware of TCP Fast Open, all though, I'm pretty sure it doesn't apply when the IP of the server changes dynamically. Getting the IP of the server quickly isn't the problem. The problem is that I ...
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Packets lost with correct TCP sequence number. Is it possible?

I'm analysing some communication issues that we have between a server (SCADA) and remote terminal units (RTU) that we have in the field. The communications are IEC104 protocol which use TCP/IP. 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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Why do corporate networks prefer application-level over network-level proxies? [closed]

I was recently using an application at work, which was unable to download needed files because proxy settings were not configured for the application. The company firewall blocks non-proxy connections....
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Can TCP stand for “Transport Control Protocol”

I know it might sound like a silly question, but afaik TCP stands for transmission control protocol. However I found a couple of websites using the term Transport Control Protocol. So I was wondering ...
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30 views

Unable to receive logs from a device to our SIEM Syslog server via TCP 514 [closed]

I want to collect logs from a security device (McAfee Email Gateway) to our SIEM Syslog server. This security device can forward logs only via TCP syslog on any port (in our case it is 514). We are ...
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1answer
36 views

How does triple handshake avoid establishing connection for duplicate packets(coming later down the line)

The idea behind triple handshake seems to be for duplicates to not cause issues. The way I understand it host sends a sequence x to server. Server acknowledges it and sends it's own sequence y. Host ...
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50 views

Do sequence and acknowledgment numbers treat 3-Way Handshake differently?

1- Just as the message ID that is assigned to each message in PAR, the "sequence number" is a means of providing reliability in a transfer of a byte stream. So sequence numbers are assigned to every ...
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latency in the network layer and transport layer [duplicate]

We have several way to measure latency (ping command (ICMP packets), hping(TCP SYN), iperf..).What is the difference between measuring the latency in the network layer and measuring in the transport ...
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3answers
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Analyzing TCP connection by running Wireshark in two endpoint

I am trying to find the number of lost packets in the network. I have 2 devices say DeviceA and DeviceB. IP addresses are respectively DeviceA : 192.168.0.104 and DeviceB: 192.168.0.105. In order ...
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What will be the behaviour of TCP in a case when application layer is changed to send small packets

Assume I have an application layer protocol that segments the packet itself. So if it has 100 MBytes of data, then it will divide the data into 10000 segments and send each segment individually to TCP....
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TCP Payload vs Cellular Data Usage

I have a device that connects to the AWS via a LTE CAT1 modem. In the effort to reduce cellular data consumption, I put some monitoring code to keep track the amount of data usage at the TCP layer. ...
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Why does DHCP use UDP and not TCP?

DHCP uses UDP as its transport protocol. DHCP messages that a client sends to a server are sent to well-known port 67 (UDP—Bootstrap Protocol and DHCP). DHCP Messages  that a server sends to a client ...
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Transport layer segmentation and Ip layer fragmentation [duplicate]

From the OSI Model's point of view: If we already have Ip fragmentation which happen due to the network limitation, why the transport layer provides the segmentation mechanism via TCP protocol? why ...
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TCP flow control active waiting

To perform flow control between a sender and a receiver during a TCP connection, the receiver includes in each packet to the sender, the size of available space ‘rwnd’ in its receiving buffer. This is ...
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450 views

Is a datagram from an upper network layer converted 1:1 to one of the lower layer?

I know datagrams from upper layers are converted to those of lower layers by adding metadata, but I cannot seem to find this information anywhere. Which one of the below is correct? A single TCP ...
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Why TCP is not in layer 5? [duplicate]

I read that TCP is in layer 4. But i also read that to send data with TCP i have to establish a session (in the handshaking phase). Does this mean that if we work only up to layer 4 TCP is useless (...
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1answer
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TCP implementation [closed]

Can one speed up TCP transmission of packets if the no.of bits in sequence field and no. Of bits in acknowledgement field are reduced ? If yes , then how much time is saved? Mathematical equations for ...
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43 views

Is it possible for two TCP connections to have the same SEQ/ACK number?

Say we have many TCP connections established between various ports. Is it possible for two of these connections on different ports (eg. 50000 -> 80, 40000 -> 80) to have identical SEQ or ACK numbers?
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TCP handshake immediately RST [closed]

I'm trying to set up a modbus TCP connection on port 502 but get a RST packet immediatly. So the TCP connection handshake doesn't even succeed. This is done on a windows machine on an ESX server. The ...
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1answer
27 views

Does network layer provide connection oriented service

I know that in TCP/IP model the data link layer provides connection less service. While reading IPv6 Header. 'The flow label is used for connection oriented servie'. How does TCP/IP model provide ...
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What is the time of the first RTO in the TCP protocol without knowing the RTT?

I know that 3 way handshake is used. But, the first time a connection is established and there is no RTT data, what is the expected time before sending another packet? How does the client know how ...
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2answers
321 views

Why are session states synchronized with high availability?

Like my title says, why are session states synchronized between peers in most HA protocols? I assume TCP states like Esablished, Invalid, New and Related are synchronized, but I don't get why you want ...
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1answer
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Packet analyze on router does not match client and server

thank you for your time. My (virtual) network has 3 objects : a client, a server and a router between them. I'm sniffing the traffic on the 3 machine with the command tcpdump -i any -s 0 -w [path] ...
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2answers
146 views

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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1answer
55 views

Is TCP aware of MAC adress

lets say I would like to make connection between client and server on port 80. Is 3 way handshake aware of server MAC address? I mean: client send SYN data packet to specific IP:port and MAC. In ...
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1answer
43 views

How retransmission timer is set/reset in TCP after receiving ACK?

I come across following, while reading TCP from Forouzan's book: We can define the following rules for the retransmission timer: When TCP sends the segment in front of the sending queue, it ...
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1answer
92 views

What layers of the TCP/IP model does an SDN involve?

New to Software-Defined Networks. I know that an SDN involves an Application plane, a control plane and infrastructure plane. By definition, I know that the application plane is in the Application ...

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