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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How many times is the data packet copied before finally reaching the NIC? [closed]

On a typical linux machine, how many times would packets be copied from the application layer to all the way in its journey to the network card. I am assuming the protocol being used here is TCP/IP ...
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What steps must be accomplished in each layer of the TCP/IP model to connect a website?

What steps must be accomplished in each layer of the TCP/IP model to connect a website?
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Determining the sequence numbers of sent packets in TCP [closed]

I'm trying to learn TCP well from a textbook, and this is a problem that I am having trouble solving. A sender using TCP Reno (with fast retransmit and fast recovery) is going to transmit 15 packets ...
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Why and how slow clients slow Websockets (RFC 5455) network? [closed]

I want to ask why a Websocket connection RFC 6455 - https://www.rfc-editor.org/rfc/rfc6455 Usually websocket connection is fast when clients are fast enough however, when slow clients connects to it ...
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Juniper SRX Application Inactivity Timeout

Will the inactivity timeout set for the application "TCP-ALL" of 900 trump the default value of 1800 for junos-ssh if the application-set were matched in a security policy? Does it matter if the order ...
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4 answers
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Layering unicast addressing over multicasts

My question has to do with layering of unicast over multicast and has two parts. Part 1. IP unicast over MAC multicast First part of the question is whether there is a standard that prohibits use of ...
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-1 votes
1 answer
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Real time video streaming over TCP [closed]

One of the topics I have been following for quite sometime is real-time streaming. Over the course of my research everyone suggested and says WebRTC (based on UDP) is the only solution to achieve real-...
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When port-forwarding, will a port only be listed as OPEN if the service host is actually reachable?

I'm fiddling around in my lab today and attempting to learn more about port-forwarding. I've noticed that when I set up port-forwarding for a given port and run a port scan from outside the network, ...
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TCP Bandwidth and delay guarantees

I was wondering if TCP can provide bandwidth and delay guarantees? Or does it have to implemented on the application layer?
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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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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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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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5 votes
1 answer
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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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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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1 answer
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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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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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2 answers
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Why can some people use public ip address to access a server from an internal network with the client device within the internal network [duplicate]

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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1 answer
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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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2 votes
2 answers
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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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3 votes
1 answer
100 views

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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1 vote
0 answers
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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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2 answers
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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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1 answer
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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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1 vote
1 answer
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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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1 vote
1 answer
250 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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3 answers
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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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0 answers
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TCP Payload vs Cellular Data Usage [closed]

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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27 votes
8 answers
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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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1 vote
2 answers
117 views

How TCP connections between origin and node servers over a BGP Anycast gets established?

Server A and B have the same IP address with anycast. Server B connects to the origin server that is very close to server A and very far away from server B, since server A is closer, the response will ...
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1 vote
1 answer
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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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5 votes
2 answers
618 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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1 answer
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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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1 vote
1 answer
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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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1 vote
1 answer
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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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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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1 vote
2 answers
380 views

Which port determines the protocol?

If we have a common protocol port on both ends.. say source point is 443 and destination port is 80 (hypothetical situation, I know this combination of ports probably makes no sense).. how do we ...
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3 votes
2 answers
394 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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1 vote
1 answer
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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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1 vote
2 answers
1k 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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1 answer
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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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2 answers
362 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 starts ...
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1 answer
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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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1 vote
1 answer
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Understanding TCP's slow start exponential increase congestion control policy

I was learning TCP slow-start exponential increase congestion control mechanism from Forouzan's book. It says following: The size of congestion window (cwnd) starts with one maximum segment size (...
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Question on windowing and determing connection speed

Hi i'm just learning computer networks and i have learned about windowing in tcp And my question is does we determine connection speed using windowing? I mean computer know the number of packets and ...
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