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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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HTTP Request Connection | Thread Safety [on hold]

I recently came to know about how a connection is first established between a server and client(browser) when a HTTP request is sent. Before sending actual data submitted by a form submit button, a ...
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Handling bad network connection client in socket io [on hold]

Currently I'm working on a MMO game which players can join and exit game whenever they want. I have a connection manager server (CMS) written in golang using socket io library. World connects to CMS ...
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ACL and ACEs Query

So i'm configuring a basic network and I need to create a couple of Extended ACLs. Now my question is, does this ACE permit any TCP connection to the following subnet? permit tcp 192.168.10.0 0.0.0....
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What will happen if an IPv4 packet’s total length field exceeds the packet’s actual length? [closed]

If a router or a host receives a packet, the value of "total length" field is larger than the packet's actual length, what will the router (or the host) do? Below is a sample, I edited a packet, then ...
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How are connections in TCP recorded for sending messages one after another?

In transport layer, TCP is connection oriented and UDP are connectionless. What is "connection" as in TCP then? In network layer, is it correct that there should be no distinction between TCP and ...
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How can TCP be used in order to implement DHCP and under which circumstances is this preferable?

I am pretty new to the computer networking studies and was learning about the DHCP protocol. It is implemented based on UDP, as I've gathered, but is there a way for it to be implemented over TCP? ...
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28 views

Analyzing packets using wireshark display filter [closed]

!udp && !arp && !tcp && !icmpv6 && !stp && !pim && !ospf what does this display filter do other than filtering out all packets which have any of the ...
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49 views

Why do TCP/IP stacks send individual ACK packets?

I've been reading more about TCP and found out that since multiple flags can be set at once, basically every packet after the initial SYN has the ACK flag set, and serves as an acknowledgment of all ...
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What is the Acknowledgement number in connection synchronisation between client and server?

I came across this article in an attempt to understand sequence and acknowledgment numbers better. Here is the excerpt: Connection set-up uses the SYN flags. They are not used except for ...
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Role of TCP window header field [duplicate]

What is the role of that field in the header of a TCP segment? From what i understand,after the end hosts tell each other how much data they can send until the "buffer" fills up (what is the buffer?),...
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1answer
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How do TCP connections work?

The TCP establishes a connection between the source and the destination. My questions are: What do we mean by end-to-end communication? What is the role of that connection?Couldn't reliability be ...
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Data Transmission Rate Video Stream

Given a web-server with an sd-card (storing 720p (7.2 Mbit/s) videos and 800 Mbit/s read-speed) and a wireless interface with 1200 Mbit/s transmission speed. I have to know how many clients can ...
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How do TCP/IP packets manifest in the RJ45 electric pinout?

Sorry if this is a stupid question. Given you could observe signals going through RJ45 pins, would you see single TCP packets or their fragments?
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How does the transport layer tell UDP apart from TCP?

So I'm reading Computer Networking: A top down approach (where these images are from) and I was looking at the Transport layer. A generic segment in the transport layer has a pretty simple structure: ...
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1answer
36 views

How MPTCP closed connection?

how MPTCP connection with more than one subflow closed? what would happen to MPTCP connection if a client decide to close one of the subflows? it would be very kind of you if you explain it step by ...
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Understanding acknowledgement mechanism in sliding window protocol

I came across following problem: Node A sends packets to B through router R. The link A-R is instantaneous , but the R->B link transmits only 1 packet each second , one at a time . Assume A sends ...
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1answer
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How are websites accessed without port numbers?

I am confused on how requests to websites are received. If I type in 172.217.5.110 to my browser, google.com sends me its home page. I didn't have to specify the port number. How does that work? I ...
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1answer
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Can a ACK or SEQ Number exceed a range and crash the NIC?

I was watching the TCP Stream out of pure curiosity of my FTP Server and saw that the ACK and SEQ number increases by one with each sequence being transmitted successfully. I am not sure, but ...
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acknowledgment by TCP does not guarantee that the data has been delivered

In RFC 793 there is a part about the acknowledgment of TCP segments: When the TCP transmits a segment containing data, it puts a copy on a retransmission queue and starts a timer; when the ...
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103 views

TCP errors explain

Could anyone explain these errors: TCP ACKed unseen segment TCP Dup ACK TCP Previous segment not captured TCP Out-Of-Order TCP Retransmission
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217 views

tcp connection and stream flow question

Could anyone explain the main principe of tcp flow when making a session ? I have take a tcp dump when i'm trying to browse a site. when I analyse the packet by wireshark, i have found many Three way ...
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1answer
29 views

Is it possible to make a TCP connection connect back to the destination port? [closed]

I'm new in this forum, I thought I could ask a question here. I've set up a proxy by using nginx and Openresty, which supports LUA scripts, that changes the body of a HTTP SOAP POST request. The ...
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1answer
85 views

Is there any video streaming online service that actually uses UDP?

We usually hear that UDP is used with data with which a few packets loss/out-of-order can be tolerated like video streaming. And the instructor typically goes on saying "so if you lose a few ...
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AWS tunnel TCP retransmissions and DUP ACKs

I have a IPsec tunnel from my firewall towards AWS, the tunnel is up in both phases. If I run traffic sniffer in the firewall, I can see interesting traffic going through, but there are MANY TCP ...
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2answers
64 views

Gather the BGP data by using TCP connection on port 179

In order to gather the information shared between BGP peers, what port number should be used to connect using TCP (I am using 179, and don't see the connection being established)? Will I be able to ...
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1answer
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When TCP SACK is already enabled, it is lost again

Because the No. 4245 packet loss, a new segment block is generated, but why the original 3040050-3048810 segment block will disappear. Can anyone help me to explain this situation?
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Why is retransmission delayed when the RTO is long?

I am new to networking and learning about TCP Timer Management and read this in my textbook: "If the value of time-out (RTO) is too small then unnecessary re-transmission will take place. If time-out ...
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1answer
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How common are low MTU links (<1492) in the public internet?

Are there any kind of statistics how common are low MTU links (MTU is below 1492) in the common Internet?
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1answer
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Initial TCP congestion window sizes

I have tried to look for this information on Google, but I haven't been able to find a good source for this information. So, I am interested in what are the initial TCP congestion windows on ...
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2answers
188 views

Calculating the throughput of a given TCP connection

Given a TCP session, is there a way to determine the throughput of the sender? I have a wireshark sniff, and I see that to calculate the throughput of the sender I can use the TCP-Window-Size-in-bits /...
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2answers
283 views

How does the Transport Layer construct the Pseudo-Header for TCP checksum?

THE TCP Psuedo Header needs sender and destination IP Address and protocol type. All of this informations is present in the network layer/IP header. Since the transport layer cannot access the data ...
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2answers
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How could a response be sent to the requestor without requestor's address?

I'm reading this talking about the differences between two fire-and-forget message (for example, under UDP) and a request-response communication (for example, under TCP). I came across this: The ...
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Processing received SACK information in case of reordering

I would like to understand how TCP receiver in established state should treat SACK information of out-of-order and fully within receive window segments, where rcv_nxt < seq_no < rvc_nxt + ...
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How many TCP connections are required to download a file though ftp?

Regardless of which mode is used (active or passive mode), the initial connection is done on port 21 (command port). Then a second channel starts (data port) for exchanging the files/data. Each of ...
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Random intercontinental TCP streams are slow

I have a home server in New Zealand and a remote server in Amsterdam of the following configuration: I have a simple test script: #!/bin/bash for i in `seq 1 20`; do scp root@remoteserver:~/...
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Why is a TCP Socket identified by a 4 tuple?

Newbie to networking here. I'm reading the Computer Networking (3rd edition) book, and in section 3.2 they are discussing multiplexing / demultiplexing for both UDP and TCP. In the UDP protocol, a ...
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2answers
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Is it possible for my own application to use port 20 and 21 but not for FTP purposes?

Basically, my question is that for these official ports, can I still let my own application use these ports for other data exchange purposes? What could be the downsides if I choose to do so?
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How can a TCP window size be allowed to be larger than the maximum size of an ethernet packet?

I know that TCP window sizes can be scaled to over 64KB, but looking at an ethernet packet datagram, such as this one: it looks like a layer 2 packet is limited in size to be much smaller than that. ...
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Questions about TCP packets

I am currently in college learning about networks, and I just wanted to make sure that I understood part of the TCP correctly. The question is "What does TCP use to reassemble packets in the correct ...
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What could block two simultaneous connections on one device to the same IP/port? [closed]

My company develops and sells a system where one or more client devices are deployed in the customer's network, and they establish two websocket (TCP) connections on port 443 to the cloud server. ...
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1answer
84 views

TCP connection question

Let’s say I have 4 ethernet interfaces getting IP addresses via DHCP. I make a TCP connection to a TCP server via one of the IP addresses on a certain ethernet interface. After the connection is ...
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1answer
186 views

Load-balancing one VPN-connection over multiple WANs

My internet connection will be provided by 4 different WANs (each 250 Mbit down, 100 Mbit up), which should be load-balanced to one 1 Gbit connection (full duplex, most likely ethernet (should be ...
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1answer
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If we can calculate RTT using timestamps in TCP options then why do we use the value of the backed off timer to compute next RTT in karn's algo?

I am new to learning networking concepts. This might be stupid question but please resolve this doubt. Thanks in advance.
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Are TCP 'ACK's sent per hop or per complete source-destination traversal?

Looking briefly at a TCP transmission-related youtube video: https://www.youtube.com/watch?v=GfpThGUvbrM, I see that 'ACK's are sent per hop? Is this the case of all TCP transmissions? Are there ...
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1answer
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Whether every TCP packet have a Ack Reply?

The TCP Acknowledgements you see in the diagram's green arrows, have ACK numbers separated by 3000(two 1500 bytes). I have a question, why the Ack number is separated by two packets? Or is it just ...
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1answer
232 views

What is the relationship between throughput and latency

Looking at the structure of a TCP packet, such as discussed here: What is the internal structure of a mobile phone call packet/datagram?, this indicates that a TCP packet size is 192 bytes excluding ...
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1answer
31 views

Client drops packet from server when SNAT is not enabled at Load Balancer

I understand that one reason we use SNAT on a load balancer for incoming requests is so that the response packet from server will go through the load balancer, where the source IP of returning packet ...
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1answer
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How TCP and firewall handle security?

I'm a newbie in networking, still don't quite understand about security. Let's say a person A uses TCP to establish a TCP connection with a server. And there is a hacker B who is sniffing, so B ...
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261 views

Can I force a higher TCP segment size with netcat?

I'm using netcat to send random data from A to B, both Linux machines on Ethernet networks, with a router in the middle. For pedagogic purposes I'd like to force IP fragmentation on the router (Cisco ...
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1answer
284 views

Linux TCP stack repeatedly sends “TCP window update” without acknowledging any data

My company is developing its own TCP stack for low-latency purposes and one of the tests involves running 128 instances of ncat on Linux 4.11 to listen to ports 55000 through 55127 and sending data in ...