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 to calculate the Maximum Segment Size (MSS)?

This page says the following: TCP controls this maximum size, known as Maximum Segment Size (MSS), for each TCP connection. For direct-attached networks, TCP computes the MSS by using the MTU size of ...
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FTP - Active and Passive modes, and Firewalls [closed]

I am studying FTP for my CCNA. I know that there are 2 FTP data connection modes - Passive and Active. Passive is when the client initiates the connection and Active is when the server initiates the ...
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RFC 5681 Fast Retransmit/Fast Recovery algorithm

I am reading RFC 5681, in particular §3.2 on the Fast Retransmit/Fast Recovery algorithm. I see that, in the event of the detection of a dropped packet, the receiver should send an immediate DUP ACK (...
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1 answer
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How does TCP knows the correct order of data?

TCP will re-order the data if they arrived in the wrong order, but how does TCP knows the correct order of data, does TCP knows the correct order of data by looking at the sequence numbers?
2 votes
1 answer
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What's the difference between MTU and MRU ? How come people talk so often about MTU and little consideration is given to MRU?

I don't understand why MRU isn't mentioned as frequently as its counterpart MTU. Are they always arranged to have the same value on a device ? A few days ago I noticed that my Windows machine accepted ...
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HTTP2 Flow Control VS TCP Flow Control [closed]

What is the difference between tcp flow control and http2 flow control. More specifically, with window_update frames that work on the whole connection vs tcp window size. To my understanding, ...
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2 answers
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IP packet expired by TTL generate an ICMP response in any case?

Acording to Wikipedia IPv4 article for TTL header field: An eight-bit time to live field limits a datagram's lifetime to prevent network failure in the event of a routing loop. It is specified in ...
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1 answer
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Wireshark only shows single HTTP request instead of its constituent TCP packets and ACKs

To my understanding, in packet no.39, the post request actually consists of multiple tcp packets getting sent, and they all get acked once by no.40. The server has received it. Now, the server sends ...
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Code implementation of Karn'r round trip time calculation [closed]

I am reading on different ways of reliable estimating the round trip time for TCP connections, and the Karn's algorithm seems pretty interesting. It is also listed in the RFC6298 as the way to ...
1 vote
2 answers
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TCP Reno - Is a timeout guaranteed in this situation (loss of segment in fast retransmit)?

In this situation: Is there a way for this situation to not end with a timeout? From my understanding, duplicate acks (Acks that require segment #1 to be sent) that are received during fast recovery ...
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1 answer
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TCP RESET randomly between DB and Server

we have some customer complains regarding a flow between a DB and Server crossing our FW. It involved 2 DB and several Servers, there are 2 VLANs connected to same FW. When failover to FW-2, we ...
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Tcp/Ip to OSI model [duplicate]

The universal standard of communication using the TCP/IP is this: Now comparing it to the OSI model,can we conclude that the Internet layer is the Network layer in the OSI model and the Link layer is ...
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1 answer
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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 answer
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Relation between the BACnet 4 layers and the TCP/IP 5 layers

How are the BACnet 4 layers (physical, data link, network, application), related to the TCP/IP 5 layers (physical, data link, network, transport, application)? Are they separate of them, or build on ...
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1 answer
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Why don't tcp sequence number start from 0?

In TCP, one purpose of 3-way-handshake is to exchange initial sequence number for both sides. So why not use 0 instead, and the exchange is not necessary. That is to say, sequence numbers can be ...
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1 answer
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TCP Congestion Window

Looking at example of congestion window graph pasted below and wanted to confirm my understanding. Looking at the red bar would that be the timeout happening here due to ACK being lost? and the b1 ...
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why is the length same with the MSS value? [duplicate]

I have read this I have issue with MSS and window size and what is difference between MSS and Window Size? I'm confused. I have a setup like this: my host machine (Macbook) and a virtual machine (...
7 votes
2 answers
1k views

TCP - Why do RST packets not require acknowledgements (and FIN packets do)?

From what I can tell, RST packets do not require acknowledgments. My question is, what happens if a RST packet doesn't reach the other participant? How can the other participant tell something has ...
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1 answer
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GNS3 - hosted or VM?

I know that there is a gns3 client that is installed in the operating system. but i see there is a gns3 for vm that gns3 for VM In a few words it is a virtual software to use it with a hypervisor It's ...
5 votes
2 answers
1k views

Can a client-side outbound TCP port be reused concurrently for multiple destinations?

Can a client-side outbound TCP port be reused concurrently for multiple destinations? If it's possible, this would let NAT gateways milk an IP Address much more, and make it practically impossible to ...
3 votes
2 answers
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Behaviour of TCP SACK

I will ask the question based on the following scenario. Assume I have to send 10 packets using TCP using a window size of 5. I send 1, 2 and receive ACK for them, I send 3 and the ACK is lost, I send ...
1 vote
2 answers
46 views

For TCP, what is the justification that ACKs are Last Byte Received + 1 and not just Last Byte Received?

Intuitively, it makes more sense that the ACK be the last byte received. Essentially, the receiving end says. I have received up to N bytes Then, the sender will receive that ACK that says N and ...
2 votes
3 answers
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QOS operation doubt

First of all, thanks for taking the time to read. I have a doubt. Does QOS marking in the IP header occur on every packet or does it need TCP segmentation established (TCP handshake)?
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2 answers
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How to benchmark time a packet spend in each OSI layer?

I'm benchmarking latency of sending a TCP packet from a client to a server. The payload of the packet is the nanosecond timestamp (using clock_gettime() on Linux) right before the send() socket ...
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1 answer
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Is the TCP Reno Fast Recovery algorithm really linear?

I'm reading through Computer Networking, 8th Edition by Kurose & Ross, and I came upon this figure(Figure 3.52 pictured below), which graphs the operation of TCP Tahoe & TCP Reno. The graph ...
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How does wireshark calculate the TCP length when there is no header indiciating such?

In wireshark, you have this field: [TCP Segment Len: 1380] # How is this calculated? My assumption is using the IP headers plus TCP's. TCP Segment Len = IP Total Length - IHL - TCP Header Length In ...
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why TCP window size is restricted to 1GB even with TCP window-scaling option?

TCP window size = 16 bits , TCP scale factor size = 14 bits. So, overall the max TCP window size can be 2^30 = 1GB. For networks where the latency is high like 500 milli-second. 1GB of TCP window ...
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Constraint on length of message & segment to be integral number of bytes, as mentioned in Cerf & Kahn's Paper

I have a question about the below excerpt from Cerf, V.; Kahn, R. (1974). "A Protocol for Packet Network Intercommunication". IEEE Transactions on Communications. 22 (5): 637–648. ... ...
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1 answer
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HTTP and TCP relationship

I always wondered how HTTP knows when it has enough TCP segments in order to process a request or response. Can someone give me more information about the process? Thanks.
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Can UDP traffic be transmitted over TCP ports on OpenVpn to avoid the TCP meltdown

I understand the TCP meltdown problem is associated with overcompensation from errors and incorrect sequencing when arriving the the receiver end. OpenVpn connections are recommended to use the UDP ...
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2 answers
112 views

Why in the TCP/IP model the link & physical are one?

I'm currently learning about the OSI model and the TCP/IP models, and I was wondering: Why in the TCP/IP model the physical layer and the data link layer are combined? I'll state how I understand the ...
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1 answer
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TCP segment with flags ACK, PSH, URG

Can a TCP data segment with a 1 byte length have, at the same time, the flags ACK, PSH, URG set ? Is it conform or not to the TCP protocol ? Thank you.
8 votes
6 answers
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How Does A Layer 2 Switch Differentiate Between Different Networks?

I know that different IP-based networks can be connected to the same layer-2 switch. and I know each network's nodes can communicate just fine, however, no normal traffic can occur between two nodes ...
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5 answers
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Why is Packet Size Limited?

I was reading: this answer to "Maximum packet size for a TCP connection", where it says: The absolute limitation on TCP packet size is 64K (65535 bytes), but in practicality this is far ...
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1 answer
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How to change the source port without interrupt the TCP connection? [closed]

I use TCP socket to connect a client(source) and a server(destination), the connection has been established. Now the project need to change the source port without interrupt the connection. Both ...
3 votes
3 answers
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Why is an empty TCP segment at right edge of receive window not acceptable?

The TCPv4 specification (RFC 793) classifies a received segment as unacceptable if it has zero length, a sequence number equal to RCV.NXT+RCV.WND while the receive window is not zero (second row in ...
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1 answer
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Why sender window or congestion window size becomes 2^n mss after nRTT in slow start mechanism?

I seen everywhere in slow start mechanism if initial sender size denoted by cwnd= 1mss , then after 1 RTT cwnd becomes = 2 mss, and after 2 RTT cwnd becomes = 4 mss and so on. My question is why ...
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2 answers
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Is it possible for TCP can accept out of order segments?

TCP is connection-oriented protocol whereas IP isn't connection-oriented protocol. Any packets before sending into transport layer sorted operation must have been done in network layer. That's why we ...
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UDP supports multicasting and broadcasting in transport layer or application layer?

We know that UDP does supports multicasting and broadcasting. My question is which layer "UDP supports multicasting and broadcasting"? Is it transport layer or application layer? We know ...
3 votes
1 answer
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What is the maximum value that a receiver can set in its advertising window

I know an advertising window is set by the receiver to inform the sender not to send more than what is advertised in the receiver's window to avoid packet loss due to overflow of packets at receiver(...
2 votes
1 answer
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Why does TCP need more than just one port?

With TCP you listen to some port (say port 80) and then when an incoming connection pops up, you accept it, establishing the connection over a new port. Why is this necessary? Why can't you just keep ...
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Why need Ack flag if we already have ack number in TCP

If we have ack number so from there we can trace that how many bytes are received and which byte is need next so then what is the use of Ack flag there?
1 vote
1 answer
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What is difference between socket connection and TCP connection?

We know TCP socket is port numbers and IP addresses. Is TCP socket connection is 3-way handshake:the SYN packet, the SYN-ACK packet, and the ACK packet? Is TCP socket connection follows TCP stack? And ...
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How IP packet's payload bigger than the whole former PDU (segment)? [duplicate]

As far as I know: File is too big ---> Fourth layer (TCP or UDP) divide it to a multiple segments ---> Then each segment encapsulated separately into a packet. What means if I have 10 segments, ...
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1 answer
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Inherent flaw in stateless firewalls?

I am but a lowly (software) developer dabbling with setting up a network in AWS and am having trouble understanding the fundamentals of stateless firewalls, or Network ACLs as they're also referred to ...
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Is there any other scenario of TCP segment window size equal 0?

Is there any other scenario of window size equal 0? in my impression, if the window_size == 0, there have two cases: 1.the TCP acceptance area is full, then send window_size = 0 2.send RST package, ...
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2 answers
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Does window size in tcp header include tcp header size?

Let's say a TCP segments has in the field of "window size" = 1400 bytes. Does that mean that we can send 1400 bytes counted in tcp segments = TCP headers + data or it does specify only ...
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1 answer
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How n level come to know the n+1 level contents?

Suppose in application layer is running some application. And application has respective source port number and destination port number. And know that n layer has no authentication to know about n+1 ...
1 vote
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TCP Three Way Handshake?

I have the following query about the tcp handshake. To establish a connection the server must send a packet with SYN flag to 1 Then the server replies with a SYN,ACK flag to 1 , and afterwards the ...
1 vote
2 answers
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Pros and cons of the idea of parallell data transmission

I am learning the basics of internet protocols and related principles. I recently performed experiments comparing UDP and TCP. But when I did that (using the ttcp program) it was only one process and ...

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