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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142
votes
9answers
79k views

Why do we need a 3-way handshake? Why not just 2-way?

The TCP 3-way handshake works like this: Client ------SYN-----> Server Client <---ACK/SYN---- Server Client ------ACK-----> Server Why not just this? Client ------SYN-----> Server ...
57
votes
4answers
350k views

PING port number?

Yesterday interviewer ask me what is port number for ping and which protocol ping use TCP/UDP. After interview I search on internet and found different results someone says ICMP uses Port 7, someone ...
55
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10answers
97k views

Why only port 80 for web services?

Why isn't it sensible to dedicate more than one TCP/IP port to http? Although admittedly naive, isn't it somehow intuitive to think that server performance could somehow be increased?
37
votes
3answers
109k views

What is the difference between MSS and MTU?

I'm confused as to the difference between maximum segment size and a maximum transmission unit. Can someone please explain in relation to layers 2 and 3? If I had a packet of 800 bytes in the ...
28
votes
7answers
6k views

Why isn't UDP with reliability (implemented at Application layer) a substitute of TCP?

TCP provides reliability at transport layer while UDP does not. So, UDP is fast. But, a protocol at application layer can implement reliable mechanism while using UDP. In this sense, why isn't UDP ...
26
votes
8answers
14k views

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 ...
22
votes
4answers
9k views

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 ...
18
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4answers
3k views

How is 8 bits sufficient for the TTL in an IP header?

The TTL (Time to Live) is an 8-bit field in the IPv4 header. It can take any value from 0 to 255. If this means that the packet can take a maximum of 255 hops (routers) on its way to its destination, ...
18
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3answers
8k views

What do TCP/UDP add to “raw ip”?

I know that both TCP and UDP are built on top of IP, and I know the differences between TCP & UDP, but I'm confused about what exactly "raw ip" is. Would it be fair to say that TCP & UDP both ...
17
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1answer
18k views

How multiple client connections are made to single web server?

Actually I am learning Computer Networks and while at it, I am confused in how a web server maintains multiple connections? Simply to state, I learned trough some googling is that sockets handles a ...
15
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8answers
21k views

Does TCP open a new connection for every packet that is sent?

This might be a silly question but a me and few buddies have been discussing the potential limitations of TCP. We have an application that is going to listen for clients (think of a gateway) and route ...
14
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2answers
6k views

Troubleshooting low Metro Ethernet TCP throughput

The setup We have rented a few leased lines that present themselves as a layer 2 network, i.e. you have one big pipe at the datacenter and the remote sites have smaller pipes. Inside the layer 2 ...
14
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1answer
2k views

Why BGP implements its own keepalive instead of using tcp keepalive?

BGP doesn't use TCP keepalive, it uses its own keepalive mechanism. My question is why can't bgp turn-on the SO_KEEPaLIVE of TCP and live happily? why does it not use tcp keepalive and implement its ...
13
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6answers
11k views

How does BGP work over TCP?

As far as I know we are using routing protocols to achieve Layer 3 connectivity, I am confused with the fact that BGP works over TCP which is L4. How can L4/TCP be established without prior L3 ...
13
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8answers
15k views

TCP acceleration over satellite or high latency networks [closed]

What viable companies, products or options are out there today for TCP Acceleration over satellite or high latency IP networks? The average satellite RTT is upwards from 600ms (depends on the ...
13
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2answers
28k views

Open a range of TCP ports in Cisco IOS NAT

ip nat inside source static 192.168.1.10 10.10.10.9 route-map RANGE ! route-map RANGE permit 100 match ip address 102 ! access-list 102 permit tcp host 192.168.1.10 range 3000 3389 any The ...
12
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4answers
2k views

How can I formulate the communication latency in TCP/IP?

I have difficulty in deriving a mathematical model/equation to estimate the round trip latency between two nodes communicating using TCP/IP. The nodes are exchanging data based on HTTP protocol. In ...
12
votes
2answers
4k views

How NAT / PortForwarding / TCP/IP works?

I recently read an article entitled how NAT works. Some things still remain unclear to me. I would be thankful if someone could explain. Below is the part of the article regarding DynamicNAT that is ...
12
votes
3answers
23k views

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 ...
12
votes
3answers
29k views

What is the purpose of TIME WAIT in TCP connection tear down?

I found that the reason the active closer enters TIME WAIT is to make sure that the final ACK is not lost. But how does it know if the final ACK is lost? Will the passive closer resend the FIN and ...
11
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3answers
3k views

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 ...
11
votes
1answer
5k views

Is a TCP server limited to 65535 clients?

One might think that this places a hard limit on the number of clients that a single computer/application can maintain. One could be overseeing a web server, and be required to ensure that it can ...
11
votes
1answer
371 views

Is a FIN only segment legal?

It would be convenient to mark TCP segments with just the FIN flag set, as an intrusion (without tracking the reply). I have always assumed that a FIN without an ACK, while rude and rare, is legal, ...
10
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3answers
11k views

Is a TCP three-way handshake required for an HTTP POST?

I don't quite understand if i posting http form data from the browser to the server, does the protocol still need to make three-way handshake (syn-ack-data) or it only works for GET http requests?
10
votes
3answers
7k views

What happens when SYN and FIN flags in TCP headers are both set to 1?

In TCP header, what happens when both SYN and FIN flags are set to 1? Or, can both even be simultaneously set to 1 ?
10
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2answers
2k views

How does nmap distinguish closed ports from filtered ports

Let's suppose we are doing a TCP connect scan. a nmap scan on google returns the following output : PORT STATE SERVICE 80/tcp open http 443/tcp open https However, if I try to ...
10
votes
1answer
87k views

What does TCP DUP ACK mean?

In Wireshark, I see TCP duplicate ACK packets sent from the receiver to the sender. What does it mean? Does it imply packet loss? Thank you
10
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5answers
5k views

Packet sizes in a TCP stream

I'm network traffic and wish to divide each TCP session into a series of requests and responses (the protocols I'm working with all work that way, like HTTP or SSL). I had a simple assumption (...
9
votes
4answers
28k views

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. ...
9
votes
2answers
17k views

Trying to find out exact TCP overhead cost

Corresponding this topic: https://stackoverflow.com/questions/3613989/what-of-traffic-is-network-overhead-on-top-of-http-s-requests The maximum segment size (which does not include the TCP or IP ...
9
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2answers
3k views

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 ...
9
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2answers
5k views

Is TCP maximum segment size (MSS) “clamping” compatible with IPv6?

With IPv4, TCP MSS "clamping" (a network device editing the MSS value in a TCP header) can help when path maximum transmission unit discovery is not working. (e.g., when ICMP is being blocked ...
9
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2answers
24k views

Window Size and ACK Number

Copy-pasting from my lecturer's slides: • Receiver indicates the window size is 3000 • Transfer goes ahead • Acknowledge every 3000 bytes • Receiver increases window size to 4000 • 4000 bytes ...
8
votes
1answer
7k views

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. ...
8
votes
3answers
17k views

Traceroute Over TCP vs UDP

For what purpose would one wish to send traceroute over TCP rather than UDP? What advantages/disadvantages are there in doing so? I know that traceroute normally uses UDP ICMP "echo" packets while ...
8
votes
4answers
11k views

How would a firewall kill a TCP connection without RST or FIN? [closed]

Situation is like this: http client ----> corporate firewall ----> http server Due to a keepalive, server and client would keep TCP connections open and the client would use a connection pool ...
8
votes
4answers
8k views

How is a TCP connection maintained over a changing IP address

I remember when I connected to the internet via the phone line and a 56kbps modem, changing ISPs was as simple as changing the phone number dialled by the modem. I remember that my IP address would ...
8
votes
1answer
3k views

How exactly does TCP react to a retransmission timeout?

Hi! Could someone explain to me what happens at the time-out? Then the window size completely drops. I thought that at time-out the same thing as in 3 duplicate ACKs would happen; half the cwnd and go ...
8
votes
4answers
6k views

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 ...
8
votes
3answers
4k views

How is tcp/ip implemented

Well, first of all I am new to networking. And I have studied the layered structure of tcp/ip protocol stack. I know that the layered structure is an abstract model, but I didn't know how the ...
8
votes
1answer
1k views

Dropped data packet on satellite connection

We have several embedded pcs on farms in the UK and US. Among other connections these talk to our server sending a small packet of data (100 - 600 bytes) every 20 seconds. Over DSL this is fine. ...
7
votes
6answers
2k views

Why do we need FTP when there are layers to transmit data?

In OSI, there are layers for routing, encapsulating and transmitting the data. Then why do we need FTP? I read the following definition of FTP in books: FTP is used for transferring files on ...
7
votes
3answers
4k views

How HTTP is converted to TCP and then how TCP converted to IP?

I know that in Internet Protocol Stack there are actually three layer. They are Application, Internet and Transport. Let's say HTTP in Application layer will be converted to TCP in Transport layer and ...
7
votes
3answers
4k views

How does NAT decide which connections are inbound, and which are outbound?

I'm building a P2P application that needs to be able to access nodes behind a NAT. This NAT does not allow inbound connections, therefore the nodes outside the network cannot reach out to the nodes ...
7
votes
2answers
11k views

F5 session timeouts

Our F5 load balancers run version 10.2.4. We migrated from Cisco load balancer cards on the Catalyst 6500 and used to be able to run xterm sessions to our solaris and linux servers without the ...
7
votes
5answers
3k views

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: ...
7
votes
4answers
2k views

Can throughput exceed the bandwidth of a network

I took an introductory course to networking this semester and I was wondering: looking at things at the layer 4 level using TCP can the throughput on the network exceed its bandwidth? According to the ...
7
votes
1answer
4k views

How do Endpoints in a TCP conversation determine their MSS?

I understand the MSS is the Maximum Segment Size, which is the size of the Payload TCP will send. I also understand that a "receiving" MSS value is suggested by both parties in a TCP conversation ...
7
votes
1answer
2k views

TCP Handshake Not Happening [closed]

Not sure if this is a good stack exchange site to post this on but here goes nothing, The problem, As you can see from my Wireshark screenshot the TCP handshake is not happening. The remote is ...
7
votes
1answer
21k views

tcp.length and tcp.data wireshark filters

I was playing with Wireshark and noticed two filters: tcp.len and tcp.data. What is the difference between the two? As far as I know, the tcp.len (length) field tells how many bytes of data travel ...

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