| Dns and Ftp
Hello,
I am doing a report on DNS and FTP... My report needs to be based on how it is used, how it interacts with TCP/IP, describe the most common client applications used with it, and where it fits in the OSI model. I believe that the only thing I'm missing is how it interacts with TCP/IP.. Can you help?
DNS and FTP are protocols which are the part of the ISO 7-layer protocol stack. FTP is an application layer protocol while DNS is a layer 4 protocol, thus it falls under the transport layer protocol. Every packet that these protocols use have to traverse all ISO layers and thus they also pass through the TCP/IP protocol, FTP in particular, as that uses TCP as the transport layer whereas DNS uses UDP as the transport layer. DNS and FTP deal with Windows too. They are basically two of the major network protocols used. DNS is basically the name given to all the name servers on the Internet. This is how we find a particular website amongst millions on the Internet. It's like having an address for each site and the requests send by the client are sent from a DNS server to another until they reach the destination. FTP is a way of transferring files or receiving files from a remote/local server. Many people use this protocol to upload their websites to a web server. It can also be used to retrieve logs and syslog files from a syslog server. Its uses are extremely vast. ISO OSI model is a relatively formal model and TCP-IP doesn't insist on all 7 being used. Basically, IP sits on Layer 3, while TCP sits in Layer 4. Some of the OSI model requirements are not fulfilled in TCP/IP, but we all live with it. UDP is somewhere in between 3 and 4, more in 3. DNS and FTP both sit in Layer 7, where layers 5 and 6 are not covered, at least not by some network stack. They do have some functionality of L5 and L6, but definitely not all.
Every application as such has to traverse the entire OSI stack in order to cross the internet. Only on certain routers/switches does a packet not climb the entire way to the top. Also, DNS is a TCP based protocol. UDP is used only for "stateless" connections, such as VoIP traffic or things like SNMP where many messages that do not result in a full connection could "clog" a router or network.
TCP and IP are layers 4 and 3, respectively. On layer 4 (the Transport Layer) each application transmitting data is assigned a port number, such as 53 for DNS and a packet type (TCP, UDP, ICMP) and is prepared for layer 3 encapsulation. Basically, a frame is built and the fields representing these flags are defined and assigned to the data, with the last field being the actual data or "payload."
Once Layer 4 has finished assembling the TCP/UDP/ICMP/etc frame, the packet is then handed down to the Network Layer (Layer 3) and another frame is built around the existing frame containing source and destination IP addresses, packet type and QoS (also known as DSCP) flags and so on. Once this is completed, the packet is then handed down to Layer 2 (Logical Link Layer) and is prepared to be shipped across the wire.
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