FTP

FTP
----

File Transfer Protocol (FTP) adalah protokol lapisan aplikasi yang umum digunakan.
FTP dikembangkan untuk memungkinkan transfer file antara klien dan server.
Sebuah klien FTP merupakan aplikasi yang berjalan pada komputer yang digunakan untuk mendorong dan tarik file dari server yang menjalankan daemon FTP (FTPd).

Untuk berhasil mentransfer file, FTP memerlukan dua koneksi antara klien dan server: satu untuk perintah dan balasan, yang lain untuk transfer file yang sebenarnya.

Klien menetapkan koneksi pertama ke server pada TCP port 21. Koneksi ini digunakan untuk kontrol lalu lintas, yang terdiri dari perintah klien dan balasan server.

Klien menetapkan koneksi kedua ke server melalui TCP port 20. Koneksi ini adalah untuk transfer file yang sebenarnya dan dibuat setiap kali ada file yang ditransfer.

Transfer file dapat terjadi di kedua arah. Klien dapat men-download (tarik) file dari server atau, klien dapat meng-upload (push) file ke server.

------------------------------------------------

DHCP
------

Without DHCP, users have to manually input the IP address, subnet mask and other network settings in order to join the network. The DHCP server maintains a pool of IP addresses and leases an address to any DHCP-enabled client when the client is powered on. Because the IP addresses are dynamic (leased) rather than static (permanently assigned), addresses no longer in use are automatically returned to the pool for reallocation. When a DHCP-configured device boots up or connects to the network, the client broadcasts a DHCP DISCOVER packet to identify any available DHCP servers on the network. A DHCP server replies with a DHCP OFFER, which is a lease offer message with an assigned IP address, subnet mask, DNS server, and default gateway information as well as the duration of the lease.

The client may receive multiple DHCP OFFER packets if there is more than one DHCP server on the local network, so it must choose between them, and broadcast a DHCP REQUEST packet that identifies the explicit server and lease offer that the client is accepting. A client may choose to request an address that it had previously been allocated by the server.

Assuming that the IP address requested by the client, or offered by the server, is still valid, the server would return a DHCP ACK message that acknowledges to the client the lease is finalized. If the offer is no longer valid - perhaps due to a time-out or another client allocating the lease - then the selected server will respond with a DHCP NAK message (Negative Acknowledgement). If a DHCP NAK message is returned, then the selection process must begin again with a new DHCP DISCOVER message being transmitted.

SEMOGA BERMANFAAT

---