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Unformatted text preview: ems without a disk drive (normally diskless workstations or X terminals)
but requires manual configuration by the system administrator. We describe it in Chapter 5. 4.2 An Example
Whenever we type a command of the form
% ftp bsdi
the following steps take place. These numbered steps are shown in Figure 4.2.
1. The application, the FTP client, calls the function gethostbyname(3) to convert the file:///D|/Documents%20and%20Settings/bigini/Docu...homenet2run/tcpip/tcp-ip-illustrated/arp_addr.htm (1 of 12) [12/09/2001 14.46.39] Chapter 4. ARP: Address Resolution Protocol 2.
4. 5. hostname (bsdi) into its 32-bit IP address. This function is called a resolver in the DNS
(Domain Name System), which we describe in Chapter 14. This conversion is done using
the DNS, or on smaller networks, a static hosts file (/etc/hosts).
The FTP client asks its TCP to establish a connection with that IP address.
TCP sends a connection request segment to the remote host by sending an IP datagram to
its IP address. (We'll see the details of how this is done in Chapter 18.)
If the destination host is on a locally attached network (e.g., Ethernet, token ring, or the
other end of a point-to-point link), the IP datagram can be sent directly to that host. If the
destination host is on a remote network, the IP routing function determines the Internet
address of a locally attached next-hop router to send the IP datagram to. In either case the
IP datagram is sent to a host or router on a locally attached network.
Assuming an Ethernet, the sending host must convert the 32-bit IP address into a 48-bit
Ethernet address. A translation is required from the logical Internet address to its
corresponding physical hardware address. This is the function of ARP. ARP is intended for broadcast networks where many hosts or routers are connected to a
6. ARP sends an Ethernet frame called an ARP request to every host on the network. This is
called a broadcast. We show the broadcast in Figure 4.2 with dashed lines. The AR...
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This test prep was uploaded on 04/04/2014 for the course ECE EL5373 taught by Professor Guoyang during the Spring '12 term at NYU Poly.
- Spring '12