exam, you can assume that a default router of 10.1.1.100 is
configured on PC1 and that it is R1's Ethernet IP address.
finish building the Ethernet header (see Figure 3-18). In the case
of TCP/IP, the ARP process is used to dynamically learn R1's
MAC address. (See Chapter 5 for a discussion of ARP.) When
R1's MAC address is known, PC1 completes the Ethernet header
with the destination MAC address being R1's MAC address.
consider. First, the incoming frame (Ethernet interface) is
processed only if the Ethernet FCS is passed and the router's MAC
address is in the destination address field. Then, the appropriate
protocol type field is examined so that R1 knows what type of
packet is in the data portion of the frame. At this point, R1 discards
the Ethernet header and trailer.
table for network 168.1.0.0, the network of which PC2 is a
member. In this case, the route in R1 references 168.1.0.0 and lists
R1's serial interface as the interface by which to forward the
packet.
place around the IP packet. Because HDLC data link uses the
same address field every time, no process like ARP is needed to
allow R1 to build the HDLC header.
frame. The HDLC FCS is checked; the type field is examined to
learn that the packet inside the frame is an IP packet, and then the
HDLC header and trailer are discarded. The IP routing table in R2
is examined for network 168.1.0.0, and a match is made. The entry
directs R2 to forward the packet to its Frame Relay serial
interface. The routing entry also identifies the next router's IP
address--namely R3's IP address on the other end of the Frame
Relay VC.
algorithm, R2 must build a Frame Relay header and trailer. Before
it can complete the task, the correct DLCI for the VC to R3 must
be decided. In most cases today, the dynamic Inverse ARP process
will have associated R3's IP address with the DLCI R2 uses to