echo request. ICMP responds to this by immediately discarding the
packet and generating a new payload as an echo reply.
protocol field, and payload. The destination device is now Host A.
the local LAN or on a remote network. Since the destination device is on
a remote network, the packet needs to be sent to the default gateway.
device, and the ARP cache is checked to see if the hardware address
has already been resolved from an IP address.
and destination hardware address are handed down to the Data Link
layer for framing.
following in the header:
over the network medium one bit at a time.
frame. The CRC is run, and the FCS field is checked to make sure
the answers match.
checked. Since the router's interface is a match, the packet is pulled
from the frame and the Ether-Type field is checked to see what proto-
col at the Network layer the packet should be delivered to.
CRC check on the IP header first, and then checks the destination IP
address. (Note: IP does not run a complete CRC like the Data Link
layer--it only checks the header for errors.) Since the IP destination
address doesn't match any of the router's interfaces, the routing table
is checked to see whether it has a route to 172.16.10.0. If it doesn't