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DES-3326S Layer 3 Fast Ethernet Switch User’s Guide
Switch Management and Operating Concepts 101
There is no relationship between the MAC address of a network
node and its IP address. There must be a database of Ethernet
addresses and their corresponding IP addresses.
Different protocol families can be in use on the same network.
The type code field allows each protocol family to have its own
entry.
A checksum is calculated and when the packet is received, the
checksum is recalculated. If the two checksums are different,
the packet is dropped.
Figure 5-12. Ethernet Packet Header
When a packet is received, the headers are removed. The
Ethernet Network Interface Card (NIC) removes the Ethernet
header and checks the checksum. It then looks at the type
code. If the type code is for IP, the packet is given to IP. IP
then removes the IP header and looks at its protocol field. If
the protocol field is TCP, the packet is sent to TCP. TCP then
looks at the sequence number and uses this number and other
data from the headers to reassemble the data into the original
file.