D-Link DES-3250TG User Manual page 64

DES-3250TG Layer 2 Fast Ethernet Switch User's Guide
IP
TCP sends its packets to IP with the source and destination IP
addresses. IP is only concerned with these IP addresses. It is
not concerned with the contents of the packet or the TCP
header.
IP finds a route for the packet to get to the other end of the TCP
connection. IP adds its own header to the packet to accomplish
this.
The IP header contains the source and destination addresses,
the protocol number, and another checksum.
The protocol number tells the receiving IP which protocol to
give the packet to. Although most IP traffic uses TCP, other
protocols can be used (such as UDP).
The checksum is used by the receiving IP in the same way as
the TCP checksum.
Figure 5- 9. IP Packet Header
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