D-Link DES-3326SR, User Manual

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DES-3326SR Layer 3 Fast Ethernet Switch User’s Guide
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determine the maximum packet size across all of the networks
that may make up the route for a connection. IP has,
therefore, a method to divide packets into multiple, smaller
packets to cross such networks. This division of large packets
into smaller packets is referred to as fragmentation.
A field in the TCP header indicates that a packet has been
fragmented, and other information aids in the reassembly of
the packets into the original data.
Gateways that connect networks of different packet size limits
split the large packets into smaller ones and forward the
smaller packets on their attached networks.
ARP
The Address Resolution Protocol (ARP) determines the MAC
address and IP address correspondence for a network device.
A local computer will maintain an ARP cache which is a table of
MAC addresses and the corresponding IP addresses. Before a
connection with another computer is made, the local computer
first checks its ARP cache to determine whether the remote
computer has an entry. If it does, the local computer reads the
remote computer’s MAC address and writes it into the
destination field of the packets to be sent.
If the remote computer does not have an ARP cache entry, the
local computer must send an ARP request and wait for a reply.
When the local computer receives the ARP reply packet, the
local ARP reads the IP MAC address pair, and then checks the
ARP cache for this entry. If there is an entry, it is updated with
the new information. If there is no entry, a new entry is made.
There are two possible cases when an ARP packet is received
by a local computer. First, the local computer is the target of