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6620-3201
Max Rx rate (kbps):
On models with multiple LAN ports, this parameter may be used to specify a maximum data rate in
kbps that the unit will receive on this port. This may be useful in applications where separate LAN
ports are allocated to separate LAN’s and it is necessary to prioritise traf
fi
c from one LAN over
another.
Max Tx rate (kbps):
On models with multiple LAN ports, this parameter may be used to specify a maximum data rate
in kbps that the unit will transmit on this port. This may be useful in applications where separate
LAN ports are allocated to separate LAN’s and it is necessary to prioritise traf
fi
c from one LAN over
another.
Group:
On units with a built-in hub/switch, the Group parameter for each port is normally set to 0. This means
that all ports “belong” to the same hub. If required however, the Group parameter may be used to
isolate speci
fi
c ports to create separate hubs. For example, if Ethernet 0 and Ethernet1 have their
Group parameter set to 0 whilst Ethernet 2 and Ethernet 3 have their Group parameter set to 1, the
unit will in effect be con
fi
gured as two 2-port hubs instead of one 4-port hub. This means that traf
fi
c on
physical ports “LAN 0” and “LAN 1” will not be visible to traf
fi
c on physical ports “LAN 2” and “LAN 3”
(and vice versa).
This parameter is not available on the web page when the unit is con
fi
gured for VLAN operation.
(Changing it at the command line will have no effect when the unit is con
fi
gured for VLAN operation.)
DNS server:
This parameter speci
fi
es the IP address of a DNS server to be used by the unit for resolving IP
hostnames.
Gateway:
This parameter speci
fi
es the IP address of a gateway to be used by the unit. IP packets whose
destination IP addresses are not on the LAN to which the unit is connected will be forwarded to this
gateway.
NAT mode:
This parameter is used to select whether IP Network Address Translation (NAT) or Network Address
and Port Translation (NAPT) are used at the Ethernet interface. When the parameter is set to Off, no
address or port translation takes place.
NAT and NAPT can have many uses but they are generally used to allow a number of private IP hosts
(PC’s for example) to connect to the Internet through a single shared public IP address. This has
two main advantages, it saves on IP address space (the ISP only need assign you one IP address),
and it isolates the private IP hosts from the Internet (effectively providing a simple
fi
rewall because
unsolicited traf
fi
c from the Internet cannot be routed directly to the private IP hosts.
To use NAT or NAPT correctly in the example of connecting private hosts to the Internet, NAT or
NAPT should be enabled on the router’s interface with the public Internet IP address and should be
disabled on the router’s interface with the private IP address.
NAT and NAPT Explanation
In order to explain the difference between NAT and NAPT the behaviour of these features in the
above example is covered below:
NAT
When a private IP host sends a UDP or TCP packet to an Internet IP address, the router will change
the source address of the packet from the private host IP to the router’s public IP address before
forwarding the packet onto the Internet host. Additionally it will create an entry in a “NAT table”
containing the private IP source address, the private IP port number, the public IP destination address
and the destination port number. Conversely, when the router receives a reply packet back from the
public host, it checks the source IP, source port number and destination port number in the NAT table
to determine which private host to forward the packet to. Before it forwards the packet back to the
