Westermo MR Series - Manual (Page 85)

85 6622-3201
Web Interface and Command Line Reference Guide www.westermo.com
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 LANs and it is necessary to prioritise traffic 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 LANs and it is necessary to prioritise traffic 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 specific 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 configured as two 2-port hubs instead of
one 4-port hub. This means that traffic on physical ports “LAN 0” and “LAN 1” will not be vis-
ible to traffic on physical ports “LAN 2” and “LAN 3” (and vice versa).
This parameter is not available on the web page when the unit is configured for VLAN opera-
tion. (Changing it at the command line will have no effect when the unit is configured for VLAN
operation.)
DNS server:
This parameter specifies the IP address of a DNS server to be used by the unit for resolving IP
hostnames.
Gateway:
This parameter specifies 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.
Metric:
This parameter specifies the connected metric of an interface, changing this value will alter the
metric of dynamic routes created automatically for this interface. The default metric of a con-
nected interface is 1. By allowing the interface to have a higher value (lower priority), static
routes can take preference to interface generated dynamic routes. For normal operation, leave
this value unchanged.
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 (PCs 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
firewall because unsolicited traffic 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