46 | About the Radio
Aprisa SRi User Manual 1.1.0
Port Forwarding NAT (NAPT) Description
Port Forwarding NAT method is based on the remapping (translating) of an external / public TCP/UDP port
of a single public IP addresses (e.g. BS radio Eth port-1 IP address) into multiple internal / private IP space
(e.g. remote and RTUs IP address space) and vice versa, by translating public TCP/UDP ports space to the
private IP space. The NAT translation function is performed before routing for inbound packets and after
routing for outbound packets. NAT can translate and handle TCP, UDP, ICMP query, IP fragments and FTP
packet types.
Port Forwarding NAT translates inbound session packets per public interface based on the NAT Address Map
Table supporting max 20 entries. Outbound session packets are translated based on the reverse of the
Address Map Table based on dynamic table entries created whenever a session is not configured in the
Address Map Table (no dynamic session is allowed on inbound session). The user can configure the public
port and Address Map Table in ‘
’ page. NAT translates inbound packets (IP address) originating in
public network domain and destined for devices in private network domain. Outbound NAT translation refers
to packets originating in a private network and destined for devices in a public network. Inbound packets
will be dropped if they don’t match any translation criteria defined for the appropriate public interface and
Address Map Table configuration.
Monitoring the NAT
translation sessions is available in ‘
’ with max 250 entries in NAT session
table. Entries with a max idle time will be aged in favour of a new entry if the limit is reached. Entries are
automatically removed after a period of inactivity as configured at ‘
> Settings TAB’ in ‘
Session Idle
Timeout
’. NAT pack
et statistics of inbound and outbound sessions are also reported in the NAT session table
on a per session basis.
NAT alarms are supported for any invalid configuration settings, including improper translation entries,
invalid timeout, along with any incompatibilities with other feature settings which will cause a
‘configuration not supported’ alarm.
IP addresses used in one NAT internal domain can be reused by any other NAT internal domain.
A NAT router radio will respond to inbound ARP requests for IP addresses in public range as defined in the
Address Map Table with the MAC address of the public interface. An outbound ARP request for a private IP
range will respond with the MAC address of the NAT radio private/local interface.
In a protected station, all NAT configurations are shared between both the active and standby radios. The
standby radio will not perform any NAT translation and routing. After a protection switch-over, the NAT
session table will be aged. For smooth protection switching and continuous traffic flow, the public interface
MAC address will be used.
