Ethernet Interface Redundancy; Nat (Network Address Translation) Support; Figure 10-1: Nat Functioning - AudioCodes Mediant 2000 User Manual

10.2

Ethernet Interface Redundancy

The device supports an Ethernet redundancy scheme. At the beginning of the start-up
procedure, the device tests whether the 'primary' Ethernet interface is connected, by
checking the existence of the Ethernet link carrier. If it's connected, the start-up procedure
commences as usual. If not, the start-up application tries the 'secondary' Ethernet interface.
If this interface is connected, the whole start-up procedure is performed using it. If both
interfaces are not connected, the start-up procedure commences using the parameters,
tables, and software residing on the device's non-volatile memory. Note that Ethernet
switchover occurs only once during the start-up procedure (at the beginning). If the Ethernet
interface fails after the selection is made, the device does not switch over to the second
port.
After start-up is complete and the operational software is running, the device continues to
use the Ethernet port used for software upload. The device switches over from one
Ethernet port to the other each time an Ethernet link carrier-loss is detected on the active
Ethernet port, and if the Ethernet link of the other port is operational. Switchover occurs
only once per link loss (i.e., the 'secondary' interface stays the active one even if the
'primary' interface has returned to life). After start-up, the device generates a gratuitous
ARP message each time a switchover occurs.
For correct functionality of the redundancy mechanism, it's recommended to configure both
links to the same mode. It is essential that both link partners (primary and secondary) have
the same capabilities. This ensures that whenever a switchover occurs, the device is able
to provide at least the same Ethernet services as were provided prior to the switchover. In
addition, it's recommended to set the physical secondary link prior to resetting the device
(since the MAC configuration cannot be changed thereafter).
Note that since the two Ethernet ports use the same MAC address, the external switches
connected to the device can in some cases create a noticeable switchover delay due to
their internal switching logic, though at the device level, the switchover delay is minimal
(milliseconds).
10.3

NAT (Network Address Translation) Support

Network Address Translation (NAT) is a mechanism that maps a set of internal IP
addresses used within a private network to global IP addresses, providing transparent
routing to end hosts. The primary advantages of NAT include (1) Reduction in the number
of global IP addresses required in a private network (global IP addresses are only used to
connect to the Internet); (2) Better network security by hiding its internal architecture.
The following figure illustrates the device's supported NAT architecture.
SIP User's Manual

Figure 10-1: NAT Functioning

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Mediant 2000
Document #: LTRT-68809