3Com TP-1610, Руководство пользователя

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V6100 and V7122 User Guide
Ethernet Interface Redundancy
The V7122 supports the following redundancy scheme:
At the beginning of the start-up procedure, the gateway tests whether the ‘Primary’ Ethernet
interface is connected by checking the existence of the Ethernet link carrier. If it is
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 out of order, the start-up procedure
commences using the parameters, tables, and software residing in the gateway’s non-
volatile memory. Note that Ethernet switchover occurs only once during the start-up
procedure (at its beginning). If the Ethernet interface fails after the selection is made, the
gateway does not switch over to the second port.
After start-up has completed and the operational software is running, the gateway continues
to use the Ethernet port used for program load. The gateway switches over from one
Ethernet port to the other one every 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 takes
place only once per link loss (that is, the ‘secondary’ interface stays the active one even if
the ‘primary’ interface has returned to life).
After start-up, the gateway generates a gratuitous ARP message each time a switchover
occurs.
For correct functionality of the redundancy mechanism, it is recommended to configure both
links to the same mode. It is essential that both link partners (the primary link partner and the
secondary link partner) have the same capabilities, so that whenever a switchover occurs the
gateway is able to provide at least the same Ethernet services as were provided prior to the
switchover.
For correct functionality of the redundancy mechanism, it is recommended to set the physical
secondary link prior to the gateway being reset (since the MAC configuration cannot be
changed thereafter).
As the two Ethernet ports use the same MAC address, the external switches
connected to the gateways can in some cases create a noticeable switchover
delay due to their internal switching logic, though on the gateway level, the
switchover delay is minimal (milliseconds).
NAT (Network Address Translation) Support
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 are (1) reduces the number of global IP addresses required in a private network
(global IP addresses are only used to connect to the Internet); (2) provides a better network
security by hiding its internal architecture.
Figure 88 illustrates the supported NAT architecture.