AR8327/AR8327N Seven-port Gigabit Ethernet Switch - La Fibre

Table 2-33. RESERVED ATU Entry
Bit Name Description
54:48 DES_PORT These bits indicate which ports are associated with this MAC address when
they are set to ‘1’. Bit 48 is assigned to Port0, 49 to Port1, 50 to Port2, etc.
47:0 ADDRESS 48bit MAC address
2.19 HNAT
The AR8327N supports hardware NAT (Network Address Translation) to offload the CPU loading
and achieve the full wire speed when doing the NAT. The AR8327N support the following mode of
NAT.
1. Basic NAT: This involves IP address translation only, not port mapping.
2. Network Address Port Translation (NAPT): This involves the translation of both IP addresses and
port numbers. For the NAPT mode, the AR8327N can support Full cone NAT, Restricted cone NAT,
Port-Restricted cone NAT and Symmetric NAT.
The HNAT can automatically check the inbound and outbound traffic. If the traffic is matched the
entry in the NAT or NAPT tables, then the HNAT can modify the packets accordingly without the
CPU involved. For the outbound traffic from private network to public network, the HANT will do
the SNAT. For the inbound traffic, the HNAT will do the DNAT.
SNAT involves the following two steps:
1. Router will use frame DIP to lookup the ARP table and use the DA in the ARP table to replace the
original DA in the frame. Router will also replace the original SA with the Router MAC address.
2. NAT will replace the frame SIP and SP with the translation IP and Port number in the NAPT table.
DNAT involves the following two steps.
1. NAT will replace the frame DIP and DP with the private IP and private port number in the NAPT
table.
2. Router will lookup the private IP in ARP table and will replace the DA by the MAC address in the
table. Router will also replace the SA with Router MAC address.
2.19.1 Basic NAT Table
There are 32 entries in the Basic NAT table. This table is maintained by the CPU only.
Table 2-34. Basic NAT Table
Bit Name Description
79 VALID 1'b1: entry valid; 1'b0: invalid entry
78 PORT NUM EN Port number compare enable
When do SNAT, compare to frame SP
When do DNAT, compare to frame DP
77:76 PROTOCOL Protocol, compare to frame type.
2'b00:TCP
2'b01:UDP
2'b10:GRE
2'b11:Reserved
75:74 HASHKEY The value will be compared with the hash value generated by the
frame's SIP and/or SP depending on the NAT_HASH_MODE.
50 • AR8327/AR8327N Seven-port Gigabit Ethernet Switch Atheros Communications, Inc.
50 • June 2011 COMPANY CONFIDENTIAL