AR8327-AL1A-R datasheet(50/394 Pages) ETC2

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50 • AR8327/AR8327N Seven-port Gigabit Ethernet Switch

Atheros Communications, Inc.

50 • June 2011

COMPANY CONFIDENTIAL

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.

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

Table 2-34.

Basic NAT Table

Bit

Name

Description

VALID

1'b1: entry valid; 1'b0: invalid entry

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.

Table 2-33.

RESERVED ATU Entry

Bit

Name

Description

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