R0106-HP MSR Router Series Layer 3 - IP Services Configuration Guide(V7)

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NAT address
An IP address for translation, which can be manually specified or dynamically allocated. The address in
the external network must be routable from the NAT address.
NAT entry
An entry recording the translation between a private and a public address on a NAT device. For more
information, see "NAT entries."
Easy IP
Easy IP uses the IP address of an interface on the device as the NAT address. The IP address of the
interface is obtained through DHCP or PPPoE. To implement Easy IP, you can specify an interface instead
of a NAT address.
NAT types
Traditional NAT
Traditional NAT translates the source IP addresses of outgoing packets and translates destination IP
addresses of incoming packets on the NAT interface. NAT is configured on the interface that connects the
public network.
Bidirectional NAT
NAT translates the source and destination IP addresses of a packet at the same time when the packet
passes through the NAT device. Bidirectional NAT is performed on incoming packets on the receiving
interface and on outgoing packets on the sending interface.
Bidirectional NAT is applied when source and destination addresses overlap.
Twice NAT
Twice NAT translates the destination IP address on the receiving interface, and translates the source IP
address on the sending interface. The receiving and sending interfaces are both NAT interfaces.
Twice NAT implements access between VPNs with overlapping address.
NAT hairpin
NAT hairpin allows internal hosts behind the same NAT device to access each other only after they uses
the NAT addresses. NAT hairpin can be in P2P or C/S mode, depending on the scenarios.
P2P
The P2P mode applies to the scenario where users in the internal network can see each other only by
using NAT addresses. In this mode, you must configure outbound PAT on the interface that connects the
external network and enable the EIM mapping behavior mode.
Internal hosts first register their NAT addresses to an external server. Then, the hosts communicate with
each other by using the registered IP addresses.