Configuration Guide Configuring NAT
Run the ip nat { inside | outside } command to specify a couple of NAT interfaces.
NAT does not work on a data packet unless a route exists between the outside interface and the inside interface and
the data packet meets a certain rule. Therefore, at least one inside interface and one outside interface need to be
configured on the router.
Configuring Static NAPT
Static NAPT is not configured by default.
Use the ip nat inside source static local-ip interface interface [ permit-inside] command to configure static
one-to-one NAPT mapping.
Configuring Dynamic NAPT
Dynamic NAPT is not configured by default.
Use the ip nat inside source list access-list-number { [ pool address-pool ] | [ interface interface-type
interface-number ] } overload command to configure dynamic NAPT mapping. For NAPT, generally only one IP
address is defined in the address pool, and one IP address supports up to 64,512 times of NAT. If one IP address is
not enough, multiple IP addresses can be defined in the address pool.
10.3.3 Overlapping NAT
When the same IP address is allocated to two private networks to interconnect with each other or the same global IP
address is allocated to a private network and a public network, this situation is called address overlapping. Two
overlapping network hosts cannot communicate, because both hosts consider that the peer host is in the local network.
Overlapping NAT is especially designed to implement the communications between two networks with the same IP
address. After overlapping NAT is configured, an extranet host address will be represented as another host address in the
intranet, and vice versa.
Working Principle
For mutual access between an intranet and an extranet with the same IP address, NAT needs to translate the inside
address into a unique outside address. In addition, NAT needs to translate the outside address that overlaps with the
inside address into another unique inside address.
Related Configuration
Configuring NAT Interfaces
By default, no interfaces are NAT interfaces.
Run the ip nat { inside | outside } command to specify a couple of NAT interfaces.
NAT does not work on a data packet unless a route exists between the outside interface and the inside interface and
the data packet meets a certain rule. Therefore, at least one inside interface and one outside interface need to be
configured on the router.
Configuring Inside Source Address Translation
Inside source address translation is not configured by default.
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