Communication method and a branch apparatus

A branch apparatus, which communicates with a central apparatus through a public network, wherein the branch apparatus comprises:

• a processor;
• a transceiver;
• a machine-readable storage medium having stored thereon machine-executable instructions executable by the processor, wherein the machine-executable instructions cause the processor to execute following processes:
• receiving a public internet protocol IP address sent by the central apparatus, wherein the public IP address is an IP address of a target interface comprised in a target NAT gateway, the target interface being connected to the public network, and the target NAT gateway being a NAT gateway closest to the public network among NAT gateways between the branch apparatus and the public network;
• sending a probe request packet to the target interface, wherein the probe request packet comprises a destination IP address, which is different from the public IP address and in the same network segment as the public IP address;
• obtaining the number of network apparatuses in a forwarding path for forwarding the probe request packet based on a probe result;
• sending a NAT keepalive packet to the central apparatus based on a preset period, wherein the NAT keepalive packet comprises a first time to live TTL, the first TTL being a sum of the number and a first value.

A NAT keepalive device applied to a branch apparatus which communicates with a central apparatus through a public network, wherein the NAT keepalive device comprises:

• an IP address receiving module, to receive a public internet protocol IP address sent by the central apparatus after determining that a network address translation, NAT, gateway exists between the branch apparatus and the public network, wherein the public IP address is an IP address of a target interface comprised in a target NAT gateway, the target interface being connected to the public network, and the target NAT gateway being a NAT gateway closest to the public network among NAT gateways between the branch apparatus and the public network;
• a probe packet sending module, to send a probe request packet to the target interface, wherein the probe request packet comprises a destination IP address, which is different from the public IP address and in the same network segment as the public IP address;
• a number determining module, to obtain the number of network apparatuses in a forwarding path for forwarding the probe request packet based on a probe result;
• a keepalive packet sending module, to send a NAT keepalive packet to the central apparatus based on a preset period, wherein the NAT keepalive packet comprises a first time to live TTL, the first TTL being a sum of the number and a first value.