Get wrong port in external ipfs node

Hello.

Version information:

0.4.15-rc1

###Type
question
Why a external ipfs node get wrong port from internal ipfs node.

###Description
my ipfs node:

internal ipfs node ip:172.16.3.1
gateway ip: 218.72.122.165
external ipfs node ip: 40.125.164.111

When the internal ipfs node connected to external ipfs node, the bound upnp port is 63302.

internal ipfs (172.16.3.1:4001)=====>gateway(218.72.122.165:63302)===========>external ipfs(40.125.164.111)

But when i use ipfs swarm peers in external ipfs server, it get the follow information.

/ip4/218.72.122.165/tcp/4001/ipfs/QmfHqqhLHzQzGUpCrwbPiTTNHj3AUb2PQqvUKyBXrmBTC8

Why not 63302 but 4001 ???