I have cloned the cpp-ethereum for Linux (Ubuntu) from git as follows:

    $ git clone https://github.com/ethereum/cpp-ethereum

    $ cd cpp-ethereum

    cpp-ethereum$ git checkout 5669c209f4f8dbb7dc3f744e8e2a9c92f1104ca3

    cpp-ethereum$ git checkout -b develop

    cpp-ethereum$ git submodule update --init --recursive

    cpp-ethereum$ mkdir -p build cpp-ethereum$ cd build

    cpp-ethereum/build$ git clone https:///github.com/cinemast/libjson-rpc-cpp

    cpp-ethereum/build/$ cmake .. && make

    cpp-ethereum/build/$ eth

It shows the following error:

>12:27:18|p2p Couldn't punch through NAT (or no NAT in place).

How to solve this problem?

Also when we are running in local machine, what is the need of NAT? Is it using looking for some server outside our network?