How can I connect the EPC to an external eNB ?

The following parameters should be changed in your MME config file to point to the external eNB:

• gtp_addr: This is the GTP bind address, ie the address of the Ethernet interface connected to MME/EPC. It must be modified if the MME runs on a different host.
• plmn: This is the PLMN identity. It should be changed to match the one in eNB.

Let's say MME is running in a PC with IP = "192.168.30.1" and ENB is running on a PC with IP="192.168.30.2", the configuration shall be done as following.

1) MME:

gtp_addr: "192.168.30.1"

2) ENB:

If you use Amarisoft eNB, the following fields should be changed in eNB config file.

mme_addr: "192.168.30.1"

gtp_addr: "192.168.30.2"

Otherwise, you should check for equivalent parameters in your eNB configuration.