=== Open ports

Please ensure, that the xref:ROOT::understand-blockchain/mainchain.adoc[necessary ports] are open to run Lisk Core as intended.

For example, in case https://wiki.ubuntu.com/UncomplicatedFirewall[ufw^] is used on Ubuntu to manage the firewall settings, the respective ports can be opened as follows:

NOTE: `7667` and `7887` are the default ports.
If you configured custom ports in the node config file, adjust the examples to these specific ports.

.Node P2P communication
[source,bash]
----
ufw allow 7667
----

.Node API
[source,bash]
----
ufw allow 7887
----

