# Define contact IP addresses

Contact addresses are required when NAT is applied between to SMC components. You can define contact addresses for Security Engines, Master Engines, and most types of server elements.

You can specify an IP address or Fully Qualified Domain Name (FQDN) as the contact address to enable Security Engine to contact SMC management server or log server. If FQDN is specified, then you must also specify a DNS server in the engine configuration. The DNS server is used to match server host names to their corresponding IP addresses.
Note: FQDN resolves to IPv4 or IPv6 address. If FQDN resolves to multiple addresses, then all the addresses are attempted and the first IP address that works is used.

The contact addresses are defined in the element properties. The contact addresses are based on Location elements. You can also define a Default contact address that is used whenever no contact address is defined for a certain Location.

You create the Locations and add elements to the Locations based on how your network is set up. Then you define the Contact Addresses for each element for each Location in the properties of the elements. All SMC components in other Locations then use the addresses defined for their Location for contact.