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Private and Global Addresses Section 5-3
3. Sending Mail
The PLC can send the Ethernet Unit's IP address to the SMTP server by
mail via the intranet, even if it as a private address.
The TCP port number (default: 25) to be used for SMTP cannot be used if
prohibited by a firewall in the communications path. Also, with some com-
munications companies, there may be restrictions, based on mail security
considerations, on using POP before SMTP.
4. Receiving Mail
The PLC can receive the Ethernet Unit's IP address from the POP3
server by mail via the intranet, even if it as a private address.
The TCP port number (default: 110) to be used for POP3 cannot be used
if prohibited by a firewall in the communications path.
5. Automatic Clock Adjustment
• The PLC can acquire clock data through the Ethernet Unit's IP address
from the SNTP server via the intranet, even if it is a private address.
The TCP port number (default: 123) to be used for SNTP cannot be used
if prohibited by a firewall in the communications path.
6. Host Name Designation
The PLC can acquire the server IP address for the Ethernet Unit's IP
address from the DNS server via the intranet, even if Ethernet Unit's IP
address is a private address.
• The UDP/TCP port number (default: 53) to be used for DNS cannot be
used if prohibited by a firewall in the communications path.
Note Network Security and Firewalls
Setting a global IP address for an Ethernet Unit involves network security con-
siderations. It is recommended that the user contract with a communications
company for a dedicated line, rather than using a general line such as a blue
band. Also, be sure to consult with a network specialist and consider security
measures such as a firewall.
Once a firewall has been set up by a communications company, on the other
hand, there may be some applications that cannot be used. Be sure to check
first with the communications company.