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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.
