Loopback-Addr.

Source address shown in the SYSLOG messages.

SNMP ID:
2.17.20.5 
Telnet path:
Setup > DNS > Syslog
Possible values:

Max. 16 characters from [A-Z][0-9]@{|}~!$%&'()+-,/:;<=>?[\]^_.

Special values:
Name of the IP networks whose address should be used
"INT" for the address of the first Intranet
"DMZ" for the address of the first DMZ
LB0 to LBF for the 16 loopback addresses
Any valid IP address