If a SIP trunk needs to be authenticated against multiple IP addresses, do as follows:

• Login to the administration interface
• Navigate to 'Trunks'
• Add/Edit SIP trunk
• Set 'Type'='peer'
• Set 'Insecure'='very'
• Set 'Host'='1.2.3.0/255.255.255.0' (range in format 'start/end' ip address)
• Click on 'Save'