In order for SagePay and Meddbase to comunicate, all of Meddbase's IP ranges (listed below) need to be added to SagePay's List of Valid IP's in order to insure the current and any future comunication between the two programs.
A common error experienced if this is not configured correctly is as follows:
"4020 : Information received from an Invalid IP address"
To resolve this, please log in to https://live.sagepay.com/mysagepay/ and add the following to your list of Valid IP addresses
|IP Address: 126.96.36.199||Subnet Mask:255.255.255.248|
|IP Address: 188.8.131.52||Subnet Mask:255.255.255.248|
|IP Address: 184.108.40.206||Subnet Mask:255.255.255.128|
|IP Address: 220.127.116.11||Subnet Mask:255.255.255.240|
|IP Address: 18.104.22.168||Subnet Mask:255.255.255.240|
These can be named however you feel fit.
A recommendation would be "Meddbase IP range 1,2,3,4,5" as the naming of these IP Ranges does not affect the functionality, its simply for your internal referencing.