How to add internal IP pool for PACI?
Normally when you add IP pool, error is displayed in CP: Unable to register the network group. Error: IDL:Plesk/ExSystem:1.0 The private subnet is too large..
To allow this, it is needed to modify IM-config.xml. For instance you need to increase pool size from 10.127.0.0/16 to 10.0.0.0./8. After you do it, IM may fail after restarting:
PACI-im-error logs shows the following: 2014-03-06 11:59:43,323 () ERROR CloudHelperImpl [main] - Global private network mask width  does not match the one of existing VEs
To fix this, you will need to update all VEs to use new pool mask:
#im: update ve set private_ip=set_masklen(private_ip, 8)