We are an ISP , we are using a 7206VXR Router as our ISG which is working with Broadhop SME. For last few days we are facing a problem in the ISG - the error message is continiously scrolling up called " Portbundle depleted. No Portbundle can be allocated. " - as a result we were facing a various problems in our network like subscribers cannot log in or logout. However we have incremented number of loopbacks in ISG and increased the number of Portbundles . After auditing the network it was found that there is some kind of mal- application which was intentionally filling up the free portbundles.
My question is - is there any kind of security measures - may it be an external firewal or ACL written in the ISG itself which will be used to protect ISG from external threats ?
Any suggestion is welcome.