Thank you ppalias, as your suggestion of http proxy interfering with my firewall rules, helped me out.
As I required http proxy to be running for atleast one connection, I just shifted these modems to another vmware based zeroshell setup, where proxy was DOWN and all my Firewall Rules were followed to the letter. Thank you very much. Also, many thanks to Fulvio for making it so easy to configure, anything in Zeroshell.
Also, can you suggest with your experience, whether :
1. A workaround is possible to stop the Netbalancer from hopping to the next available interface, if it senses that the current interface has gone down ? ( I see this message in its logs : Default Route has been changed: nexthop via )
2. This workaround can also be called a “StandAlone” mode as it just follows our dictates in the “netbalancer balancing rules” and does not initiate balancing or failover in this case. Helpful for group of modems with varying cost usage plans and not suitable for use of all. Hope this can be considered as a feature in a new release. And yes, in this case, the “failover checking” just becomes “failure checking” for restarting the modems, individually, should their connections go down !