Thanks for the response. I will go for 877 this time as we dont have plan to implement the Voice now.

I went through the datasheet of the 877 router, would you please let me know what does mean the "Stateful Inspection firewall"? how it differ from the normal 'firewall"? Does this router support Access list?

Thanks for your help

Credit goes to google:

"Also referred to as dynamic packet filtering. Stateful inspection is a firewall architecture that works at the network layer. Unlike static packet filtering, which examines a packet based on the information in its header, stateful inspection tracks each connection traversing all interfaces of the firewall and makes sure they are valid. An example of a stateful firewall may examine not just the header information but also the contents of the packet up through the application layer in order to determine more about the packet than just information about its source and destination. A stateful inspection firewall also monitors the state of the connection and compiles the information in a state table. Because of this, filtering decisions are based not only on administrator-defined rules (as in static packet filtering) but also on context that has been established by prior packets that have passed through the firewall.

As an added security measure against port scanning, stateful inspection firewalls close off ports until connection to the specific port is requested"

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Yes, all IOS routers support the implementation of Access Lists.