Perimeter Router, Internal Router and Firewall

Perimeter Router, Internal Router and Firewall 
 

The perimeter Router is typically a standard router providing a serial connection to the outside world and a LAN connection to the internal network. The perimeter router should provide any filtering of outside traffic to implement basic security for the dirty DMZ and preliminary filtering for the inside network. This device could be running the firewall feature set for additional security options.

 Because the perimeter router is often connected to a slower WAN interface on one side and it doesn’t normally provide routing functions for internal networks, the LAN interface speed isn’t as critical as making sure adequate memory and features exist to handle the outside connection.

The internal router is to provide mitigation function of the network in case the trusted network inside had been compromise to prevent spreading of the attacks to the DMZ side. On top of that, the router also provides better routing options thus improving the performance of the network.

A firewall is a device or set of devices designed to permit or deny network transmissions based on a set of rules and is frequently used to protect networks from unauthorized access while permitting legitimate communications to pass.

Many personal computer operating systems include software-based firewalls to protect against threats from the public Internet. Many routers that pass data between networks contain firewall components and, conversely, many firewalls can perform basic routing functions.

There are different types of firewalls depending on where the communication is taking place, where the communication is intercepted and the state that is being traced

• Application-layer -  Application-layer firewalls work on the application level of the TCP/IP stack (i.e., all browser traffic, or all telnet or ftp traffic), and may intercept all packets traveling to or from an application. They block other packets (usually dropping them without acknowledgment to the sender.

• Network layer -  Network layer firewalls, also called packet filters, operate at a relatively low level of the TCP/IP protocol stack, not allowing packets to pass through the firewall unless they match the established rule set. The firewall administrator may define the rules; or default rules may apply. The term "packet filter" originated in the context of BSD operating systems.