The Cisco 4000 series ISRs (Integrated Service Routers) are designed to greatly improve enterprise branch networks routing and network services. Because of their application-aware networking features and a wide array of voice, security and application expansion licenses, the ISR4000 series can be custom fitted to meet the needs of a wide variety of enterprise networks.
The Cisco ISR4331/K9 has 3 gigabit Ethernet ports, 2 network interface module slots and 1 service module slot. These 3 ports include one dedicated RJ-45 port, one dedicated SFP port, and one dual mode RJ-45/SFP port. This dual mode port can only be used as either copper of SFP at any given time, not both. Because of this, the ISR 4331 has a maximum of 3 usable 1G interfaces, even though 4 are physically present on the unit.
The software on the ISR4331/k9 follows a universal image scheme, providing all possible feature packs in a single image. This allows for future upgrades through security, voice, or application licensing without modification to the routers software version. Additional functionality can also be added to this router through the addition of service modules and interface cards. Addon cards are available for FXO/FXS, Ethernet port adapters, etc.