Cisco ISR4221/K9, Max Supported Size 4 GB, 4 GB, 4 GB, 4 GB, FF Rack-mountable, Protocol DVMRP, IGMPv3, GRE, RIP-1, Policy-based routing (PBR), IPv4-to-IPv6 Multicast, EIGRP, Static IPv6 routing, PIM-SSM, RIP-2, Static IPv4 routing, PIM-SM, BGP, IS-IS, OSPF, Expansion Slots 2 (total) / 2 (free) x NIM, Black, MTBF 593270 Hours. The Cisco ISR4221/K9 is the basic modular platform, and it is upgradable so you can increase capabilities and functions with added modules. The Cisco 4000 Series Integrated Services Routers (ISR) revolutionize WAN communications in the enterprise branch.