The Cisco 2851 Integrated Services Router provides the following support:
| Interfaces/Ports | |
| Total Number of Ports | 2 |
| USB | Yes |
| Management Port | Yes |
| Number of Network (RJ-45) Ports | 2 |
| I/O Expansions | |
| Number of Total Expansion Slots | 11 |
| Expansion Slot Type | NME |
| Expansion Slot Type | EVM |
| Expansion Slot Type | PVDM |
| Expansion Slot Type | AIM |
| Network & Communication | |
| Network Technology | 10/100/1000Base-T |
| Ethernet Technology | Gigabit Ethernet |
| Memory | |
| Standard Memory | 256 MB |
| Maximum Memory | 1 GB |
| Memory Technology | DRAM |
| Flash Memory | 64 MB |
| Power Description | |
| Input Voltage | 110 V AC |
| Input Voltage | 220 V AC |
| Physical Characteristics | |
| Compatible Rack Unit | 2U |
| Form Factor | Rack-mountable |
| Height | 3.5" |
| Width | 17.3" |
| Depth | 16.4" |
| Weight | 21.78 lbs |