Cisco router comparison
ISR4331/K9 vs ISR4321/K9
ISR4331/K9 adds a third routed Gigabit interface, an SM-X slot and a higher DRAM expansion limit compared with ISR4321/K9. Both have two NIM slots; their default licensed aggregate-throughput limits are 100 Mbps and 50 Mbps.
2models compared
35specs published for every model
11confirmed differences
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Key differences
Compare the specifications that shape your deployment.
| Specification | ISR4331/K9 | ISR4321/K9 |
|---|---|---|
Configurable Ethernet Ports |
3 onboard Gigabit Ethernet routed ports using 2 RJ-45 connectors and 2 SFP connectors | 2 onboard Gigabit Ethernet routed ports using 2 RJ-45 connectors and 1 SFP connector |
Built-in 1GE Ports |
3 | 2 |
Expansion Slots |
2 NIM slot(s) and 1 SM-X slot(s) | 2 NIM slot(s) and 0 SM-X slot(s) |
Aggregate Licensed Throughput |
100 Mbps | 50 Mbps |
Default Power Supply |
250 W AC supply; DC ordered as separate ISR4331-DC SKU | 125 W external AC supply; optional external PoE supply; no DC supply |
Configurable Ethernet Port Count |
3 | 2 |
Detailed comparison
Full specification comparison
| Comparison parameter | ||
|---|---|---|
| Product ID | ISR4331/K9 | ISR4321/K9 |
| Product and ordering | ||
| Product Type | Cisco 4000 Series Integrated Services Router | Cisco 4000 Series Integrated Services Router |
| Form Factor | 1RU | 1RU |
| Router Role | Modular branch integrated services router | Modular branch integrated services router |
| Routing and WAN performance | ||
| Configurable Ethernet Ports | 3 onboard Gigabit Ethernet routed ports using 2 RJ-45 connectors and 2 SFP connectors | 2 onboard Gigabit Ethernet routed ports using 2 RJ-45 connectors and 1 SFP connector |
| Configurable Ethernet Port Count | 3 | 2 |
| Integrated LAN Switch Ports | Not applicable | Not applicable |
| Integrated LAN Port Count | 0 | 0 |
| Built-in 1GE Ports | 3 | 2 |
| Built-in 10GE Ports | 0 | 0 |
| Expansion Slots | 2 NIM slot(s) and 1 SM-X slot(s) | 2 NIM slot(s) and 0 SM-X slot(s) |
| NIM Slots | 2 | 2 |
| SM-X Slots | 1 | 0 |
| Service Module Support | Cisco NIM and model-dependent SM-X service modules with online insertion/removal | Cisco NIM and model-dependent SM-X service modules with online insertion/removal |
| Ports and interfaces | ||
| Management Ports | 1 x dedicated 10/100/1000BASE-T management Ethernet | 1 x dedicated 10/100/1000BASE-T management Ethernet |
| Console Ports | RJ-45 and mini-USB console; RJ-45 auxiliary port | RJ-45 and mini-USB console; RJ-45 auxiliary port |
| Performance and scale | ||
| Aggregate Licensed Throughput | 100 MbpsDefault; 300 Mbps with the performance license | 50 MbpsDefault; 100 Mbps with the performance license |
| Configuration, licensing and management | ||
| Routing Protocols | Static routing, BGP, OSPF, EIGRP, IS-IS, RIP, MPLS and VRF | Static routing, BGP, OSPF, EIGRP, IS-IS, RIP, MPLS and VRF |
| Management Model | Cisco Catalyst Center, WebUI, CLI, NETCONF/RESTCONF and SNMP | Cisco Catalyst Center, WebUI, CLI, NETCONF/RESTCONF and SNMP |
| Licensing | Cisco Smart Licensing; performance and feature licenses by platform | Cisco Smart Licensing; performance and feature licenses by platform |
| Required Subscription | Not required for autonomous routing; subscription required for managed SD-WAN services | Not required for autonomous routing; subscription required for managed SD-WAN services |
| USB Ports | 1 x USB 2.0 Type-A storage port; 1 x Mini-USB console | 1 x USB 2.0 Type-A storage port; 1 x Mini-USB console |
| Memory and software | ||
| Default DRAM | 4 GB | 4 GB |
| Maximum DRAM | 16 GB | 8 GB |
| Storage | 4 GB | 4 GB |
| Operating System | Cisco IOS XE | Cisco IOS XE |
| Minimum Software Release | Not published by Cisco | Not published by Cisco |
| PoE and power | ||
| Integrated PoE Support | PoE through compatible EtherSwitch modules and PoE power options | PoE through compatible EtherSwitch modules and PoE power options |
| Default PoE Budget | Not applicable | Not applicable |
| Default Power Supply | 250 W AC supply; DC ordered as separate ISR4331-DC SKU | 125 W external AC supply; optional external PoE supply; no DC supply |
| Power Redundancy | Not applicable | Not applicable |
| Physical and environmental | ||
| Dimensions (H × W × D) | 44.5 × 438.2 × 438.2 mm | 44.6 × 369.6 × 294.6 mm |
| Weight | 6.2 kg | 3.5 kg |
| Operating Temperature | 0 to 40 °C | 0 to 40 °C |
| Storage Temperature | -40 to 70 °C | -40 to 70 °C |
| Storage Humidity | 5% to 95% | 5% to 95% |
| Operating Humidity | 5% to 85% | 5% to 85% |
| Operating Altitude | 0–3,050 m | 0–3,050 m |
| MTBF | 587,250 hours | 593,270 hours |
| Warranty | Cisco 90-day limited hardware warranty | Cisco 90-day limited hardware warranty |
Specifications from Cisco 4000 Family Integrated Services Router Data Sheet (checked 2026-10-11).
“Not published by Cisco” and “Not listed” indicate that a confirmed direct comparison is unavailable. These rows are not counted as confirmed differences.
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