Which ISR series is right for your network?
The ISR 4000 series routers represent a significant change in Cisco’s branch router architecture. With independent control and data planes, the ISR 4000 can provide consistent throughput numbers regardless of what features are in use.
However, total performance is most often controlled not by the router, but by the WAN circuit itself. For example, a small branch office with a cable Internet connection may only need 25 or 50Mbps of throughput. This small branch office will also have very little need of CPU-intensive features, such as internet-facing BGP or complex access control policies. Because of this limited need, routers from any of the three ISR generations can easily meet the needs of this site, so it’s important to perform a careful examination of the site requirements to make the best router selection.
Throughput Comparison Chart
| Original ISR Series | ISR G2 Series | ISR 4000 Series |
| Cisco1841 – 35Mbps | Cisco1941 – 153Mbps | ISR4321 – 50 – 100Mbps |
| Cisco2801 – 45Mbps | Cisco2901 – 167Mbps | ISR4331 – 100 – 300Mbps |
| Cisco2811 – 61Mbps | Cisco2911 – 180Mbps | ISR 4351 – 200 – 400Mbps |
| Cisco2821 – 80Mbps | Cisco2921 – 180Mbps | ISR4431 – 500 – 1000Mbps |
| Cisco2851 – 112Mbps | Cisco2951 – 297Mbps | ISR4451 – 1 – 2Gbps |
| Cisco3825 – 176Mbps | Cisco3925 – 426Mbps | |
| Cisco3845 – 256Mbps | Cisco3945 – 502Mbps | |
| Cisco3925E – 945Mbps | ||
| Cisco3945E – 1.5Gbps |
While the ISR G1 is nearing end of support and the ISR G2 is nearing end of sale, Curvature will continue to sell and maintain these product lines for as long as they remain relevant and useful.
Note: ISR 4400 throughput is governed by a license; the first number indicates the base throughput, while the second number indicates the license-upgraded throughput. ISR G1 and G2 routers have no hard throughput limit.
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If you enjoyed this Tech Guide, you might also like: https://www.curvature.com/choosing-branch-router and https://www.curvature.com/ISR_G1_vs_G2
