Side by side
Days vs NetSim
Both stand on network simulation software. Which one you can start free with, which one lets you read the code, and what each costs once you pay.
Paid LinuxMacWindows
Choose Days if you need an exact packet network simulator with configurable models and multiple execution backends. Look elsewhere if your scenarios require RED, collectives, or compute stages on Metal or CUDA, since those are rejected during validation.
Visit Days Free trial LinuxMacWeb+1
NetSim offers guided Cisco practice, feedback and custom lab design through a browser, with lab packs and certification-specific plans. Check the lab count and one-year license term for the plan you need.
Visit NetSimThe facts
| Days | NetSim | |
|---|---|---|
| Free plan | Not published | A free trial |
| Open source | Not published | Not published |
| Runs on | Linux, Mac, Windows | Linux, Mac, Web, Windows |
| Lowest paid plan | Not published | NetSim Lab Pack: IPv4 Subnetting: $29 a year |
| Plans published | None | 6 |
| Maker | Not published | Not published |
| Website | days.sh | netsim.boson.com |
| On network simulation software | #30 of 31 | #26 of 31 |
Days: what it does well
- Models fat-tree, torus, dragonfly, and custom graph topologies.
- Offers Scalar, multicore CPU, Metal, and CUDA backends.
- Uses integer-nanosecond event ordering without floating-point simulation semantics.
- Includes runnable example configurations.
- Open source under AGPL-3.0-only.
What to know first
- RED, collectives, and compute stages are limited to Scalar and CPU.
- CUDA builds require the CUDA 13 toolkit.
- Metal runs on Apple GPUs except the M1 family.
NetSim: what it does well
- Preconfigured labs include required materials
- Configuration comparisons give instant feedback
- Lab progress syncs between devices
- Network Designer supports complex custom labs
What to know first
- Online licenses last one year
- No free plan is listed
- Certification plans cost $179 a year