The ISR 4000 series routers come with a platform shaper that will limit total throughput through the L3 forwarding feature.
In the case of the 4331, these figures are:
- Default: 100Mbps
- FL-4330-PERF-K9: 300Mbps
- FL-4330-BOOST-K9: as fast as the router's CPU cores can deliver.
Having the Boost license unlocks line rate for the given 1Gbit/s sec interfaces. Hovewer, this comes at a price.
With default and PERF licensing, Cisco promises that the router can deliver up to the platform shaper's limit, no matter what combination of features you throw at it (IPSec, NAT, Hierachrical QoS, WaaS, Firewalling ...).
With the boost license, all CPU cores can be unlocked, and when running advanced combinations of features, you might hit the router's limits before line rate is achieved on the given interfaces.
Educated guess: When equipped with a switching module, L2-forwarding within that switch module is probably not subject to the platform shaper's limitations. Inter-VLAN forwarding, even when using ports of the same switching module, is probably subject to the platform shaper.
Seems I was not quite right. Inter module forwarding seems not to be subject to platform throughput licensing.
See Section "Multigigabit Fabric" in https://www.cisco.com/c/en/us/products/collateral/routers/4000-series-integrated-services-routers-isr/data_sheet_c78-612808.html
Throughput for direct module-to-module traffic using the MGF will
thereby not be limited by the platform’s performance license levels.
Layer 2 switching of packets is thus done at the full Gigabit Ethernet
line rate, either local to each LAN switch NIM or when transferring
the MGF with multiple MGF-enabled modules installed in the system;
module-to-module MGF traffic throughput is limited to 1 Gbps.
However even that document still does not say if L3 forwarded traffic from SVI to SVI is leaving the MGF and hits the CPUs, where it's probably subject to throughput licensing.