The performance license has been around on the ASR series for years and Cisco has now added it to the ISR4K series as well. You can read the datasheets for platform specifics, but what you really need to know is how performance is counted against the license. Let’s say we buy a 4331 w/o the performance license. According to the datasheets we should have 100Mbps performance. We will get that performance, however it is 100Mbps AGGREGATE bandwidth. OK, well what does that mean to me and network design? Traffic statistics are counted per interface, per direction against the performance of the router. We put the 4331 out at a remote site and it has a 20Mb MPLS connection back to HQ. Let’s say it also has a 50Mb internet connection. One user is downloading the latest Ubuntu ISO file. The data is traversing the router on two interfaces; the internet interface and the LAN interface. Let’s say we’re getting 5Mb thoughput on the download. That’s 10Mb of used performance. 5Mb inbound on the internet interface and 5Mb outbound on the LAN interface. Now imagine a couple of users streaming music, normal business traffic, general internet browsing, etc.. A 100Mbps performance doesn’t go very far. Now suppose, since this is a remote office, we’re performing inter-vlan routing on the router! You’ll max the performance on the router in no time. In fact you’ll more than likely start seeing these in the logs:
%BW_LICENSE-5-THROUGHPUT_THRESHOLD_LEVEL: SIP1: cpp_ha: Average throughput rate exceeded 95 percent of licensed bandwidth of 100000000 bps during 123 sampling periods in the last 24 hours, sampling period is 300 seconds
From a design perspective, be careful using the 4K’s as a router on a stick. You’ll need to know all the applications and their associated traffic flows. If you have not read Top-Down Network Design by Priscilla Oppenheimer, you should stop trying to design anything and read it, twice.