I'm looking for a new router for a new branch of hour company. I got experience with cisco L2 & L3 Switches but not that much with Routers.

I was looking at the ISR4000 series, specifically the ISR4221. In the datasheet it's stated that the throughput is 35Mbps. This throughput is even advertised as "good" (up to 75mbps).

Now I'm confused, this does not sound as much to me. We have a 1gbps Internet connection on that branch. I even have a 500mbit connection at home and even my cheap commercial router at home can handle that speed.

What am I getting wrong here? What is exactly meant by this throughput? Will I be able to use the full speed of my 1gpbs uplink?

Thank you for your time fellas!

2 Answers 2


That's by product design. ISR 4k come with a platform shaper (upgradeable to ~2x the value by license upgrade with the "PERF" license).

Cisco say that the limits of the platform shapers can be fully exploited, no matter how many features you turn on: NAT, QoS, IPSec, WAN Acceleration etc.

Performance/throuhgput estimations had always been a bit if a story with ISR Gen.1 (18/28/38xx) and Gen.2 (19/29/39xx) models. In pure "dragstrip" modes, they had been capable of hundreds of Mbit/s, but adding/stacking features (see above) could bring throughput down by an order of magnitute.

So with the 4k series, Cisco changed the approach, and you get restricted throughput, but fully exploitable. It seems that customers had wanted it that way.

Unless you buy the recently available "BOOST" license, then the box is uncorked and you can get (near) linerate throughput even on the lower end models, as long as the CPU can take it. It is however up to the customer to evaluate, test and balance feature set vs. performance.

There's a few more catches with the boost license, as it unlocks all CPU cores, for example running VMs on the otherwise unused cores is no longer possible.

  • Be aware you can increase throughout with a license, but still only up to 75 Mbps on the 4421, you will need a different model such as 4451 to get up to 1 Gbps
    – user27899
    Commented Jul 13, 2018 at 11:01
  • I see, that makes sense. Thank you for the extended explanation!
    – Geo
    Commented Jul 13, 2018 at 11:06
  • Karl: Almost. "PERF" License will bring the 4221 to from 35 to 75Mbps, but the BOOST license will allow for >1Gbps aggregated througput. See table in (for example) gblogs.cisco.com/ch-de/2018/02/16/isr-4000-lets-boost (allright, that blog post is in german, but the screenshot in there is in english). Commented Jul 13, 2018 at 11:25
  • @Marc'netztier'Luethi - OK, thanks for clarifying
    – user27899
    Commented Jul 13, 2018 at 11:45

The throughout is dependent on the features you have enabled (routing protocols, NAT, ACLs etc) and also packet sizes and are usually stated as maximum throughput. If the throughput is stated at 35Mbps and you have a few features enabled you may even get less than that speed. If your uplink is 1Gbps, then you need to choose a better spec router.

Home routers are specialised to only support the required features and the ISP makes sure they are capable of the throughput of the link.


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