Slow Internet Speed on Cisco Router – Need Help!

[Emma Johnson]

Hi everyone,

I’m facing an issue with my Cisco router where the internet speed is much slower than expected, even though my internet plan is high-speed. The speeds fluctuate and sometimes drop significantly, making it difficult to browse or stream content.

I’ve tried restarting the router and checking the cables, but the issue persists. Does anyone have suggestions on how to troubleshoot this or settings I should check on my Cisco router to fix the speed issue?

Any help or advice would be greatly appreciated!

Thanks in advance!

[Leo Laohoo]

Please provide more information: 

1.  Model of the router

2.  Exact firmware version

3.  What is the size is the WAN bandwidth?

[Scott Fella]

Just to add, you should look up the data sheet for your router, that should at least show you the throughput that your model can provide.  It also depends on how everything is connected up, gigabit, multigig or maybe 100mbps.  Get a baseline of your speed by connecting up a laptop to your ISP modem and see what you get first... make sure you have your firewall enabled on your laptop.  Then you can connect your router and test directly from your router with your laptop connected to one of the LAN ports on the RTR.

[Emma Johnson]

Absolutely, great advice! Starting with the router’s datasheet is a smart move—it really helps set expectations for what your hardware is capable of. And testing directly from the modem first is such a solid way to get a clear baseline before factoring in the router or network setup. Appreciate the reminder about the firewall too—easy to overlook but super important. Thanks for laying it out so clearly!

[Joseph W. Doherty]

"Starting with the router’s datasheet is a smart move—it really helps set expectations for what your hardware is capable of."

Well, that's a very big maybe, maybe not.  Datasheets don't "lie", but they often don't highlight the many possible reasons the device will NOT provide its max performance (or even anything close to it), as listed on its datasheet.

The questions @Leo Laohoo posed would be very helpful in providing you possibly realistic performance expectations.

If I remember, I'll post a Cisco paper describing various router models performance under different situations.  At this point, the routers are older models, but the takeaway, which hadn't changed, is how very highly variable router performance can be.  I.e. how a router is shown, for its best case, with gig+ performance, to have a Cisco recommendation to only be used for 10 Mbps!

BTW, The 4k router series initially had licensing caps that pretty much insured they can almost always provide the licensed performance.  Then Cisco provided a new license, which didn't have a limit.  It was described as providing "up to" throughput, and in best case it might, but not made clear, for worst case, it might not provide any additional throughput.

[Joseph W. Doherty · Accepted solution]

Attached, find the Cisco White Paper for Cisco Integrated Services Routers—Performance Overview.

Unmentioned in my prior reply, the Miercom report, https://miercom.com/pdf/reports/20150817.pdf, is also worth reviewing.  Take note of CPU loading and actual throughput, in different scenarios, for different 4K router models.  Again, not in this report, a later license uncapped these routers, but depending on what the router is doing, there may no additional throughput capacity to a notable increase.

Lastly, some of the latest Cisco routers have been adding in switch like hardware, but very model dependent.

[Leo Laohoo]

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@Joseph W. Doherty wrote:
Datasheets don't "lie"

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But "exaggerate" they do often.  

[Joseph W. Doherty]

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@Leo Laohoo wrote:

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@Joseph W. Doherty wrote:
Datasheets don't "lie"

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But "exaggerate" they do often.  

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Laugh, it can sure seem that way, but a "reputable" company, like I believe Cisco is, doesn't so much "exaggerate" as just shouts out the very best possible, without doing likewise for those little and nagging details, which makes it unlikely you'll obtain the same for your usage.

I've attached another, rather old, Cisco document of various router models performance.  What's interesting, is a careful read of the beginning of the document.  Here the little and nagging details, which are generally not mentioned on a data sheet, are presented.

Don't know if you have large lotteries "down under", but here, when some lottery jackpot gets very huge, it becomes national news, with a sort of implication that the huge jackpot increases your (infinitesimal) chance of winning if you play.  But their "datasheet" might note you have zero chance of winning if you don't play, or can only win if you play (both are true).

[Leo Laohoo]

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@Joseph W. Doherty wrote:
I've attached another, rather old, Cisco document of various router models performance.

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Old timers like us are very familiar with this document. 

It saddens me that the team that knocked up this document has been made redundant >10 years ago and there is no replacement for this very important document.

[Emma Johnson]

Thanks for sharing this important notes issue was solved

[Rich R]

@Emma Johnson Please just answer the questions Leo posed if you're serious about wanting help/advice?

Without that it's pointless even starting to try answering your questions.  Also provide a diagram showing your network topology.  "Absolutely, great advice! etc etc etc" (which looks suspiciously like a ChatGPT type reply, especially with the 3rd person reference) doesn't actually help us help you at all.