cisco 2911 maximum pps/bandwith

support · ‎10-18-2013

Hello,

We are installing cisco 2911 in a production enviroment and have not yet decided if it can handle the load or need to sit behind another router.

This is the simple scenario:

The cisco 2911 is intended to be the gateway which have WAN port connected to the ISP switch and LAN port connected to our switch.

all services will be disabled except VRF and LNS (no use of NAT,IPSEC,VOICE etc..).

it should be plain gateway router which should accept connections and pass them to other routers and firewalls behind it.

our wan bandwith will be about 500Mbps and can get a lot of concurent stats (1,000,000+).

but again all service in the router except VRF and LNS will be disabled.

in the documentation it is written that the 2911 can take load up to 353,000 pps / 180Mbps with its services enabled but i am pretty sure that in our situation those number are all different.

can anyone advise what load it can take for what we have?

will have to decide if it should sit behing more CPU capble router which we have or give it a try.

Thanks.

Joseph W. Doherty · ‎10-19-2013

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Posting

500 Mbps? The 2911 is likely too small. The attachment I provided may be a better guide for sizing your router based on need. In your case, table 5 might be a starting point. (If you're usage feature needs are so basic, you might also look at using a small L3 switch.)

support · ‎10-19-2013

Thanks but table 5 is about performance with QOS which i don't intend to use or enable.

all service will be disabled except LNS server with VPND/VRF support.

still looking for some info before i decide to place the 2911 behind more cpu capble router/

thanks.

Joseph W. Doherty · ‎10-19-2013

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Thanks but table 5 is about performance with QOS which i don't intend to use or enable.

all service will be disabled except LNS server with VPND/VRF support.

still looking for some info before i decide to place the 2911 behind more cpu capble router/

thanks.

Laugh - yea I understood that, but you didn't seem to understand "starting point" for using table 5, I wasn't suggesting table 5 directly answers your need.

Unfortunately, Cisco isn't always going to have a table that predicts performance for your specific needs.

What you often need to do is "bracket" usage conditions around your usage to approximate what performance your situation might require. Or, you can go worse case, which often means you buy a box more powerful than you need.

BTW, even if there was table that seemed a usage (feature) case direct match, unless your actual traffic is also an exact match, you performance might still vary.

In general, table 5 should concern you that a 2911 is suitable for 500 Mbps. On the other hand, as table 1 shows maximum performance at 3.4 Gbps, a 2911 has ample capacity for 500 Mbps (well perhaps until you read how the 3.4 Gbps is obtained ).

Lastly, keep in mind, bandwidths in that document's tables are aggregates, i.e. assuming your 500 Mbps is duplex, you need to treat its bandwidth as gig. If that's the case, as table 5 is probably the closest use case to yours, a 3925E might be the smallest suitable ISR.

PS:

Oh, if your average bandwidth usage is much, much less than 500 Mbps (duplex?), then you might also size smaller. However, if you size too small, traffic bursts might drop packets.

support · ‎10-19-2013

thank you for the detailed answer

i saw this documentation before but all of those tests are intended for typical ISR services (qos,firewall,ipsec etc..)

i want to do some untypical use of the product and place it as a plain gateway with none of those service enabled.

now i understand that it is all about packet size in my case but i do not have a starting point to calculate it.

maybey i am getting it all wrong?

more important question will be how much concurrent connections the 2911 will be capble handling? this is much more critical to us since we have peaks scaling up to 1,000,000 concurrents and the bandwith itself is a lesser issue and usualy not passing the 150Mbps average

Joseph W. Doherty · ‎10-19-2013

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

I don't think you're getting it "all wrong" but I suspect you're expecting to much from any performance spec. Router performance is a bit of a guesstimate because it's often impacted by your specific traffic with your specific features.

Number of concurrent connections usually doesn't make much of performance difference for CEF enabled routers. (Note I wrote "usually".)

If you're configuration is "plain vanilla", then performance will start to approach "no service" PPS and/or bandwidth; table 1 in the white paper. As I noted earlier, performance is given for total throughput of the device, so you need to allow for all transit traffic, i.e. count ingress bandwidth on all interfaces. As the white paper also notes, you normally don't want the CPU to go above 75%, and so when guesstimating, allow for 50% usage. Lastly, if you allow for smallest packets, you should also have some reserve performance.

Often a quick and dirty size estimation is divide table 1's Kpps rate by 4 (which allows for duplex and 50% CPU). By such a measure the 2911 would be suitable for 352 / 4 = 88 Mbps (aggregate). Again, that's ball park, often you'll see better performance (as most packet mixes are not all minimum size), but occasionally you might see worse performance (as adding one service can degrade performance, or process switching is often 10x slower - there's a reason for the recommendations at the end of the paper, in figure 1, 35 Mbps [duplex] for a 1921.)

Even for 150 Mbps average, I would consider a 2911 on the small side, and remember, if your average has a wide variance, peaks might be subject to packet drops.