Cisco Router forwarding Performance

Answered Question
Mar 10th, 2009

Dear All,

I have two routers with me. Cisco 1841 and Cisco 1812. I want only ethernet to be present for the requirement. No serial interface is required.

I am comparing the performance only to decide.

I am seeing in the datasheets of Cisco 1812 Router stating 100 Mbps forwarding traffic performance. Another Cisco Router 1841 having the performance of 200 Mbps.

How to choose which router to implement provided i have 50 users in the LAN.

Can you please help me to know this

R.B.Kumar

I have this problem too.
0 votes
Correct Answer by Yasir Ashfaque about 7 years 9 months ago

Well for 50 to 100 users, i would say go for the 2801 to 2811.

Basically it will depend how will you use the router if your Internet bandwidth is 10 to 20Mbits 2801 will work fine with NAT, but at the mean time you will perform Intervlan routing with It between 50 to 100 users, its performance will degrade as more and more intervlan traffic will increase.

so As Joseph described it very well, you must plan your bandwidth requirments you need to route between router, then from pdf file of routerperformance decide which router should you go for, remember in your bandwidth plan you should consider all traffic which will be transiting router.

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Joseph W. Doherty Tue, 03/10/2009 - 07:15

From the performance sheet I'm looking at (attached), the 1841 is a little faster than a 1812, but neither comes close to 100 Mbps.

PS:

If you're doing just pure LAN routing, or LAN and WAN but the latter with Ethernet, you might look into the 3560 series. It's normal forwarding performance is much, much better than any software router. (NB: It isn't as feature rich.)

hclisschennai Tue, 03/10/2009 - 07:55

Hi Joseph,

Thanks for your valuable comment.

I just mentioned performance parameters for example only. Please find the attachment for cisco 1812 router. It says its IOS firewall performance as 100 Mbps.

Also i want NATing feature also in the device, But Cisco 3560 does not have this. Thats the reason i have not opted 3560 switch. Also i price is also high.

My main intention is to know how to calculate the performance and no of users.

Please guide me

R.B.Kumar

Joseph W. Doherty Tue, 03/10/2009 - 08:34

You're correct about the 3560 lack of NAT. Doesn't support a FW either.

I think I've found the 100 Mbps you've noted, but it also notes @ 1400 byte packets. Performance usually drops when packet size does, and average packet sizes tend to be much smaller. (NB: i.e. performance often looks much better for large packet than small packets so vendors will sometimes quote performance for large packets.)

If you won't be doing LAN routing beyond to/from the Internet (which I surmise from the need for NAT and FW), then you really only need to size for the performance of the bandwidth to/from the Internet. In fact, for such a purpose, even the 800 series might work well for you.

When looking at bandwidth, don't forget, performance numbers may need to support duplex traffic. So for instance, even for the 100 Mbps quoted might only support 50 Mbps in both directions (or other combinations of duplex that add to 100).

hclisschennai Tue, 03/10/2009 - 08:51

Hi Joseph,

I like appreciate your effort.

I am worried that i am not getting the exact answer. Sorry that i wouldn't have conveyed this properly. Let me put in simple words as below:

How the number of users in the LAN or behind the Router are compared to the performance of the Router.

For example, if i have 50 users what should be the minimum traffic performance of the router? and

If i have 100 users what should be the minimum traffic performance of the router?

Hope you will help me

R.B.Kumar

Joseph W. Doherty Tue, 03/10/2009 - 09:13

No, you're received the answer, but I guess I didn't make it clear.

It's not as much a question of the number of users but the bandwidth involved. Whether you have 5, 50, 500 users, what bandwidth does network device need to support? If you're running across a T-1 (1.5 Mbps), the maximum bandwidth is the same regardless of the number of users. I.e. size the device to the bandwidth, not number of users.

A related question is, how much bandwidth is needed by various number of users? This one can be very difficult to answer because it depends on how the users will be using the bandwidth.

The two issue are interrelated since less users, all other things being equal will use less bandwidth. If the average bandwidth is much less than the bandwidth available, it's possible to size a network device for the average utilization not the maximum utilization. This can save cost on the selection of the network device although it exposes you to the device not keeping up when utilization jumps above the average and you might be paying for more WAN bandwidth then you really need.

Conversely, you can size the network device to handle more bandwidth, but since the circuit will limit maximum available bandwidth, the device will not need or use its excess performance. (NB: we do sometimes size the device's performance for future growth, for bandwidth and/or feature support.)

So, to recap, sizing the network device is most dependent on bandwidth that will pass through it (and services on transit traffic). User bandwidth needs depends on many variables.

Does this make sense?

hclisschennai Tue, 03/10/2009 - 09:32

Hi Joseph,

Your explanation is very helpful. But again i am bothering you by going in deep into the concept.

I accept bandwidth plays a major role in sizing the packet.

But I am keen to know about the backplane performance of the router ie is expressed in pps or Mbps as per datasheet.

before putting a router in place, however i am going to consider the bandwidth. But also i like see the Router forwarding performance.

How this performance relates to the number of users/connections.

please help

R.B.Kumar

Joseph W. Doherty Tue, 03/10/2009 - 16:18

"How this performance relates to the number of users/connections. "

It usually isn't directly related, again because the factors involved are very variable. For example, you could have 100 users share a very low bandwidth connection if the bandwidth usage was very low, e.g. perhaps receiving one brief email text messsage a day. Conversely, one user can be very demanding upon bandwidth. An an example, years ago I supported a small group of drafters using a CADD application that constantly updated the server CADD file while they were working on it. This small group, about 10 users, generated as much network demand as was seen on the backbone for about 2,000 "normal" corporate users within the same Fortune 100 company.

"But I am keen to know about the backplane performance of the router ie is expressed in pps or Mbps as per datasheet."

Bandwidth and packets per second relationship depends on relationship between packet's (or frames) size times how many are forward per second. For Ethernet, numbers are often quoted for the minumum size (64 bytes). Some conversions to bit per second would then be (for gig):

Gig

Packet Size (Bytes) ---------- 64 128 256 512 1024 1518

Theoretical Maximum Kpps 1488 845 453 235 -120 -- 81

Correct Answer
Yasir Ashfaque Tue, 03/10/2009 - 23:16

Well for 50 to 100 users, i would say go for the 2801 to 2811.

Basically it will depend how will you use the router if your Internet bandwidth is 10 to 20Mbits 2801 will work fine with NAT, but at the mean time you will perform Intervlan routing with It between 50 to 100 users, its performance will degrade as more and more intervlan traffic will increase.

so As Joseph described it very well, you must plan your bandwidth requirments you need to route between router, then from pdf file of routerperformance decide which router should you go for, remember in your bandwidth plan you should consider all traffic which will be transiting router.

Joseph W. Doherty Wed, 03/11/2009 - 04:50

I agree with Yasir noting a 2801 or 2811 might be suitable for 10 to 20 Mbps Internet usage. But for Intervlan routing, how well does 10 or 20 Mbps support 50 to 100 users if you consider most LANs, today, will provide 100 Mbps connections. Consider the 2801 or 2811 doesn't really have enough forwarding performance to guarantee even just two users 100 Mbps.

Although bandwidth per user, again, depends on many variables. LAN switches, offen allocate 24:1 (or 8:1 for servers) ratio for uplinks. For 50 users, this then would expect two users might be using the network at any time; four users for 100 users. I.e., 200 to 400 Mpbs (or 400 to 800 Mbps [duplex]) bandwidth. A 2801 or 2811 would likely offer suboptimal performance for this many LAN users providing intervlan routing.

Note, using the forgoing, also explains why it's common to use gig connections for servers, since often the users above bandwidth is directed to/from them.

Also again, if your WAN connection is of much lower bandwidth, the lower bandwith is all the router needs to support. Selection of your router should be selected against bandwidth. Ideally, bandwidth is selected against number of users but for WAN bandwidth, ideal bandwidth might be too pricey.

[edit]

You might also note, at least in the 2800 series, Cisco recommends routers as supporting various numbers of T-1s, not in number of users. It's more common to see "users supported" for equipment directed to small businesses since they can easily count users but usually don't understand sizing equipment or bandwidths.

Incorrect sizing doesn't mean the network won't function, just either it offers less performance than it might or you've may have spent too much. (The latter isn't too common for a small business, but if you purchased a 2811 for a typical "business class" ADSL, then you've likely purchased performance that will under utilized.)

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