45Meg MPLS to Cisco 1841. Can the 1841 handle this?

Unanswered Question
Apr 29th, 2009
User Badges:


Please take a look at the attached drawing. This is only a small portion of our network but my question is, can these 1841 routers handle a 45Meg connection? I thought these routers were designed for T1/E1 type speeds. I know I saw a router performance document somewhere that showed 1841's could handle 38.4MB of traffic and that is only with routing turned on. If anything else is enabled, like access lists, NetFlow or whatever, that number will decrease because of the capacity of the router. Am I correct in these statements? Anyone have that document or anything else that shows performance of these routers? Thanks in advance.

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
Collin Clark Wed, 04/29/2009 - 12:08
User Badges:
  • Purple, 4500 points or more

I have attached the performance guide for you. Assuming you will be using DS-3 network modules, the 1841 will not support it. It is supported on the 3825 w/ no services and the 3845 w/services. Routers above support it as well.

Hope that helps.

Update: I see now that you're getting Ethernet hand-off. I would still look at the 2800 series instead of the 1841.

troymaki Wed, 04/29/2009 - 12:31
User Badges:

Thanks Collin. Our routers are part of a managed solution from our ISP. I had asked them to turn NetFlow on so we could analyze our traffic to see what was causing slow downs to certain sites. Why you would go with 28xx routers? I said the same thing and the ISP said that these 1841's are fine but yet they won't give me NetFlow data because they say it congest the pipe more and cause unnecessary CPU utilization. That to me means these 1841's aren't the correct router for the 45Meg sites. Am I way off?

are they handing it off via ethernet or serial? if ethernet it could work but then there are the features and performance problems to deal with. If serial thats a big no it won't work. Are they planning on managing the routers at the sites or are you? If you are go with the 2800 or 3800 series and skip what they deem is the "correct" routers for your sites.

In that thought process it makes me wonder if their service is worth subscribing if they don't know this already.

troymaki Wed, 04/29/2009 - 13:00
User Badges:

They are handing off Ethernet and managing the routers. Wasn't my choice as I wasn't here when this contract was signed 18 months ago.

Collin Clark Wed, 04/29/2009 - 12:45
User Badges:
  • Purple, 4500 points or more

No you're not. Looking at the performance guide (as well as real world experience), the 1841 can't handle 45MB. Since you're adding services (ACLs, netflow) I would be even more hesitant. I suspect the reason the ISP is deploying the 1841 is because it is significantly cheaper than the 2800 series. Netflow has low overhead (both CPU and bandwidth) so I would fight that fight! I would also request SNMP access (read-only would be fine) so you can monitor CPU/memory, interface utilization, etc.

troymaki Wed, 04/29/2009 - 13:27
User Badges:

Yup, I will be looking into that too. Thanks

troymaki Wed, 04/29/2009 - 13:23
User Badges:

I have been fighting the NetFlow request for 3 months now. I just wanted it turned at 5 sites, not all 10. I'm sure if I asked about SNMP access, that will hit the same black hole that all my NetFlow requests have gone into. I'm with you on the cost of the routers. What's an 1841 go for? $900 versus a 2811 for say $4K? Then, to go to a 38xx, it's probably around $12K. Do you know where I can find something that will show the overhead of Netflow?

Joseph W. Doherty Wed, 04/29/2009 - 17:07
User Badges:
  • Super Bronze, 10000 points or more

The performance sheet Collin provides, is likely where your "38.4MB" for the 1841 comes from.

Ethernet, for minimum size packets, requires 1.488 Kpps per Mbps, or for 1500 byte packets, requires 81.3 pps. So, 45 Mbps Ethernet (duplex) requires about 134 Kpps, min packets, or 7.32 Kpps, 1500 byte packets.

The 1841 is rated at 75 Kpps for 64 byte packets(?), so it's unlikely to handle 45 Mbps Ethernet line rate (duplex) for such minimum packets even without services.

We don't know the actual router's pps rate for larger packets. The 1841 might be able to process 45 Mbps Ethernet duplex at some larger packet size (w/o other services), but we don't have the pps ratings for larger packets.


Besides perhaps insufficently sized routers, if your sites have many-to-many traffic patterns, its also common to see cloud egress congestion. (You can also have cloud ingress congestion, too.)

With default(?) Ethernet FIFO queues, it only takes one bandwidth consuming flow to make the network appear slow to other flows.

lamav Thu, 04/30/2009 - 06:20
User Badges:
  • Blue, 1500 points or more

Hi, Joseph:

"Ethernet, for minimum size packets, requires 1.488 Kpps per Mbps, or for 1500 byte packets, requires 81.3 pps. So, 45 Mbps Ethernet (duplex) requires about 134 Kpps, min packets, or 7.32 Kpps, 1500 byte packets."

I like these stats.

Can you please elaborate a bit more on what they actually mean?

When you say that a certain ethernet bit rate should be complemented by a certain pps rate, what does that mean? Why should it be?


chad patterson Thu, 01/03/2013 - 15:34
User Badges:

     On a Cisco 871, via ethernet handoff, my speedtest results are almost 30Mbps. The Cisco 871 is capable of  25Kpps, and the Cisco 1841 is capable of 75Kpps. Your minimum routing on an Ethernet handoff should then be 3x the minimum routing on my Cisco 871. So I assume that your maximum should also be 3x (30Mbps?), although I have not been able to figure out what exactly my maximum is.

     I am trying to figure that out in this post https://supportforums.cisco.com/message/3819583#3819583

chad patterson Tue, 01/08/2013 - 15:42
User Badges:

     In fact upon further investigation, I have found table 6 in this document to be a fair estimate. In an IMIX (translate 'real world') environment, the Cisco 880, which processes 50Kpps, can obtain a real world speed of 60Mbps. The Cisco 890, which processes 100Kpps, can obtain a real world speed of 75Mbps. Hence I would take the median of those two speeds, which is nearly 68Mbps, since the Cisco 1841 can process 75Kpps.

     Therefore a fair, real world estimate is the Cisco 1841 can possibly obtain a routing speed of around 68Mbps.


This Discussion