I'm looking at Cisco's documentation on the issue http://www.cisco.com/web/partners/downloads/765/tools/quickreference/routerperformance.pdf and I'm having a hard time getting the numbers to add up.
Is it correct to assume that the Fast/CEF switching throughput rate applies to, for example, basic IP routing of packets between two subnets on FE interfaces?
The reason I ask is because the numbers seem somewhat low. I currently run an old 2611XM to give a simple way of providing a failover to an ADSL line (floating routes). This currently routes IP over an Ethernet line at the line's capped rate of 20Mbps, whereas the Cisco doc states that the max is 10.24Mbps for that device.
It is my intention to upgrade the fibre line to 100mbit and need a device which can handle that throughput. Should the Cisco doc be taken as a worst case and strictly followed if one wishes to route a particular throughput of traffic?
Additionally, what metrics of the router should be examined when pushing a rate of traffic through it to see how close to its limits it lies?
Best Answer
The first sentence in that document is critical.
That document is telling you the maximums for a certain type of packet. But in a real network you aren't going to be seeing only 64 byte packets. You are probably going to be transmitting packets that are much larger reaching up into 1500 bytes.
The Mbps value is simply calculated. [See the statement
Mbps calculated by pps * 64bytes * 8bits/byte]. This is not an measurement of what is possible under typical usage.The data in that sheet is telling you more about the number of packets that can be handled per second, not the throughput you would see if all your packets were at the size of the MTU.
Another important statement is alost at the top.