[c-nsp] Cisco Routers: Performance benchmark

[Jon Lewis]

On Wed, 1 Sep 2010, bored to death wrote:

> the document you pointed out
> (http://www.cisco.com/web/partners/downloads/765/tools/quickreference/routerperformance.pdf)
> was good for the start, thank you. but it was very limited.
> it just had the result for switching of 64Byte frame packets, not any static or
> dynamic routing results nor any results about other frame sizes.
> as i know, the normal frame size of ordinary networks are 1500Bytes which is
> very bigger than 64Byte. for example, in this document, the maximum switching

They use 64 byte packets to try to give you a worst case / conservative 
estimate of the router's packet forwarding capability.  If it can move 
20mbit/s of 64 byte packets, it'll do better (more mbit/s) with larger 
packets.  1500 may be the most common MTU on the internet, but it doesn't 
mean most of your packets are going to be 1500 bytes.  Internet mix 
traffic is going to be smaller than that on average because you end up 
with a mix of small request packets, large reply packets, small ack 
packets, small packets at high rates for things like VOIP, etc.

i.e. lets take counters (if you believe them) from an actual internet 
router uplink:

   30 second input rate 236138000 bits/sec, 55934 packets/sec
   30 second output rate 262583000 bits/sec, 41375 packets/sec

236138000 bits/s / 8 bits/byte / 55934 packets/s = 527 bytes avg packet size
262583000 bits/s / 8 bits/byte / 41375 packets/s = 793 bytes avg packet size

That appears to make sense for a network that's more of a hosting network 
than eyes network.  On avg, our outgoing packets are larger than our 
incoming ones.

> throughput for a 2821 router is ~90Mbit/s which is very low for a gigabit router
> (of course it's because of very small frame size).

cisco's routers typically can't forward packets at the line rates of their 
ethernet interfaces.  If you want line rate, it's going to cost you...or 
find a layer 3 switch that meets your needs.  Those generally can be 
expected to forward at line rate.

----------------------------------------------------------------------
  Jon Lewis, MCP :)           |  I route
  Senior Network Engineer     |  therefore you are
  Atlantic Net                |
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