[nsp] Cisco 2500 Traffic Limit and high cpu utilization.

[Terry Baranski]

> Hi All,
> I am wondering what is the traffic limit that a cisco 
> 2500 series routers can handle? And why do we get 
> quite often high cpu load and IP load?  How can I 
> prevent this? I tried WRED queuing on the interfaces 
> it helps a bit but not sufficient.

Depends on average packet size and what performance-reducing features
are enabled.  Make sure CEF switching is enabled and working, first and
foremost:
http://www.cisco.com/en/US/products/sw/iosswrel/ps1828/products_tech_not
e09186a00801e1e46.shtml

The 2500s are rated at 4400 packets-per-second (using CEF) with 64 byte
packets, which comes to around 2.2Mbps.  As packet size increases the
achievable packets-per-second tends to decrease, but the maximum
bandwidth one can push through a router tends to go up because the
packets are bigger.  A fairly limited number of tests with other router
models show bandwidth increasing by around 3-4x as packet size goes from
64 bytes to 1500 bytes (Ethernet traffic).  That would put a 2500 at
around 6-8Mbps with 1500 byte packets, but note that this is simply an
estimate based on the performance profiles of some other routers.
Others here may have done tests on the 2500 series specifically that
they can share.

Note also that these numbers are best case; i.e., CEF enabled, large
packets, no performance-reducing features enabled, and so forth.
Average packet size is usually much lower than 1500 bytes on real
networks.  And anytime you enable a feature that increases the work the
router has to do on each packet (e.g., ACLs, NAT, policy routing, etc),
performance will often suffer.  

-Terry