Causes of Buffer overruns?

[ek36]

Buffer overruns?

A trainee NE has asked me this question and I'm finding it difficult to find a suitable answer.

After DRAM where would buffer overruns occur on a router as a result of

- the router bus OR the processor OR the route processor OR the interface hardware

(Specifically he knows lack of DRAM is the main area in which overruns are caused)

I'm inclined to go for the processor as this is mostly closely linked to DRAM which is the main cause.

Anyone have any ideas?

Thanks

Ed

Network Enginneer

Axians

[tsettle]

Your right on all accounts. An overrun occurs when we can't move a packet out of the buffer onto it's next destination. For example, if the ingress interface is experiencing overruns it could be because the egress interface buffers are full, or if destined for the cpu then the internal buffers may be full. The issue might also be simple hw limitation. Check internal buffer pools, check cpu utilization, check interface statistics for type of fwding mechanism used. Here are some links to illustrate this:

http://www.cisco.com/en/US/tech/tk801/tk36/technologies_q_and_a_item09186a008014f919.shtml

http://www.cisco.com/en/US/products/hw/switches/ps633/products_user_guide_chapter09186a008007efab.html#xtocid691024

http://www.cisco.com/en/US/products/hw/modules/ps2033/products_tech_note09186a00800d76e5.shtml

[fnavarro]

Under what conditions does the router increment the throttles counter?

[s2193988]

see the following link

http://www.cisco.com/warp/public/121/inputdrops.pdf

raymond chow