[c-nsp] Dropped packets and poor performance

James Greig james at mor-pah.net
Mon May 4 07:18:46 EDT 2009

Hi Guys,


As per the subject we're seeing this on a 3845 (we've also swapped in a 7204vxr (npe-400) and seeing the same issue).


Background:- one upstream talking BGP to two of their peers taking 100mbit transit via Ethernet.  3845 statically routing the announced /21 to a 3750 stack behind.


We're seeing asymmetrical speed problems through the 3845 to various internet locations including another pop of ours taking transit from the same provider.  We can upstream ~80mbit/s to this location but cant do more than around 11mbit/s downstream in a single flow, the same applies to other remote locations.


We've checked cabling/duplex, checked for interface errors, cef is on, disabled things like netflow just to be sure, routers cpu utilisation is low  ~5-10%.  We had a maintenance window last night where we called in the transit provider to help debug the issue.  Eventually we got to a point where a laptop was jacked straight into their Ethernet handoff and throughput was fine at almost 90mbit/s as we'd expect, so this is pointing at router config, as mentioned we've swapped in a 7204 and still seeing the issue so its ruled out bad hardware. 

We're also seeing dropped packets when pinging from the router to the ISPs next hop, but were not seeing this when pinging from a laptop to the ISPs next hop.


At this point we don't know where to go from here, if anyone has any suggestions we'd be most greatful, config can be provided if needed.




James Greig


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