[c-nsp] ATM packet loss

James Berwick jim at jamesberwick.com
Thu Sep 3 02:50:44 EDT 2009

Mikael Abrahamsson wrote:
> On Wed, 2 Sep 2009, James Berwick wrote:
> To re-iterate.
> Set it to 120 megs and try again. If there is still a problem, lower 
> it and see if it helps.
> Also, what Cisco hardware are you using exactly? PA-A3-OC3* cards in 
> VIP2-50:s or are you using better gear?
Ok, to test I just built a 120 meg ubr pvc.  It performed identically to 
the 45 meg PVC we've been testing with.  I also built several other 
speeds (30, 45, 60, 90) and they all performed identically, packet loss 
for packets over 576 bytes and download speeds in the 1-5mbit range. 

The hardware is a Cisco 7507 chassis with an RSP16 with 1GB of RAM.  The 
VIP is a VIP-480 with 256 megs of RAM.  The only port adapter in the VIP 
is a PA-A3-OC3-SMI.  The RSP CPU load averages 20% and show proc cpu 
hist does not show any time period that the max CPU broke 50%.  The RSP 
has approximately 850 MB of free RAM.

if-con'd into the VIP, it has about 190 megs of free RAM and shows an 
average utilization between 0% and 10% over the past 72 hours, no maxes 
higher than 20%.

Our MRTG graphs show that September of last year this same hardware was 
pushing over 100mbit/sec on our ATM OC3. 

This chassis only does ATM traffic.  We have a Covad ATM DS3 in a 
VIP2-50 in slot 0.  This DS3 is working fine.  We have a Verizon OC3 in 
a VIP-480 in Slot 1.  This is our problem OC3.  We have VIP-480s in 
slots 4 and 6 also terminating Verizon ATM DS3s, these are also working 
fine.  We also have a VIP-480 in slot 5 with a gigabit adapter to uplink 
the router to the rest of our network.

I just realized something that may (or may not be) helpful. 

We use ATM mostly for schools and other educational institutes, but we 
also receive residential and business DSL traffic over our ATM 
circuits.  We've got around 400 DSL customers on this OC3 who are online 
right now, with a mixture of PPPoE and statically bridged DSL users and 
I'm not seeing anything wrong with any of their connections, ie, no 
packet loss, no performance issues.

Please excuse me if I missed something or typed it very poorly, I've 
been working on this problem for about 18 hours now and I'm fried.  
Thanks again for the suggestions!

More information about the cisco-nsp mailing list