[c-nsp] Unexplainable packet loss

[Heath Jones]

Hi

Firstly, when you say packet loss, what are you referring to? Is it just the
icmp traffic, or are customers reporting faults with non icmp traffic or...?
Is the 'internet gateway' the 7609 pictured on the diagram?

Its pretty unlikely, but worth checking that there are no duplicate mac
addresses on the network. A duplicate (of 7609 on mdf side) could cause
these symptoms.
You could swap out the RAD with your own device for testing..

I don't think that standard icmp tests will identify the problem though. If
what the engineer said is true, then you really need to be pushing some
traffic down to see it. (load related issue)
'Another engineer tells me that when our customers traffic is removed from
the picture the packet loss goes away'


The first thing though - what is the packet loss?



Cheers


On 18 September 2010 06:22, ML <ml at kenweb.org> wrote:

> I'm experiencing some packetloss on a new metro circuit which neither me or
> the provider can explain.  I've linked a quick diagram of the rough topology
> here: http://imgur.com/lXCSC
>
> Our MDF router is a ME3412, IDF Cisco 2960s.
>
> For whatever reason the CLEC couldn't drop off the circuit in the MDF.
> Therefore in one of the IDFs we have an access port in a dedicated VLAN (10)
> so we carry it back to the MDF for routing.
>
> When pinging our internet gateway from the MDF router we see intermittent
> packetloss.  Anywhere from 1-5%.  When pinging the IDF switch from the MDF I
> see 0% packetloss.  If I ping the internet gateway from the the other
> direction I see 0% packetloss.  The gateway IP for the MDF router is the
> 7609 as the box is just tagging our traffic and carrying it back to the 7609
> in another city.  If the provider pings the management IP on their RAD box
> they see 0% packetloss.   All of the pings I've mentioned are 1500-byte DF
> set.
>
> The provider has connected to the same port we are connected to on the RAD
> box and tested the circuit clean after 500,000 packets and maxing out the
> CIR for the circuit (50Mbps).  We've changed the copper patch from the RAD
> to our IDF switch. Neither me or the provider see any interface errors that
> we can see.
>
> The rate limiting for our 50/50 MetroE happens in two places, egress from
> the RAD box towards the 7609 and egress from the 7609 towards the RAD box.
>  I had the provider remove their rate limiting temporarily in case their
> rate limiting was screwy, no difference.  Another engineer tells me that
> when our customers traffic is removed from the picture the packet loss goes
> away.  When it's added back in the packet loss returns.  Our customers
> traffic has only maxed at 20Mbps so far.
>
> What have I missed?
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