Odd Packet Loss

[cc4252]

Here is an odd issue I've come across while trouble shooting. Note: For this issue let us say that the customers local loop has tested clean.

Customer has a Frame to ATM connection (1.5mb)

Senario:

Customer is experiencing packet loss.

Pings from the ATM edge router to the directly connected customer router (over the ATM LATA) indicates no packet loss.

Pings from the Backbone router to the customer router indicate packet loss.

However pings from the Backbone router to the ATM router indicate no packet loss.

A common fix for this has been to adjust ATM traffic shaping paramters on the subinterface to match the traffic shaping settings in the ATM cloud.

Question is why would this cause the BB Router to see packet loss to the customer but no the directly connected ATM Router? Again keep in mind that there is no packet loss between the BB Router and the ATM Router. Why would traffic shaping paramters drop packets 2 hops away?

Also of note is that this issue tends to appear on interface collectors with over 150 PVCs on them (but still well within normal oversubcription paramters).

[Georg Pauwen]

Hello,

just one question to clarify: are you actually seeing any traffic other than the ICMP ping traffic being dropped ? I am just asking because a packet loss reported by a ping does not necessarily mean that packets are lost, just that they might time out.

Do you see any timeouts on your pings ?

Regards,

Georg

[cc4252]

Yes we are seeing other traffic drop as well..We don't get timeouts..and other network traffic to other sites over the same transit interfaces and out the same customer OC3 show no signs of packet loss or time outs. It's weird..