help with extremely slow wan link

rhltechie · ‎07-25-2007

Hi All,

I am having an issue with a WAN link I have across my MPLS. When I ping across the wan from edge to edge I am getting upwards of 600ms. When I am on the suspect router at the suspect site and I ping the ip of the local serial interface it goes into the 1000ms range. Can someone provide some help with how I could proceed to find the problem? I have also called the telco company and they have done "tests" on the line stating that there were no problems.

update: I have a mrtg tool running collecting info from the interface and it looks to me that the interface is almost at max capacity. could line saturation cause the symptoms i am describing?

TIA,

R

Pavel Bykov · ‎07-25-2007

line saturation above 80% starts increasing delays because of peak software queue utilization.

When you have AVERAGE load over 95%, then this delay is not unnatural.

To reduce latency, you should reduce line utilization. Your standard options are:

1. Use QoS policing to limit unwanted traffic

2. Use QoS congestion management to define which traffic is more important than other

3. Increase link capacity.

jwdoherty · ‎07-25-2007

One issue that sometimes arise with MPLS, if you have a multi-point WAN or different site sized links, e.g. T-3 at HQ but T-1 at remote, is congestion on the PE's egress port. One clue to this happening is the link being busy inbound to your router. (You mention the interface is near max capacity, but don't mention whether it's in, out or both.)

I assume you don't see congestion outbound on your router, if so and if your MPLS vendor supports DSCP or IP precedence, using different class queues, try your ping test using a higher priority value (can be done using extended ping and setting TOS). If you see reduced ping times at the higher priority setting vs. the lower priority setting, then you have confirmed congestion within the lower priority class. (Note: if you do have congestion outbound, differences in ping times using different TOS values is also dependent on whether you treat them differently too.)