We help IT Professionals succeed at work.
Get Started

UDP Packet loss

Last Modified: 2015-11-24
Hey guys,

Wondering if someone can shed some light as to what is going on here. I have found this issue with multiple clients and I don't understand what is causing this. The usual complaint is slow UDP connections (usually to a SQL server). I don't see this problem when source/dest are on the same subnet, this only occurs when a router is involved (usually a cisco). I have tested this every way i can possibly think of and all yield the same results; 0% packet loss in one direction, >30% packet loss in the other direction. Many times its 99% packet loss at 100Mbit. I have tested this on multiple workstations, servers, virtual hosts, network cards, as to eliminate them as a potential cause. All yield the same results.

In the test below ..
Server is connected at 1Gbps, Workstation is 100Mbit.
Server is
Workstation is

The two pictures below show the server and client side of iperf. acting as the iperf server. Reversing iperf server / client has 0 impact on the results.

First test: Send from -> = 0% packet loss @ 50Mbit
Second test: Send from -> = ~35% packet loss @ 50Mbit
If i bump the test up to 70Mbit:
First test: Send from -> = 0% packet loss @ 70Mbit
Second test: Send from -> = ~43% packet loss @ 70Mbit

Any ideas as to why one direction 0% packet loss while the other direction on the exact same network >35%.

Just to add, TCP has no problem and will max the connection without issue.

Watch Question
This problem has been solved!
Unlock 1 Answer and 5 Comments.
See Answer
Why Experts Exchange?

Experts Exchange always has the answer, or at the least points me in the correct direction! It is like having another employee that is extremely experienced.

Jim Murphy
Programmer at Smart IT Solutions

When asked, what has been your best career decision?

Deciding to stick with EE.

Mohamed Asif
Technical Department Head

Being involved with EE helped me to grow personally and professionally.

Carl Webster
CTP, Sr Infrastructure Consultant
Ask ANY Question

Connect with Certified Experts to gain insight and support on specific technology challenges including:

  • Troubleshooting
  • Research
  • Professional Opinions
Did You Know?

We've partnered with two important charities to provide clean water and computer science education to those who need it most. READ MORE