Major consideration – If you have duplicate packets in your network:
- Find out if you have problems in your network
- Then solve the issues
Duplicate Packets (DP) are there for a reason whether it be good or bad (usally bad though).
Do NOT just ignore them, as it will make further troubleshooting difficult.
Here are some of the causes for DP in your network...
Why, Oh Why do I have Duplicate Packets?
Duplex Mismatch
- Auto-negotiation issues – different deployments
- Incorrect settings, speed, duplex, etc.
- Highly mobile devices do not get connected correctly
- Monitoring devices that try to take over auto negotiation, causing storms
- Mismatch can also cause higher collisions, network congestion, more DP and dropped/lost packets
- Collisions can cause DP – Bad Layer 2, Link Layer issues
- Multiple Ethernet stacks on one adaptor
UDP/TCP
- UDP does not know when a packet is missing, and the application can cause it to resend
- TCP can recognize when you have lost packets, resulting in retransmissions
Applications and Servers
- Applications that cannot recognize DP may reset the conversation or terminate the connection/inquiry
Route Paths
- Incorrectly configured load balancing
- More than one routed path to/from the host
- Two or more non-routed paths to/from the host
- NAT failure
- Multiple WAN or WIFI links
- WIFI devices may resend packets
- PIM-SM – many router paths to group members (multicast events)
Monitoring Your Network With SPAN (RSPAN) Or VACL
- CAM table issues – IP to MAC mapping
- All rely on the port bandwidth – easily flooded, causing LL2 issues
- Programming the SPAN/VACL can cause issues
- SPAN copies all packets, which leads to duplicate packets being sent to MON
- VACL does not know if the packet was sent or received – which one to block?
Solution – Just use REAL TAPS for your visibility plane access. They will not fail you!
A de-duplication device hides all duplicates after the first one received, but the first one may not be the issue causing your network/application issues. How do you know?
This is a guest post by Tim O'Neill, Senior Technology Consultant & Chief Editor at LoveMyTool that was originally published on 10/8/2014 and updated on 9/1/2016.
Want to learn more about the many network tools that help you manage your network? Download What Your Network Is Missing: 7 Tools To TAP