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Why Are You Hiding Your Duplicate Packets?

August 31, 2016

Duplicate PacketsMajor consideration – If you have duplicate packets in your network:

  1. Find out if you have problems in your network
  2. 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

What Your Network Is Missing 7 Tools To TAP

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

 

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Heartbeats Packets Inside the Bypass TAP

If the inline security tool goes off-line, the TAP will bypass the tool and automatically keep the link flowing. The Bypass TAP does this by sending heartbeat packets to the inline security tool. As long as the inline security tool is on-line, the heartbeat packets will be returned to the TAP, and the link traffic will continue to flow through the inline security tool.

If the heartbeat packets are not returned to the TAP (indicating that the inline security tool has gone off-line), the TAP will automatically 'bypass' the inline security tool and keep the link traffic flowing. The TAP also removes the heartbeat packets before sending the network traffic back onto the critical link.

While the TAP is in bypass mode, it continues to send heartbeat packets out to the inline security tool so that once the tool is back on-line, it will begin returning the heartbeat packets back to the TAP indicating that the tool is ready to go back to work. The TAP will then direct the network traffic back through the inline security tool along with the heartbeat packets placing the tool back inline.

Some of you may have noticed a flaw in the logic behind this solution!  You say, “What if the TAP should fail because it is also in-line? Then the link will also fail!” The TAP would now be considered a point of failure. That is a good catch – but in our blog on Bypass vs. Failsafe, I explained that if a TAP were to fail or lose power, it must provide failsafe protection to the link it is attached to. So our network TAP will go into Failsafe mode keeping the link flowing.

Glossary

  1. Single point of failure: a risk to an IT network if one part of the system brings down a larger part of the entire system.

  2. Heartbeat packet: a soft detection technology that monitors the health of inline appliances. Read the heartbeat packet blog here.

  3. Critical link: the connection between two or more network devices or appliances that if the connection fails then the network is disrupted.

NETWORK MANAGEMENT | THE 101 SERIES