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Mismatch MTU size will cause packet drop - Lan to Lan VPN

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Article ID: KB6450 KB Last Updated: 04 Feb 2014Version: 4.0
Summary:
Mismatch MTU size will cause packet drop - Lan to Lan VPN
Symptoms:
LAN to LAN VPN Packet drop MTU 35% Packet drop IP fragmentation Packet loss MTU sizes are configured differently on both VPN devices Increasing counts of Auth fail
Solution:

THIS SOLUTION APPLIES TO ALL NETSCREEN FIREWALL PRODUCTS.

  1. To prevent packet drop or packet loss issue, it is recommended to match the MTU size on both ends of the VPN Connections (Network or Client). To adjust MTU on Netscreen, please use this command: set flow tcp-all-mss
  2. Use Screen Option on WebUI to block IP Fragmentation: set zone screen block-frag

Here is the problem or goal:

  • 35% Packet drop
  • IP fragmentation
  • Packet loss
  • MTU sizes are configured differently on both VPN devices
  • Increasing counts of Auth fail
  • How to: Prevent Packet Drop or Packet Loss

Problem Environment:

  • LAN-to-LAN VPN
  • Packet drop
  • MTU

Applicable Products:

  • NetScreen-5XP
  • NetScreen-5XT
  • NetScreen-10
  • NetScreen-25
  • NetScreen-50
  • NetScreen-100
  • NetScreen-204
  • NetScreen-208
  • NetScreen- 500
  • NetScreen-1000
  • NetScreen-5200


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