Question

OSPF over GRE with MTU set to Jumbo

  • 13 January 2021
  • 0 replies
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I have multiple links between the MLX routers connecting to other vendor devices (Ruckus ICX7750 and Cisco Catalyst 9500) via GRE which randomly get stuck in OSPF Exchange start.  While the MTU at each end matches, I am able to restore the service by simply changing the MTU at each end of the tunnel to any value other that what is currently configured.  I can go up with the MTU or I can go down with the MTU, if both sides match it works.  I can then change the MTU setting back to its previous configuration (when I was stuck in EXST) and OSPF will remain up and stable.  This condition randomly appears and I have NOT been able to identify any trigger for the event to take place.  During troubleshooting I am able successfully send ICMP packets set with an MTU of the tunnel’s MTU size packets to the tunnel’s destination from its source without fragmentation or loss.  Has anyone seen an issue like this in their environments?  The MLX in question is running NetIron 0600c


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