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Symptoms: Jumbo Frames Enabled But Some Paths Failing

  • Storage replication between two data centers is failing for large transfers but small ones succeed.
  • NFS mounts hang or produce "message too long" errors intermittently.
  • Ping with default size works between all servers, but ping -s 8972 fails on certain paths.
  • Jumbo frames (MTU 9000) were enabled on all servers as part of a storage optimization project.
  • Servers in the same rack communicate at full jumbo frame size without issue.
  • Cross-rack traffic or traffic traversing the aggregation switch fails for large packets.
  • No ICMP "fragmentation needed" messages are received because DF bit is set.
  • Throughput on affected paths drops significantly because TCP MSS negotiation uses 8960 but packets are silently dropped mid-path.