u/HoaNV9

Hi everyone,

I’m hitting a wall with an OCI FastConnect (On-prem to OCI) setup and wanted to see if anyone else has encountered this recently.

The Symptoms:

• Everything was working perfectly for months.
• Suddenly, all large file transfers (SCP, SMB, Oracle DB, HTTP uploads) started failing/hanging.
• Ping (standard size) and Telnet to specific ports work fine.
• Small packets pass through, but large packets are dropped.

The "Workaround":

• We changed the MTU on an On-prem server from 1500 to 1400, and immediately, the connection started working again for that specific server.

The Mystery:

• ISP/Carrier: Confirmed no changes to the FastConnect circuit.
• VCN/OCI: No configuration changes (MTU remains default).
• Firewalls: No changes on either the On-prem firewall or OCI Security Lists/NSGs.
• Support: Oracle Support is stuck in a loop and hasn't provided a solution yet.

Has anyone experienced a sudden MTU shift on OCI FastConnect without manual config changes? Has anyone faced a similar situation recently? If so, how did you fix it?
Thank you.