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Should Path MTU Discovery (PMTUD) work on FastConnect

Antti ElonheimoFeb 27 2024

We are having trouble with some network connections and we have found out that the reason for this is that Path MTU Discovery is not working over FastConnect. Should the FastConnect Virtual Circuit send ICMP Type 3 Code 4 message if it's set to 1500 MTU and a bigger packet is sent over it? What does the setting for MTU (either 1500 or 9000) in FC Virtual Circuit mean?

We tried it with an instance which had attached a security group which allowed all ingress and egress traffic and even added a rule to accept all ICMP in the iptables of the instance.

Should PMTUD even work for connection from OCI to outside over FastConnect?

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Added on Feb 27 2024