Why ICMP error type3code4 does not change MTU on management interface?
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Created On 10/10/22 05:13 AM - Last Modified 12/20/23 15:02 PM
Question
Why ICMP error type3code4 does not change MTU on management interface?
Environment
This can be seen where permitted IP address list is set on management interface and the router/hop IP sourcing the ICMP error message is not present in the permitted IP list. The packets from the management interface can be seen retransmitting with the same size and eventually connection fails.
Answer
As permitted IP list is used to control the inbound connections on management interface, the icmp error message is discarded and has no effect on MTU. In such cases, either reduce the MTU manually or add the IP/IP-range of the router/hop sourcing the ICMP error message.
Additional Information
Same behaviour is applicable to all ICMP error messages.