Why does not the MTU configuration take effect on tunnel interfaces of a switch


The maximum transmission unit (MTU) configuration is valid for packets sent to and from the control plane, but invalid for packets directly forwarded by hardware. To limit the size of packets forwarded by hardware, configure the MTU on physical interfaces.

Other related questions:
Can the MTU of the GRE tunnel interface take effect
If you set an MTU value on a GRE tunnel interface, forwarding of data packets through the GRE tunnel will be affected. If the packet length exceeds the MTU value on the tunnel interface, the device fragments the packet.

The reason of S series switches TUNNEL port MTU does not take effect
S series switches (except S1700) MTU of the TUNNEL port is valid only for the uplink control plane and the packets sent from the control plane. The MTU does not take effect for the data packets directly forwarded at the hardware level. The hardware level MTU need to configure the MTU value of the physical interface.

Why the MAC-VLAN does not take effect
MAC address-based VLANs take effect only to untagged packets. If an MAC address-based VLAN does not take effect, check whether the incoming packets contain VLAN tags.

Why does the CPCAR rate limit configuration not take effect
The CPU committed access rate (CPCAR) is configured in the attack defense policy view. The CPCAR takes effect only when the attack defense policy is applied on the main control board or interface board on the local area network (LAN) side.

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