Hi We noticed that after an interface (physical interface VirtualFunctionEthernet0/7/0) is up state (vppctl set interface state <ifname> up), if we modify the mtu of the interface (e.g. vppctl set interface <ifname> mtu 1500) the interface starts doing rx-miss forever. The interface becomes completely blocked and is not transient. It is possible that the interface is receiving and transmitting packets while mtu is being altered from default 8000 to 1500.
This occurs with i40e VF interfaces and VPP 20.05. I am wondering if this is observed by others as well. It is not clear from the documentation (either DPDK or VPP) if an interface needs to be in "down" (link down) state before the mtu can be modified. The VPP document does say it programs the NIC but does not clearly state if the interface must be in down state. The DPDK rte_dev_ether_set_mtu() API does not mention any such restriction either. I am wondering if this is specific to i40e VF only or applies for other NIC as well. What's the recommended way of updating mtu? If we modify the mtu of logical/sub interface (e.g. VirtualFunctionEthernet0/7/0.400) will alter the mtu of the physical interface ( VirtualFunctionEthernet0/7/0) as well. How could we ensure that mtu setting is consistent on a VF which might have multiple sub interfaces in use including the raw physical interface (without any VLAN) I would really appreciate it if you could provide some advice in this regard. We use physical interface (e.g. VirtualFunctionEthernet0/7/0) for internal communication between two applications since memif is not high performance and use sub interfaces (VirtualFunctionEthernet0/7/0.400, 500, 600) for external networks. Thank you very much - Pranab K Das
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