UDP packet destined for VM over port 4791 is not seen at the RX vmnic
Article ID: 396622
Updated On:
Products
VMware vSphere ESXi
Issue/Introduction
- Traffic sent from virtual machine source ports 4790, 4791, and 4792.
- Response to port 4791 is not received by the client VM.
- Packet capture confirms that the packet response to port 4791 was not seen at the intended ESXi uplink.
Environment
- ESXi 7.x
- ESXi 8.x
- ESX 9.x
Cause
- 4791 is an IANA-assigned port number for RoCEv2 (IP Routable RoCE).
- Network Adapter supports RDMA configuration and is enabled by default.
- When RDMA is enabled, any traffic with UDP destination port number 4791 will be treated as RDMA traffic and hence will not be forwarded to vmnic (Uplink).
Resolution
This behavior is expected if the NIC card supports RDMA/RoCEv2 and the RDMA feature is enabled, as port 4791 is an assigned port for RoCEv2 (IP Routable RoCE).
Workaround:
- By disabling RoCE, a VM can utilize the RoCE UDP port 4791 for standard UDP traffic if RDMA functionality is not being used by the ESXi servers.
- If RCoE is enabled and needed, please engage your hardware vendor on further recommendations to use reserved port 4791.
Additional Information
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