Random network packet loss (ping drops) is seen for Virtual Machines (VMs) residing on a specific ESXi host configured with Active/Active uplinks.
Article ID: 433226
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Products
Issue/Introduction
- Ping drops persist even when targeting the default gateway from the VM
- Same VM's when migrated to different ESXI hosts in the same cluster dont have any ping drops
- Disabling one uplink for example vmnic2 stabilizes the connection, indicating a path-specific failure
- Using pktcap-uw on the suspect uplink (vmnic2), ARP requests are observed leaving the host but no ARP replies are received, leading to an incomplete adjacency
pktcap-uw --uplink vmnic2 --capture UplinkSndKernel,UplinkRcvKernel -o - | tcpdump-uw -enr -| grep #.#.#.10The name of the uplink is vmnic2.The session capture point is UplinkSndKernel,UplinkRcvKernel.pktcap: The output file is -.pktcap: No server port specifed, select 58832 as the port.pktcap: Local CID 2.pktcap: Listen on port 58832.pktcap: Main thread: 100774202240.pktcap: Dump Thread: 100774737664.pktcap: Recv Thread: 100775266048.pktcap: Accept...pktcap: Vsock connection from port 1038 cid 2.reading from file -, link-type EN10MB (Ethernet)04:02:10.946529 ##:##:##:##:##:## > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has #.#.#.1 tell #.#.#.10, length 4604:02:11.949969 ##:##:##:##:##:## > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has #.#.#.1 tell #.#.#.10, length 46
- Multiple "who-has" requests for the gateway IP are transmitted, but the capture shows no inbound response (UplinkRcvKernel) for these requests
- The packet capture confirms that traffic is successfully egressing vmnic2 (UplinkSndKernel), but the return traffic (ARP Reply) is not reaching the ESXi kernel via that same interface. The fact that the issue disappears when the uplink is shut down proves that the physical network path associated with that specific vmnic is black-holing traffic
Environment
VMware vSphere ESXI
Cause
Mismatched or incorrect physical switch port configuration on the specific port connected to vmnic2
Resolution
Identify the physical switch and port ID connected to the vmnic and Align the physical switch port configuration with the VMware Virtual Switch requirements ensures that the physical fabric correctly learns MAC addresses and forwards return packets to the appropriate physical interface in an Active/Active pair
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