This article provides steps to configure the size of network packet trace buffer.
You can run the command tcpdump-uw on ESXi hosts to capture packet traces from a VMkernel ( vmk) interface. The buffer size for packet traces in ESXi 4.x, ESXi 5.0, and ESXi 5.1 is limited to 8138 bytes. In ESXi 5.5, you can configure the buffer size manually.