Communication issues with guest OS using flexible adapter and a legacy linux kernel

Products

• VMware vSphere ESXi

Issue/Introduction

• Impact the guest OS traffic such as ARP resolution.
• The guest OS uses flexible adapter and a legacy kernel such as CentOS 5.5 (Linux 2.6.18-194.el5).
• The guest OS and an NSX Edge in the communication path are running on the same ESXi Host prepared by NSX.

Environment

VMware vSphere ESXi
VMware NSX

Cause

Flexible adapter inserts a priority-tag field (802.1Q VLAN 0) to packets such as ARP reply in some scenarios, and the guest OS drops those packets by the legacy kernel behavior.

Resolution

One of the followings will unblock this situation. However all of them are recommended because flexible adapter and the linux kernel are quite outdated and their behaviors are not suitable for some current architectures.

• Use vmxnet3 or e1000 adapters instead of flexible adapter.
• Upgrade guest OS to modern one.