Pings are not passing over GRE tunnel

Products

• VMware NSX

Issue/Introduction

• ICMP ping from a VM on an overlay segment through a T0 GRE tunnel is failing.
• Other traffic such as SSH works without issue.
• The T0 is in active-standby .
• Packet capture on the ESX host where the active T0 edge is running shows ICMP requests, but no response.
  
  pktcap-uw --uplink vmnic[X] --capture UplinkSndKernel,UplinkRcvKernel -o - | tcpdump-uw -enr - | grep "[source-ip]"
[Timestamp] [src-mac] > [dst-mac], ethertype IPv4 (0x0800), length 122: [gre-src-ip] > [gre-dst-ip]: GREv0, proto IPv4 (0x0800), length 88: [vm-src-ip] > [vm-dst-ip]: ICMP echo request, id [ID], seq 1, length 64
[Timestamp] [src-mac] > [dst-mac], ethertype IPv4 (0x0800), length 122: [gre-src-ip] > [gre-dst-ip]: GREv0, proto IPv4 (0x0800), length 88: [vm-src-ip] > [vm-dst-ip]: ICMP echo request, id [ID], seq 2, length 64
• From the ESX level, no drops are observed on the physical NICs.
  
  vsish -e cat /net/pNics/vmnic[X]/stats

device {
   -- General Statistics:
   Rx Packets:6766914
   Tx Packets:2477917
   Rx Bytes:6332301478
   Tx Bytes:454060823
   Rx Errors:0
   Tx Errors:0
   Rx Dropped:0
   Tx Dropped:0
   Rx Multicast:1474704
   Rx Broadcast:204867
   Tx Multicast:811
   Tx Broadcast:317
   Collisions:0
   Rx Length Errors:0
   Rx Over Errors:0
   Rx CRC Errors:0
   Rx Frame Errors:0
   Rx Fifo Errors:0
   Rx Missed Errors:0
   Tx Aborted Errors:0
   Tx Carrier Errors:0
   Tx Fifo Errors:0
   Tx Heartbeat Errors:0
   Tx Window Errors:0
   Module Interface Rx packets:0
   Module Interface Tx packets:0
   Module Interface Rx dropped:0
   Module Interface Tx dropped:0
  
  

Environment

VMware NSX

Resolution

This behaviour indicates an issue on the physical network.