Ping from specific VMkernel adapter in vSphere 6

When troubleshooting network problems on ESXi hosts you want to specify the outgoing VMkernel adapter. As explained here you can ping from a specific VMkernel adapter with the -I parameter. In vSphere 6.0, or with VXLAN activated, this might not work as expected and displays the following error.

[root@esx:~] ping -I vmk1 10.1.1.1
Unknown interface 'vmk1': Invalid argument

The problem is related to the multiple TCP/IP Stack features introduced in vSphere 6.0. To ping from specific VMkernel adapters that are not in the default Stack (defaultTcpipStack) you have to manually specify the NetStack with the -S parameter.

Ping from a vmkernel Interface that is not part of the defaultTcpipStack default stack fails with the following error message:

[root@esx:~] ping -I vmk1 10.1.1.1
Unknown interface 'vmk1': Invalid argument

Additionally it's not even possible to ping local interfaces:

[root@esx5:~] esxcli network ip interface ipv4 get
Name  IPv4 Address    IPv4 Netmask   IPv4 Broadcast   Address Type  DHCP DNS
----  --------------  -------------  ---------------  ------------  --------
vmk0  192.168.222.25  255.255.255.0  192.168.222.255  STATIC           false
vmk1  10.1.1.5        255.255.255.0  10.1.1.255       STATIC           false
vmk2  192.168.222.56  255.255.255.0  192.168.222.255  STATIC           false
[root@esx5:~] ping 10.1.1.5
PING 10.1.1.5 (10.1.1.5): 56 data bytes

--- 10.1.1.5 ping statistics ---
4 packets transmitted, 0 packets received, 100% packet loss

vmk1 is the interface I use for vMotion, so it's not part of the defaultTcpipStack. You can identify the TCP/IP Stack with the following commands:

• esxcfg-vmknic -l (NetStack Column)
• esxcli network ip interface list (Netstack Instance)
• esxcli network ip interface list |grep -E 'vmk|Netstack' (Filtered Version)

After identifying that vmk1 uses the TCP/IP Stack named vmotion you can successfully ping by using the correct NetStack with the -S [NetStack] parameter.

[root@esx5:~] ping -I vmk1 -S vmotion 10.1.1.1
PING 10.1.1.1 (10.1.1.1): 56 data bytes
64 bytes from 10.1.1.1: icmp_seq=0 ttl=64 time=0.299 ms
64 bytes from 10.1.1.1: icmp_seq=1 ttl=64 time=0.328 ms
64 bytes from 10.1.1.1: icmp_seq=2 ttl=64 time=0.653 ms

--- 10.1.1.1 ping statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/max = 0.299/0.427/0.653 ms

Local pings in the correct NetStack are also possible:

[root@esx5:~] ping -S vmotion 10.1.1.5
PING 10.1.1.5 (10.1.1.5): 56 data bytes
64 bytes from 10.1.1.5: icmp_seq=0 ttl=64 time=0.538 ms
64 bytes from 10.1.1.5: icmp_seq=1 ttl=64 time=0.041 ms
64 bytes from 10.1.1.5: icmp_seq=2 ttl=64 time=0.034 ms

--- 10.1.1.5 ping statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/max = 0.034/0.204/0.538 ms