multiple subnets per VLAN and port binding

[compendius]

Hi,

I need some clarification.

Our iSCSI SAN storage (Dell MD3660i0 requires a separate subnet per port.

We require multipathing and load balancing in VMware.

To achieve this in ESXi 5.1 we need port binding...BUT port binding is only supported if the vmks are all in the SAME broadcast domain accorrding to these two KBs

VMware KB: Considerations for using software iSCSI port binding in ESX/ESXi

VMware KB: When using multiple VMkernel ports with port binding to access two or more storage arrays...

Ok...surely then I can simply put all my ISCSI storage subnets in one VLAN and all will be ok (a VLAN is after all a broadcast domain, both are L2 stuff)..this would satisfy the KBs requirements....if VMware really mean 'broadcast domain' in the true sense of the term.

So my question is can you configure port binding in this way? Is it supported by VMware?

[compendius]

I have asked VMware this question and so far have not had a meaningful response.

All I want is a definition of what VMware mean by 'broadcast domain' in the context of the KBs I have referenced.

This is important as in the OSI model a 'broadcast domain' is Layer 2  along with VLANs

A subnet is Layer 3

So many subnets can be part of the SAME broadcast domain by including many subnets in one VLAN.

So in the context of ISCSI sw port binding, by 'same broadcast domain' are VMware referring solely to Layer 2, or are they referring to Layer 3 (subnets) as well. In which case the KBs should explicitly mention 'subnet'?

If anyone has any pointers it would be most welcome.

Thanks

[compendius · Accepted solution]

VMware have come back to me (in fact the author of one of the KBs I referenced)

http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=203886...

He has confirmed that the terminology in the KB is misleading and by 'broadcast domain' he actually means 'subnet' So layer 3 not layer 2.

This means that you CANNOT have multiple subnets in one broadcast domain (VLAN) AND use iSCSI SW port binding.

BUT

He told me (he is very familiar with the Dell MD3660i iSCSI kit), you do not have to have port binding to achieve multi pathing and load balancing. If you have a requirement for multiple subnets from your iSCSI SAN vendor then just create multiple vmks on different subnets and DO NOT do port binding. The fact they are on different subnets will be enough to achieve multipathing

He is updating the KB to make all of this much clearer.

I hope this helps someone