When Is A Trunk Not A Trunk?

Very good article here – http://networkingnerd.net/2011/02/02/when-is-a-trunk-not-a-trunk/

Particuly like setting of Native vLAN and tagged networks over an HP trunk;

So, if HP refers to an uplink carrying multiple VLANs are a tagged port, then does HP have a “trunk”? In fact they do. In HPvania, a trunk is a logical construct that aggregates multiple ports into one logical link. For those of you that might be out there scratching your heads about this one, this means that when you “trunk” a group of ports on an HP switch, you are creating one LACP link from up to four individual ports. This kind of configuration should look like this:

Switch(config)#trunk 19-24
Switch(config-trk)#vlan 1
Swtich(config-vlan)#untagged trk1
Swtich(config-vlan)#vlan 10
Swtich(config-vlan)#tagged trk1
Swtich(config-vlan)#vlan 99
Swtich(config-vlan)#tagged trk1

Those of you that are fans of irony will appreciate that the above config sets up this LACP port aggregation to pass multiple VLANs to another switch. In other words, we are configuring a Cisco “trunk” on top of an HP “trunk”.

vmware and load balancing NFS trunks

Straight from the post below, this is the best way (currently) to load balance your NFS datastores…  No MPIO magic here unfortunately.


Basically you can setup IP alias on the NFS side and then setup multiple connections (using a unique IP) per datastore  on each ESX host. This works well if you are using a team of nics running IP-hash load balancing…

Static EtherChannel.

My setup is as follows:

ESXi 4.0 U1, Cisco 3750 Switches, and NetApp NFS on the storage side.

I have a total of 8 nics. I divided the nics into 3 groups.

2 nics on vSwitch0 for Mgmt & vMotion
3 nics on vSwitch1 for VM’s (Multiple port groups (3 VLANS))
3 nics on vSwitch2 for IP Storage (Mostly NFS, a little iSCSI)
(One vSwitch3 I also have a VM port group for iSCSI access from within the VM)

Since I have 3 nics on my IPStorage port group I needed a way to be able to utilize all three nics and not have the server just use one for ingress and egress traffic. This was done by:

Setting up a static EtherChannel on the cisco switch (Port Channel).
Configuring the cisco switch to IP Hash
Configure the vSwitch to “Route based on IP Hash” as well.

The next part is to create multiple datastores on the NFS device. Each of my NFS datastores is about 500GB in size. Reason for this is that my larger luns are iSCSI and are access directly from the VM using the MS iSCSI initiator from the VM itself.
My NetApp NAS has an address of, let say, So all my data stores are accessible by utilizing the address of “\\\NFS-Store#”. This will not be useful as the esx box and the cisco switch will always use the same nic/port to access the nas device. This is due to the algorithm (IP HASH) to decide what link it’ll go over. So to resolve the issue, I added IP aliases to the NFS box. NetApp allows to have multiple Ip addresses pointing to the same NFS export, I suspect EMC would do the same. So, I added 2 aliases 51 & 52. Now my NFS datastores are accessible by using Ip address,.51, & .52.

So I went ahead and added the datastores to the ESX box using the multiple IP addresses:

Datastore1 = \\\NFS-Store1
Datastore2 = \\\NFS-Store2
Datastore3 = \\\NFS-Store3

If you have more datastores it’ll just repeat: Datastore4 = \\\NFS-Store4 and so on…

Since having multiple datastores and address to each, the 3 nics on the ESX box dedicated to IP Storage get utilized. It does not aggregate the bandwidth but it does use all three to send and recieve packets. So the fastest speed you will get is 1Gbit, theoretically, each way for traffic but, it is better than trying to cram all the traffic over 1 nic.

I also enabled Jumbo Frames on the vSwitch as well as the vmNic for IP-Stroage. (need the best performance!)
I should mention that your NFS storage device should have EtherChannel setup on it as well. Otherwise, you’ll be on the same boat just on the other end of it.

Hope it helps!

Larry B.

I should mention that you should not use different addresses to access the same NFS share (datastore). It is not supported and may cause you issues.

vmware – hp procurve lacp / trunk

Cisco’s Etherchannel and HP’s LACP are very similar – probably why I assumed both are supported by vmware. But as per below – it is not the case.


From a procurve perspective the differences between a “trunk” and “static lacp” trunk is the total bandwidth per connection. A typical end point on a “trunk” trunk can transmit various connections down both pipes, but only receive down one – sometimes refered to as TLB (transmit load balancing). In vmwares case when you are using a “trunk” trunk you will have ip hash set as a load balancer, effectively meaning a different nic will be used on the vmware side for each connection a virtual machine makes.

This most probably explains why we hit a 1GBit limit per connection over vmware since a switch “trunk” can only receive back down a single interface. Where as LACP the interface is the team itself (i.e. it is considered as a larger single interface) – and can load balance. Matches up with what i’ve seen on the live switch statistics.

HP’s LACP – should be used where possible – between switches and servers that support it. LACP is a protocol that is wrapped around packets (why both ends need to support it).

“trunk” trunks  – have to be used with vmware at the moment – limits each connections bandwidth to a single interface. (i.e. you will never get more than 1gbit per connection if your nics are all 1gbit).