Configuring Distributed Trunking on HP K-Series Switches

The HP Procurve K-Series switches (such as the 3500yl or 8200zl) has a feature that allows you to use 802.3ad link aggregation across switches for server port redundancy and physical switch redundancy. HP’s Distributed Trunking is a proprietary protocol that allows two or more port trunk links to be distributed across two switches to create a trunk group. These grouped links appear to the downstream device as if they are coming from a single device. DT links are created between two switches with an interface called the InterSwitch-Connect (ISC) port. For more information, refer to the HP Management & Configuration guide.

This tutorial will talk about how to configure two switches going down two one server. We’ll assume Switch-1 is and Switch-2 is

Switch-1# conf t
Switch-1(config)# trunk ethernet 1/24 trk10 lacp
Switch-1(config)# switch-interconnect trk10
Switch-1(config)# interface 24
Switch-1(eth-24)# name uplink-switch-interconnect-sw2
Switch-1(eth-24)# exit
Switch-1(config)# distributed-trunking peer-keepalive vlan 1
Switch-1(config)# distributed-trunking peer-keepalive destination
Switch-1(config)# trunk ethernet 1/10 trk1 dt-lacp
Switch-1(config)# exit
Switch-1# wr mem

So what did we just do? First, we created a trunk (a different number other than 10 can be used) that will be used to carry the interconnect traffic. You can think of this as something similar to a stack port. In most cases you will want this to go across more than one interface for higher speeds and redundancy. It could become a bottleneck if for example you have 20 1 gb/s server ports and only a 1 gb/s interconnect. Next, we gave the port a name so it is easier to determine the purpose. Note: Multiple ports bound together are a different type of trunk and the configuration beyond the scope of this post.

An interconnect VLAN was then used to carry the traffic which must be the same on the second switch. I used the default management VLAN but you can choose a different number here. Next, we set the keep-alive destination to switch #2. This is used to determine if the interconnect protocol or entire switch is has gone down. Finally, we created our actual server trunk port with dt-lacp. The switch will see the port as a distributed trunk port, but the server will see it as standard LACP.

Ok let’s do a similar configuration for Switch #2.

Switch-2# conf t
Switch-2(config)# trunk ethernet 1/24 trk10 lacp
Switch-2(config)# switch-interconnect trk10
Switch-2(config)# interface 24
Switch-2(eth-24)# name uplink-switch-interconnect-sw1
Switch-2(eth-24)# exit
Switch-2(config)# distributed-trunking peer-keepalive vlan 1
Switch-2(config)# distributed-trunking peer-keepalive destination
Switch-2(config)# trunk ethernet 1/10 trk1 dt-lacp
Switch-2(config)# exit
Switch-2# wr mem

You can issue the following commands to check the status of the trunk:

  • show trunk – shows trunk information of the switch and their types
  • show switch-interconnect – shows port, availability, and VLAN information for the interconnect port(s).
  • show distributed-trunking peer-keepalive – shows information on the keepalive/heartbeat

Now that dt-lacp was configured on both switches, you can use the server’s networking software to create a team using multiple NIC ports. If using the above configuration, you will want each server port plugged into Interface 10 on both switches and the team configured for 802.3ad or LACP.

For fun you can set up a second server and second set of dt-lacp ports (only the one interconnect is needed). Use the ping -t command to start a continuous ping to the second server from the first and unplug a cable. The ping should continue working and only drop 1 packet. Plug it back in a try it with the second cable. The same behavior should occur where 1 packet is dropped. We now have redundant paths between two servers.

3 thoughts on “Configuring Distributed Trunking on HP K-Series Switches

  1. Hi,

    May I know whether these switches act as the gateway for the downstream devices? If yes, what will be their gateway IP, the .1 or .2? Or VRRP is needed? Thanks!

  2. These switches do have Layer 3 support and can act as a gateway. Distributed trunking works at layer 2 however. You cannot use DT and VRRP at the same time. What are you trying to setup?

    • Hi Nicholas

      Could you expand on your comment “You cannot use DT and VRRP at the same time”. Currently we run HP as Router/Switches and the devices we need to use DT on also run OSPF with VRRP? Also I have seen in the manual not to use Multicast Routing do you know what happens when these are all combined?

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