Distributed Trunking in HP ProCurve Switches

Distributed Trunking allows the aggregation of links from one device to two upstream switches. To the downstream device, the two upstream switches appear to be just one single switch.

In the figure above, a trunk (or if you prefer, an aggregated link) named Trk2 is formed from two links, the first link going from Port 1 in Switch 3 to Port A2 in Switch 1, the second one going from Port 2 in Switch 3 to Port A2 in Switch 2. So instead of link aggregation between 2 switches, here we have link aggregation between 1 switch and 2 others. Hence the name "Distributed Trunking".

To the downstream switch, i.e. Switch 3, the two upstream switches (i.e. Switch 1 and Switch 2) appear just like one single switch. This is made possible by the ISC (Inter-switch Connection) between Switch 1 and Switch 2. Switch 1 and Switch 2 must be of the same model and running the exactly same software version for the ISC to work. The ISC could be a single link, or an aggregated link as shown in the example figure above (Trk1).

The keepalive link helps monitoring the status of the ISC. It must be in a separate, non-default VLAN with ports dedicated just for that purpose. No data or synchronization traffic is sent over the keepalive link, so it is not essential to the operation of Distributed Trunking.

Here's how to configure Distributed Trunking using the example in the figure above. Besides LACP, static non-ptotocol trunks can be used as well.

In Switch 1:

trunk A1,A3 trk1 lacp
trunk A2 trk2 dt-lacp
switch-interconnect trk1

vlan 1024
     untag A4
     ip address 192.168.124.1/24
distributed-trunking peer-keepalive vlan 1024
distributed-trunking peer-keepalive destination 192.168.124.2

In Switch 2:

trunk A1,A3 trk1 lacp
trunk A2 trk2 dt-lacp
switch-interconnect trk1

vlan 1024
     untag A4
     ip address 192.168.124.2/24
distributed-trunking peer-keepalive vlan 1024
distributed-trunking peer-keepalive destination 192.168.124.1

In Switch 3:

trunk 1-2 trk2 lacp

For verification, run the command show lacp distributed. The output will look like below:

Certain network features are not supported when Distributed Trunking is configured. As of K/KA/KB.15.16:

- ARP Protection is not supported on the distributed trunks.
- Dynamic IP Lockdown Protection is not supported on the distributed trunks.
- QinQ in mixed mode is not supported.
- Meshing is not supported.
- Multicast routing is not supported.
- IPv6 routing is not supported.