Less known Solaris Features - Data Link Multipathing
I used this feature in the HA-loadbalancing tutorial already. However the future too useful to stay just a “by-word” in a different article. It is DLMP. Or by its full name:”Data Link Multipathing”.
DLMP is a somewhat distant relative of IPMP, however it works on a different layer of the network stack. Whereas IPMP is something totally IP related and thus works on IP interfaces, the DLMP features works on the data links. Out of this reason you can do a lot of more things with it … for example setting up VRRP on it (as you manipulate MAC addresses with VRRP, it doesn’t work on IPMP interfaces). DLMP is a closer relative of an trunk aggregation also known as IEEE 802.1ax respectively 802.3ad (Etherchannel, LACP are other related names for the same or similar things). I will call this type of aggregation “trunk aggregation” in this article.
You configure the DLMP aggregation with the
dladm command and the configuration is quite similar to the trunk aggregation. You can even transform a trunk aggregation to DLMP aggregation. However both methods have different capabilities and constraints. With an trunk aggregation, all cables have to terminate in the same switch, with DLMP you can connect each interface to a different switch. Trunk aggregation can spread the load over all member interfaces of an aggregation. DLMP isn’t capable to do so like a trunk aggregation. With DLMP you are just doing HA when you have just a single vnic. However when you configure multiple VNICs on an aggregation, it will distribute the VNICs on all the member interfaces. As DLMP doesn’t support load spreading, you don’t configure a load spreading policy for it. With trunks the switch has to support trunks and you have to configure the switch to accept such aggregations or you have to use LACP, a DLMP aggregation needs no support and no configuration on the switch.
How to use it
DLMP really easy to use. Compared to the setup of a trunk aggregation, it is an additional
With a show-link you will see that you have an additional data link, which is an aggregation consisting out
net1. Just as we configured a second ago.
show-aggr you can lookup more details:
Now unplug one of the cables
One use case for this feature is to solve a constraint introduced by using VRRP to make the integrated loadbalancing feature highly available as described in blog entry. Or you could use it to give all the VNICs you are using for zones a redundant connection to the network without working with IPMP and even introduce for example network resource manager much simpler than with IPMP working with resource controlled VNICs. Such configurations gets complex very fast and DLMP can reduce this complexity.