Link aggregation is pretty easy to configure on solaris. Bellow is a quick example that puts 2 interfaces into a LAGG and balances based on IP.
It also shows how you change the MTU correctly, it will propegate to the underlying interfaces.
root@gravity:~# dladm create-aggr -l active -P L4 -d e1000g0 -d e1000g1 host0 root@gravity:~# dladm set-linkprop -p mtu=9000 host0
-l flag sets the LACP-mode this can be either
off. If you switch is set to passive, make sure to set it to active on your server!
-P flag set the LACP-policy, this can be either:
L2Select outbound device according to source and destination MAC addresses of the packet.
L3Select outbound device according to source and destination IP addresses of the packet.
L4Select outbound device according to the upper layer protocol information contained in the packet. For TCP and UDP, this includes source and destination ports. For IPsec, this includes the SPI (Security Parameters Index.)
Removing a member:
root@gravity:~# dladm remove-aggr -d e1000g1 host0
Adding a member:
root@gravity:~# dladm add-aggr -d e1000g2 host0
Well that gives you a general idea, for different policies and modes, you can use