Since Build 103 it is possible to snoop on loopback interfaces

With the Build 103 and the project clearview it is now possible to trace on
the loopback interface and also in zones as shown in the following blog:

Here is an example of a snoop on the loopback interface lo0:

# snoop -I lo0
Using device ipnet/lo0 (promiscuous mode)
localhost -> localhost ICMP Echo request (ID: 4577 Sequence number: 0)
localhost -> localhost ICMP Echo reply (ID: 4577 Sequence number: 0)