the output of "show ip protocols " looks something like this - starting at line 6 on page 395
------------------------
Default version control: send version 1, receive any version
Interface
Serial0/0
Serial0/1

Routing for Networks:
10.0.0.0

Routing Information Sources:
Gateway
10.168.11.14
------------------------

Now moving on to the output of "show ip int brief" command on the same page - only the first two columns of the output
------------------------
Interface IP-Address
FastEthernet0/0 192.168.18.1
Serial0/0 10.168.11.17
FastEthernet0/1 unassigned
Serial0/1 192.168.11.21
------------------------

The text after the output says, "we're using RIP routing for network 10.0.0.0"
and then it says, "only serial0/0 and serial0/1 are participating in the RIP network."

MY QUESTION IS:
How is interface serial0/1 participating in the RIP network when the network it's configured in (i.e. 192.168.11.0) is not being advertised by RIP?