Cisco CCNP and CCIE Study Notes

Consider the following output from a router running OSPF

R1#show ip interface brief 
Interface           IP-Address      OK? Method Status  Protocol
Serial2             20.20.20.1      YES NVRAM  up      up      
Serial3             30.30.30.1      YES NVRAM  up      up      
Loopback0           1.1.1.1         YES manual up      up      

R1#sh running-config | begin ospf
router ospf 100
 log-adjacency-changes
 network 1.1.1.1 0.0.0.0 area 0
 network 20.20.20.0 0.0.0.255 area 0
 network 30.30.30.0 0.0.0.255 area 0
!
ip classless
no ip http server
!
line con 0
line aux 0
line vty 0 4
 login
!
end

R1#sh ip protocols 
Routing Protocol is "ospf 100"
  Outgoing update filter list for all interfaces is not set
  Incoming update filter list for all interfaces is not set
  Router ID 223.223.223.223
  Number of areas in this router is 1. 1 normal 0 stub 0 nssa
  Maximum path: 4
  Routing for Networks:
    1.1.1.1 0.0.0.0 area 0
    20.20.20.0 0.0.0.255 area 0
    30.30.30.0 0.0.0.255 area 0
  Routing Information Sources:
    Gateway         Distance      Last Update
    223.223.223.223      110      00:00:38
  Distance: (default is 110)

R1#

Note that the OSPF router ID is seen to be 223.223.223.223 even though the only loopback interface in the system does not have that IP address and the router-id is not explicitly set under the router ospf command. How could it be possibly be that given this configuration the OSPF router id is 223.223.223.223?