[quagga-dev 16586] Why ospf hello packet without Designated Router and Backup Designated Router?

Hi all,
I want to know why ospf hello packet without Designated Router and Backup
Designated Router?

ospf.conf has any setting?

This is our setting

==================================
password zebra
!
access-list vty permit 127.0.0.0/8
access-list vty deny any
!
line vty
 access-class vty
!
!
interface br0
 ip ospf cost 1
 ip ospf priority 1
!
interface usb0
 ip ospf cost 10
 ip ospf priority 1
!
interface gretunnel
 ip ospf cost 10
 ip ospf priority 1
!
router ospf
 network 192.168.15.0/24 area 0
 network 192.168.4.56/30 area 0
 network 192.168.3.0/24 area 0
 redistribute connected
 redistribute kernel
!
log syslog
==================================

Thanks