[Master / slave] router election in DD message

DD The message is not only used to announce its own LSA Outside of header information , It can also be used in elections Mater/Slave【 Lord / from Router 】,Rrouter-ID Big for the main ; It is worth noting that ： For election Mater/Slave Of DD The message does not carry any LSA Head , That is, empty DD message .

# This article is only a supplement to the original [ Link to the original text ：OSPFB note - Five messages ]