Dr and BDR in OSPF

in the in OSPF, there are two fairly important concepts:DR and BDR. Let 's take a look at what DR is, what's called BDR, and then see what they do.

DR:designatedrouter Specifies the router.

BDR:backupdesignated Router backup the specified router.

   in a LAN connection, ospf< Span style= "font-family: ' The song Body '; > will elect a router as dr Bdr all the other and dr bdr connected routers form a fully contiguous state and only transmit LSA ( link status advertisement ) to Dr

  in other words, in a network of Ospf (DR/BDR) las sent to DR Ospf routers will not establish a neighbor relationship with each other. In other words, ospf network, dr and Bdr link state database ) |

 dr forwarding updates from neighbors to another neighbor. dr lan all routers in the same database , Lan non- dr/ Bdr, drothers) maintain a partial neighbor relationship (two-way adjacency) OSPF , Lsa will carry out a reliable flood.

  When the election Dr/bdr when you want to compare hello< Span style= "font-family: ' The song Body '; The priority in the package ' Set command route (config-if) #ip OSPF cost{priority} 0~255), Dr bdr 1 Rid dr bdr ospf routers will no longer be dr/bdr drother

when using the default priority In The Dr election of OSPF, all routers exchange their own Router-id to determine the Dr. Router-id can be specified manually. If you do not specify Router-id manually , then the router will first see if they have a loopback interface (Loopback), if there is a loopback interface, then use the loopback interface on the IP address as their own Router-id. If there is no loopback interface, it will compare the IP address on all of its physical interfaces , and choose the largest IP address from which to participate in DR's election as its own Router-id .

So, The election of DR and BDR can be determined in the following ways:

1 If there is a manually designated Router-id, the Router-id is used to participate in the election;

2 If there is no manually specified Router-id, then see if they have Loopback interface, there is the use of IP on the Loopback interface as Router-id participation in elections;

3 If there is no Loopback interface, compare all the physical interfaces and use the largest of them as Router-id to participate in the election;

4 All OSPF routers exchange their own Router-id, the routerwith the largest one in all Router-id will act as the DR, with the second largest the Router-id router becomes a BDR.

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Dr and BDR in OSPF