OSPF:
DR is designated Router
BDR is backup designated Router
DROTHER when a Router is not a DR or BDR
DR BDR Election
DR highest Priority or highest router-id
BDR is second highest Priority or second highest router-id.
Router-id election :
1.Highest router-id manually configured.
1.Highest loopback IP
2.Highest interface IP
Note OSPFv3 uses the same election process and the
loopback or interface ip must be IPv4 note.
Priority configuration
Router(config)#interface fastEthernet 0/0
Router(config-if)#ip ospf priority 200
0 means that Router will never become DR/BDR
Two Multicast addresses:
224.0.0.6: All Routers send messages/LSA's to only the DR and BDR using
this Multicast address. All designated Routers address.
224.0.0.5: Designated Routers or DR's send information too all Routers
using this Multicast address. All OSPF Routers address.
The way in which OSPF routers address OSPF packets varies with the
OSPF network type.
Broadcast Networks For broadcast networks, OSPF routers use
the following two reserved IP multicast addresses:
NBMA Networks NBMA networks have no multicasting capability.
Therefore, the destination IP address of any Hello or Link State packets
is the unicast IP address of a specific neighbor. The neighbor IP address
is a required part of OSPF configuration for NBMA network links.
If DR fails, BDR takes over its role of redistributing
routing information.
Router#clear ip ospf process
or use
Router#reload
show ip ospf neighbor
Best Place to Learn LINK
DR is designated Router
BDR is backup designated Router
DROTHER when a Router is not a DR or BDR
DR BDR Election
DR highest Priority or highest router-id
BDR is second highest Priority or second highest router-id.
Router-id election :
1.Highest router-id manually configured.
1.Highest loopback IP
2.Highest interface IP
Note OSPFv3 uses the same election process and the
loopback or interface ip must be IPv4 note.
Priority configuration
Router(config)#interface fastEthernet 0/0
Router(config-if)#ip ospf priority 200
0 means that Router will never become DR/BDR
Two Multicast addresses:
224.0.0.6: All Routers send messages/LSA's to only the DR and BDR using
this Multicast address. All designated Routers address.
224.0.0.5: Designated Routers or DR's send information too all Routers
using this Multicast address. All OSPF Routers address.
The way in which OSPF routers address OSPF packets varies with the
OSPF network type.
Broadcast Networks For broadcast networks, OSPF routers use
the following two reserved IP multicast addresses:
-
224.0.0.5 - AllSPFRouters: Used to send OSPF messages
to all OSPF routers on the same network. The AllSPFRouters address is
used for
Hello packets. The DR and BDR use this address to send Link State
Update and Link State Acknowledgment packets.
-
224.0.0.6 - AllDRouters: Used to send OSPF messages to
all OSPF DRs
(the DR and the BDR) on the same network. All OSPF routers except
the DR use this address when sending Link State Update and Link
State Acknowledgment packets to the DR.
NBMA Networks NBMA networks have no multicasting capability.
Therefore, the destination IP address of any Hello or Link State packets
is the unicast IP address of a specific neighbor. The neighbor IP address
is a required part of OSPF configuration for NBMA network links.
NOTE – on point-to-point links a DR and BDR are not elected
since only two routers are directly connected.
since only two routers are directly connected.
On LANs, DR and BDR have to be elected.
DR/BDR election is per multi-access segment,not per area.
Multi access segment is not a subnet as can have multiple
subnets.For each segment there will be a DR/BDR election.
DR/BDR election is per multi-access segment,not per area.
Multi access segment is not a subnet as can have multiple
subnets.For each segment there will be a DR/BDR election.
Router#clear ip ospf process
or use
Router#reload
show ip ospf neighbor
Best Place to Learn LINK
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