R5#show ospf interface g0/0
^ Displays info about OSPF on interface g0/0
R2(config)#int g0/0
R2(config-if)#ip ospf priority 255
^ Sets the priority of OSPF on an interface to "rig" future elections. Recall that the DR/BDR election is 'non-preemptive'.
DR = Designated Router
BDR = Backup Designated Router
R5#clear ip ospf process
^ Don't do this in a production network.
Forces an election. When the DR goes down, the current BDR will become the DR. Then, an election will occur and this rigged router will become the BDR. I guess the next election will cause this router to become the DR.
R5#show ip ospf neighbor
^ Displays info about OSPF neighbors and their state
R3#show ip ospf interface brief
^ Displays interfaces and OSPF info for each
R3#show ip ospf interface g0/0
^ Displays detailed OSPF info on interface g0/0
Serial interfaces:
- DR and BDR are not elected because there are only 2 neighbors on the interface
- One side functions as DCE (Data Communications Equipment)
- The other side functions as DTE (Data Terminal Equipment)
- DCE needs to specify clock rate (speed) of connection
R1(config-if)#clock rate 64000
^ Sets the clock rate (bps) of the DCE router
R1(config-if)#ip address 192.168.1.1 255.255.255.0
R1(config-if)#no shut
Ethernet interfaces use the speed command.
Serial interfaces use the clock rate command.
Default encapsulation on serial interface is HDLC
R1(config)#int s2/0
R1(config-if)#encapsulation ppp
^ Sets encapsulation to PPP instead of the default HDLC
Encapsulation type must match on both ends.
R1#show controllers s2/0
^ This will reveal which side is the DCE vs the DTE
R1(config-if)#ip ospf network <type>
^ This command manually configures the OSPF network type with the following <type> options:
broadcast (Ethernet and FDDI)
non-broadcast (Frame Relay and X.25)
point-to-point (Serial)
point-to-multipoint
You might configure an Ethernet link between two routers since there is no need for a DR/BDR. This might be a time to config a point-to-point network.
R2(config-router)#router-id 1.2.3.4
^ Configures the router-id of a router
The hello-interval and dead-interval values must match between OSPF neighbors:
R2(config-if)#ip ospf hello-interval <seconds>
^ Sets the number of seconds between hello announcements
Default is 10 seconds
R2(config-if)#ip ospf dead-interval <seconds>
^ Sets how long before the neighbor is considered dead
Default is 40 seconds
R2(config-if)#ip ospf authentication-key banana
^ Sets the authentication password to banana but does not yet enable authentication
R2(config-if)#ip ospf authentication
^ Enables authentication on the interface
R2(config-if)#ip mtu <number>
^ Sets the maximum size of an IP packet that can be sent ot of the interface. Defaults to 1500 bytes.
Must match on both neighbors or will have problems.
OSPF LSA types:
Type 1 - Router LSA - Identifies itself by stating its router ID and lists networks attached to the router's OSPF attached interfaces.
Type 2 - Network LSA - Generated by the DR of each 'multi-access' (broadcast) network. Lists the routers which are attached to the multi-access network.
Type 5 - AS-External LSA - Generated by ASBRs (Autonomous System Boundary Routers) to describe routes to destinations outside of the AS (Autonomous System) (OSPF domain)
R1#show ip ospf database
^ Displays LSDB (OSPF database) including neighbors, each router (type 1 LSA), network (type 2) LSA, and external link states (type 5)
OSPF Neighbor process:
[These are my notes from Jeremy's excellent CCNA course which can be viewed here.]
