Cisco 113 - OSPF Part 1

(config)#router ospf 1
^ Enters OSPF configuration mode.
The "1" is the process ID.
A router can run multiple OSPF processes at once.
Process ID is unrelated to area.

(config-router)#network 10.0.12.0 0.0.0.3 area 0
(config-router)#network 10.0.13.0 0.0.0.3 area 0
(config-router)#network 172.16.1.0 0.0.0.15 area 0
^ These three commands activate OSPF on all interfaces that match the given parameters.  They are configured as area 0.
The commands tell the router to find all interfaces that match the ranges specified.
Recall the network command uses wildcard matching.  So 0.0.0.15 = 255.255.255.240
Also recall that these commands don't specify which networks to advertise.
The commands activate OSPF on interfaces that fall in the range of the given wildcard matching patterns.

(config-router)#passive-interface g2/0
^ Tells the interface to stop sending OSPF 'hello' messages out that interface - probably because there are no further routers for that interface to neighbor with.
Use this command on any interface that doesn't have any OSPF neighbors.

(config)#ip route 0.0.0.0 0.0.0.0 203.0.113.2
^ Adds a default route and points to the next hop as the ISP's IP address
(This becomes our gateway of last resort)

(config-router)#default-information originate
^ This advertises the default route into OSPF so the other routers learn about it

R1#show ip protocols
^ Displays information about the routing protocol being used.
For us, that's OSPF

(config-router)#router-id 1.1.1.1
^ Manually configure the router ID as 1.1.1.1
The router will continue to use the old ID until we reload the router or use the command:
clear ip ospf process
^ Dangerous command because it clears out the routing map for a while until things are rebuilt.  This means downtime.

(config-router)#maximum-paths <#>
^ Change the maximum number of redundant paths that can be added to the routing table from 4 to #

(config-router)#distance <#>
^ Set the administrative distance

R4(config)#int l0
^ That's "L" 0 <-- Loopback0 (not the number 10)
This command creates a loopback interface
R4(config-if)#ip address 1.1.1.1 255.255.255.255
^ Assigns IP address 1.1.1.1/24 to interface Loopback0

R4>show ip int | begin Loop
^ Displays IP addresses assigned to interfaces beginning with the first match of "Loop" (Loopback0)

R4>show ip int brief
Shows a summary of interfaces and their IP assigned IP addresses

R4>show int l0
^ Again, that's loopback0, not the number 10
^ Command shows details of interface Loopback0

R1#show ip ospf neighbor
^ Shows OSPF neighbors

R1#show ip ospf database
^ Shows LSDB (link-state database)

R1#show ip ospf interface
^ Displays details about OSPF settings on each interface




[These are my notes from Jeremy's excellent CCNA course which can be viewed here.]