OSPF

  • What is OSPF?
  • What is a Process ID?
  • What is an Area #?
  • Single Area vs Multi Area? single-area-vs-multi-area.md
  • What is a wildcard mask?
  • What does it mean for a Router to form - an Adjacency?
  • What does it mean for a Router to form a - Neighboring?
  • Explain DR and BDR
    • DR - Designated Router
    • BDR - Backup Designated Router
    • Election process
  • Router ID
    • What is a Router ID?
    • Why is the router ID important?
    • What are the method a router uses to obtain a router ID?
      • Static (Manually configured)
      • Highest loopback IP (note: loopbacks are enabled by default when IP is assigned to it, unlike regular interfaces).
      • Highest interface IP (note: the interface must be enabled).
Enabling OSPF on a Router (remember, you are enabling OSPF on the "whole" router which includes all of its interfaces). * Enable OSPF Process (instance). * Enter OSPF Process configuration via Global Config (just like you would with any interface). * Declare the networks that should be "Part of this OSPF Process (instance)" and which area. * Let the neighbor relationship to occur (could range from milliseconds to minutes). * Verify _show ip route or show ip route ospf_ to see the "routes" learned by the router. **Example:** ``` // Enabling OSPF on P1R1 P1R1#conf t Enter configuration commands, one per line. End with CNTL/Z. P1R1(config)#router ospf 1 P1R1(config-router)#network 192.168.1.0 0.0.0.255 area 0 P1R1(config-router)#end ``` * Breaking the commands above; * Enter Configuration Terminal (Aka global config). * Enable OSPF on this router with a process ID of 1 (instance). * Note: The process ID does NOT need to be same with other routers on the same area to form a "Relationship". It is simply an instance and you can have many instance of OSPF running on the "same router". Typically though, you would only have 1 instance, unless the admin wants to separate or organize some areas of the network, in which case they may use multiple instances. * "Declare" which networks should be part of this OSPF instance. * 
P1R1(config-router)#network 192.168.1.0 0.0.0.255 area 0

      This means any "interfaces" that has an IP that falls under 192.168.1.x will be included (thus advertised) to other Routers in the same Area.

      The wildcard 0.0.0.255 means the first "3 octet" NEEDS TO MATCH. While the last octet containing .255 DOES NOT need to match and can be anything from 0-255.
* Exit global config. * The router will take some time and will start advertising the "declared network" to other neighboring routers that it has formed "Adjacency" with in the "Same Area #"
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