OSPF Flashcards
Which version of OSPF is in deployment in most modern systems today?
V2
Which version of OSPF supports IPv6?
V3
What is the selection priority for a router’s OSPF Router ID
- Manual configuration
- Highest IP address on a loopback interface
- Highest IP address on a physical interface
What is the command to issue on an ASBR for it to share default route information?
default-information originate
What is the command to change the OSPF cost reference bandwidth
auto-cost reference-bandwidth reference-bandwidth
Does OSPF reference bandwidth need to be the same across an area?
Yes, otherwise the cost calculations get messed up
What is the command to manually configure OSPF cost for a particular interface?
ip ospf cost
What is the multicast IP address OSPF hello messages are sent to?
224.0.0.5
What are the 4 OSPF neighbor states?
- Down
- Init
- 2-way
- Exstart
- Exchange
- Loading
- Full
What neighbor state do two OSPF routers enter after they receive a hello message with their own Router IDs in them?
2-way
What are the main OSPF network types?
- Broadcast
- Point-to-Point
- Non-Broadcast
- Point-to-Multipoint
Broadcast OSPF networks are enabled by default on _____ and _____ connections
Ethernet, FDDI
Point-to-Point OSPF networks are enabled by default on _____ and _____ connections
PPP, HDLC
Non-Broadcast OSPF networks are enabled by default on ____ and _____ connections
Frame Relay, X.25
What is the command to manually configure an interface as a specific OSPF network type?
ip ospf network type
In what OSPF network type is a DR and BDR elected?
Broadcast
What is the selection priority for DR/BDR elections?
- Highest OSPF interface priority
- Highest OSPF router ID
How is OSPF interface priority determined?
They are the same by default, so manual configuration
After a DR and a BDR are chosen, what do all other routers in an OSPF network become?
DROther
What is the command to change the OSPF priority on an interface?
ip ospf priority priority
Is OSPF DR/BDR election preemptive or non-preemptive?
Non-preemptive
Do DROther routers enter the FULL state with other DROther routers?
No, they only enter the full state with the DR and the BDR
Do DROther routers enter the FULL state with the DR and BDR routers?
Yes
What is the multicast IP address used to send messages to the DR and the BDR
224.0.0.6
Do the DR and BDR form a full adjacency?
Yes
What are the 3 CCNA-relevant OSPF LSA types
- Type 1 (Router LSA)
- Type 2 (Network LSA)
- Type 5 (AS External LSA)
What is a Type 1 OSPF LSA
Router LSA
Used to identify the router using the Router ID, lists networks attached to the router’s OSPF activated interfaces
What is a Type 2 OSPF LSA
Network LSA
Used by the DR. Lists the routes which are attached to the OSPF broadcast network
What is a Type 5 OSPF LSA
AS-External LSA
Generated by ASBRs to describe routes to destinations outside the AS
What are basic troubleshooting steps for OSPF?
- Area number must match
- Hello and dead timers must match
- Interfaces need to be on the same subnet
- Ensure OSPF process isn’t shut down
- Ensure OSPF RIDs are unique
- Ensure authentication settings match
- Ensure IP MTU settings match
- Ensure OSPF network types match
