Day 12 - Fine-Tuning and Troubleshooting OSPF Flashcards
R1 has a link to the internet which makes it an ASBR (autonomous system boundary router). Configure a default route on R1 that will propagate throughout the network. Use a process ID of 10
R1
ip route 0.0.0.0 0.0.0.0 serial 0/1/0
router ospf 10
default-information originate
With R1’s default route successfully propagated what should R2 and R3’s routing tables show?
O*E2 routes that point to R1
What is the default OSPF hello interval on multiaccess and point-to-point networks?
10 seconds
What is the nonbroadcast multiaccess network default hello interval?
30 seconds
What is the default OSPF dead interval?
40 seconds OR 4 times the hello interval
True or False:
The default hello and dead intervals are configured at the interface level
True
Based on the topology, configure a hello interval of 5 for interface S0/0/0 (don’t forget the dead interval as well)
int serial 0/0/0
ip ospf hello-interval 5
ip ospf dead-interval 20
True or False:
Hello and Dead intervals don’t need to be consistent between neighbors
False
What are the 5 types of OSPF networks?
Point-to-point
Broadcast multiaccess
NBMA (Nonbroadcast multiaccess)
Point-to-multipoint
Virtual links
The solution to managing the number of adjacencies and the flooding of LSAs on a multiaccess network is the use of a __________ __________
Designated Router
To reduce the amount of OSPF traffic on multiaccess networks, OSPF elects a __________ and a __________
DR
BDR
The __________ __________ is responsible for updating all other OSPF routers when a change occurs in the multiaccess network
Designated Router
The DR is the router with the highest __________ ___________ __________
OSPF interface priority
The BDR is the router with second highest __________ __________ __________
OSPF interface priority
When the DR is elected, it remains the DR until what of any of 3 conditions occurs?
The DR fails
The OSPF process on the DR fails
The multiaccess interface on the DR fails
What is the range of OSPF priority numbers?
0 - 255
What is the default priority value for all router interfaces unless manually changed?
1
What does a value of 0 indicate when it comes to priority and electing DR and BDRs?
It makes the router ineligible to become the DR or BDR
Based on the topology, why would R3 and R2 be DR and BDR respectively?
Because R3 has a router ID 3.3.3.3 and R2 has a router ID of 2.2.2.2
3.3.3.3 is the highest router id and 2.2.2.2 is the second highest
Based on the topology, elect R1 and R2 as DR and BDR
R1
int gi0/0
ip ospf priority 200
R2
int gi0/0
ip ospf priority 100
What are the general steps for Neighbor State Summary?
- Down - No active neighbor detected
- Initilialization - Hello packets sent and received by neighbors
- 2 WAY - Bi-Directional communication. Can see it’s own router ID received in Hello packets
- Exstart - Primary and secondary roles determined
- Exchange - DBD packets sent
- Loading - Exchange of LSRs and LSU (With LSAs within the LSU)
- Full - Neighbors full adjacent
What settings must be matched for a pair of OSPF routers to form an adjacency?
- They must be in each other’s neighbor list
- Hello & Dead Intervals
- Area ID
- IP Subnet
- Authentication Flag
- Stub Area Flag
- MTU and MTU IP Size
Solve for definition of the correct show command when verifying OSPF:
Verifies vital OSPF configuration information, including the OSPF process ID, the router ID, networks the router is advertising, neighbors the router is receiving updates from, default AD, etc.
show ip protocols
Solve for definition of the correct show command when verifying OSPF:
Verifies that the router has formed an adjacency with its neighboring router
show ip ospf neighbor
Solve for definition of the correct show command when verifying OSPF:
Displays the OSPF parameters configured on an interface, such as the process ID, area, cost and timer intervals
show ip ospf interface
Solve for definition of the correct show command when verifying OSPF:
Displays only the OSPF learned routes in the routing table
show ip route ospf
This command clears and resets the OSPFv2 neighbor adjacencies
clear ip ospf process
What 3 out of 7 OSPF states are establishing neighbor adjacencies?
Down State
Init State
Two-Way State
What 3 out of the 7 OSPF states are synchronizing the OSPF database?
ExStart State
Exchange State
Loading State
What is the last of the 7 states of OSPF?
Full State
What 3 things / questions should you check or ask when troubleshooting OSPF?
Is the neighbor table correct? (show ip ospf neighbor)
Is the routing table correct? (show ip route ospf)
Does the traffic take the desired path? (show ip route ospf)
What OSPF network type is assigned to Ethernet interfaces of directly connected neighbors?
Broadcast
What is the default number of paths that OSPF will load balance packets?
4 equal cost paths
Where is OSPF priority for DR and BDRs configured?
On the interface level
