8. OSPF Flashcards
What are the five types of OSPF pakcets?
Hello - Discovering and maintaining neighbors DBD - After first adjacency has formed LSR - Databse request LSU - Database update LS ack - to acknowledge flooding LSAs
What are the multicast addresses of OSPF?
- 0.0.5 - Allspfrouters
224. 0.0.6 - AllDrouters
When is a OSPF neighbors fully adjacent?
When they share a synchronized database
What are the 8 OSPF neighbor states?
Down -
Attempt - NBMA networks
Init - hello packet received
2way - Bidirectional communication, election takes place
Exstart - First adjacency. Master/slave is choosen in LSDB proces
Exchange - Exchanging DBD packets
Loading - LSR are sent for discovered but not received LSAs
Full - Fully adjacent
What is the formula to calculate adjacencies?
n(n-1)/2
What steps are taken in DR/BDR update process?
An OSPF router learns a new route and sends a LSA to 224.0.0.6
DR sends ACK to router to confirm LSA received
DR floods LSA to 224.0.0.5
How is the router ID chosen?
Highest loopback first, if not highest active int ip address
How do you restart the OSPF process?
CLEAR IP OSPF PROCESS
What does a passive interface do?
It does not send out hellos does not process received OSPF packets
What are the six requirements to form an OSPF neighborship?
Unique RID Same subent MTU match AREA ID match DR enablement must match OSPF Hello and Dead match
How do you calculate the cost (metric)?
Reference bandwidth/interface bandwidth Ref = 100mb
How is the Dr chosen?
Hellos with 0.0.0.0
If priority is higher wins
If prio is equal –> Highest RID
How do you exclude an interface from the DR election?
By changing to prio to zero
What are the 5 OSPF network types?
Broadcast - default for ethernet Non broadcast P2P - No DR - default for serial only hello timer P2-mulitP - No DR Loopback
What is the command to change an OSPF link to P2P?
ip ospf network point-to-point
