07 - Implementing OSPF Flashcards
Do routers have to have the same process ID?
No
What is the router ID election process?
- Manually set RID
- Highest loopback
- Highest set active IPv4
Hello packets are periodically sent to the multicast address _____.
224.0.0.5
Neighbour relationship is formed if two routers agree on:
- Area ID
- Hello and dead intervals
- Authentication
- Same subnet
What are the OSPF packet types?
- Hello
- DBD
- LSR
- LSU
- LSAck
OSPF packet type - discovers and maintains neighbours
Hello
OSPF packet type - contain the LSA headers that help build the database
DBD
OSPF packet type - After DBDs are exchanged, router checks the LSA headers again its own database. If it does not have current information for any LSA, it generates a ___ packet and sends it to its neighbour
LSR
OSPF packet type - contains a list of LSAs that should be updated. Often used in flooding
LSU
OSPF packet type - help to ensure a reliable transmission of LSAs. Each LSA is explicitly acknowledged
LSAck
OSPF has protocol number __.
89
What are the LSA types?
- 1 Router LSA
- 2 Network LSA
- 3 ABR Summary
- 4 ASBR summary
- 5 Autonomous system
- 6-11 other types
LSA type: describes the state of the router links to the area and flooded within that particular area
1 - router LSA
LSA type: describe the set of routers that are attached to a particular multiaccess network
2 - Network LSA
LSA type: takes the information it learned in one area and summarised it for another area
3 - ABR summary
LSA type: informs the rest of the OSPF domain how to get to the ASBR.
4 - ASBR summary
LSA type: generated by ASBRs, describes routes to destinations that are external to the AS. They get flooded everywhere except special areas.
5 - Autonomous system
In the configuration of the OSPF router if either of the following commands are used, the route becomes an ASBR:
- Resdistribute….
* Default-information originate
What are the OSPF neighbour states?
- Down – no neighbour detected
- Init – hello packet received from neighbour
- Two way – own router id in received hello
- Exstart – master and slave roles determined
- Exchange – DBD packets sent
- Loading – exchange of LSRs and LSUs
- Full – fully adjacent
How do you observe routes in a routing table?
show ip route ospf
How do you observe all ospf routes?
show ip ospf route
How do you observe ospf neighbour adjacency formation?
- Debug ip ospf adj
2. Clear ip ospf process
What are the benefits of having a DR/BDR?
- Reduces routing update traffic – central point of contact for link-state information exchange
- Manages link-state synchronisation – DR & BDR ensures other routes have same link-state information about common segment
What is the multicast IP to communicate with the DR ?
224.0.0.6
