Chapter 3-5: Adjust and Troubleshoot Single-Area OSPF Flashcards
What are five [5] network types of OSPF Network.
- Point-to-point – WAN links
- Broadcast Multiaccess – Ethernet network
- NBMA (non-broadcast multiple access network ) – Frame Relay, ATM or x.25
- Point-to-multipoint – hub-and-spoke topology over NBMA
- Virtual links – connect distant OSPF areas to the backbone
What are two [2] challengers for multiaccess Network?
- Multiple adjacencies
2. Extensive LSA Flooding - every LSA must be ACKed
What are two [2] solutions for LSA flooding issue
- Designated router (DR)
2. Backup DR (BDR)
What are the IPv4 and IPv6 address for sending and receiving LSA
Designated router (DR) other to:
IPv4 224.0.0.6
IPv6 FF02::05
What are five [5] reasons that a OSPF Designated Router is used?
- The DR helps manage adj and flooding on multi-access nets
- The BDR is elected in case the DR fails
- All other routers become DROTHERs; form adj with the DR/BDR
- DR/BDR elections take place only on multi-access networks
- They DO NOT occur in point to point networks
What are the four [4] states of neighbours in multi-access networks
- FULL/DROTHER
- FULL/DR
- FULL/BDR
- 2-WAY/DROTHER
What are the three [3] Default DR/BDR Election Process
- The router with the highest interface priority is elected as the DR
- The router with the 2nd highest interface priority → BDR
- Priority range: 0-255 (0 → cannot become the DR, 255 → usually only two “best” routers set to this value )
DR remains the DR until one of the following three [3] issues occurs
- The DR fails
- The OSPF process on the DR fails or is stopped
- The multi-access interface on the DR fails or is shutdown
What two [2] things happens with the DR (Designated router) fails?
- The BDR (backup Designated Router ) is automatically promoted to DR (Designated Router)
- There is then a new BDR election and the DROTHER with the higher priority or router ID is elected as the new BDR
What are three [3] types of authentication of OSPF secure routing?
- Null – no authentication
- Simple password authentication – plain text (outdated)
- MD5 – Most secure and recommended method
What are seven [7] reasons why adjacencies will not form?
- Interfaces are not on same network
- Network types no identical
- Hello or Dead timers don’t match
- Passive interfaces are set
- There are missing/incorrect network commands
- Authentication is mis-configured
- RouterID is missing or duplicated
What are the Seven [7] Transitioning via OSPF States
- Down – no Hellos received
- Init – Hello’s received, but not with my RouterID
- 2-Way → Adjacency ← DR Elections happen
- Exstart – Master/Slave relationship established
- Exchange – LSDBDs exchanged
- Loading – LSUs exchanged
- Full – convergence
Command to configure MD5 on a per-interface basis
ip ospf message-digest-key md5
ip ospf authentication message-digest
Describe the down state
No Hellos received
Describe the init state
Hello received but not with my RouterID
Describe the 2-way state
DR Elections take place
Describe the Exstart state
Master/slave relationship established
Describe the Exchange state
LS DBD exchanged
Describe the Loading state
LSU exchanged
Describe the Full state
Fully converged
Command to show adjacencies
show ip ospf neighbour
Command to show process ID and router ID
show ip ospf
Command to show OSPF learned routes
show ip route ospf
Command to show process ID, timers, DR/BDR info
Show ip ospf interface
Command to rest adjacency
clear ip ospf process
