OSPF Point-to-Multipoint Non-Broadcast

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Pic. 1 - Topology Diagram.

Task 1

On R1, R3, and R4 disable pseudo-broadcast on Frame-Relay interfaces.

Task 2
Reconfigure OSPF on R1, R3, and R4 to use OSPF point-to-multipoint non-broadcast mode. Ensure OSPF domain has full connectivity.

Questions

Try to answer the following questions:

1. What happened when you have removed 'broadcast' keyword in Task 1 as far as OSPF communication?
2. What is/are the difference(s) between OSPF point-to-multipoint and point-to-multipoint non-broadcast?
3. Is the mode used in this lab Cisco proprietary or RFC standard?

Lab Solution

Solution configuration below:
https://docs.google.com/file/d/0BwE5C95tpjZOMnhPdmFuMUJ2b3c/edit?usp=sharing

Task 1

On R1, R3, and R4 disable pseudo-broadcast on Frame-Relay interfaces.

R1 Config:
!
interface Serial0/0
 frame-relay map ip 172.16.0.3 103
 frame-relay map ip 172.16.0.4 104
!

R3 Config:
!
interface Serial0/0
  frame-relay map ip 172.16.0.1 301
!

R4 Config:
!
interface Serial0/0
 frame-relay map ip 172.16.0.1 401
!

What You Should See

Pic. 2.

R1 has lots R3 and R4 as its OSPF neighbors. The reason is that multicast 224.0.0.5 (hello) is no longer supported (no DLCI for multicast/broadcast). The 'debug ip packet detail' should reveal the cause of the problem:

Pic. 3.

Task 2
Reconfigure OSPF on R1, R3, and R4 to use OSPF point-to-multipoint non-broadcast mode. Ensure OSPF domain has full connectivity.

R1 Config:
!
interface Serial0/0
 ip ospf network point-to-multipoint non-broadcast
!
router ospf 1
 neighbor 172.16.0.4
 neighbor 172.16.0.3
!

R3 Config:
!
interface Serial0/0
ip ospf network point-to-multipoint non-broadcast
!

R4 Config:
!
interface Serial0/0
 ip ospf network point-to-multipoint non-broadcast
!

What You Should See

Pic. 4.

Study Drill

If you cannot use pseudo-broadcast (for instance, this is an exam stipulation)on NBMA links (or there is no support for), you can use OSPF point-to-multipoint non-broadcast mode. This will behave just like OSPF point-to-multipoint (treats connections as point-to point, no DR/BDR election).

This mode of OSPF is Cisco proprietary. The timers are 30/120 seconds (hello, dead). Since this mode does not assume pseudo broadcast/multicast support, it requires the 'neighbor' statement in the configuration on R1 (the hub router). The spoke routers will respond using unicast upon receiving unicast hello. As for the next-hop address, this option also behaves like OSPF point-to-multipoint mode.

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� Jarek Rek 2013