OSPF over Frame-Relay, focus on Network Types

Don't forget that in Frame-Relay "broadcast" is defined ONLY DIRECTLY HUB AND A SPOKE, ON BOTH SIDES of the pvc!!! What this does is tell the routers “Hey if you have any broadcast messages, go ahead and send them down this DLCI as a unicast” So basically it is a way to send broadcast messages on a non-broadcast medium. Don't include "broadcast" between the SPOKEs, as the Hellos won't be able to traverse the HUB.

Type 1: NON-BROADCAST - use "neighbor" command on HUB to use UNICAST for OSPF

OSPF uses Multicast, which Router considers to be a kind of Broadcast. Due to the non-broadcast nature of Frame-Relay it can be assumed that this is the DEFULT OSPF network type over FR.

- Set the OSPF Priority to 0 on all the SPOKEs, so HUB is elected as the DR, and SPOKEs neither DR nor BDR

- Non-broadcast network type in OSPF uses “slow” timers meaning 30 second hello and 120 second dead-time. Here it will not affect us, as all neighbor types match.

Type 2: BROADCAST - two important things:

- As BROADCAST is meant to be FASTER timers are 10/40 seconds by default

- Include the "broadcast" when mapping DLCI to IP. Also set the SPOKEs OSPF Priority to 0, we don’t want them to be DR

Type 3: POINT-TO-POINT

- Really simple, POINT-TO-XXX (P2P or P2MP) does not do the DR/BDR election

- Timers 10/40 seconds

TIP: When doing a HUB-AND-SPOKE, configure Point-to-Multipoint on a HUB, and ADJUST THE TIMERS!!!

Type 4: POINT-TO-MULTIPOINT

No DR, no "neighbor" command. Slow timers (120/30 seconds). "broadcast" is mandatory on FR Mappings!!!

HUB will just advertise the learned routes from ONE SPOKE to the other, like if it were the DR.

!!!HUB must have .multipoint Sub-interface, while on SPOKES you can do .multipoint or Physical Interface.

Type 5: POINT-TO-MULTIPOINT NON-BROADCAST

Cisco Proprietary, like P2MP, with NO BROADCASTS ALLOWED! Timers are still slow, 30 and 120 Seconds.

Next hop is ALWAYS the router you are directly connected to.

(config-if)#ip ospf network point-to-multipoint non-broadcast