when to use OSPF network type - p2p or broadcast ?

hendychow

Hello All,

I need help.
Do you know when to use OSPF network type - point to point or broadcast ?
In my company where I work, Core routers 6500s are connected directly both in LAN and WAN.
LAN is using ethernet cable and WAN is using leased line.
For Layer 3 Routing, Alll of the routers are configured using point to point OSPF network, both in LAN and WAN

Based on theory in BSCI book, I thought that for OSPF in LAN, It is better to use Broadcast where we elect BR/BDR.
I assume LAN is Ethernet network.

Do you know why for all of LAN/WAN, my company are only using OSPF Point to Point ?
[ I can't get the answer, because the Tier 3 engineer is not located in my location ]

I thought Point to Point is used just for serial WAN connection ? They even used it in leased line WAN connection.


Please suggest.

Thank You Very Much..

Hendy

kpjungle

hendychow wrote:

Hello All,

I need help.
Do you know when to use OSPF network type - point to point or broadcast ?
In my company where I work, Core routers 6500s are connected directly both in LAN and WAN.
LAN is using ethernet cable and WAN is using leased line.
For Layer 3 Routing, Alll of the routers are configured using point to point OSPF network, both in LAN and WAN

Based on theory in BSCI book, I thought that for OSPF in LAN, It is better to use Broadcast where we elect BR/BDR.
I assume LAN is Ethernet network.

Do you know why for all of LAN/WAN, my company are only using OSPF Point to Point ?
[ I can't get the answer, because the Tier 3 engineer is not located in my location ]

I thought Point to Point is used just for serial WAN connection ? They even used it in leased line WAN connection.


Please suggest.

Thank You Very Much..

Hendy

Cant tell you why your company choose to use that unfortunally. But where the OSPF network types really comes into play, is on NBMA (Non-Broadcast Multiple Access) networks, such as frame-relay. In theory you have a one-to-many sort of connectivity, but you have no inherent broadcast capability. In this scenario it certainly eases both configuration and management to use point-to-point, because you dont have to make sure the right DR is choosen by tweaking the election.

On "real" LAN's with broadcast capability you save alot of management and OSPF packets by using the broadcast option. The DR/BDR handles most of the tasks, and some fault-tolerance is built into it by the BDR being able to take over after a DR breakdown.

I would be very interested if you learn the reason for it though.

unclerico

Would you be able to include a topology of your network? Also, if you have the clearance on the 6500 can you include the contents of a sh ip ospf interface ? Just as kp is interested I am also, I've never seen such a configuration before.

GT-Rob

I find a lot of unexplained things configured on networks. It only takes 1 engineer (who may not even work there anymore) to implement something and then it is there forever.


pt-pt does not hurt anything, as it will still work, but is obviously not as efficient.