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when to use OSPF network type - p2p or broadcast ?


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#1 mariusac

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Posted 01 December 2008 - 02:02 AM

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
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#2 super_thundercats

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Posted 01 December 2008 - 02:30 AM

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




Its depends upon the scenario on which you want to deploy your network. Point-to-point mode is better than among other modes but its need Cisco routers on both the ends. Also, IP addresses blocks are wasted as each point to point link is now on separate subnets (but usually no one cares as private address blocks are used here).

If your company network policy follows the standardized procedures then its better to use RFC compliant modes for OSPF.

Regardless of the mode, you will get the same answer. Point to point mode is better than the other modes because other modes usually requires more configurations.

Edited by super_thundercats, 01 December 2008 - 02:32 AM.

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#3 jafar2048

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Posted 01 December 2008 - 02:38 AM

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




Hello there,


Well, it's a good idea to ask them, why they chose point-to-point for both LAN and WAN. However, as far as I know in a broadcast network the neighbors are discovered automatically and DR/BDR are elected. The main problem is that the broadcast type requires a full connectivity between the designated router and every other router. Unfortunately this is not always possible due to variant types of network topologies.

By using point-to-point type, neighbor discovery is done automatically, because for each link there is only one possible neighbor: the other endpoint (point-to-point) and as in each link, there are exactly two routers, there is no need for DR/BDR election. Point-to-point is a very good solution for networks having a partial-mesh topology, where a signle router (which is supposed to be the designated router) does not have a physical connectivity or PVC (for example through a FR switch) to every other router. In these kinds of situations, splitting the topology into several point-to-point links (or both point-to-point and point-to-multipoint) can solve the accessibility and neighbor discovery problem.

One other interesting feature of point-to-point (serial/WAN) links is that there can be unnumbered. Besides, each endpoint can have even a different IP subnet and each sender is identified by the Router ID (instead of physical interface address). This means that the subnet mask in hello packets doesn't need to be the same on both routers (this is not possible in a broadcast network).


Regards,

:rolleyes:

Edited by jafar2048, 01 December 2008 - 03:28 AM.

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#4 talent pk

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Posted 01 December 2008 - 03:36 AM

well explained thanks
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