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The OSPF point-to-multipoint non-broadcast option!

Hello all,

Probably this question has been asked thousands of times before, but, after going through the answers carefully, I have to admit that I could not find a satisfactory explanation for the OSPF point-to-multipoint non-broadcast option.

What exactly is this option for ?

There were a couple of posts which said that it allows cost to be assigned for individual virtual circuits, but, another user configured point-to-multipoint without the non-broadcast option and showed that the cost is taken care of, and there is no need for the non-broadcast keyword.

There were also suggestions to point that it should be used for packet delivery (unicast, multicast & broadcast) method, but I am more confused than before after reading the answers.

After all these years, can we just say that this option is redundant, and not necessary to be configured?

Disclaimer: I have not tried the latest software in the lab. I am just looking at the articles and the books.

Thanks & Best Regards,

Venkat.

 

Everyone's tags (2)
1 ACCEPTED SOLUTION

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Silver

Hi Venkat,OSPF point-to-point

Hi Venkat,

OSPF point-to-point nonbroadcast network type is a non-standard feature. As far as I know it was introduced by Cisco to support NBMA network that does not support multicast (or better to overcame limitation in using OSPF point to multipoint network in case the network doesn't support multicast). For example Frame Relay  network can have multicast PVC (and in  that case you can use NBMA network type or point-to-multipoint network type)  but, at least in  my country, this feature wasn't  widely supported. In this case, configuring an interface as OSPF point-to-multipoint network, OSPF process can't discover neighbor because OSPF neighbor discovery is based on mutlicast packet. So Cisco gives you 3 additional feature to overcome this problem:

  • point to multipoint non broadcast: in this case you have a network type very similar  to RFC point-to-multipoint network type but you can manually configure neighbor's IP address  and OSPF will send hello packet using you neighbor unicast address insted of  224.0.0.5
  • point to point: in this case multicast support is not a problem: all outgoing traffic is mapped to the PVC configured for that interface, at layer 2 address in point to point network is useless
  • broadcast: in this case IOS simulates a broadcast network replicating every multicast packet on all PVC associated to an interface

 

So, what's now a day that FR networks are not very popular ? In modern MPLS network I might have Frame Relay as layer 2 protocol between CE and PE but with just one PVC, so point to multipoint is not required. I think that this kind of network cloud be useful in VPN  that are similar to NBMA in the fact that spokes has no direct link.

 

Bye,

enrico

 

PS please rate if useful

1 REPLY
Silver

Hi Venkat,OSPF point-to-point

Hi Venkat,

OSPF point-to-point nonbroadcast network type is a non-standard feature. As far as I know it was introduced by Cisco to support NBMA network that does not support multicast (or better to overcame limitation in using OSPF point to multipoint network in case the network doesn't support multicast). For example Frame Relay  network can have multicast PVC (and in  that case you can use NBMA network type or point-to-multipoint network type)  but, at least in  my country, this feature wasn't  widely supported. In this case, configuring an interface as OSPF point-to-multipoint network, OSPF process can't discover neighbor because OSPF neighbor discovery is based on mutlicast packet. So Cisco gives you 3 additional feature to overcome this problem:

  • point to multipoint non broadcast: in this case you have a network type very similar  to RFC point-to-multipoint network type but you can manually configure neighbor's IP address  and OSPF will send hello packet using you neighbor unicast address insted of  224.0.0.5
  • point to point: in this case multicast support is not a problem: all outgoing traffic is mapped to the PVC configured for that interface, at layer 2 address in point to point network is useless
  • broadcast: in this case IOS simulates a broadcast network replicating every multicast packet on all PVC associated to an interface

 

So, what's now a day that FR networks are not very popular ? In modern MPLS network I might have Frame Relay as layer 2 protocol between CE and PE but with just one PVC, so point to multipoint is not required. I think that this kind of network cloud be useful in VPN  that are similar to NBMA in the fact that spokes has no direct link.

 

Bye,

enrico

 

PS please rate if useful

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