Subject: [OSPF] p2p and nbma networks

From: "Pat Murphy - (650)329-4044" <[email-masked]>
Date: Wed, 21 Jan 2009 08:00:51 -0700 (PDT)

>I want to understand what data link layer technology is referred to
>when we talk of p2p and nbma networks in OSPF? I believe nbma alludes
>to ATM and Frame Relay networks. If so, then we will see the # of nbma
>networks going down as more and more ethernet networks are replacing
>atm and FR.

A p2p network type configuration is commonly deployed over ATM, FR, and 
Serial. I suppose p2p between two routers connected by an ethernet 
crossover cable would be possible. But what would be the point of 
complicating a configuration by choosing p2p over the default broadcast 
network type? The broadcast network type is normally thought to be 
Ethernet technology; but some ATM and FR clouds will also support OSPF 
multicast packets. I personally have never seen this used. Perhaps 
others can share some unusual p2p and broadcast network type 
deployments. The key requirement for deploying p2p and broadcast network 
types is support for OSPF multicast packets.

p2mp and nbma can be configured over any technology. I have seen both 
deployed for different reasons over carrier ethernet service. Their 
distinct advantage is that all OSPF packets are unicast (versus 
multicast) between neighbors. Note that a p2mp cloud with only two 
routers is just a unicast version of p2p.

>Can a MPLS tunnel be a p2p network in OSPF? What is a p2p network - 
>serial interface?

In OSPF (RFC 2328 Section 9.5) a p2p network is simply a connection 
between two routers who discover each other using Hello packets sent to 
the multicast address AllSPFRouters (224.0.0.5). Many implementation 
interface types support this.

Pat

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From: Greg Mirsky <[email-masked]>
Date: Thu, 22 Jan 2009 16:41:54 -0500