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OSPF NETWORK

Network

Types

Neighbor

Selection

DR / BDR

Selection

RFC 2328-compliant modes


NBMA (Non Broadcast Mulit Access)

Manual

Required

Point-to-multipoint

Automatic

NotRequired



Cisco modes



Point-to-multipoint nonbroadcast

Manual

Not Required

Broadcast (BMA)

Automatic

Required

Point-to-point

Automatic

Not Required

* Point-to-Multipoint mode treats non-broadcast network as collection of point-to-point link

Everyone's tags (2)
1 REPLY
Cisco Employee

OSPF NETWORK

Hello,

This table is a nice sum up of how many textbooks and Cisco Networking Academy curricula present the OSPF network types.

However, the split into RFC 2328-compliant and Cisco modes is not entirely precise. RFC 2328 recognizes broadcast (BMA), non-broadcast (NBMA), point-to-point (PtP) and Point-to-Multipoint (PtMP) network types (see Section 9). As you can see, BMA and PtP are RFC-compliant and not Cisco proprietary.

It is noteworthy that these network types are discussed most often when NBMA link layer technologies come into play, like Frame Relay, X.25 or ATM. The RFC behavior would be to use NBMA network type on such technologies. However, in Cisco IOS, you are given the option of overriding the network type and forcing the OSPF to treat the NBMA technology as if it was a different type - either PtMP-NB, BMA or PtP by splitting it into subinterfaces.

So this table does not really divide the network types into "which are recognized by RFC" and "which were invented by Cisco". Instead, this table explains how RFC 2328 would approach an NBMA link layer technology, and how you could approach it in Cisco IOS. The only network type unrecognized by RFC 2328 is the PtMP-NB type.

Best regards,

Peter

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