OSPF network types

======================= OSPF network type  ==============

1.Non_Broadcast Network

+ connect more than two routers but has no native broadcast capability

+ Default network type on multipoint Frame-relay interface

+ elect DR/BDR , but OSPF packets are unicast => specified neighbor with "neighbor" cmd.        

+ Next-hop IP NOT change and remains the IP address of the originating router

+ default PRIORITY = 1

> should be disable ( PRIORITY = 0) on all SPOKES to prevent a spoke from becoming a blackhole DR/BDR

+ hello time = 30s /dead time = 120s.

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> Frame-relay :

default network type FR interface : NON_BROADCAST

=> for establish adjacencies

 using cmd : neighbor a.b.c.d

all OSPF packet will use UNICAST instead MULTICAST = > DO NOT need configured with "Broadcast" keyword.

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2. Broadcast Network

+ Default network type on ETHERNET interface

+ elect a DR and a BDR

+ used multicast 224.0.0.5 for all SPFrouter and 224.0.0.6 for ALLDrouter.

*+ NO NEXT-HOP modify . NEXT-HOP IP remains that of the originating route

+ Layer3 to layer 2 resolution is required

+ Broadcast network can't have unicast neighbors configure

+ hello time = 10s/dead time = 40s.

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> Frame relay :

"broadcast" keyword should NOT be used when configuring the " frame-relay map"

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3.Point-to-point Network.

+ NO select DR/BDR        

+ used multicast dest to allSPFrouter (224.0.0.5)

+ next-hop IP is that of the advertising router

+ OSPF ignores subnet mask missmatch on point-to-point link

OSPF neighbor cants up when different network.

=> establish adjacencies when subnet mask missmatch

+ hello time = 10s / dead time = 40s

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> Frame-relay :

default network type FR interface : NON_BROADCAST

=> for establish adjacencies

 using cmd : neighbor a.b.c.d

all OSPF packet will use UNICAST instead MULTICAST = > DO NOT need configured with "Broadcast" keyword.

=======================================================================

4.point-to-multipoint Network.

+NOT a default option but arguably the best choice for NBMA networks ( in cisco device)

+ Special config of NBMA networks in which the networks are treated as a collection of P2P links.

+ NOT elect a DR and BDR

+ OSPF packets are multicast (224.0.0.5) to  neighbor.

+ next-hop IP is that of the advertising neighbor.

Ip next-hop not change and change when olny in EIGRP but can modify with command "no ip next-hop selft"

+ Layer3 to layer2 resolution is ONLY needed for the directly-connected neighbors.

+ Non-direct neighbors use recursive layer3 IP routing to reach each other.

+ In addition, the endpoints of point-to-multipoint networks are advertised as host routes (/32).

+ hello time = 30s/dead time = 120s

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5.Point-to-Multipoint Non-Broadcast Network

+ same as point-to-multipoint, but configured with  'non-broadcast' keyword

.

+ NO DR/BDR election

+ uses unicast opposed to multicast, to each manually specified neighbor.

+ directly connected neighbor must be manually defined with the "neighbor" command.

It is only required on one side, but it is best to do it on both sides.

+ next-hop IP is that of the advertising neighbor.

+ IP routing will be used to establish reachability between devices that are non-adjacent at layer2.

+ allow for the assignment of the cost per neighbor instead of using the interface's cost.

>> cost is based on the 'incoming' interface's bandwidth and not the bandwidth of the neighbor's interface.

+ hello time = 30s /dead time = 120s

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Note :

• NBMA mặc định là non-broadcast .NBMA  also have the ptential (tiềm năng) for multiple adjacencies, but they do not all send broadcast, they cannot guarantee the proper relationships will form.
• Point-to-point 

A method of configuring NBMA networks that allows OSPF to operate as if the routers were connected via point-to-point links instead of via an NBMA network. There are no DRs or BDRs in this configuration because each link is treated as a point-to-point link.