OSPF (Open Shortest Path First)

It is an Open Standard Protocol

It could be configured in all routers

It is Link state Protocol

It maintains three tables:-

Routing Table

Topology Table

Neighbor ship table

AD value is 110

It has unlimited hop counts

It supports unlimited no: of routers

It is implemented in big networks

Areas

A single autonomous system is divided into many Areas.

Area 0 is the backbone area.

ABR (Area Border Router) is used to communicate Routers in one Area to another.

Link

According to OSPF the interface connected to a network or a Router is called a Link

Router ID

Address identified in each interface is called Router ID.

Highest interface IP among the Network will be the Router ID.

If there are Loopback interfaces configured in a network, then loopback interfaces will be considered as Router ID.

Cost

Metric of OSPF is called Cost

Cost = /Bandwidth

Designated Router & Backup Designated Router

Designated router is one which controls whole network, which also has highest priority.

The second highest priority Router is Backup Designated router.

One which has Highest router ID is called DR.

If there are multiple interfaces and they are not needed, then the priority value is made to 0 that they wont participate to find Router ID.

Loop addresses will be Router ID if configured.

Wild Card Mask

Reverse of Subnet Mask is called Wild card Mask.

Network bits will be 0 and Host bits will be 1.

Ex: 192.168.1.0/30

Broadcast = 255.255.255.255 –

Mask = 255.255.255.0

WCM = 0.0.0.255

OSPF Configuration

R1#config t

Enter configuration commands, one per line. End with CNTL/Z.

R1(config)#router ospf 1

R1(config-router)#network ‘Network Address’ ‘Wildcard Mask’ area 0

Verify OSPF

Router#show ip protocols (Verify OSPF)

Router#show ip route ospf (Routing Table)

Router#show ip ospf interface (Router ID, Area ID)