Sunday, August 29, 2010

BSCI - OSPF - Network Types - Broadcast

Broadcast:

  • Cisco proprietary
  • Full mesh required
  • Single subnet required
  • DR/BDR elected
  • Timers = 10 seconds
Configuration:
Lacking a diagram, assume we have 4 routers in a hub and spoke design. R1 is the Hub and R2,R3, and R4 are spoke routers. Frame-relay is in use.

On R1:
R1(config)#router ospf 1
R1(config-router)#network 192.168.1.0 0.0.0.255 area 0
!
R1(config)#int s0/0
R1(config-if)#ip address 192.168.1.1 255.255.255.0
R1(config-if)#encapsulation frame-relay
R1(config-if)#ip ospf network broadcast
R1(config-if)#ip ospf priority 10
R1(config-if)#frame-relay map ip 192.168.1.2 102 broadcast*
R1(config-if)#frame-relay map ip 192.168.1.3 103 broadcast
R1(config-if)#frame-relay map ip 192.168.1.4 104 broadcast
!
*broadcasts and multi-casts are now forwarded

On R2:
R2(config)#router ospf 1
R2(config-router)#network 192.168.1.0 0.0.0.255 area 0
!
R2(config)#int s0/0
R2(config-if)#ip address 192.168.1.2 255.255.255.0
R2(config-if)#encapsulation frame-relay
R2(config-if)#ip ospf network broadcast
R2(config-if)#ip ospf priority 0
R2(config-if)#frame-relay map ip 192.168.1.1 25 broadcast
R2(config-if)#frame-relay map ip 192.168.1.3 25 broadcast
R2(config-if)#frame-relay map ip 192.168.1.4 25 broadcast
!

On R3:
R3(config)#router ospf 1
R3(config-router)#network 192.168.1.0 0.0.0.255 area 0
!
R3(config)#int s0/0
R3(config-if)#ip address 192.168.1.3 255.255.255.0
R3(config-if)#encapsulation frame-relay
R3(config-if)#ip ospf network broadcast
R3(config-if)#ip ospf priority 0
R3(config-if)#frame-relay map ip 192.168.1.1 35 broadcast
R3(config-if)#frame-relay map ip 192.168.1.2 35 broadcast
R3(config-if)#frame-relay map ip 192.168.1.4 35 broadcast
!

On R4:
R4(config)#router ospf 1
R4(config-router)#network 192.168.1.0 0.0.0.255 area 0
!
R4(config)#int s0/0
R4(config-if)#ip address 192.168.1.4 255.255.255.0
R4(config-if)#encapsulation frame-relay
R4(config-if)#ip ospf network broadcast
R4(config-if)#ip ospf priority 0
R4(config-if)#frame-relay map ip 192.168.1.1 45 broadcast
R4(config-if)#frame-relay map ip 192.168.1.2 45 broadcast
R4(config-if)#frame-relay map ip 192.168.1.3 45 broadcast
!

In the example above you should note that R1 has a priority of 10 manually configured whilst R2, R3, and R4 each have their ospf priority set to 0. This will ensure that regardless of any future configuration R1 will always be the OSPF DR.

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