Broadcast Configuration

Broadcast Configuration
A full mesh among all OSPF routers is required for this environment to be configured and work
properly. A full explanation of the PVC configuration is beyond the scope of this chapter, but
here is a sample configuration:
RouterA#conf t
Enter configuration commands, one per line. End with CNTL/Z.
RouterA(config)#int serial 1
RouterA(config-if)#ip address 172.16.11.1 255.255.255.0
RouterA(config-if)#ip ospf network broadcast
RouterA(config-if)#encapsulation frame-relay
RouterA(config-if)#frame-relay map ip 172.16.11.2 102 broadcast
RouterA(config-if)#frame-relay map ip 172.16.11.3 103 broadcast
RouterA(config-if)#frame-relay map ip 172.16.11.4 104 broadcast
RouterA(config-if)#router ospf 1
RouterA(config-router)#network 172.16.11.0 0.0.0.255 area 0
RouterA(config-router)#^Z
RouterA#show running-config
Building configuration...
Current configuration:
!
version 11.2
no service password-encryption
no service udp-small-servers
no service tcp-small-servers
!
hostname RouterA
!
enable password cisco
!
!
168 Chapter 5  OSPF Operation in a Single Area
interface Loopback0
ip address 172.16.240.1 255.255.255.0
!
interface Ethernet0
ip address 172.16.230.20 255.255.255.0
!
interface Serial0
ip address 172.16.10.5 255.255.255.252
clockrate 2000000
dce-terminal-timing-enable
!
interface Serial1
ip address 172.16.11.1 255.255.255.0
encapsulation frame-relay
ip ospf network broadcast
frame-relay map ip 172.16.11.2 102 broadcast
frame-relay map ip 172.16.11.3 103 broadcast
frame-relay map ip 172.16.11.4 104 broadcast
!
interface Serial2
no ip address
shutdown
!
interface Serial3
no ip address
shutdown
!
interface BRI0
no ip address
shutdown
!
router ospf 1
network 172.16.10.5 0.0.0.0 area 0
network 172.16.11.0 0.0.0.255 area 0
!
Connected routers would have similar configurations. The key to this configuration is to
override the default network type by using the ip ospf network broadcast command.
Non-Broadcast Configuration
This environment requires all neighbors to be statically configured so that a DR may be chosen from
the attached routers on the network segment. We use the same commands as for the configuration
Configuring OSPF 169
of a broadcast network, with the exception of the neighbor statements used under the OSPF routing
process. Here is a sample configuration:
RouterB#conf t
Enter configuration commands, one per line. End with CNTL/Z.
RouterB(config)#interface serial1
RouterB(config-if)#ip address 172.16.25.1 255.255.255.0
RouterB(config-if)#ip ospf network non-broadcast
RouterB(config-if)#encapsulation frame-relay ietf
RouterB(config-if)#frame-relay map ip 172.16.25.10 210 broadcast
RouterB(config-if)#frame-relay map ip 172.16.25.11 211 broadcast
RouterB(config-if)#frame-relay map ip 172.16.25.12 212 broadcast
RouterB(config-if)#router ospf 1
RouterB(config-router)#neighbor 172.16.25.10 priority 1
RouterB(config-router)#neighbor 172.16.25.11 priority 1
RouterB(config-router)#neighbor 172.16.25.12 priority 1
RouterB(config-router)#network 172.16.25.0 0.0.0.255 area 0
RouterB(config-router)#^Z
RouterB#
Note the parameters priority 1 at the end of the neighbor statements. The value of 1 overrides
the default of 0. If left at the default value, the neighbor would be considered ineligible to
become the DR by the local router, and the local router would not initially send Hello statements
to the neighbor. For NBMA networks, a DR eligible router initially only sends Hello
packets to and enters the ATTEMPT state with other routers that also have DR potential. A priority
value greater than 0 causes the local router to consider the neighbor to have DR potential.
Only if the local router is elected DR will it start sending Hello packets to all other routers.