广播式网络是一个渐进的操作过程,它可以定义所有邻居。当给一个接口配置广播时，这个接口就好像是连入了LAN中，网络中仍要选出DR和BDR，需特别保证路由器选出的DR/BDR与网络中所有路由器都有物理连接。
 
使用接口命令ip ospf network broadcast可以向所有路由器上设置网络类型。R2、R4的串行接口被配置成OSPF PRIORITY为0，这将保证R3成为DR。
 
// 帧交换机
frame-relay switching
 
int s2/0
  encapsulation frame-relay
  clock rate 64000
  frame-relay intf-type dce
  frame-relay route 200 int s3/0 300
 
int s3/0
  encapsulation frame-relay
  clock rate 64000
  frame-relay intf-type dce
  frame-relay route 300 int s2/0 200
  frame-relay route 399 int s4/0 400
 
int s4/0
  encapsulation frame-relay
  clock rate 64000
  frame-relay intf-type dce
  frame-relay route 400 int s2/0 399
 
 
// R2 //
int lo0
  ip ad 2.2.2.2 255.255.255.0
 
int s2/0
  encapsulation frame-relay
  ip ospf network broadcast    //将OSPF网络类型设置为广播模式
  ip ospf priority 0    //优先级为0，不参与DR选举
  ip ad 192.1.1.2 255.255.255.0
  frame-relay map ip 192.1.1.3 200 broadcast
  frame-relay map ip 192.1.1.4 200 broadcast
 
router os 1
  network 2.2.2.2 0.0.0.0 area 0
  network 192.1.1.2 0.0.0.0 area 0
 
 
// R3 //
int lo0
  ip ad 3.3.3.3 255.255.255.0
 
int s3/0
  encapsulation frame-relay
  ip ospf network broadcast    //将OSPF网络类型设置为广播模式
  ip address 192.1.1.3 255.255.255.0
  frame-relay map ip 192.1.1.2 300 broadcast
  frame-relay map ip 192.1.1.4 399 broadcast
 
router os 1
  network 3.3.3.3 0.0.0.0 area 0
  network 192.1.1.3 0.0.0.0 area 0
 
// R4 //
int lo0
  ip ad 4.4.4.4 255.255.255.0
 
int s4/0
  encapsulation frame-relay
  ip ad 192.1.1.4 255.255.255.0
  ip ospf network broadcast    //将OSPF网络类型设置为广播模式
  ip ospf priority 0    //优先级为0，不参与DR选举
  frame-relay map ip 192.1.1.2 400 broadcast
  frame-relay map ip 192.1.1.3 400 broadcast
 
router os 1
  network 4.4.4.4 0.0.0.0 area 0
  network 192.1.1.4 0.0.0.0 area 0
 
 
 
 
验证过程：
一、首先来检查DR选举是否按我们的设计，R3被选举为DR，R2、R4不参与选举，同时注意网络类型是否为NBMA，hello时间间隔是否为30秒。。。。。。
 
r3#sh ip os int s3/0
Serial3/0 is up, line protocol is up
  Internet Address 192.1.1.3/24, Area 0
  Process ID 1, Router ID 3.3.3.3, Network Type BROADCAST, Cost: 64
  Transmit Delay is 1 sec, State DR, Priority 1
  Designated Router (ID) 3.3.3.3, Interface address 192.1.1.3
  No backup designated router on this network
  Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
    Hello due in 00:00:27
  Index 2/2, flood queue length 0
  Next 0x0(0)/0x0(0)
  Last flood scan length is 2, maximum is 2
  Last flood scan time is 0 msec, maximum is 0 msec
  Neighbor Count is 2, Adjacent neighbor count is 2
    Adjacent with neighbor 4.4.4.4
    Adjacent with neighbor 2.2.2.2
  Suppress hello for 0 neighbor(s)
 
 
r2#sh ip os int s2/0
Serial2/0 is up, line protocol is up
  Internet Address 192.1.1.2/24, Area 0
  Process ID 1, Router ID 2.2.2.2, Network Type BROADCAST, Cost: 64
  Transmit Delay is 1 sec, State DROTHER, Priority 0
  Designated Router (ID) 3.3.3.3, Interface address 192.1.1.3
  No backup designated router on this network
  Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
    Hello due in 00:00:06
  Index 2/2, flood queue length 0
  Next 0x0(0)/0x0(0)
  Last flood scan length is 1, maximum is 1
  Last flood scan time is 0 msec, maximum is 0 msec
  Neighbor Count is 1, Adjacent neighbor count is 1
    Adjacent with neighbor 3.3.3.3  (Designated Router)
  Suppress hello for 0 neighbor(s)
 
 
r4#sh ip ospf int s4/0
Serial4/0 is up, line protocol is up
  Internet Address 192.1.1.4/24, Area 0
  Process ID 1, Router ID 4.4.4.4, Network Type BROADCAST, Cost: 64
  Transmit Delay is 1 sec, State DROTHER, Priority 0
  Designated Router (ID) 3.3.3.3, Interface address 192.1.1.3
  No backup designated router on this network
  Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
    Hello due in 00:00:05
  Index 2/2, flood queue length 0
  Next 0x0(0)/0x0(0)
  Last flood scan length is 1, maximum is 1
  Last flood scan time is 0 msec, maximum is 0 msec
  Neighbor Count is 1, Adjacent neighbor count is 1
    Adjacent with neighbor 3.3.3.3  (Designated Router)
  Suppress hello for 0 neighbor(s)
 
二、接下来观察各路由器邻居建立情况：
r2#sh ip os nei
Neighbor ID     Pri   State           Dead Time   Address         Interface
3.3.3.3           1   FULL/DR         00:01:50    192.1.1.3       Serial2/0
 
r3#sh ip os nei
Neighbor ID     Pri   State           Dead Time   Address         Interface
4.4.4.4           0   FULL/DROTHER    00:01:41    192.1.1.4       Serial3/0
2.2.2.2           0   FULL/DROTHER    00:01:30    192.1.1.2       Serial3/0
 
r3#sh ip os nei
Neighbor ID     Pri   State           Dead Time   Address         Interface
3.3.3.3           1   FULL/DR         00:01:48    192.1.1.3       Serial4/0
 
 
三、最后验证路由：
r2#sh ip ro   
     2.0.0.0/24 is subnetted, 1 subnets
C       2.2.2.0 is directly connected, Loopback0
     3.0.0.0/32 is subnetted, 1 subnets
O       3.3.3.3 [110/65] via 192.1.1.3, 00:00:17, Serial2/0
     4.0.0.0/32 is subnetted, 1 subnets
O       4.4.4.4 [110/65] via 192.1.1.4, 00:00:17, Serial2/0
C    192.1.1.0/24 is directly connected, Serial2/0
 
 
 
r3#sh ip ro
     2.0.0.0/32 is subnetted, 1 subnets
O       2.2.2.2 [110/65] via 192.1.1.2, 00:00:38, Serial3/0
     3.0.0.0/24 is subnetted, 1 subnets
C       3.3.3.0 is directly connected, Loopback0
     4.0.0.0/32 is subnetted, 1 subnets
O       4.4.4.4 [110/65] via 192.1.1.4, 00:00:38, Serial3/0
C    192.1.1.0/24 is directly connected, Serial3/0
 
 
 
r4#sh ip ro
     2.0.0.0/32 is subnetted, 1 subnets
O       2.2.2.2 [110/65] via 192.1.1.2, 00:01:04, Serial4/0
     3.0.0.0/32 is subnetted, 1 subnets
O       3.3.3.3 [110/65] via 192.1.1.3, 00:01:04, Serial4/0
     4.0.0.0/24 is subnetted, 1 subnets
C       4.4.4.0 is directly connected, Loopback0
C    192.1.1.0/24 is directly connected, Serial4/0
r4#
 
 
如果我们将R2路由器的优先级调整为10，重启后R2将成为DR，R3作为BDR，R4作为DROTHER，这样的结果会导致R4无法收到R2、R3的路由更新，原因如下：
 
r4#sh ip ospf database
            OSPF Router with ID (4.4.4.4) (Process ID 1)
                Router Link States (Area 0)
Link ID         ADV Router      Age         Seq#       Checksum Link count
2.2.2.2         2.2.2.2         99          0x80000009 0xCF69   2
3.3.3.3         3.3.3.3         109         0x8000000B 0xDF4A   2
4.4.4.4         4.4.4.4         107         0x8000000C 0xFB1F   2
                Net Link States (Area 0)
Link ID         ADV Router      Age         Seq#       Checksum
192.1.1.2       2.2.2.2         108         0x80000001 0x4910 
 
r4#sh ip os database router
            OSPF Router with ID (4.4.4.4) (Process ID 1)
                Router Link States (Area 0)
  Adv Router is not-reachable
  LS age: 124
  Options: (No TOS-capability, DC)
  LS Type: Router Links
  Link State ID: 2.2.2.2
  Advertising Router: 2.2.2.2
  LS Seq Number: 80000009
  Checksum: 0xCF69
  Length: 48
  Number of Links: 2
    Link connected to: a Transit Network
     (Link ID) Designated Router address: 192.1.1.2
     (Link Data) Router Interface address: 192.1.1.2
      Number of TOS metrics: 0
       TOS 0 Metrics: 64
    Link connected to: a Stub Network
     (Link ID) Network/subnet number: 2.2.2.2
     (Link Data) Network Mask: 255.255.255.255
      Number of TOS metrics: 0
       TOS 0 Metrics: 1

  Adv Router is not-reachable
  LS age: 198
  Options: (No TOS-capability, DC)
  LS Type: Router Links
  Link State ID: 3.3.3.3
  Advertising Router: 3.3.3.3
  LS Seq Number: 8000000B
  Checksum: 0xDF4A
  Length: 48
  Number of Links: 2
    Link connected to: a Transit Network
     (Link ID) Designated Router address: 192.1.1.2
     (Link Data) Router Interface address: 192.1.1.3
      Number of TOS metrics: 0
       TOS 0 Metrics: 64
    Link connected to: a Stub Network
     (Link ID) Network/subnet number: 3.3.3.3
     (Link Data) Network Mask: 255.255.255.255
      Number of TOS metrics: 0
       TOS 0 Metrics: 1
         
  LS age: 215
  Options: (No TOS-capability, DC)
  LS Type: Router Links
  Link State ID: 4.4.4.4
  Advertising Router: 4.4.4.4
  LS Seq Number: 8000000C
  Checksum: 0xFB1F
  Length: 48
  Number of Links: 2
    Link connected to: a Transit Network
     (Link ID) Designated Router address: 192.1.1.3
     (Link Data) Router Interface address: 192.1.1.4
      Number of TOS metrics: 0
       TOS 0 Metrics: 64
    Link connected to: a Stub Network
     (Link ID) Network/subnet number: 4.4.4.4
     (Link Data) Network Mask: 255.255.255.255
      Number of TOS metrics: 0
       TOS 0 Metrics: 1