ensp模拟 通过 bfd 快速实现 ospf 邻居的断开

发布于 作者:

ospf 邻居断开 判断的规则是 4 倍的hello 时间，未收到回复，则认为断开。所以通常是 40秒或者 120秒。

OSPF 路由器如果在 Dead Interval 时间内没有收到邻居的 Hello 包，就会宣告该邻居失效。

  • 广播/点对点网络：约 40 秒后判定邻居失效
  • NBMA 网络：约 120 秒后判定邻居失效

网络拓扑图

实验目的

通过 display ospf peer bref 查看邻居建立的情况。 对比开启 bfd 和 未开启bfd ospf 邻居断开的时间。

实验配置

# AR1


system-view
sysname R1
bfd

ospf 1 router-id 1.1.1.1
bfd all-interface enable
area 0

int g0/0/0
ip address 12.0.0.1 24
ospf enable area 0


# AR2

system-view
sysname R2
bfd

ospf 1 router-id 2.2.2.2
bfd all-interface enable
area 0

int g0/0/0
ip address 12.0.0.2 24
ospf enable area 0

实验现象

80秒后ospf 完成收敛

80秒后ospf 完成收敛

ospf 收敛之后，开始发送 bfd 报文

ospf 收敛之后，开始发送 bfd 报文

可以看到 bfd 有三种状态

  1. Down
  2. Init
  3. Up

之后大约每秒种发送一次 bfd 报文。

查看ospf 的邻居状态

<R1>display ospf peer brief 

	 OSPF Process 1 with Router ID 1.1.1.1
		  Peer Statistic Information
 ----------------------------------------------------------------------------
 Area Id          Interface                        Neighbor id      State    
 0.0.0.0          GigabitEthernet0/0/0             2.2.2.2          Full        
 ----------------------------------------------------------------------------
<R1>

首先在R1上显示当前的时间，在R2上shutdown 链路，然后再R1 上查看ospf 的状态。

<R1>display clock
2025-04-14 16:16:47
Monday
Time Zone(China-Standard-Time) : UTC-08:00
<R1>display clock
2025-04-14 16:16:59
Monday
Time Zone(China-Standard-Time) : UTC-08:00
<R1>display ospf peer brief
Apr 14 2025 16:17:05-08:00 R1 %%01BFD/4/STACHG_TODWN(l)[0]:BFD session changed t
o Down. (SlotNumber=0, Discriminator=2097152, Diagnostic=DetectDown, Application
s=OSPF, ProcessPST=False, BindInterfaceName=GigabitEthernet0/0/0, InterfacePhysi
calState=Up, InterfaceProtocolState=Up) 
<R1>display ospf peer brief
Apr 14 2025 16:17:05-08:00 R1 %%01OSPF/3/NBR_CHG_DOWN(l)[1]:Neighbor event:neigh
bor state changed to Down. (ProcessId=256, NeighborAddress=2.2.2.2, NeighborEven
t=KillNbr, NeighborPreviousState=Full, NeighborCurrentState=Down) 
<R1>display ospf peer brief
Apr 14 2025 16:17:05-08:00 R1 %%01OSPF/3/NBR_DOWN_REASON(l)[2]:Neighbor state le
aves full or changed to Down. (ProcessId=256, NeighborRouterId=2.2.2.2, Neighbor
AreaId=0, NeighborInterface=GigabitEthernet0/0/0,NeighborDownImmediate reason=Ne
ighbor Down Due to Kill Neighbor, NeighborDownPrimeReason=BFD Session Down, Neig
hborChangeTime=2025-04-14 16:17:05-08:00) 
<R1>display ospf peer brief

	 OSPF Process 1 with Router ID 1.1.1.1
		  Peer Statistic Information
 ----------------------------------------------------------------------------
 Area Id          Interface                        Neighbor id      State    
 ----------------------------------------------------------------------------
<R1>display clock
2025-04-14 16:17:09
Monday
Time Zone(China-Standard-Time) : UTC-08:00

可以看到，三秒内就完成了，邻居的断开。

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