OSPF的NBMA模式，2端不加NEIGHBOR也可以建邻居

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OSPF的NBMA模式，2端不加NEIGHBOR也可以建邻居

OSPF综合专题
第一阶段：INIT/ATTEMPT（NBMA特有）阶段，初始化。
1．此阶段若不正常，说明物理链路或二层链路有问题
2．NBMA网络在ATTEMPT阶段时，ROUTER用HELLO INTERVAL定时器取代POLL INTERVAL。

第二阶段：2-WAY阶段，此阶段双方交换HELLO包，并协商DR/BDR/DROTHER
1．HELLO包中DC位用于识别DoNotAge位（其它包除开LSA确认包外也有DC位）。
2．OSPF是第四层协议，在三层包中用协议号89标识。
3．CRC不检查AGE字段，因为AGE会变化。
4．OSPF五种报文都包含了AUTH。
5．P2P，P2M不进行DR选举，DR，BDR位均至为0。0。0。0。

第三阶段：EXSTART阶段，此阶段协商DBD包中的主从关系。
1．第一个DBD包用于同步SEQ，以其中较大的为准。
2．DBD包中的主从关系只跟RID大小有关，较大的为MASTER。

第四阶段：EXCHANGE阶段，此阶段双方交换DBD。
1．DBD包和LSA请求总是以单播形式传播。
2．邻居在EXCHANGE状态时，就可以发送链路请求报文了。

第五阶段：LOADING阶段，加载完整链路信息。
1．显性链路状态确认只包含LSA头部信息。
2．包含重传条目的LSA总是以单播形式传播。
3．确认DELAY用于接受更多的LSA请求之后再发送LSA更新，默认为1S，且必须小于重传时间。
4．在LSA更新报文中，LINK-TYPE 4指定为虚链路，V位不置位。

第六阶段：FULL状态，成为邻居。
1．ROUTER判断FULL ADJECENSE的方法：链路请求列表中已经没有LSA条目。

具体情况分析：
一、当两端都为NBMA模式时，若两端都不加NEIGHBOR，则现象均如下：

14:56:26: OSPF: end of Wait on interface Serial1
14:56:26: OSPF: DR/BDR election on Serial1
14:56:26: OSPF: Elect BDR 3.3.3.3
14:56:26: OSPF: Elect DR 3.3.3.3
14:56:26: OSPF: Elect BDR 0.0.0.0
14:56:26: OSPF: Elect DR 3.3.3.3
14:56:26: DR: 3.3.3.3 (Id) BDR: none
14:56:27: OSPF: No full nbrs to build Net Lsa for interface Serial1

若其中一端加上NEIGHBOR，则加上的邻居会向另外一端发送单播更新，另一端接受到单播更新，则根据源地址发送单播更新，则两端可以建立邻居，现象如下：

14:58:41: OSPF: Rcv hello from 2.2.2.2 area 0 from Serial1 192.168.23.2
14:58:41: OSPF: 2 Way Communication to 2.2.2.2 on Serial1, state 2WAY
14:58:41: OSPF: Neighbor change Event on interface Serial1
14:58:41: OSPF: DR/BDR election on Serial1
14:58:41: OSPF: Elect BDR 0.0.0.0
14:58:41: OSPF: Elect DR 3.3.3.3
14:58:41: DR: 3.3.3.3 (Id) BDR: none
14:58:41: OSPF: Send DBD to 2.2.2.2 on Serial1 seq 0x1909 opt 0x42 flag 0x7 len 32
14:58:41: OSPF: End of hello processing
14:58:41: OSPF: Rcv DBD from 2.2.2.2 on Serial1 seq 0x1A77 opt 0x42 flag 0x7 len 32 mtu 1500 state EXSTART
14:58:41: OSPF: First DBD and we are not SLAVE
14:58:41: OSPF: Rcv DBD from 2.2.2.2 on Serial1 seq 0x1909 opt 0x42 flag 0x2 len 52 mtu 1500 state EXSTART
14:58:41: OSPF: NBR Negotiation Done. We are the MASTER
14:58:41: OSPF: Send DBD to 2.2.2.2 on Serial1 seq 0x190A opt 0x42 flag 0x3 len 52
14:58:41: OSPF: Database request to 2.2.2.2
14:58:41: OSPF: sent LS REQ packet to 192.168.23.2, lTEength 12
14:58:41: OSPF: Rcv DBD from 2.2.2.2 on Serial1 seq 0x190A opt 0x42 flag 0x0 len 32 mtu 1500 state EXCHANGE
14:58:41: OSPF: Send DBD to 2.2.2.2 on Serial1 seq 0x190B opt 0x42 flag 0x1 len 32
14:58:41: OSPF: Rcv DBD from 2.2.2.2 on Serial1 seq 0x190B opt 0x42 flag 0x0 len 32 mtu 1500 state EXCHANGE
14:58:41: OSPF: Exchange Done with 2.2.2.2 on Serial1
14:58:41: OSPF: Synchronized with 2.2.2.2 on Serial1, state FULL
14:58:41: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Serial1 from LOADING to FULL, Loading Done

此时若将刚才打上的那句NEIGHBOR一句拿掉，则被拿掉的那端会由于无法发送单播更新而切断邻居关系，现象如下：
TEST-R3#sh ip ospf nei

Neighbor ID Pri State Dead Time Address Interface
2.2.2.2 1 FULL/BDR 00:01:51 192.168.23.2 Serial1
TEST-R3(config)#router ospf 1
TEST-R3(config-router)#no nei 192.168.23.2
TEST-R3(config-router)#
15:02:34: OSPF: 2.2.2.2 address 192.168.23.2 on Serial1 is dead, state DOWN
15:02:34: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Serial1 from FULL to DOWN, Neighbor Down: Neighbor deconfigured

此时它会象最开始那样发送组播数据包，现象如下：

15:02:34: OSPF: Neighbor change Event on interface Serial1
15:02:34: OSPF: DR/BDR election on Serial1
15:02:34: OSPF: Elect BDR 0.0.0.0
15:02:34: OSPF: Elect DR 3.3.3.3
15:02:34: DR: 3.3.3.3 (Id) BDR: none
15:02:35: OSPF: Build router LSA for area 0, router ID 3.3.3.3, seq 0x80000005
15:02:35: OSPF: No full nbrs to build Net Lsa for interface Serial1
15:02:35: OSPF: Build network LSA for Serial1, router ID 3.3.3.3

此时又因为另外一端的邻居并未发觉邻居已经DOWN掉：

TEST-R2#sh ip ospf nei

Neighbor ID Pri State Dead Time Address Interface
3.3.3.3 1 FULL/DR 00:01:41 192.168.23.3 Serial0

紧接着它又收到了刚才TEST-R3发送的组播数据包，并还是向R3发送单播数据包：

TEST-R2#
15:02:40: OSPF: Rcv DBD from 3.3.3.3 on Serial0 seq 0x22DC opt 0x42 flag 0x7 len 32 mtu 1500 state FULL
15:02:40: OSPF: Bad seq received from 192.168.23.3 on Serial0
15:02:40: OSPF: Send DBD to 3.3.3.3 on Serial0 seq 0xB12 opt 0x42 flag 0x7 len 32
15:02:40: OSPF: Build router LSA for area 0, router ID 2.2.2.2, seq 0x80000005
TEST-R2#
15:02:45: OSPF: Rcv DBD from 3.3.3.3 on Serial0 seq 0x22DC opt 0x42 flag 0x7 len 32 mtu 1500 state EXSTART
15:02:45: OSPF: NBR Negotiation Done. We are the SLAVE
15:02:45: OSPF: Send DBD to 3.3.3.3 on Serial0 seq 0x22DC opt 0x42 flag 0x2 len 92
15:02:45: OSPF: Rcv DBD from 3.3.3.3 on Serial0 seq 0x22DD opt 0x42 flag 0x3 len 72 mtu 1500 state EXCHANGE
15:02:45: OSPF: Send DBD to 3.3.3.3 on Serial0 seq 0x22DD opt 0x42 flag 0x0 len 32
15:02:45: OSPF: Database request to 3.3.3.3
15:02:45: OSPF: sent LS REQ packet to 192.168.23.3, length 12
15:02:45: OSPF: Rcv DBD from 3.3.3.3 on Serial0 seq 0x22DE opt 0x42 flag 0x1 len 32 mtu 1500 state EXCHANGE
15:02:45: OSPF: Exchange Done with 3.3.3.3 on Serial0
15:02:45: OSPF: Send DBD to 3.3.3.3 on Serial0 seq 0x22DE opt 0x42 flag 0x0 len 32
15:02:45: OSPF: Synchronized with 3.3.3.3 on Serial0, state FULL
15:02:45: %OSPF-5-ADJCHG: Process 1, Nbr 3.3.3.3 on Serial0 from LOADING to FULL, Loading Done

这里加入TEST-R3收到的数据包：
15:02:41: OSPF: Rcv hello from 2.2.2.2 area 0 from Serial1 192.168.23.2
15:02:41: OSPF: 2 Way Communication to 2.2.2.2 on Serial1, state 2WAY
15:02:41: OSPF: Neighbor change Event on interface Serial1
15:02:41: OSPF: DR/BDR election on Serial1
15:02:41: OSPF: Elect BDR 2.2.2.2
15:02:41: OSPF: Elect DR 3.3.3.3
15:02:41: DR: 3.3.3.3 (Id) BDR: 2.2.2.2 (Id)
15:02:41: OSPF: Send DBD to 2.2.2.2 on Serial1 seq 0x22DC opt 0x42 flag 0x7 len 32
15:02:41: OSPF: End of hello processing
15:02:41: OSPF: Rcv DBD from 2.2.2.2 on Serial1 seq 0xB12 opt 0x42 flag 0x7 len 32 mtu 1500 state EXSTART
15:02:41: OSPF: First DBD and we are not SLAVE
TEST-R3(config-router)#
15:02:45: OSPF: service_maxage: Trying to delete MAXAGE LSA
15:02:46: OSPF: Send DBD to 2.2.2.2 on Serial1 seq 0x22DC opt 0x42 flag 0x7 len 32
15:02:46: OSPF: Retransmitting DBD to 2.2.2.2 on Serial1 [1]
15:02:46: OSPF: Rcv DBD from 2.2.2.2 on Serial1 seq 0x22DC opt 0x42 flag 0x2 len 92 mtu 1500 state EXSTART
15:02:46: OSPF: NBR Negotiation Done. We are the MASTER
15:02:46: OSPF: Send DBD to 2.2.2.2 on Serial1 seq 0x22DD opt 0x42 flag 0x3 len 72
15:02:46: OSPF: Database request to 2.2.2.2
15:02:46: OSPF: sent LS REQ packet to 192.168.23.2, length 24
15:02:46: OSPF: Rcv DBD from 2.2.2.2 on Serial1 seq 0x22DD opt 0x42 flag 0x0 len 32 mtu 1500 state EXCHANGE
15:02:46: OSPF: Send DBD to 2.2.2.2 on Serial1 seq 0x22DE opt 0x42 flag 0x1 len 32
15:02:46: OSPF: No full nbrs to build Net Lsa for interface Serial1
15:02:46: OSPF: Rcv DBD from 2.2.2.2 on Serial1 seq 0x22DE opt 0x42 flag 0x0 len 32 mtu 1500 state EXCHANGE
15:02:46: OSPF: Exchange Done with 2.2.2.2 on Serial1
15:
T02:46: OSPF: Synchronized with 2.2.2.2 on Serial1, state FULL

因为两端已经用NTP同步，所以可以根据时间判断出第二次同步发生在15:02:41，是由于TEST-R3收到了R2（R2上的邻居死亡时间为120秒）的HELLO包。



二、当相连的接口分别为P-2-M和NBMA，P-2-P和P-2-M，NBMA和BROADCAST时情况分别如下：（其中R1的S0和S1为P-2-M，E0为NBMA，R2为NBMA，R3为P-2-P，R4为P-2-P ）
Rack01R1#sh ip os database router

OSPF Router with ID (1.1.1.1) (Process ID 1)

Router Link States (Area 0)

LS age: 56
Options: (No TOS-capability, DC)
LS Type: Router Links
Link State ID: 1.1.1.1
Advertising Router: 1.1.1.1
LS Seq Number: 8000000A
Checksum: 0x61DC
Length: 96
Number of Links: 6

Link connected to: a Transit Network-----------------NBMA模式
(Link ID) Designated Router address: 10.0.0.4
(Link Data) Router Interface address: 10.0.0.1
Number of TOS metrics: 0
TOS 0 Metrics: 10

Link connected to: another Router (point-to-point)
(Link ID) Neighboring Router ID: 3.3.3.3
(Link Data) Router Interface address: 192.168.13.1
Number of TOS metrics: 0
TOS 0 Metrics: 64

Link connected to: a Stub Network-----------------------P-2-M模式自动生成一条主机路由
(Link ID) Network/subnet number: 192.168.13.1
(Link Data) Network Mask: 255.255.255.255
Number of TOS metrics: 0
TOS 0 Metrics: 0

Link connected to: another Router (point-to-point)
(Link ID) Neighboring Router ID: 2.2.2.2
(Link Data) Router Interface address: 192.168.12.1
Number of TOS metrics: 0
TOS 0 Metrics: 64

Link connected to: a Stub Network-----------------------P-2-M模式自动生成一条主机路由
(Link ID) Network/subnet number: 192.168.12.1
(Link Data) Network Mask: 255.255.255.255
Number of TOS metrics: 0
TOS 0 Metrics: 0

Link connected to: a Stub Network
(Link ID) Network/subnet number: 1.1.1.1
(Link Data) Network Mask: 255.255.255.255
Number of TOS metrics: 0
TOS 0 Metrics: 1


Adv Router is not-reachable----------------邻居不可达，现象：邻居能建立，但不能传路由
LS age: 63
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: 80000004
Checksum: 0xE5F2
Length: 48
Number of Links: 2

Link connected to: a Transit Network---------对方接口类型由此得出，和本端不匹配，因此不可达
(Link ID) Designated Router address: 192.168.12.2
(Link Data) Router Interface address: 192.168.12.2
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


LS age: 150
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: 80000004
Checksum: 0x5424
Length: 60
Number of Links: 3

Link connected to: another Router (point-to-point)-------------同样类型，可达。
(Link ID) Neighboring Router ID: 1.1.1.1
(Link Data) Router Interface address: 192.168.13.3
Number of TOS metrics: 0
TOS 0 Metrics: 64

Link connected to: a Stub Network
(Link ID) Network/subnet number: 192.168.13.0
(Link Data) Network Mask: 255.255.255.0
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


Adv Router is not-reachable
LS age: 109
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: 80000005
Checksum: 0x327D
Length: 60
Number of Links: 3

Link connected to: another Router (point-to-point) ---------同理，不可达
(Link ID) Neighboring Router ID: 1.1.1.1
(Link Data) Router Interface address: 10.0.0.4
Number of TOS metrics: 0
TOS 0 Metrics: 10

Link connected to: a Stub Network
(Link ID) Network/subnet number: 10.0.0.0
(Link Data) Network Mask: 255.255.255.0
Number of TOS metrics: 0
TOS 0 Metrics: 10

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


此后R4的E0口改为NBMA模式
Rack01R1#
00:18:37: %OSPF-5-ADJCHG: Process 1, Nbr 4.4.4.4 on Ethernet0 from LOADING to FULL, Loading Done
Rack01R1#sh ip os da
Rack01R1#sh ip os database

OSPF Router with ID (1.1.1.1) (Process ID 1)

Router Link States (Area 0)

Link ID ADV Router Age Seq# Checksum Link count
1.1.1.1 1.1.1.1 6 0x8000000C 0x003FFF 6
2.2.2.2 2.2.2.2 180 0x80000004 0x00E5F2 2
3.3.3.3 3.3.3.3 259 0x80000004 0x005424 3
4.4.4.4 4.4.4.4 6 0x80000007 0x001FAA 2

Net Link States (Area 0)

Link ID ADV Router Age Seq# Checksum
10.0.0.1 1.1.1.1 6 0x80000001 0x00DF37
192.168.12.2 2.2.2.2 181 0x80000001 0x008F1F
Rack01R1#sh ip os database ro
Rack01R1#sh ip os database router

OSPF Router with ID (1.1.1.1) (Process ID 1)

Router Link States (Area 0)

LS age: 9
Options: (No TOS-capability, DC)
LS Type: Router Links
Link State ID: 1.1.1.1
Advertising Router: 1.1.1.1
LS Seq Number: 8000000C
Checksum: 0x3FFF
Length: 96
Number of Links: 6

Link connected to: a Transit Network
(Link ID) Designated Router address: 10.0.0.1
(Link Data) Router Interface address: 10.0.0.1
Number of TOS metrics: 0
TOS 0 Metrics: 10

Link connected to: another Router (point-to-point)
(Link ID) Neighboring Router ID: 3.3.3.3
(Link Data) Router Interface address: 192.168.13.1
Number of TOS metrics: 0
TOS 0 Metrics: 64

Link connected to: a Stub Network
(Link ID) Network/subnet number: 192.168.13.1
(Link Data) Network Mask: 255.255.255.255
Number of TOS metrics: 0
TOS 0 Metrics: 0

Link connected to: another Router (point-to-point)
(Link ID) Neighboring Router ID: 2.2.2.2
(Link Data) Router Interface address: 192.168.12.1
Number of TOS metrics: 0
TOS 0 Metrics: 64

Link connected to: a Stub Network
(Link ID) Network/subnet number: 192.168.12.1
(Link Data) Network Mask: 255.255.255.255
Number of TOS metrics: 0
TOS 0 Metrics: 0

Link connected to: a Stub Network
(Link ID) Network/subnet number: 1.1.1.1
(Link Data) Network Mask: 255.255.255.255
Number of TOS metrics: 0
TOS 0 Metrics: 1


Adv Router is not-reachable
LS age: 186
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: 80000004
Checksum: 0xE5F2
Length: 48
Number of Links: 2

Link connected to: a Transit Network
(Link ID) Designated Router address: 192.168.12.2
(Link Data) Router Interface address: 192.168.12.2
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


LS age: 267
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: 80000004
Checksum: 0x5424
Length: 60
Number of Links: 3

Link connected to: another Router (point-to-point)
(Link ID) Neighboring Router ID: 1.1.1.1
(Link Data) Router Interface address: 192.168.13.3
Number of TOS metrics: 0
TOS 0 Metrics: 64

Link connected to: a Stub Network
(Link ID) Network/subnet number: 192.168.13.0
(Link Data) Network Mask: 255.255.255.0
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: 15
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: 80000007
Checksum: 0x1FAA
Length: 48
Number of Links: 2

Link connected to: a Transit Network---------可达，因为网络类型一致
(Link ID) Designated Router address: 10.0.0.1
(Link Data) Router Interface address: 10.0.0.4
Number of TOS metrics: 0
TOS 0 Metrics: 10

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

OSPF通过宣告路由器的第一条LSA判断对方接口类型，从而得知对方是否NOT-REACHABLE。