OSPF邻居建立出现错包计数增长

组网如上：

现网建立OSPF邻居的设备上dis ospf statistics error， bad ack和less recent lsa均有历史计数增长

首先在A设备上通过配置产生新的LSA， 此时A会将这个lsa发给B， B会将这个lsa洪泛给C，同时将这个lsa挂到重传链上并启动重传定时器。如果B收到了C应答的ack就会从重传链上摘除这个lsa，否则，等待重传定时器超时后，就会再次向C发送lsa，一直到收到C应答的ack为止。

 重传定时器的时间可以配置，同时为了避免大量重传发生时，重传的时间点太过集中对设备性能造成较大影响，协议有一个重传定时器的抖动机制。 默认情况下，重传定时器是5秒，由于抖动机制的存在，第一次重传定时器的超时时间会均匀的分布在1~5秒后。 而对端设备收到LSU报文，应答ACK报文不会实时发送，通常会过1秒左右。

因此，在这种串联组网中概率会出现短时间内（1秒左右）B给C已经发送了2个lsu报文，C才开始应答ack，此时C会将之前收到了2个lsu对应的ack都返回，通过抓包或者debug调试也可以看到B收到了C发送的ack报文中，有两个一样的ack信息。 随后B处理该ACK报文时， 逐个ack解析处理，解析第一个ack时，摘除了重传链，形成闭环，处理第二个ack的时候，由于重传链上已经没有数据了，就会记录invalid的bad ack。

因此，这个bad ack的少量增长，是正常的报文交互过程中满足特定的时序产生的，不存在功能的问题。 

实验复现通过debug的详细过程来解析下这个过程：

组网中A、B、C建立OSPF邻居，A设备引入直连。B设备从C收到重复lsack，产生Bad ack计数。

我们实施的复现操作： OSPF邻居建立后，A设备引入直连。

debug过程分析如下：

B设备debug ospf packet update、debug ospf packet ack

A->B LSU

*Dec  29 21:12:30:020 2022 MSR5660-2 OSPF/7/DEBUG: Source address: 10.0.0.1                                                       

*Dec  29 21:12:30:020 2022 MSR5660-2 OSPF/7/DEBUG: Destination address: 224.0.0.5                                                 

*Dec  29 21:12:30:020 2022 MSR5660-2 OSPF/7/DEBUG: Version 2, Type: 4, Length: 184.                                               

*Dec  29 21:12:30:020 2022 MSR5660-2 OSPF/7/DEBUG: Router: 10.0.0.1, Area: 0.0.0.0, Checksum: 20701.                              

*Dec  29 21:12:30:020 2022 MSR5660-2 OSPF/7/DEBUG: Authentication type: 00, Key(ASCII): 0 0 0 0 0 0 0 0.                          

*Dec  29 21:12:30:020 2022 MSR5660-2 OSPF/7/DEBUG: LSA count: 4.

B->C LSU                                                         

*Dec  29 21:12:30:047 2022 MSR5660-2 OSPF/7/DEBUG: OSPF 1: Sending packets.                                                       

*Dec  29 21:12:30:047 2022 MSR5660-2 OSPF/7/DEBUG: Source address: 20.0.0.1                                                       

*Dec  29 21:12:30:047 2022 MSR5660-2 OSPF/7/DEBUG: Destination address: 224.0.0.5                                                 

*Dec  29 21:12:30:047 2022 MSR5660-2 OSPF/7/DEBUG: Version 2, Type: 4, Length: 184.                                               

*Dec  29 21:12:30:047 2022 MSR5660-2 OSPF/7/DEBUG: Router: 10.0.0.2, Area: 0.0.0.0, Checksum: 20696.                              

*Dec  29 21:12:30:047 2022 MSR5660-2 OSPF/7/DEBUG: Authentication type: 00, Key(ASCII): 0 0 0 0 0 0 0 0.                          

*Dec  29 21:12:30:047 2022 MSR5660-2 OSPF/7/DEBUG: LSA count: 4.

B->A LSACK                                                                  

*Dec  29 21:12:31:027 2022 MSR5660-2 OSPF/7/DEBUG: OSPF 1: Sending packets.                                                       

*Dec  29 21:12:31:027 2022 MSR5660-2 OSPF/7/DEBUG: Source address: 10.0.0.2                                                       

*Dec  29 21:12:31:027 2022 MSR5660-2 OSPF/7/DEBUG: Destination address: 224.0.0.5                                                  

*Dec  29 21:12:31:027 2022 MSR5660-2 OSPF/7/DEBUG: Version 2, Type: 5, Length: 104.                                               

*Dec  29 21:12:31:027 2022 MSR5660-2 OSPF/7/DEBUG: Router: 10.0.0.2, Area: 0.0.0.0, Checksum: 62267.                               

*Dec  29 21:12:31:027 2022 MSR5660-2 OSPF/7/DEBUG: Authentication type: 00, Key(ASCII): 0 0 0 0 0 0 0 0.                          

*Dec  29 21:12:31:027 2022 MSR5660-2 OSPF/7/DEBUG: LSA type: 1, Link state ID: 10.0.0.1, Advertising router: 10.0.0.1.            

*Dec  29 21:12:31:027 2022 MSR5660-2 OSPF/7/DEBUG: LSA age: 2 Options: External routing:ON.                                       

*Dec  29 21:12:31:027 2022 MSR5660-2 OSPF/7/DEBUG: Length: 48 Sequence number: 80000004 Checksum: 12693.                           

*Dec  29 21:12:31:027 2022 MSR5660-2 OSPF/7/DEBUG: LSA type: 5, Link state ID: 1.1.1.1, Advertising router: 10.0.0.1.             

*Dec  29 21:12:31:027 2022 MSR5660-2 OSPF/7/DEBUG: LSA age: 2 Options: External routing:ON.                                        

*Dec  29 21:12:31:027 2022 MSR5660-2 OSPF/7/DEBUG: Length: 36 Sequence number: 80000001 Checksum: 44244.                          

*Dec  29 21:12:31:027 2022 MSR5660-2 OSPF/7/DEBUG: LSA type: 5, Link state ID: 2.2.2.2, Advertising router: 10.0.0.1.             

*Dec  29 21:12:31:027 2022 MSR5660-2 OSPF/7/DEBUG: LSA age: 2 Options: External routing:ON.                                       

*Dec  29 21:12:31:027 2022 MSR5660-2 OSPF/7/DEBUG: Length: 36 Sequence number: 80000001 Checksum: 32510.                          

*Dec  29 21:12:31:028 2022 MSR5660-2 OSPF/7/DEBUG: LSA type: 5, Link state ID: 10.0.0.0, Advertising router: 10.0.0.1.            

*Dec  29 21:12:31:028 2022 MSR5660-2 OSPF/7/DEBUG: LSA age: 2 Options: External routing:ON.                                       

*Dec  29 21:12:31:028 2022 MSR5660-2 OSPF/7/DEBUG: Length: 36 Sequence number: 80000001 Checksum: 22563.   

C->B LSACK                  

*Dec  29 21:12:31:052 2022 MSR5660-2 OSPF/7/DEBUG: OSPF 1: Receiving packets.                                                     

*Dec  29 21:12:31:052 2022 MSR5660-2 OSPF/7/DEBUG: Source address: 20.0.0.2                                                       

*Dec  29 21:12:31:052 2022 MSR5660-2 OSPF/7/DEBUG: Destination address: 224.0.0.5                                                 

*Dec  29 21:12:31:053 2022 MSR5660-2 OSPF/7/DEBUG: Version 2, Type: 5, Length: 104.                                               

*Dec  29 21:12:31:053 2022 MSR5660-2 OSPF/7/DEBUG: Router: 20.0.0.2, Area: 0.0.0.0, Checksum: 59703.                              

*Dec  29 21:12:31:053 2022 MSR5660-2 OSPF/7/DEBUG: Authentication type: 00, Key(ASCII): 0 0 0 0 0 0 0 0.                          

*Dec  29 21:12:31:053 2022 MSR5660-2 OSPF/7/DEBUG: LSA type: 1, Link state ID: 10.0.0.1, Advertising router: 10.0.0.1.            

*Dec  29 21:12:31:053 2022 MSR5660-2 OSPF/7/DEBUG: LSA age: 3 Options: External routing:ON.                                       

*Dec  29 21:12:31:053 2022 MSR5660-2 OSPF/7/DEBUG: Length: 48 Sequence number: 80000004 Checksum: 12693.                          

*Dec  29 21:12:31:053 2022 MSR5660-2 OSPF/7/DEBUG: LSA type: 5, Link state ID: 1.1.1.1, Advertising router: 10.0.0.1.             

*Dec  29 21:12:31:053 2022 MSR5660-2 OSPF/7/DEBUG: LSA age: 3 Options: External routing:ON.                                       

*Dec  29 21:12:31:053 2022 MSR5660-2 OSPF/7/DEBUG: Length: 36 Sequence number: 80000001 Checksum: 44244.                           

*Dec  29 21:12:31:054 2022 MSR5660-2 OSPF/7/DEBUG: LSA type: 5, Link state ID: 2.2.2.2, Advertising router: 10.0.0.1.             

*Dec  29 21:12:31:054 2022 MSR5660-2 OSPF/7/DEBUG: LSA age: 3 Options: External routing:ON.                                        

*Dec  29 21:12:31:054 2022 MSR5660-2 OSPF/7/DEBUG: Length: 36 Sequence number: 80000001 Checksum: 32510.                          

*Dec  29 21:12:31:054 2022 MSR5660-2 OSPF/7/DEBUG: LSA type: 5, Link state ID: 10.0.0.0, Advertising router: 10.0.0.1.            

*Dec  29 21:12:31:054 2022 MSR5660-2 OSPF/7/DEBUG: LSA age: 3 Options: External routing:ON.                                       

*Dec  29 21:12:31:054 2022 MSR5660-2 OSPF/7/DEBUG: Length: 36 Sequence number: 80000001 Checksum: 22563.  

B->C 第二次发LSU，与第一次21:12:30:047发LSU间隔约1s。             

*Dec  29 21:12:31:067 2022 MSR5660-2 OSPF/7/DEBUG: OSPF 1: Sending packets.                                                       

*Dec  29 21:12:31:067 2022 MSR5660-2 OSPF/7/DEBUG: Source address: 20.0.0.1                                                        

*Dec  29 21:12:31:067 2022 MSR5660-2 OSPF/7/DEBUG: Destination address: 224.0.0.5                                                 

*Dec  29 21:12:31:067 2022 MSR5660-2 OSPF/7/DEBUG: Version 2, Type: 4, Length: 184.                                                

*Dec  29 21:12:31:067 2022 MSR5660-2 OSPF/7/DEBUG: Router: 10.0.0.2, Area: 0.0.0.0, Checksum: 20692.                              

*Dec  29 21:12:31:067 2022 MSR5660-2 OSPF/7/DEBUG: Authentication type: 00, Key(ASCII): 0 0 0 0 0 0 0 0.                          

*Dec  29 21:12:31:067 2022 MSR5660-2 OSPF/7/DEBUG: LSA count: 4.                                       

C->B 第二次发LSACK，与第一次21:12:31:052发的LSACK相同。

*Dec  29 21:12:31:068 2022 MSR5660-2 OSPF/7/DEBUG: OSPF 1: Receiving packets.                                                     

*Dec  29 21:12:31:068 2022 MSR5660-2 OSPF/7/DEBUG: Source address: 20.0.0.2                                                       

*Dec  29 21:12:31:068 2022 MSR5660-2 OSPF/7/DEBUG: Destination address: 224.0.0.5                                                 

*Dec  29 21:12:31:068 2022 MSR5660-2 OSPF/7/DEBUG: Version 2, Type: 5, Length: 104.                                               

*Dec  29 21:12:31:068 2022 MSR5660-2 OSPF/7/DEBUG: Router: 20.0.0.2, Area: 0.0.0.0, Checksum: 59703.                              

*Dec  29 21:12:31:068 2022 MSR5660-2 OSPF/7/DEBUG: Authentication type: 00, Key(ASCII): 0 0 0 0 0 0 0 0.                          

*Dec  29 21:12:31:068 2022 MSR5660-2 OSPF/7/DEBUG: LSA type: 1, Link state ID: 10.0.0.1, Advertising router: 10.0.0.1.            

*Dec  29 21:12:31:068 2022 MSR5660-2 OSPF/7/DEBUG: LSA age: 3 Options: External routing:ON.                                       

*Dec  29 21:12:31:068 2022 MSR5660-2 OSPF/7/DEBUG: Length: 48 Sequence number: 80000004 Checksum: 12693.                          

*Dec  29 21:12:31:069 2022 MSR5660-2 OSPF/7/DEBUG: LSA type: 5, Link state ID: 1.1.1.1, Advertising router: 10.0.0.1.             

*Dec  29 21:12:31:069 2022 MSR5660-2 OSPF/7/DEBUG: LSA age: 3 Options: External routing:ON.                                       

*Dec  29 21:12:31:069 2022 MSR5660-2 OSPF/7/DEBUG: Length: 36 Sequence number: 80000001 Checksum: 44244.                           

*Dec  29 21:12:31:069 2022 MSR5660-2 OSPF/7/DEBUG: LSA type: 5, Link state ID: 2.2.2.2, Advertising router: 10.0.0.1.             

*Dec  29 21:12:31:069 2022 MSR5660-2 OSPF/7/DEBUG: LSA age: 3 Options: External routing:ON.                                        

*Dec  29 21:12:31:069 2022 MSR5660-2 OSPF/7/DEBUG: Length: 36 Sequence number: 80000001 Checksum: 32510.                          

*Dec  29 21:12:31:069 2022 MSR5660-2 OSPF/7/DEBUG: LSA type: 5, Link state ID: 10.0.0.0, Advertising router: 10.0.0.1.            

*Dec  29 21:12:31:069 2022 MSR5660-2 OSPF/7/DEBUG: LSA age: 3 Options: External routing:ON.                                       

*Dec  29 21:12:31:069 2022 MSR5660-2 OSPF/7/DEBUG: Length: 36 Sequence number: 80000001 Checksum: 22563.   

此时B设备记录了bad ack的增长。

<B>dis ospf statistics error

         OSPF Process 1 with Router ID 10.0.0.2

                 OSPF Packet Error Statistics

0         : Router ID confusion        0         : Bad packet

0         : Bad version                0         : Bad checksum

0         : Bad area ID                0         : Drop on unnumbered link

0         : Bad virtual link           0         : Bad authentication type

0         : Bad authentication key     0         : Packet too small

0         : Neighbor state low         0         : Transmit error

0         : Interface down             0         : Unknown neighbor

0         : HELLO: Netmask mismatch    0         : HELLO: Hello-time mismatch

0         : HELLO: Dead-time mismatch  0         : HELLO: Ebit option mismatch

0         : DD: MTU option mismatch    0         : DD: Unknown LSA type

0         : DD: Ebit option mismatch   1         : ACK: Bad ack

0         : ACK: Unknown LSA type      0         : REQ: Empty request

0         : REQ: Bad request           0         : UPD: LSA checksum bad

0         : UPD: Unknown LSA type      0         : UPD: Less recent LSA

另外如果现网为ABCD四台设备环形组网建立OSPF邻居，A发出的报文在B、C上重新打时间戳，发到D的时候的先后和时间戳都无法保证，正常报文交互过程中出现less recent lsa很常见，不会影响业务。

综上，OSPF错包技术中缓慢出现BAD ACK和Less recent LSA，属于报文交互时间差导致的正常现象，无需纠结。当出现大量、急速的增长时才需要特意关注。