一、故障根因判断
AR29的LOOPBACK0地址无法访问AR28的LOOPBACK0地址的根本原因是因为AR29与AR28用于建立ospf邻居关系的接口不在同一个广播域中，LSW6上连接AR29与AR28的接口VLAN划分错误
二、故障分析
2.1故障重现，在AR２９上以自身LOOPBACK０接口的地址为源地址，去PINGAR28的LOOPBACK0接口的地址，测试结果如下输出所示：
ping -a 10.5.1.29 10.5.1.28
PING 10.5.1.28: 56 data bytes, press CTRL_C to break
Request time out
Request time out
Request time out
Request time out
Request time out
由以上输出结果可知确实存在此故障，由于AR29与AR28之间运行OSPF路由协议，所以在AR29上进一步查看路由表以确定是否存在AR28的LOOPBACK0接口地址的路由信息。
2.2在AR２９上检查路由表，看是否存在到AR２８的LOOPBACK０接口地址的路由，测试输出结果如下所示：
dis ip routing-table
Route Flags: R - relay, D - download to fib
Routing Tables: Public
Destinations : 12 Routes : 12
Destination/Mask Proto Pre Cost Flags NextHop Interface
10.5.1.29/32 Direct 0 0 D 127.0.0.1 LoopBack0
10.5.1.33/32 OSPF 10 1 D 10.5.40.34 GigabitEthernet0/0/1
10.5.40.0/24 Direct 0 0 D 10.5.40.30 GigabitEthernet0/0/1
10.5.40.30/32 Direct 0 0 D 127.0.0.1 GigabitEthernet0/0/1
10.5.40.255/32 Direct 0 0 D 127.0.0.1 GigabitEthernet0/0/1
10.5.128.0/24 Direct 0 0 D 10.5.128.30 GigabitEthernet0/0/0
10.5.128.30/32 Direct 0 0 D 127.0.0.1 GigabitEthernet0/0/0
10.5.128.255/32 Direct 0 0 D 127.0.0.1 GigabitEthernet0/0/0
由以上输出可知AR29并没有到工AR28LOOPBACK0接口地址的路由，所以需要检查工AR29与AR28的OSPF邻居关系是否正常。
2.3在AR29上检查OSPf邻居关系是否正常，输出结果如下所示：
dis ospf peer brief
OSPF Process 1 with Router ID 10.5.1.29
Peer Statistic Information
----------------------------------------------------------------------------
Area Id Interface Neighbor id State
0.0.0.2 GigabitEthernet0/0/1 10.5.1.33 Full
如上输出可知AR29在区域0没有与AR28 AR27建立OSPF的邻居关系，所以初步判断OSPF配置错误，需要进一步检查。
2.4由于AR27与AR28 AR29处于同一个OSPF域中，所以可以通过AR27的测试结果来判断AR28配置是否正确，测试及输出结果如下：
dis ospf peer brie
OSPF Process 1 with Router ID 10.5.1.27
Peer Statistic Information
----------------------------------------------------------------------------
Area Id Interface Neighbor id State
0.0.0.0 GigabitEthernet0/0/0 10.5.1.28 Full
dis ip routing-table
Route Flags: R - relay, D - download to fib
Routing Tables: Public
Destinations : 26 Routes : 26
Destination/Mask Proto Pre Cost Flags NextHop Interface
10.5.1.27/32 Direct 0 0 D 127.0.0.1 LoopBack0
10.5.1.28/32 OSPF 10 1 D 10.5.128.28 GigabitEthernet0
/0/0
由以上输出可知AR27与AR28能正常建立OSPF邻居关系，并且AR27能够学习到AR28的LOOPBACK0地址，说明AR28 OSPF 配置正确，此时需要对比AR27与AR29的OSPF配置是否一致来判断AR29的OSPF是否配置正确。
2.5在AR27/AR29上分别用
dis ospf brie
OSPF Process 1 with Router ID 10.5.1.27
OSPF Protocol Information
RouterID: 10.5.1.27 Border Router: AS
Multi-VPN-Instance is not enabled
Global DS-TE Mode: Non-Standard IETF Mode
Graceful-restart capability: disabled
Helper support capability : not configured
Applications Supported: MPLS Traffic-Engineering
Spf-schedule-interval: max 10000ms, start 500ms, hold 1000ms
Default ASE parameters: Metric: 1 Tag: 1 Type: 2
Route Preference: 10
ASE Route Preference: 150
SPF Computation Count: 7
RFC 1583 Compatible
Retransmission limitation is disabled
Area Count: 1 Nssa Area Count: 0
ExChange/Loading Neighbors: 0
Process total up interface count: 2
Process valid up interface count: 1
Area: 0.0.0.0 (MPLS TE not enabled)
Authtype: MD5 Area flag: Normal
SPF scheduled Count: 7
ExChange/Loading Neighbors: 0
Router ID conflict state: Normal
Area interface up count: 2
Interface: 10.5.128.27 (GigabitEthernet0/0/0)
Cost: 1 State: DR Type: Broadcast MTU: 1500
Priority: 1
Designated Router: 10.5.128.27
Backup Designated Router: 10.5.128.28
Timers: Hello 10 , Dead 40 , Poll 120 , Retransmit 5 , Transmit Delay 1
Interface: 10.5.1.27 (LoopBack0)
Cost: 0 State: P-2-P Type: P2P MTU: 1500
Timers: Hello 10 , Dead 40 , Poll 120 , Retransmit 5 , Transmit Delay 1
dis ospf brief
OSPF Process 1 with Router ID 10.5.1.29
OSPF Protocol Information
RouterID: 10.5.1.29 Border Router: AREA AS NSSA
Multi-VPN-Instance is not enabled
Global DS-TE Mode: Non-Standard IETF Mode
Graceful-restart capability: disabled
Helper support capability : not configured
Applications Supported: MPLS Traffic-Engineering
Spf-schedule-interval: max 10000ms, start 500ms, hold 1000ms
Default ASE parameters: Metric: 1 Tag: 1 Type: 2
Route Preference: 10
ASE Route Preference: 150
SPF Computation Count: 6
RFC 1583 Compatible
Retransmission limitation is disabled
Area Count: 2 Nssa Area Count: 1
ExChange/Loading Neighbors: 0
Process total up interface count: 3
Process valid up interface count: 2
Area: 0.0.0.0 (MPLS TE not enabled)
Authtype: MD5 Area flag: Normal
SPF scheduled Count: 6
ExChange/Loading Neighbors: 0
Router ID conflict state: Normal
Area interface up count: 1
通过以上输出可以看AR29的OSPF配置正确，并且把LOOPBACK0也加入了区域0中，所以需要进一步检查OSPF邻居建立是滞出现了其他错误。
2.6**在AR29上使用
dis ospf error interface GigabitEthernet 0/0/0
OSPF Process 1 with Router ID 10.5.1.29
OSPF error statistics
Interface: GigabitEthernet0/0/0 (10.5.128.30)
General packet errors:
0 : Bad version 0 : Bad checksum
0 : Bad area id 0 : Bad authentication type
0 : Bad authentication key 0 : Unknown neighbor
0 : Bad net segment 0 : Extern option mismatch
0 : Router id confusion
HELLO packet errors:
0 : Netmask mismatch 0 : Hello timer mismatch
0 : Dead timer mismatch 0 : Invalid Source Address
DD packet errors:
0 : MTU option mismatch
LS REQ packet errors:
0 : Bad request
LS UPD packet errors:
0 : LSA checksum bad
Receive Grace LSA errors:
0 : Number of invalid LSAs 0 : Number of policy failed LSAs
0 : Number of wrong period LSAs
由以上输可知OSPF并没有接收到任何错误 的报文信息，因为只有两种情奖品会造成此现像，一是OSPF邻居正常建立，二是OSPF完全没有接收到任何报文。由到OSPF邻居没有正常建立，所以可以判断OSPF没有正常接收到任何报文，初步判断为AR29与AR28用户建立OSPF的三层地址不通，需进一步判断。
2.7在AR29上命令ping
ping -a 10.5.128.29 10.5.128.28
Warning: The specified source address is not a local address, the ping command wi
ll not check the network connection.
PING 10.5.128.28: 56 data bytes, press CTRL_C to break
Request time out
Request time out
Request time out
Request time out
Request time out
由以上输出结果可知，AR29与AR28之间用于建立的ospf邻居关系的三层地址IP不可达，进一步判断二层是否互通。
2.8在AR29上检查ARP表，看是否有AR28的IP-MAC的映射关系，输出结果如下所示：
dis arp
IP ADDRESS MAC ADDRESS EXPIRE(M) TYPE INTERFACE VPN-INSTANCE
VLAN/CEVLAN PVC
10.5.128.30 00e0-fca0-04f8 I - GE0/0/0
10.5.40.30 00e0-fca0-04f9 I - GE0/0/1
10.5.40.34 00e0-fcbd-4f8e 9 D-0 GE0/0/1
Total:3 Dynamic:1 Static:0 Interface:2
由以上输出可知AR29的ARP表中并没有AR28 10.5.128.28地址的IP-MAC映射关系，所以初步判断AR29连接LSW6接口DOWN，需进一步检查。
2.9在AR上采用两次dis int g0/0/0
dis int g0/0/0
Input: 917 packets, 109123 bytes
Unicast: 0, Multicast: 917
Broadcast: 0, Jumbo: 0
Discard: 0, Total Error: 0
CRC: 0, Giants: 0
Jabbers: 0, Throttles: 0
Runts: 0, Symbols: 0
Ignoreds: 0, Frames: 0
dis int g0/0/0
Input: 948 packets, 112812 bytes
Unicast: 0, Multicast: 948
Broadcast: 0, Jumbo: 0
Discard: 0, Total Error: 0
CRC: 0, Giants: 0
Jabbers: 0, Throttles: 0
Runts: 0, Symbols: 0
Ignoreds: 0, Frames: 0
由以上输出可以看AR２９连接LSW6接口的物理和协议正常，并且能够两次输出结果中的组播报文在增长，所以可以判断端口正常。
结论：通过以上测试结果可以发现，AR29的OSPF配置正常，AR29与LSW6直连的接口正常，AR28 OSPF配置正常，但是AR29与AR28用于建立OSPF邻居关系的三层及二层地址不可达。所以可以判断故障的根本原因为AR29与AR28用于建立OSPF邻居关系的IP地址不在同一个广播域，LSW上用于连接AR２９与AR２８接口VLAN划分错误。
三、故障处理
3.1LSW VLAN划分错误的故障需在LSW6上执行以下命令：
dis port vlan
sys
int 连接AR29的接口
port link-type access
port default vlan 与AR27 28相同的VLANID
执行完成以上命令后在AR29采用以后命令进行测试：
ping -a 10.5.128.29 10.5.128.28
3.2其他高可能性故障-LSW6上配置了muxvlan 则需要在LSW6上执行以下命令：
dis muxvlan
sys
int 连接AR29的接口
undo port muxvlan en
执行完成以上命令后，在AR29上采用以下命令进行测试：
ping -a 10.5.128.29 10.5.128.28 /*AR29与AR28用于建立OSPF邻居关系的IPV4地址三层应该可达*/
display ospf peer brief /*AR29与AR28的ospf邻居关系应该正常建立*/
display ip routing-table | include 10.5.1.28 /*AR29能够正常学习到AR28的loopback0 IPV4地址*/
ping -a 10.5.1.29 10.5.1.28 /*AR29的loopback0 IPV4地址能够与AR28的loopback0 IPV4地址互通，故障解决*/
3.3.其他高可能性故障——LSW6和AR28上配置了过滤策略则需要在AR28LSW6上执行以下命令
dis traffic-policy applied-record
sys
int 所有相关接口
undo traffic-filter inbound /out
执行完成以上命令后在AR29上采用以下命令进行测试：
ping -a 10.5.128.29 10.5.128.28 /*AR29与AR28用于建立OSPF邻居关系的IPV4地址三层应该可达*/
display ospf peer brief /*AR29与AR28的ospf邻居关系应该正常建立*/
display ip routing-table | include 10.5.1.28 /*AR29能够正常学习到AR28的loopback0 IPV4地址*/
ping -a 10.5.1.29 10.5.1.28 /*AR29的loopback0 IPV4地址能够与AR28的loopback0 IPV4地址互通，故障解决*/
3.4如果执行以上命令都无法解决问题，则需要用户提供完整的设备配置联系华为TAC专家到场协助。或者播打华为400售后电话。