题目：AR34没有学习到两条等价默认路由，只从AR30学习到一条。
一、故障根因判断
AR31配置了错误的ISIS路由器类型和区域地址。 二、故障分析
2.1 故障重现，在AR34上查看IP路由表，命令及输出结果如下：
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<AR34>dis ip routing-table Route Flags: R - relay, D - download to fib ------------------------------------------------------------------------------ Routing Tables: Public Destinations : 14 Routes : 14
Destination/Mask Proto Pre Cost Flags NextHop Interface
0.0.0.0/0 ISIS-L1 15 10 D 10.5.34.30 GigabitEthernet0/0/0
. . . . . .
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由以上输出可见，AR34只存在一条缺省路由，下一跳为AR30的接口IP地址。由拓扑可知AR34和AR30、AR31需要建立ISIS邻居关系，进一步检查ISIS邻居关系。
2.2 在AR34上查看ISIS邻居关系，命令及输出结果如下：
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<AR34>dis isis peer
Peer information for ISIS(1)
System Id Interface Circuit Id State HoldTime Type PRI ------------------------------------------------------------------------------- 0000.0000.0030 GE0/0/0 0000.0000.0034.01 Up 29s L1 64
Total Peer(s): 1
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由以上输出可见，AR34只和AR30建立ISIS邻居关系，与AR31没有建立ISIS邻居关系，需要进一步检查AR34和AR31的ISIS邻居无法建立的原因。
2.3 在AR34上查看ISIS的摘要信息，命令及输出结果如下：
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[AR34]display isis brief
ISIS Protocol Information for ISIS(1) ------------------------------------- SystemId: 0000.0000.0034 System Level: L1 Area-Authentication-mode: NULL Domain-Authentication-mode: NULL Ipv6 is not enabled ISIS is in invalid restart status ISIS is in protocol hot standby state: Real-Time Backup
Interface: 10.5.34.34(GE0/0/0) Cost: L1 10 L2 10 Ipv6 Cost: L1 10 L2 10 State: IPV4 Up IPV6 Down Type: BROADCAST MTU: 1497 Priority: L1 64 L2 64 Timers: Csnp: L1 10 L2 10 ,Retransmit: L12 5 , Hello: L1 10 L2 10 , Hello Multiplier: L1 3 L2 3 , LSP-Throttle Timer: L12 50
Interface: 10.5.14.34(GE0/0/1) Cost: L1 10 L2 10 Ipv6 Cost: L1 10 L2 10 State: IPV4 Up IPV6 Down Type: BROADCAST MTU: 1497 Priority: L1 64 L2 64 Timers: Csnp: L1 10 L2 10 ,Retransmit: L12 5 , Hello: L1 10 L2 10 , Hello Multiplier: L1 3 L2 3 , LSP-Throttle Timer: L12 50
Interface: 10.5.1.34(Loop0) Cost: L1 0 L2 0 Ipv6 Cost: L1 0 L2 0 State: IPV4 Up IPV6 Down Type: P2P MTU: 1500 Priority: L1 64 L2 64 Timers: Csnp: L12 10 , Retransmit: L12 5 , Hello: 10 , Hello Multiplier: 3 , LSP-Throttle Timer: L12 50
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由以上输出可见，AR34是level-1类型的ISIS路由器，并且接口g0/0/0和g0/0/1都启用了ISIS，链路cost相同都为10，接口类型为Broadcast，需要进一步检查AR34和AR31的直连链路网络层连通性。
2.4 在AR34进行ping命令测试，命令及输出结果如下：
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<AR34>ping 10.5.14.31 PING 10.5.14.31: 56 data bytes, press CTRL_C to break Reply from 10.5.14.31: bytes=56 Sequence=1 ttl=255 time=90 ms Reply from 10.5.14.31: bytes=56 Sequence=2 ttl=255 time=30 ms Reply from 10.5.14.31: bytes=56 Sequence=3 ttl=255 time=20 ms Reply from 10.5.14.31: bytes=56 Sequence=4 ttl=255 time=20 ms Reply from 10.5.14.31: bytes=56 Sequence=5 ttl=255 time=20 ms
--- 10.5.14.31 ping statistics --- 5 packet(s) transmitted 5 packet(s) received 0.00% packet loss round-trip min/avg/max = 20/36/90 ms
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由以上输出结果可见，该链路网络层通信正常，此时需要检查AR31的ISIS邻居。
2.5 在AR31上查看ISIS邻居关系，命令及输出结果如下：
<AR31>display isis peer
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没有任何的输出，可见AR31没有与任何路由器形成ISIS邻居关系，进一步查看AR31的ISIS摘要信息。
2.6 在AR31上查看ISIS摘要信息，命令及输出结果如下：
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<AR31>display isis brief
ISIS Protocol Information for ISIS(1) ------------------------------------- SystemId: 0000.0000.0031 System Level: L1 Area-Authentication-mode: NULL Domain-Authentication-mode: NULL Ipv6 is not enabled ISIS is in invalid restart status ISIS is in protocol hot standby state: Real-Time Backup
Interface: 10.5.14.31(GE0/0/1) Cost: L1 10 L2 10 Ipv6 Cost: L1 10 L2 10 State: IPV4 Up IPV6 Down Type: BROADCAST MTU: 1497 Priority: L1 64 L2 64 Timers: Csnp: L1 10 L2 10 ,Retransmit: L12 5 , Hello: L1 10 L2 10 , Hello Multiplier: L1 3 L2 3 , LSP-Throttle Timer: L12 50
Interface: 10.5.130.31(GE0/0/2) Cost: L1 10 L2 10 Ipv6 Cost: L1 10 L2 10 State: IPV4 Up IPV6 Down Type: BROADCAST MTU: 1497 Priority: L1 64 L2 64 Timers: Csnp: L1 10 L2 10 ,Retransmit: L12 5 , Hello: L1 10 L2 10 , Hello Multiplier: L1 3 L2 3 , LSP-Throttle Timer: L12 50
Interface: 10.5.1.31(Loop0) Cost: L1 0 L2 0 Ipv6 Cost: L1 0 L2 0 State: IPV4 Up IPV6 Down Type: P2P MTU: 1500 Priority: L1 64 L2 64 Timers: Csnp: L12 10 , Retransmit: L12 5 , Hello: 10 , Hello Multiplier: 3 , LSP-Throttle Timer: L12 50
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由以上输出可见，AR31的接口g0/0/1和g0/0/2都正常启用了ISIS，接口类型为Broadcast，且AR31为level-1的ISIS路由器。存在故障AR31的ISIS路由器类型配置错误，应该配置为Level1/2，需要进一步检查R31的ISIS的接口信息。
2.7 在AR31上查看ISIS的接口信息，命令及输出结果如下：
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<AR31>display isis interface
Interface information for ISIS(1) --------------------------------- Interface Id IPV4.State IPV6.State MTU Type DIS GE0/0/1 001 Up Down 1497 L1/L2 No/No GE0/0/2 002 Up Down 1497 L1/L2 No/No Loop0 001 Up Down 1500 L1/L2 --
由以上输出可见，AR31的接口均为类型L1/2，继续对比AR34和AR31互发的ISIS报文是否错误。
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2.8 在AR31上查看ISIS接口错误信息，命令及输出结果如下：
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<AR31>display isis error interface g0/0/1 Statistics of errored packets for GE0/0/1: -------------------------------------------------------------------- LSP packet errors: Longer LSP : 0 Smaller LSP : 0 Mismatched Level : 0 Invalid Sysid : 0 Zero Sequence Number : 0 Illegal IS Type : 0 Zero Checksum : 0 Incorrect Checksum : 0 Bad Authentication : 0 Bad Auth Count : 0 More Protocol TLV : 0 Bad Nbr TLV : 0 Bad Extended IS TLV : 0 Bad IF Addr TLV : 0 Bad Reach TLV : 0 Bad Inter Domain TLV : 0 Mismatched Area Id(L1) : 0 Bad TLV Length : 0 Bad Alias TLV : 0 Bad Area TLV : 0 Bad SRLG TLV : 0 Unknown Adjacency : 0 Bad Protocol ID : 0 Bad Version : 0 Zero Lifetime : 0 Bad Ext Reach TLV : 0 Bad TE Router ID TLV : 0 Bad TE Sub TLV : 0
Hello packet errors: Bad Packet Length : 0 Reserved CircType : 0 Repeated System ID : 0 Bad Circuit Type : 0 Longer packet : 0 More Area Addr : 0 Longer Area Addr : 0 Bad Area Addr TLV : 0 More IF Addr : 0 Bad Formatted IF TLV : 0 More Nbr SNPA(LAN) : 0 Invalid Sysid : 0 Bad TLV Length : 0 Zero HoldingTime : 0 Unusable IP Addr : 0 Repeated IPv4 Addr : 0 Mismatched Area Addr(L1): 137 Mismatched Proto : 0 SNPA Conflicted(LAN) : 0 Mismatched Level : 0 Mismatched Max Area Addr: 0 Bad Authentication : 0 More Auth TLV : 0 3-Way Option Error(P2P) : 0 No Area Addr TLV : 0 Bad Protocol ID : 0 Bad Version : 0 Invalid IPv6 Addr : 0 More IPv6 IF Addr : 0 Duplicate IPv6 Addr : 0 More Optional Checksum : 0 Bad Optional Checksum : 0 ---------------------------------------------------------------------------------------------------------------------------------------------------------------
由以上输出可见，有错误计数“Mismatched Area Addr(L1): 137”，说明AR34和AR31能够正常交互Level-1的Hello报文，无法建立ISIS Level-1邻居的原因是ISIS区域地址不匹配。进一步查看AR34和AR31的区域配置参数。
2.9 分别在AR31和AR34上查看ISIS区域配置参数，命令及输出结果如下：
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<AR31>dis isis lsdb local verbose
Database information for ISIS(1) --------------------------------
Level-1 Link State Database
LSPID Seq Num Checksum Holdtime Length ATT/P/OL ------------------------------------------------------------------------------- 0000.0000.0031.00-00* 0x00000004 0x4c0f 1152 88 0/0/0 SOURCE 0000.0000.0031.00 NLPID IPV4 AREA ADDR 49.0006
. . . . . .
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<AR34>dis isis lsdb local verbose
Database information for ISIS(1) --------------------------------
Level-1 Link State Database
LSPID Seq Num Checksum Holdtime Length ATT/P/OL ------------------------------------------------------------------------------- 0000.0000.0034.00-00* 0x0000000d 0xe154 1068 102 0/0/0 SOURCE 0000.0000.0034.00 NLPID IPV4 AREA ADDR 49.0005
. . . . . .
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由以上输出可见，AR31的ISIS区域地址为49.0006 ，AR34的ISIS区域地址为49.0005。
结论：AR31和AR34无法建立ISIS L1邻居关系的原因是ISIS区域地址不匹配，需要将AR31的ISIS区域地址配置为49.0005；AR31和AR28无法建立ISIS L2邻居关系的原因是AR31不是类型L1/2的ISIS路由器。
三、故障处理
3.1 在AR31上执行以下命令：
system-view
isis {isis进程号}
undo network 49.0006.0000.0000.0031.00
network 49.0005.0000.0000.0031.00
is-level level-1-2
执行完以上命令在AR34上使用“display ip routing-table”查看故障是否解决。
3.2 其他高可能性故障
（1）AR31上配置了不通告ATT比特位的命令，在AR31上执行以下命令：
system-view
isis {isis进程号}
undo attached-bit advertise
（2）在AR34上针对下一跳配置了weight值，在AR34上执行以下命令：
system-view
isis {isis进程号}
dis this
undo nexthop 10.5.x.x
（3）AR28的g0/0/2接口配置了认证
system-view
interface g0/0/2
undo isis authticate-mode
（4）AR28的g0/0/2接口没有启用ISIS
system-view
interface g0/0/2
isis enable {isis进程号}
3.3 执行完以上命令后在AR34上再次查看IP路由表。如果故障依然存在，请提供完整的设备配置信息并拨打华为400服务热线寻求华为专家的协助！
