诊断六
AR34没有两条等价默认路由
TAC6-1:变种1
解答
一、故障根因
AR31的区域ID配置错误和isis进程级别配置错误。
二、故障分析
2.1 故障重现
查看AR34的路由表，结果如下：
"""
<AR34>display 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 10.5.134.30 GigabitEthernet
0/0/0
10.5.1.30/32 ISIS-L1 15 10 D 10.5.134.30 GigabitEthernet
0/0/0
10.5.1.34/32 Direct 0 0 D 127.0.0.1 LoopBack0
10.5.134.0/24 Direct 0 0 D 10.5.134.34 GigabitEthernet
0/0/0
10.5.134.34/32 Direct 0 0 D 127.0.0.1 GigabitEthernet
0/0/0
10.5.134.255/32 Direct 0 0 D 127.0.0.1 GigabitEthernet
0/0/0
10.5.230.0/24 ISIS-L1 15 20 D 10.5.134.30 GigabitEthernet
0/0/0
10.5.234.0/24 Direct 0 0 D 10.5.234.34 GigabitEthernet
0/0/1
10.5.234.34/32 Direct 0 0 D 127.0.0.1 GigabitEthernet
0/0/1
10.5.234.255/32 Direct 0 0 D 127.0.0.1 GigabitEthernet
0/0/1
127.0.0.0/8 Direct 0 0 D 127.0.0.1 InLoopBack0
127.0.0.1/32 Direct 0 0 D 127.0.0.1 InLoopBack0
127.255.255.255/32 Direct 0 0 D 127.0.0.1 InLoopBack0
255.255.255.255/32 Direct 0 0 D 127.0.0.1 InLoopBack0
"""
结果显示，AR34的路由表中只存在一条指向AR30的默认路由，缺少指向AR31的默认路由。
2.2 检查接口的cost值
接口下的cost值会影响等价默认路由的产生，检查AR34与AR31、AR30互联接口下的cost值是否一致，结果如下：
"""
<AR34>display isis interface verbose
Interface information for ISIS(1)
---------------------------------
Interface Id IPV4.State IPV6.State MTU Type DIS
GE0/0/0 001 Up Down 1497 L1/L2 No/No
Circuit MT State : Standard
Description : HUAWEI, AR Series, GigabitEthernet0/0/0 Interfac
e
SNPA Address : 00e0-fc83-528a
IP Address : 10.5.134.34
IPV6 Link Local Address :
IPV6 Global Address(es) :
Csnp Timer Value : L1 10 L2 10
Hello Timer Value : L1 10 L2 10
DIS Hello Timer Value : L1 3 L2 3
Hello Multiplier Value : L1 3 L2 3
LSP-Throttle Timer : L12 50
Cost : L1 10 L2 10
Ipv6 Cost : L1 10 L2 10
Priority : L1 64 L2 64
Retransmit Timer Value : L12 5
Bandwidth-Value : Low 1000000000 High 0
Static Bfd : NO
Dynamic Bfd : NO
Fast-Sense Rpr : NO
Interface Id IPV4.State IPV6.State MTU Type DIS
GE0/0/1 002 Up Down 1497 L1/L2 No/No
Circuit MT State : Standard
Description : HUAWEI, AR Series, GigabitEthernet0/0/1 Interfac
e
SNPA Address : 00e0-fc83-528b
IP Address : 10.5.234.34
IPV6 Link Local Address :
IPV6 Global Address(es) :
Csnp Timer Value : L1 10 L2 10
Hello Timer Value : L1 10 L2 10
DIS Hello Timer Value : L1 3 L2 3
Hello Multiplier Value : L1 3 L2 3
LSP-Throttle Timer : L12 50
Cost : L1 10 L2 10
Ipv6 Cost : L1 10 L2 10
Priority : L1 64 L2 64
Retransmit Timer Value : L12 5
Bandwidth-Value : Low 1000000000 High 0
Static Bfd : NO
Dynamic Bfd : NO
Fast-Sense Rpr : NO
Interface Id IPV4.State IPV6.State MTU Type DIS
Loop0 001 Up Down 1500 L1/L2 --
Circuit MT State : Standard
Circuit Parameters : passive
Description : HUAWEI, AR Series, LoopBack0 Interface
SNPA Address : 0000-0000-0000
IP Address : 10.5.1.34
IPV6 Link Local Address :
IPV6 Global Address(es) :
Csnp Timer Value : L12 10
Hello Timer Value : 10
DIS Hello Timer Value :
Hello Multiplier Value : 3
Cost : L1 0 L2 0
Ipv6 Cost : L1 0 L2 0
Retransmit Timer Value : L12 5
LSP-Throttle Timer : L12 50
Bandwidth-Value : Low 0 High 0
Static Bfd : NO
Dynamic Bfd : NO
Fast-Sense Rpr : NO
"""
结果显示，AR34与AR30互联的接口GE0/0/0接口的cost值为10，与AR31互联的接口GE0/0/1接口的cost值也为10，即这两个接口下cost值相等。
2.3 检查isis邻居
由于AR34与AR31、AR30之间运行isis协议，查看AR34上的isis邻居是否正常，结果如下：
"""
<AR34>display isis peer
Peer information for ISIS(1)
System Id Interface Circuit Id State HoldTime Type PRI
-------------------------------------------------------------------------------
0000.0000.0030 GE0/0/0 0000.0000.0030.01 Up 7s L1 64
Total Peer(s): 1
"""
结果显示，AR34上只存在AR30的level-1级别的邻居，无AR31无任何邻居关系。
2.4 检查三层连通性
isis邻居的建立依赖三层的连通性，检查AR31与AR34之间三层通信是否正常，结果如下：
"""
# 从AR31上获取AR31的g0/0/1接口的地址
<AR31>display ip interface brief
*down: administratively down
^down: standby
(l): loopback
(s): spoofing
The number of interface that is UP in Physical is 4
The number of interface that is DOWN in Physical is 1
The number of interface that is UP in Protocol is 4
The number of interface that is DOWN in Protocol is 1
Interface IP Address/Mask Physical Protocol
GigabitEthernet0/0/0 unassigned down down
GigabitEthernet0/0/1 10.5.234.31/24 up up
GigabitEthernet0/0/2 10.5.231.31/24 up up
LoopBack0 10.5.1.31/32 up up(s)
NULL0 unassigned up up(s)
# 在AR34上测试与AR31的连通性
<AR34>ping 10.5.234.31
PING 10.5.234.31: 56 data bytes, press CTRL_C to break
Reply from 10.5.234.31: bytes=56 Sequence=1 ttl=255 time=70 ms
Reply from 10.5.234.31: bytes=56 Sequence=2 ttl=255 time=20 ms
Reply from 10.5.234.31: bytes=56 Sequence=3 ttl=255 time=20 ms
Reply from 10.5.234.31: bytes=56 Sequence=4 ttl=255 time=40 ms
Reply from 10.5.234.31: bytes=56 Sequence=5 ttl=255 time=20 ms
--- 10.5.234.31 ping statistics ---
5 packet(s) transmitted
5 packet(s) received
0.00% packet loss
round-trip min/avg/max = 20/34/70 ms
"""
结果显示，AR34与AR31之间的三层通信正常。
2.5 检查isis错误情况
在AR34上检查其与AR31互联接口的isis报错情况，结果如下：
"""
<AR34>display isis error interface GigabitEthernet 0/0/1
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): 129 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
--------------------------------------------------------------------
"""
结果显示，“Mismatched Area Addr(L1): 129 ”表明AR31与AR34之间有交互level-1级别的hello报文，但故障的原因是isis的区域ID不一致。
2.6 查看AR31和AR34的链路状态数据库
为确认AR31和AR34之间isis区域ID不一致的情况，需要进一步查看AR31和AR34的链路状态数据库，结果如下：
"""
# AR34的链路状态数据库
<AR34>display isis lsdb verbose
Database information for ISIS(1)
--------------------------------
Level-1 Link State Database
LSPID Seq Num Checksum Holdtime Length ATT/P/OL
-------------------------------------------------------------------------------
0000.0000.0030.00-00 0x00000009 0xe6e6 648 102 1/0/0
SOURCE 0000.0000.0030.00
NLPID IPV4
AREA ADDR 49.0005
INTF ADDR 10.5.1.30
INTF ADDR 10.5.230.30
INTF ADDR 10.5.134.30
NBR ID 0000.0000.0030.01 COST: 10
IP-Internal 10.5.1.30 255.255.255.255 COST: 0
IP-Internal 10.5.230.0 255.255.255.0 COST: 10
IP-Internal 10.5.134.0 255.255.255.0 COST: 10
0000.0000.0030.01-00 0x00000002 0xdb1e 648 55 0/0/0
SOURCE 0000.0000.0030.01
NLPID IPV4
NBR ID 0000.0000.0030.00 COST: 0
NBR ID 0000.0000.0034.00 COST: 0
0000.0000.0034.00-00* 0x00000007 0xd2ea 605 102 0/0/0
SOURCE 0000.0000.0034.00
NLPID IPV4
AREA ADDR 49.0005
INTF ADDR 10.5.1.34
INTF ADDR 10.5.134.34
INTF ADDR 10.5.234.34
NBR ID 0000.0000.0030.01 COST: 10
IP-Internal 10.5.1.34 255.255.255.255 COST: 0
IP-Internal 10.5.134.0 255.255.255.0 COST: 10
IP-Internal 10.5.234.0 255.255.255.0 COST: 10
Total LSP(s): 3
*(In TLV)-Leaking Route, *(By LSPID)-Self LSP, +-Self LSP(Extended),
ATT-Attached, P-Partition, OL-Overload
# AR31的链路状态数据库
<AR31>display isis lsdb 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* 0x00000005 0x20b5 618 88 0/0/0
SOURCE 0000.0000.0031.00
NLPID IPV4
AREA ADDR 49.0006
INTF ADDR 10.5.1.31
INTF ADDR 10.5.234.31
INTF ADDR 10.5.231.31
IP-Internal 10.5.1.31 255.255.255.255 COST: 0
IP-Internal 10.5.234.0 255.255.255.0 COST: 10
IP-Internal 10.5.231.0 255.255.255.0 COST: 10
Total LSP(s): 1
*(In TLV)-Leaking Route, *(By LSPID)-Self LSP, +-Self LSP(Extended),
ATT-Attached, P-Partition, OL-Overload
"""
结果显示，AR34的区域ID为49.0005，AR31的区域ID为49.0006，区域ID不相同影响level-1级别邻居的建立，但是不影响level-2级别邻居的建立，因此AR31的区域ID配置错误。同时还发现，AR34上只收到来自AR30的ATT置1的lsp，并未收到任何来自AR31的lsp。AR34上如果要产生指向AR31的默认路由，不仅需要AR34与AR31之间建立level-1级别的邻居，还需要AR31与AR28之间建立level-2级别的邻居，因此AR31的isis级别只能为level-1-2，但是上面结果显示的AR31的链路状态数据库只产生level-1级别的lsp，初步断定AR31的isis级别也是错误的。
2.7 查看AR31的isis进程信息和邻居
为确认AR31的isis级别是否错误，需要查看AR31的isis进程信息，结果如下：
"""
# isis进程信息
<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: 10.5.234.31(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: 10.5.231.31(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
# isis邻居
<AR31>dis isis peer
<AR31>
"""
结果显示，AR31的isis级别为level-1，配置错误，因此无法与AR28之间建立level-2级别的邻居，需要修改成level-1-2。
2.8 结论
通过上述分析，故障的根本原因为AR31的区域ID配置错误和isis进程级别配置错误。
三、故障解决
3.1 AR31的区域ID配置错误和isis进程级别配置错误，需要在AR31上执行以下命令：
system-view //进入系统视图
isis {isis进程ID} //进入isis进程下
undo network-entity 49.0006.0000.0000.0031.00 //删除错误的区域ID
network-entity 49.0005.0000.0000.0031.00 //配置正确的区域ID
is-level level-1-2 //修改isis级别为level-1-2
执行完以上命令之后，需要在AR31上执行以下命令进行检查：
display isis peer //查看是否与AR28建立level-2级别的邻居，与AR34建立level-1级别的邻居
需要在AR34上执行以下命令进行检查：
display isis peer //查看是否与AR31建立level-1级别的邻居
display isis lsdb verbose //查看是否收到来自AR31的ATT位置1的lsp
display ip routing-table //查看故障是否解决
3.2 如果执行以上命令未能解决故障，则存在以下高可能性故障：
与AR31和AR28之间的isis邻居相关：
3.2.1 AR28的g0/0/2接口下没有使能isis，需要在AR28上执行以下命令：
system-view
interface GigabitEthernet 0/0/2
display this
isis enable {isis进程ID}
3.2.2 AR28的isis进程下配置domain认证，需要在AR31上执行以下命令：
system-view
interface GigabitEthernet 0/0/2
undo isis authentication-mode
isis xx
domain-authentication-mode md5 1 cipher xx
3.2.3 AR28与AR31互联接口下isis认证不一致，需要在AR31和AR28上执行以下命令：
system-view
interface GigabitEthernet 0/0/2
undo isis authentication-mode
3.2.4 AR28与AR31互联接口下的mtu不一致，需要在AR28上执行以下命令：
system-view
interface GigabitEthernet 0/0/2
mtu 1497
3.2.5 AR28与AR31互联接口的链路类型不一致，需要在AR31和AR28上执行以下命令：
system-view
interface GigabitEthernet 0/0/2
isis circuit-type xxx
3.2.6 AR28与AR31的isis进程下的cost类型不一致，需要在AR31和AR28上执行以下命令：
system-view
isis xx
cost-style xxx
执行完以上命令之后，需要在AR31上执行以下命令进行检查：
display isis peer //查看是否与AR28建立level-2级别的邻居
与AR31和AR34之间的isis邻居相关：
3.2.7 AR31与AR34互联接口下的isis认证不一致，需要在AR31和AR34上执行以下命令：
system-view
interface GigabitEthernet 0/0/1
undo isis authentication-mode
3.2.8 AR31与AR34的isis进程下的cost类型不一致，需要在AR31和AR34上执行以下命令：
system-view
isis xx
cost-style xxx
需要在AR34上执行以下命令进行检查：
display isis peer //查看是否与AR31建立level-1级别的邻居
其他因素：
3.2.9 AR31的isis进程下设置强制ATT不能置1，需要在AR31上执行以下命令：
system-view
isis xx
undo attached-bit advertise
3.2.10 AR34的isis进程下针对下一跳设置不同的weight，需要在AR34上执行以下命令：
system-view
isis xx
undo nexthop 10.5.x.x
3.2.11 AR34在isis进程下设置最大负载为1，需要在AR34上执行以下命令：
system-view
isis xx
undo maximum load-balancing
执行完以上命令之后，需要在AR31上执行以下命令进行检查：
display isis peer //查看是否与AR28建立level-2级别的邻居，与AR34建立level-1级别的邻居
需要在AR34上执行以下命令进行检查：
display isis peer //查看是否与AR31建立level-1级别的邻居
display isis lsdb verbose //查看是否收到来自AR31的ATT位置1的lsp
display ip routing-table //查看故障是否解决
3.3 如果执行以上命令成功排除故障，则需要在执行过命令的设备上继续执行以下命令：
return //回到用户视图
save //保存修改之后的配置
3.4 如果执行以上命令未能排除故障，则需要用户提供完整的设备配置信息或者派遣一线工程师到达用户现场进行现场排障，同时拨打华为400服务热线请求华为专家的协助，谢谢！
TAC6-2:变种2
解答
一、故障根因
AR31的区域ID配置错误，与AR34的区域ID不一致，导致AR31与AR34之间无法建立level-1的isis邻居。
二、故障分析
2.1 故障重现
查看AR34的路由表，结果如下：
"""
<AR34>display 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 10.5.134.30 GigabitEthernet
0/0/0
10.5.1.30/32 ISIS-L1 15 10 D 10.5.134.30 GigabitEthernet
0/0/0
10.5.1.34/32 Direct 0 0 D 127.0.0.1 LoopBack0
10.5.134.0/24 Direct 0 0 D 10.5.134.34 GigabitEthernet
0/0/0
10.5.134.34/32 Direct 0 0 D 127.0.0.1 GigabitEthernet
0/0/0
10.5.134.255/32 Direct 0 0 D 127.0.0.1 GigabitEthernet
0/0/0
10.5.230.0/24 ISIS-L1 15 20 D 10.5.134.30 GigabitEthernet
0/0/0
10.5.234.0/24 Direct 0 0 D 10.5.234.34 GigabitEthernet
0/0/1
10.5.234.34/32 Direct 0 0 D 127.0.0.1 GigabitEthernet
0/0/1
10.5.234.255/32 Direct 0 0 D 127.0.0.1 GigabitEthernet
0/0/1
127.0.0.0/8 Direct 0 0 D 127.0.0.1 InLoopBack0
127.0.0.1/32 Direct 0 0 D 127.0.0.1 InLoopBack0
127.255.255.255/32 Direct 0 0 D 127.0.0.1 InLoopBack0
255.255.255.255/32 Direct 0 0 D 127.0.0.1 InLoopBack0
"""
结果显示，AR34的路由表中只存在一条指向AR30的默认路由，缺少指向AR31的默认路由，故障存在。
2.2 检查接口的cost值
接口下的cost值会影响等价默认路由的产生，首先检查AR34与AR31、AR30互联接口下的cost值，结果如下：
"""
<AR34>display isis interface verbose
Interface information for ISIS(1)
---------------------------------
Interface Id IPV4.State IPV6.State MTU Type DIS
GE0/0/0 001 Up Down 1497 L1/L2 No/No
Circuit MT State : Standard
Description : HUAWEI, AR Series, GigabitEthernet0/0/0 Interfac
e
SNPA Address : 00e0-fc83-528a
IP Address : 10.5.134.34
IPV6 Link Local Address :
IPV6 Global Address(es) :
Csnp Timer Value : L1 10 L2 10
Hello Timer Value : L1 10 L2 10
DIS Hello Timer Value : L1 3 L2 3
Hello Multiplier Value : L1 3 L2 3
LSP-Throttle Timer : L12 50
Cost : L1 10 L2 10
Ipv6 Cost : L1 10 L2 10
Priority : L1 64 L2 64
Retransmit Timer Value : L12 5
Bandwidth-Value : Low 1000000000 High 0
Static Bfd : NO
Dynamic Bfd : NO
Fast-Sense Rpr : NO
Interface Id IPV4.State IPV6.State MTU Type DIS
GE0/0/1 002 Up Down 1497 L1/L2 No/No
Circuit MT State : Standard
Description : HUAWEI, AR Series, GigabitEthernet0/0/1 Interfac
e
SNPA Address : 00e0-fc83-528b
IP Address : 10.5.234.34
IPV6 Link Local Address :
IPV6 Global Address(es) :
Csnp Timer Value : L1 10 L2 10
Hello Timer Value : L1 10 L2 10
DIS Hello Timer Value : L1 3 L2 3
Hello Multiplier Value : L1 3 L2 3
LSP-Throttle Timer : L12 50
Cost : L1 10 L2 10
Ipv6 Cost : L1 10 L2 10
Priority : L1 64 L2 64
Retransmit Timer Value : L12 5
Bandwidth-Value : Low 1000000000 High 0
Static Bfd : NO
Dynamic Bfd : NO
Fast-Sense Rpr : NO
Interface Id IPV4.State IPV6.State MTU Type DIS
Loop0 001 Up Down 1500 L1/L2 --
Circuit MT State : Standard
Circuit Parameters : passive
Description : HUAWEI, AR Series, LoopBack0 Interface
SNPA Address : 0000-0000-0000
IP Address : 10.5.1.34
IPV6 Link Local Address :
IPV6 Global Address(es) :
Csnp Timer Value : L12 10
Hello Timer Value : 10
DIS Hello Timer Value :
Hello Multiplier Value : 3
Cost : L1 0 L2 0
Ipv6 Cost : L1 0 L2 0
Retransmit Timer Value : L12 5
LSP-Throttle Timer : L12 50
Bandwidth-Value : Low 0 High 0
Static Bfd : NO
Dynamic Bfd : NO
Fast-Sense Rpr : NO
"""
结果显示，AR34与AR31互联的GE0/0/1、与AR30互联的GE0/0/0接口的cost值均为10。
2.3 检查isis邻居
AR34与AR31、AR30之间运行isis路由协议，检查AR34上的isis邻居是否正常，结果如下：
"""
<AR34>display isis peer
Peer information for ISIS(1)
System Id Interface Circuit Id State HoldTime Type PRI
-------------------------------------------------------------------------------
0000.0000.0030 GE0/0/0 0000.0000.0030.01 Up 9s L1 64
Total Peer(s): 1
"""
结果显示，AR34只和AR30之间建立level-1级别的邻居，缺少了与AR31之间的isis邻居关系。
2.4 检查三层连通性
isis邻居的建立依赖三层的连通性，检查AR34与AR31之间三层通信是否正常，结果如下：
"""
# 获取AR31与AR34互联接口的地址
<AR31>display ip interface brief
*down: administratively down
^down: standby
(l): loopback
(s): spoofing
The number of interface that is UP in Physical is 4
The number of interface that is DOWN in Physical is 1
The number of interface that is UP in Protocol is 4
The number of interface that is DOWN in Protocol is 1
Interface IP Address/Mask Physical Protocol
GigabitEthernet0/0/0 unassigned down down
GigabitEthernet0/0/1 10.5.234.31/24 up up
GigabitEthernet0/0/2 10.5.231.31/24 up up
LoopBack0 10.5.1.31/32 up up(s)
NULL0 unassigned up up(s)
<AR31>
# 测试三层通信情况
<AR34>ping 10.5.234.31
PING 10.5.234.31: 56 data bytes, press CTRL_C to break
Reply from 10.5.234.31: bytes=56 Sequence=1 ttl=255 time=70 ms
Reply from 10.5.234.31: bytes=56 Sequence=2 ttl=255 time=10 ms
Reply from 10.5.234.31: bytes=56 Sequence=3 ttl=255 time=10 ms
Reply from 10.5.234.31: bytes=56 Sequence=4 ttl=255 time=10 ms
Reply from 10.5.234.31: bytes=56 Sequence=5 ttl=255 time=10 ms
--- 10.5.234.31 ping statistics ---
5 packet(s) transmitted
5 packet(s) received
0.00% packet loss
round-trip min/avg/max = 10/22/70 ms
"""
结果显示，AR34与AR31三层通信正常。
2.5 检查isis报错情况
在AR34上检查与AR31互联接口下的isis报错情况，结果如下：
"""
<AR34>display isis error interface GigabitEthernet 0/0/1
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): 85 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
--------------------------------------------------------------------
"""
结果显示，“Mismatched Area Addr(L1): 85 ”表明AR34与AR31之间有交互Level-1级别的hello报文的能力，邻居未建立的原因是isis的区域ID不一致。
2.6 查看AR34与AR31的链路状态数据库
为了确认AR34与AR31之间区域ID是否一致，需要对比查看AR31与AR34的链路状态数据库，结果如下：
"""
# AR34
<AR34>display isis lsdb verbose
Database information for ISIS(1)
--------------------------------
Level-1 Link State Database
LSPID Seq Num Checksum Holdtime Length ATT/P/OL
-------------------------------------------------------------------------------
0000.0000.0030.00-00 0x00000007 0xeae4 1011 102 1/0/0
SOURCE 0000.0000.0030.00
NLPID IPV4
AREA ADDR 49.0005
INTF ADDR 10.5.1.30
INTF ADDR 10.5.230.30
INTF ADDR 10.5.134.30
NBR ID 0000.0000.0030.01 COST: 10
IP-Internal 10.5.1.30 255.255.255.255 COST: 0
IP-Internal 10.5.230.0 255.255.255.0 COST: 10
IP-Internal 10.5.134.0 255.255.255.0 COST: 10
0000.0000.0030.01-00 0x00000002 0xdb1e 1011 55 0/0/0
SOURCE 0000.0000.0030.01
NLPID IPV4
NBR ID 0000.0000.0030.00 COST: 0
NBR ID 0000.0000.0034.00 COST: 0
0000.0000.0034.00-00* 0x00000006 0xd4e9 1119 102 0/0/0
SOURCE 0000.0000.0034.00
NLPID IPV4
AREA ADDR 49.0005
INTF ADDR 10.5.1.34
INTF ADDR 10.5.134.34
INTF ADDR 10.5.234.34
NBR ID 0000.0000.0030.01 COST: 10
IP-Internal 10.5.1.34 255.255.255.255 COST: 0
IP-Internal 10.5.134.0 255.255.255.0 COST: 10
IP-Internal 10.5.234.0 255.255.255.0 COST: 10
Total LSP(s): 3
*(In TLV)-Leaking Route, *(By LSPID)-Self LSP, +-Self LSP(Extended),
ATT-Attached, P-Partition, OL-Overload
# AR31
<AR31>display isis lsdb 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* 0x00000008 0x5474 1037 88 1/0/0
SOURCE 0000.0000.0031.00
NLPID IPV4
AREA ADDR 49.0006
INTF ADDR 10.5.1.31
INTF ADDR 10.5.231.31
INTF ADDR 10.5.234.31
IP-Internal 10.5.1.31 255.255.255.255 COST: 0
IP-Internal 10.5.231.0 255.255.255.0 COST: 10
IP-Internal 10.5.234.0 255.255.255.0 COST: 10
Total LSP(s): 1
*(In TLV)-Leaking Route, *(By LSPID)-Self LSP, +-Self LSP(Extended),
ATT-Attached, P-Partition, OL-Overload
Level-2 Link State Database
LSPID Seq Num Checksum Holdtime Length ATT/P/OL
-------------------------------------------------------------------------------
0000.0000.0028.00-00 0x00000009 0x1829 974 97 0/0/0
SOURCE 0000.0000.0028.00
NLPID IPV4
AREA ADDR 49.0006
INTF ADDR 10.5.230.28
INTF ADDR 10.5.231.28
NBR ID 0000.0000.0030.02 COST: 10
NBR ID 0000.0000.0031.02 COST: 10
IP-Internal 10.5.230.0 255.255.255.0 COST: 10
IP-Internal 10.5.231.0 255.255.255.0 COST: 10
0000.0000.0028.00-01 0x00000005 0xb97e 974 89 0/0/0
SOURCE 0000.0000.0028.00
IP-External 10.5.1.28 255.255.255.255 COST: 64
IP-External 10.5.128.0 255.255.255.0 COST: 64
IP-External 10.5.232.0 255.255.255.0 COST: 64
IP-External 10.5.1.32 255.255.255.255 COST: 64
IP-External 10.5.1.27 255.255.255.255 COST: 64
0000.0000.0030.00-00 0x00000007 0xb8b8 984 126 0/0/0
SOURCE 0000.0000.0030.00
NLPID IPV4
AREA ADDR 49.0005
INTF ADDR 10.5.1.30
INTF ADDR 10.5.230.30
INTF ADDR 10.5.134.30
NBR ID 0000.0000.0030.02 COST: 10
IP-Internal 10.5.1.30 255.255.255.255 COST: 0
IP-Internal 10.5.230.0 255.255.255.0 COST: 10
IP-Internal 10.5.134.0 255.255.255.0 COST: 10
IP-Internal 10.5.1.34 255.255.255.255 COST: 10
IP-Internal 10.5.234.0 255.255.255.0 COST: 20
0000.0000.0030.02-00 0x00000002 0x8381 984 55 0/0/0
SOURCE 0000.0000.0030.02
NLPID IPV4
NBR ID 0000.0000.0030.00 COST: 0
NBR ID 0000.0000.0028.00 COST: 0
0000.0000.0031.00-00* 0x00000008 0x5fa4 1036 102 0/0/0
SOURCE 0000.0000.0031.00
NLPID IPV4
AREA ADDR 49.0006
INTF ADDR 10.5.1.31
INTF ADDR 10.5.231.31
INTF ADDR 10.5.234.31
NBR ID 0000.0000.0031.02 COST: 10
IP-Internal 10.5.1.31 255.255.255.255 COST: 0
IP-Internal 10.5.231.0 255.255.255.0 COST: 10
IP-Internal 10.5.234.0 255.255.255.0 COST: 10
0000.0000.0031.02-00* 0x00000002 0x8c76 1036 55 0/0/0
SOURCE 0000.0000.0031.02
NLPID IPV4
NBR ID 0000.0000.0031.00 COST: 0
NBR ID 0000.0000.0028.00 COST: 0
Total LSP(s): 6
*(In TLV)-Leaking Route, *(By LSPID)-Self LSP, +-Self LSP(Extended),
ATT-Attached, P-Partition, OL-Overload
"""
结果显示，AR34的区域ID为49.0005，而AR31的区域ID为49.0006，区域ID不相同无法建立level-1级别邻居的建立，但是不影响level-2级别邻居的建立。同时也看到AR34的链路状态数据库中只接受到了来自AR30的ATT位置1的lsp，并未收到来自AR31的ATT位置1的lsp，因此无法产生指向AR31的默认路由。
2.7 查看AR31的isis进程信息与邻居
AR31想要产生ATT置1的lsp，不仅需要与AR34建立level-1级别的isis邻居，同样还需要与不同区域的AR28建立level-2级别的isis邻居，因此AR34的isis级别只能为level-1-2，查看isis进程信息，确认AR31的isis级别是否配置正确，结果如下：
"""
# isis进程信息
<AR31>display isis brief
ISIS Protocol Information for ISIS(1)
-------------------------------------
SystemId: 0000.0000.0031 System Level: L12
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: 10.5.234.31(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: 10.5.231.31(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
# isis邻居情况
<AR31>display isis peer
Peer information for ISIS(1)
System Id Interface Circuit Id State HoldTime Type PRI
-------------------------------------------------------------------------------
0000.0000.0028 GE0/0/2 0000.0000.0031.02 Up 28s L2 64
Total Peer(s): 1
"""
结果显示，AR31的isis级别确实为level-1-2，同时与AR28成功建立level-2级别的isis邻居。
2.8 结论
通过以上分析，故障的根本原因为AR31的区域ID配置错误，与AR34的区域ID不一致，导致AR31与AR34之间无法建立level-1的isis邻居。
三、故障解决
3.1 AR31的区域ID配置错误，需要在AR31上执行以下命令：
system-view //进入系统视图
isis {isis进程ID} //进入isis进程下
display this //查看当前配置
undo network-entity 49.0006.0000.0000.0031.00 //删除错误的区域ID
network-entity 49.0005.0000.0000.0031.00 //配置正确的区域ID
执行完上述命令之后，需要在AR34上执行以下命令进行检查：
display isis peer //查看AR34与AR31之间的isis邻居是否正常
display isis lsdb verbose //查看是否存在来自AR31的ATT位置1的lsp
display ip routing-table //查看等价默认路由情况，故障是否排除
3.2 如果执行以上命令未能排除故障，则存在以下高可能性故障
3.2.1 AR31在isis进程下配置ATT位不能置1的命令，需要在AR31上执行以下命令：
system-view //进入系统视图
isis {isis进程ID} //进入isis进程下
display this //查看当前配置
undo attached-bit advertise //删除ATT不置1的配置
3.2.2 AR34在isis进程下对不同的下一跳设备不同的weight，需要在AR34上执行以下命令：
system-view //进入系统视图
isis {isis进程ID} //进入isis进程下
display this //查看当前配置
undo nexthop 10.5.x.x //删除针对下一跳设置weight
3.2.3 AR34在isis进程下配置最大负载为1，需要在AR34上执行以下命令：
system-view //进入系统视图
isis {isis进程ID} //进入isis进程下
display this //查看当前配置
undo maximum load-balancing //删除最大负载设置
3.2.4 AR34与AR31互联接口的isis认证不一致，需要在AR31和AR34上执行以下命令：
system-view //进入系统视图
interface GigabitEthernet 0/0/1 //进入接口视图
display this //查看当前配置
undo isis authentication-mode //删除接口认证
isis authentication-mode {AR31和AR34之间使用相同的认证} //或者修改成一致的认证
3.2.5 AR34与AR31的isis进程下的cost类型不一致，需要在AR31和AR34上执行以下命令：
system-view //进入系统视图
isis {isis进程ID} //进入isis进程下
display this //查看当前配置
cost-style {AR34与AR31之间相同的cost类型} //修改cost类型
3.3 如果执行以上命令成功排除故障，则需要在执行过命令的设备上继续执行以下命令：
return //返回用户视图
save //保存修改之后的配置
3.4 如果执行以上命令未能排除故障，则需要用户提供完整的设备配置信息或者派遣一线工程师到达用户现场进行现场排障，同时拨打华为400服务热线请求华为专家的协助。
TAC6-2:变种3
解答
一、故障根因
AR31的isis级别配置错误，导致无法与AR28之间建立level-2级别的isis邻居。
二、故障分析
2.1 故障重现
查看AR34的路由表，结果如下：
"""
<AR34>display ip routing-table
Route Flags: R - relay, D - download to fib
------------------------------------------------------------------------------
Routing Tables: Public
Destinations : 16 Routes : 16
Destination/Mask Proto Pre Cost Flags NextHop Interface
0.0.0.0/0 ISIS-L1 15 10 D 10.5.134.30 GigabitEthernet
0/0/0
10.5.1.30/32 ISIS-L1 15 10 D 10.5.134.30 GigabitEthernet
0/0/0
10.5.1.31/32 ISIS-L1 15 10 D 10.5.234.31 GigabitEthernet
0/0/1
10.5.1.34/32 Direct 0 0 D 127.0.0.1 LoopBack0
10.5.134.0/24 Direct 0 0 D 10.5.134.34 GigabitEthernet
0/0/0
10.5.134.34/32 Direct 0 0 D 127.0.0.1 GigabitEthernet
0/0/0
10.5.134.255/32 Direct 0 0 D 127.0.0.1 GigabitEthernet
0/0/0
10.5.230.0/24 ISIS-L1 15 20 D 10.5.134.30 GigabitEthernet
0/0/0
10.5.231.0/24 ISIS-L1 15 20 D 10.5.234.31 GigabitEthernet
0/0/1
10.5.234.0/24 Direct 0 0 D 10.5.234.34 GigabitEthernet
0/0/1
10.5.234.34/32 Direct 0 0 D 127.0.0.1 GigabitEthernet
0/0/1
10.5.234.255/32 Direct 0 0 D 127.0.0.1 GigabitEthernet
0/0/1
127.0.0.0/8 Direct 0 0 D 127.0.0.1 InLoopBack0
127.0.0.1/32 Direct 0 0 D 127.0.0.1 InLoopBack0
127.255.255.255/32 Direct 0 0 D 127.0.0.1 InLoopBack0
255.255.255.255/32 Direct 0 0 D 127.0.0.1 InLoopBack0
"""
结果显示，AR34的路由表中只存在一条指向AR30的默认路由，缺少指向AR31的默认路由，故障存在。
2.2 检查接口的cost值
AR34与AR31、AR30互联接口下的cost值会影响等价默认路由的产生，在AR34上检查这两个接口下的cost值，结果如下：
"""
<AR34>display isis interface verbose
Interface information for ISIS(1)
---------------------------------
Interface Id IPV4.State IPV6.State MTU Type DIS
GE0/0/0 001 Up Down 1497 L1/L2 No/No
Circuit MT State : Standard
Description : HUAWEI, AR Series, GigabitEthernet0/0/0 Interfac
e
SNPA Address : 00e0-fc83-528a
IP Address : 10.5.134.34
IPV6 Link Local Address :
IPV6 Global Address(es) :
Csnp Timer Value : L1 10 L2 10
Hello Timer Value : L1 10 L2 10
DIS Hello Timer Value : L1 3 L2 3
Hello Multiplier Value : L1 3 L2 3
LSP-Throttle Timer : L12 50
Cost : L1 10 L2 10
Ipv6 Cost : L1 10 L2 10
Priority : L1 64 L2 64
Retransmit Timer Value : L12 5
Bandwidth-Value : Low 1000000000 High 0
Static Bfd : NO
Dynamic Bfd : NO
Fast-Sense Rpr : NO
Interface Id IPV4.State IPV6.State MTU Type DIS
GE0/0/1 002 Up Down 1497 L1/L2 No/No
Circuit MT State : Standard
Description : HUAWEI, AR Series, GigabitEthernet0/0/1 Interfac
e
SNPA Address : 00e0-fc83-528b
IP Address : 10.5.234.34
IPV6 Link Local Address :
IPV6 Global Address(es) :
Csnp Timer Value : L1 10 L2 10
Hello Timer Value : L1 10 L2 10
DIS Hello Timer Value : L1 3 L2 3
Hello Multiplier Value : L1 3 L2 3
LSP-Throttle Timer : L12 50
Cost : L1 10 L2 10
Ipv6 Cost : L1 10 L2 10
Priority : L1 64 L2 64
Retransmit Timer Value : L12 5
Bandwidth-Value : Low 1000000000 High 0
Static Bfd : NO
Dynamic Bfd : NO
Fast-Sense Rpr : NO
Interface Id IPV4.State IPV6.State MTU Type DIS
Loop0 001 Up Down 1500 L1/L2 --
Circuit MT State : Standard
Circuit Parameters : passive
Description : HUAWEI, AR Series, LoopBack0 Interface
SNPA Address : 0000-0000-0000
IP Address : 10.5.1.34
IPV6 Link Local Address :
IPV6 Global Address(es) :
Csnp Timer Value : L12 10
Hello Timer Value : 10
DIS Hello Timer Value :
Hello Multiplier Value : 3
Cost : L1 0 L2 0
Ipv6 Cost : L1 0 L2 0
Retransmit Timer Value : L12 5
LSP-Throttle Timer : L12 50
Bandwidth-Value : Low 0 High 0
Static Bfd : NO
Dynamic Bfd : NO
Fast-Sense Rpr : NO
"""
结果显示，AR34与AR31互联的GE0/0/1接口、与AR30互联的GE0/0/0接口的cost值均为10。
2.3 检查isis邻居
AR34与AR31、AR30之间运行isis路由协议，检查AR34上的isis邻居是否正常，结果如下：
"""
<AR34>display isis peer
Peer information for ISIS(1)
System Id Interface Circuit Id State HoldTime Type PRI
-------------------------------------------------------------------------------
0000.0000.0030 GE0/0/0 0000.0000.0030.01 Up 9s L1 64
0000.0000.0031 GE0/0/1 0000.0000.0031.01 Up 8s L1 64
Total Peer(s): 2
"""
结果显示，AR34与AR31、AR30之间均存在level-1级别的isis邻居。
2.4 检查isis的链路状态数据库
AR34上想要产生默认路由，需要isis接收到ATT位置1的lsp，查看AR34的链路状态数据库确认是否存在来自AR31的ATT置1的lsp，结果如下：
"""
<AR34>display isis lsdb verbose
Database information for ISIS(1)
--------------------------------
Level-1 Link State Database
LSPID Seq Num Checksum Holdtime Length ATT/P/OL
-------------------------------------------------------------------------------
0000.0000.0030.00-00 0x0000000a 0xe4e7 942 102 1/0/0
SOURCE 0000.0000.0030.00
NLPID IPV4
AREA ADDR 49.0005
INTF ADDR 10.5.1.30
INTF ADDR 10.5.230.30
INTF ADDR 10.5.134.30
NBR ID 0000.0000.0030.01 COST: 10
IP-Internal 10.5.1.30 255.255.255.255 COST: 0
IP-Internal 10.5.230.0 255.255.255.0 COST: 10
IP-Internal 10.5.134.0 255.255.255.0 COST: 10
0000.0000.0030.01-00 0x00000003 0xd91f 942 55 0/0/0
SOURCE 0000.0000.0030.01
NLPID IPV4
NBR ID 0000.0000.0030.00 COST: 0
NBR ID 0000.0000.0034.00 COST: 0
0000.0000.0031.00-00 0x00000007 0xdfb 837 102 0/0/0
SOURCE 0000.0000.0031.00
NLPID IPV4
AREA ADDR 49.0005
INTF ADDR 10.5.1.31
INTF ADDR 10.5.234.31
INTF ADDR 10.5.231.31
NBR ID 0000.0000.0031.01 COST: 10
IP-Internal 10.5.1.31 255.255.255.255 COST: 0
IP-Internal 10.5.234.0 255.255.255.0 COST: 10
IP-Internal 10.5.231.0 255.255.255.0 COST: 10
0000.0000.0031.01-00 0x00000003 0xe018 836 55 0/0/0
SOURCE 0000.0000.0031.01
NLPID IPV4
NBR ID 0000.0000.0031.00 COST: 0
NBR ID 0000.0000.0034.00 COST: 0
0000.0000.0034.00-00* 0x0000000a 0xee3 762 113 0/0/0
SOURCE 0000.0000.0034.00
NLPID IPV4
AREA ADDR 49.0005
INTF ADDR 10.5.1.34
INTF ADDR 10.5.134.34
INTF ADDR 10.5.234.34
NBR ID 0000.0000.0030.01 COST: 10
NBR ID 0000.0000.0031.01 COST: 10
IP-Internal 10.5.1.34 255.255.255.255 COST: 0
IP-Internal 10.5.134.0 255.255.255.0 COST: 10
IP-Internal 10.5.234.0 255.255.255.0 COST: 10
Total LSP(s): 5
*(In TLV)-Leaking Route, *(By LSPID)-Self LSP, +-Self LSP(Extended),
ATT-Attached, P-Partition, OL-Overload
"""
结果显示，来自AR31的lsp的ATT位均为置1。要想产生ATT位置1的lsp，需要AR31与AR34之间建立level-1级别的isis邻居，同时还需要AR31与不同区域的AR28之间建立level-2级别的邻居，即AR31的isis级别只能为level-1-2。
2.5 查看AR31的isis进程信息和邻居
为确认AR31的isis级别是否正确，需要查看AR31的isis进程信息，同时查看AR31与AR28之间的isis邻居是否正常，结果如下：
"""
# isis进程信息
<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: 10.5.234.31(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: 10.5.231.31(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
# isis邻居
<AR31>display isis peer
Peer information for ISIS(1)
System Id Interface Circuit Id State HoldTime Type PRI
-------------------------------------------------------------------------------
0000.0000.0034 GE0/0/1 0000.0000.0031.01 Up 25s L1 64
Total Peer(s): 1
"""
结果显示，AR31的isis级别为level-1，配置错误，同时AR31上无法产生level-2的lsp，因此，无法与AR28之间建立level-2级别的isis邻居关系。
2.6 结论
通过以上分析，故障的根本原因为AR31的isis级别配置错误，导致无法与AR28之间建立level-2级别的isis邻居。
三、故障解决
3.1 AR31的isis级别配置错误，需要在AR31上执行以下命令：
system-view //进入系统视图
isis {isis进程ID} //进入isis进程下
display this //查看当前配置
is-level level-1-2 //修改正确的isis级别
执行完以上命令需要在AR31上执行以下命令进程检查：
display isis peer //查看AR34与AR28之间是否建立level-2级别的邻居
在AR34上执行以下命令进程检查：
display isis lsdb verbose //查看是否存在ATT位置1的来自AR31的lsp
display ip routing-table //查看等价默认路由情况，故障是否排除
3.2 如果执行以上命令未能排除故障，则存在以下高可能性故障：
与AR31和AR28之间的isis邻居相关：
3.2.1 AR28的GigabitEthernet 0/0/2没有使能isis，需要在AR28上执行以下命令：
system-view //进入系统视图
interface GigabitEthernet 0/0/2 //进入接口视图
display this //查看当前配置
isis enable {isis进程id} //接口下使能isis
3.2.2 AR28的isis进程下配置domain认证(AR31没有配置)，需要在AR28上执行以下命令：
system-view //进入系统视图
isis {isis进程ID} //进入isis进程下
display this //查看当前配置
undo domain-authentication-mode //删除domain认证
3.2.3 AR28与AR31互联接口下的mtu不一致，需要在AR28上执行以下命令：
system-view //进入系统视图
interface GigabitEthernet 0/0/2 //进入接口视图
display this //查看当前配置
mtu 1497 //修改AR28的接口下mtu值，保持与AR31一致
3.2.4 AR28与AR31互联接口下链路类型不一致，需要在AR28上执行以下命令：
system-view //进入系统视图
interface GigabitEthernet 0/0/2 //进入接口视图
display this //查看当前配置
undo isis circuit-type //删除接口下链路类型的设置，保持与AR31一致的广播类型
3.2.5 AR28与AR31互联接口下isis认证不一致，需要在AR28和AR31上执行以下命令：
system-view //进入系统视图
interface GigabitEthernet 0/0/2 //进入接口视图
display this //查看当前配置
undo isis authentication-mode //删除接口认证
3.2.6 AR28与AR31的isis进程下的cost类型不一致，需要在AR28和AR31上执行以下命令：
system-view //进入系统视图
isis {isis进程ID} //进入isis进程下
display this //查看当前配置
cost-style {相同的cost类型} //修改成相同的cost类型
执行完以上命令需要在AR31上执行以下命令进程检查：
display isis peer //查看AR34与AR28之间是否建立level-2级别的邻居
在AR34上执行以下命令进程检查：
display isis lsdb verbose //查看是否存在ATT位置1的来自AR31的lsp
display ip routing-table //查看等价默认路由情况，故障是否排除
与不能产生ATT位置1的lsp有关：
3.2.7 AR31在isis进程下配置ATT位不置1的命令，需要在AR31上执行以下命令：
system-view //进入系统视图
isis {isis进程ID} //进入isis进程下
display this //查看当前配置
undo attached-bit advertise //删除ATT位不置1的命令
3.2.8 AR34在isis进程下针对下一跳配置不同的weight，需要在AR34上执行以下命令：
system-view //进入系统视图
isis {isis进程ID} //进入isis进程下
display this //查看当前配置
undo nexthop 10.5.x.x //删除针对下一跳配置不同的weight
3.2.9 AR34在isis进程下配置最大负载为1，需要在AR34上执行以下命令：
system-view //进入系统视图
isis {isis进程ID} //进入isis进程下
display this //查看当前配置
undo maximum load-balancing //删除最大负载设置
执行完以上命令需要在AR34上执行以下命令进程检查：
display isis lsdb verbose //查看是否存在ATT位置1的来自AR31的lsp
display ip routing-table //查看等价默认路由情况，故障是否排除
3.3 如果执行以上命令成功排除故障，则需要在执行过命令的设备上继续执行以下命令：
return //返回用户视图
save //保存修改之后的配置
3.4 如果执行以上命令未能排除故障，则需要用户提供完整的设备配置信息或者派遣一线工程师到达用户现场进行现场故障排除，同时拨打华为400服务热线请求华为专家的协助，谢谢！