引用等级二实验手册下册P94页中的一段话：

     在显示数据库输出的最后，有个ATT位，即区域关联位（Attached，ATT），当L1/L2路由器R2发送它的L1 LSP（链路状态数据包，相当于OSPF的LSA）进入一个区域时，会在LSP中设置ATT位为1，代表通知其他L1路由器可以到达其他区域，有了这个通知，L1的路由器会安装默认路由，按照（TCP/IP路由卷一）这本书的说法这个ATT位时CLNS的特性，IP协议并不能直接理解该位，解决问题需在R2和R3的链路上运行CLNS路由（在接口上配置clns router isis），但现在的IOS不需要做这个配置！

依照上面的定义做了个实验！拓扑如上图：


配置如下：
hostname R1
interface Loopback0

ip address 1.1.1.1 255.255.255.0

ip router isis
!
interface Ethernet0/0

no ip address

shutdown
!
interface Serial1/0

ip address 12.1.1.1 255.255.255.0

ip router isis

serial restart-delay 0

clock rate 64000
!
interface Serial2/0

ip address 13.1.1.1 255.255.255.0

ip router isis

serial restart-delay 0
!
router isis
net 47.0001.0000.0000.0001.00

is-type level-2-only
!
ip classless
no ip http server
no ip http secure-server
!


hostname R2
!
interface Loopback0

ip address 2.2.2.2 255.255.255.0

ip router isis
!
interface Ethernet0/0

no ip address

shutdown
!
interface Serial1/0

ip address 24.1.1.2 255.255.255.0

ip router isis

serial restart-delay 0

clock rate 64000
!
interface Serial2/0

ip address 12.1.1.2 255.255.255.0

ip router isis

serial restart-delay 0
!
router isis

net 47.0001.0000.0000.0002.00

is-type level-2-only
!
ip classless
no ip http server
no ip http secure-server
!


hostname R3
interface Loopback0

ip address 3.3.3.3 255.255.255.0

ip router isis
!
interface Ethernet0/0

ip address 10.1.1.3 255.255.255.0

ip router isis
!
interface Serial1/0

ip address 13.1.1.3 255.255.255.0

ip router isis

serial restart-delay 0

clock rate 64000
!
interface Serial2/0

ip address 35.1.1.3 255.255.255.0

ip router isis

serial restart-delay 0
!
router isis

net 48.0001.0000.0000.0003.00
!
ip classless
no ip http server
no ip http secure-server
!


hostname R4
interface Loopback0

ip address 4.4.4.4 255.255.255.0

ip router isis
!
interface Ethernet0/0

ip address 10.1.1.4 255.255.255.0

ip router isis
!
interface Serial1/0

ip address 45.1.1.4 255.255.255.0

ip router isis

serial restart-delay 0

clock rate 64000
!
interface Serial2/0

ip address 24.1.1.4 255.255.255.0

ip router isis

serial restart-delay 0
!
router isis

net 48.0001.0000.0000.0004.00
!
ip classless
no ip http server
no ip http secure-server
!
!


hostname R5
!
!interface Loopback0

ip address 5.5.5.5 255.255.255.0

ip router isis
!
interface Ethernet0/0

no ip address

shutdown
!
interface Serial1/0

ip address 35.1.1.5 255.255.255.0

ip router isis

serial restart-delay 0

clock rate 64000
!
interface Serial2/0

ip address 45.1.1.5 255.255.255.0

ip router isis

serial restart-delay 0
!
router isis

net 48.0001.0000.0000.0005.00

is-type level-1
!
ip classless
no ip http server
no ip http secure-server


配置没有问题，用show isis data命令查看R3的数据库：
R3#sho isis dat

IS-IS Level-1 Link State Database:
LSPID
LSP Seq Num
LSP Checksum
LSP Holdtime
ATT/P/OL
R3.00-00
* 0x00000006
0xFF43
1087


1/0/0
R4.00-00
0x00000009
0xBC65
1090


1/0/0
R4.01-00
0x00000001
0xBC8E
937
0/0/0
R5.00-00
0x00000007
0xA51B
1090
0/0/0
IS-IS Level-2 Link State Database:
LSPID
LSP Seq Num
LSP Checksum
LSP Holdtime
ATT/P/OL
R1.00-00
0x00000005
0x4DD1
879
0/0/0
R2.00-00
0x00000005
0xE822
925
0/0/0
R3.00-00
* 0x00000009
0x7DE3
1089
0/0/0
R4.00-00
0x0000000C
0x2136
1097
0/0/0
R4.01-00
0x00000001
0x4C87
937
0/0/0
R5.00-00
0x00000006
0x2D20
1006
0/0/0

R4的数据库如下：
IS-IS Level-1 Link State Database:
LSPID
LSP Seq Num
LSP Checksum
LSP Holdtime
ATT/P/OL
R3.00-00
0x00000006
0xFF43
1068

1/0/0
R4.00-00
* 0x00000009
0xBC65
1075

1/0/0
R4.01-00
* 0x00000001
0xBC8E
921
0/0/0
R5.00-00
0x00000007
0xA51B
1071
0/0/0
IS-IS Level-2 Link State Database:
LSPID
LSP Seq Num
LSP Checksum
LSP Holdtime
ATT/P/OL
R1.00-00
0x00000005
0x4DD1
860
0/0/0
R2.00-00
0x00000005
0xE822
911
0/0/0
R3.00-00
0x00000009
0x7DE3
1069
0/0/0
R4.00-00
* 0x0000000C
0x2136
1081
0/0/0
R4.01-00
* 0x00000001
0x4C87
921
0/0/0
R5.00-00
0x00000006
0x2D20
989
0/0/0

数据库正确说明：属于L1/L2的路由器R3和R4分别向属于L1的路由器R5发送了L1 LSP，当R5收到L1 LSP时会在路由表中安装一条默认路由！！
R5的路由表：


35.0.0.0/24 is subnetted, 1 subnets
C
35.1.1.0 is directly connected, Serial1/0

3.0.0.0/24 is subnetted, 1 subnets
i L1
3.3.3.0 [115/20] via 35.1.1.3, Serial1/0

4.0.0.0/24 is subnetted, 1 subnets
i L1
4.4.4.0 [115/20] via 45.1.1.4, Serial2/0

5.0.0.0/24 is subnetted, 1 subnets
C
5.5.5.0 is directly connected, Loopback0

24.0.0.0/24 is subnetted, 1 subnets
i L1
24.1.1.0 [115/20] via 45.1.1.4, Serial2/0

10.0.0.0/24 is subnetted, 1 subnets
i L1
10.1.1.0 [115/20] via 35.1.1.3, Serial1/0

[115/20] via 45.1.1.4, Serial2/0

13.0.0.0/24 is subnetted, 1 subnets
i L1
13.1.1.0 [115/20] via 35.1.1.3, Serial1/0

45.0.0.0/24 is subnetted, 1 subnets
C
45.1.1.0 is directly connected, Serial2/0
i*L1 0.0.0.0/0 [115/10] via 35.1.1.3, Serial1/0

[115/10] via 45.1.1.4, Serial2/0
这时我们改变一下配置，我们把5台路由器的NET地址的区域号全部改成47。0001
这时，R3和R4不会向R5发送L1 LSP，所以R5不会安装默认路由！


35.0.0.0/24 is subnetted, 1 subnets
C
35.1.1.0 is directly connected, Serial1/0

3.0.0.0/24 is subnetted, 1 subnets
i L1
3.3.3.0 [115/20] via 35.1.1.3, Serial1/0

4.0.0.0/24 is subnetted, 1 subnets
i L1
4.4.4.0 [115/20] via 45.1.1.4, Serial2/0

5.0.0.0/24 is subnetted, 1 subnets
C
5.5.5.0 is directly connected, Loopback0

24.0.0.0/24 is subnetted, 1 subnets
i L1
24.1.1.0 [115/20] via 45.1.1.4, Serial2/0

10.0.0.0/24 is subnetted, 1 subnets
i L1
10.1.1.0 [115/20] via 35.1.1.3, Serial1/0

[115/20] via 45.1.1.4, Serial2/0

13.0.0.0/24 is subnetted, 1 subnets
i L1
13.1.1.0 [115/20] via 35.1.1.3, Serial1/0

45.0.0.0/24 is subnetted, 1 subnets
C
45.1.1.0 is directly connected, Serial2/0
R3和R4的数据库中ATT数值时0
R3#sho isis dat

IS-IS Level-1 Link State Database:
LSPID
LSP Seq Num
LSP Checksum
LSP Holdtime
ATT/P/OL
R3.00-00
* 0x00000016
0xD269
756

0/0/0
R4.00-00
0x00000018
0x918A
1084

0/0/0
R4.01-00
0x0000000B
0xA898
1028
0/0/0
R5.00-00
0x00000013
0x882D
983
0/0/0
IS-IS Level-2 Link State Database:
LSPID
LSP Seq Num
LSP Checksum
LSP Holdtime
ATT/P/OL
R1.00-00
0x0000000F
0x39DB
780
0/0/0
R2.00-00
0x0000000F
0xD42C
806
0/0/0
R3.00-00
* 0x0000001A

0x82CE
921
0/0/0
R4.00-00
0x0000001B
0xFD4B
943
0/0/0
R4.01-00
0x00000009
0x3C8F
428
0/0/0
R4#sho isi dat

IS-IS Level-1 Link State Database:
LSPID
LSP Seq Num
LSP Checksum
LSP Holdtime
ATT/P/OL
R3.00-00
0x0000000E
0xE261
1197


0/0/0
R4.00-00
* 0x00000010
0xA182
1199



0/0/0
R4.01-00
* 0x00000003
0xB890
1192
0/0/0
R5.00-00
0x0000000B
0x9825
1193
0/0/0
IS-IS Level-2 Link State Database:
LSPID
LSP Seq Num
LSP Checksum
LSP Holdtime
ATT/P/OL
R1.00-00
0x00000007
0x49D3
1131
0/0/0
R2.00-00
0x00000007
0xE424
1192
0/0/0
R3.00-00
0x00000011
0x447F
1193
0/0/0
R4.00-00

* 0x00000012
0xA282
1195
0/0/0
R4.01-00
* 0x00000002
0x4A88
1192
0/0/0
R5.00-00
0x00000006
0x2D20
785
0/0/0



然后，我们把R1和R2的区域数值改成47。0001
把R3和R4的区域数值改成 48。0001
把R5的区域数值改成47。0001
这时R5和其他的路由器失去了邻居关系

35.0.0.0/24 is subnetted, 1 subnets
C
35.1.1.0 is directly connected, Serial1/0

5.0.0.0/24 is subnetted, 1 subnets
C
5.5.5.0 is directly connected, Loopback0

45.0.0.0/24 is subnetted, 1 subnets
C
45.1.1.0 is directly connected, Serial2/0
问题出来了，R3和R4的数据库里会显示：
R3#sho isis dat
IS-IS Level-1 Link State Database:
LSPID
LSP Seq Num
LSP Checksum
LSP Holdtime
ATT/P/OL
R3.00-00
* 0x00000054
0xEC49
1197

1/0/0
R4.00-00
0x00000057
0x745E
1030

1/0/0
R4.02-00
0x00000005
0xAD98
1028
0/0/0
R5.00-00
0x0000003D
0x6133
1029
0/0/0
IS-IS Level-2 Link State Database:
LSPID
LSP Seq Num
LSP Checksum
LSP Holdtime
ATT/P/OL
R1.00-00
0x0000005A
0xD8B0
1198
0/0/0
R2.00-00
0x00000044
0xBF3F
1028
0/0/0
R3.00-00
* 0x0000006F
0x4006
1194
0/0/0
R4.00-00
0x00000069
0xAC05
1195
0/0/0
R4.02-00
0x0000001C
0x1614
1028
0/0/0
R4#sho isis dat

IS-IS Level-1 Link State Database:
LSPID
LSP Seq Num
LSP Checksum
LSP Holdtime
ATT/P/OL
R3.00-00
0x00000006
0xFF43
1068

1/0/0
R4.00-00
* 0x00000009
0xBC65
1075

1/0/0
R4.01-00
* 0x00000001
0xBC8E
921
0/0/0
R5.00-00
0x00000007
0xA51B
1071
0/0/0
IS-IS Level-2 Link State Database:
LSPID
LSP Seq Num
LSP Checksum
LSP Holdtime
ATT/P/OL
R1.00-00
0x00000005
0x4DD1
860
0/0/0
R2.00-00
0x00000005
0xE822
911
0/0/0
R3.00-00
0x00000009

0x7DE3
1069
0/0/0
R4.00-00
* 0x0000000C
0x2136
1081
0/0/0
R4.01-00
* 0x00000001
0x4C87
921
0/0/0
R5.00-00
0x00000006
0x2D20
989
0/0/0

大家看到了吗？这时R3和R4的数据库中还时会显示Level-1 Link State 的ATT数值为1


R5#sho clns nei
System Id
Interface
SNPA
State
Holdtime
Type Protocol
R4
Se2/0
*HDLC*
Up
275
IS
ES-IS
R3
Se1/0
*HDLC*
Up
255
IS

ES-IS
R5和R3、R4的邻居关系变成了ES-IS的关系，R5相当于一个终端的PC，那么为什么R3和R4还要发送LEVEL 1的LSP包呢？发送的作用时什么？发送的LSP包发到了何处？是用来保持邻居关系的建立的吗？
如果按照文章前的那段话理解这个ATT值，就是L1/L2的路由器，发送L1 LSP，当L1的路由器收到这个LSP包的时候，就会添加一条默认路由，以此达到与L2路由器互相通信的目的！
主要的目的就时让L1的路由器添加一条默认路由！！
但是，以上实验R3和R4发送LSP包，R5并不可能安装默认路由，那发送L1 LSP的目的是什么？

我以为是什么问题,原来是这样呀,知道拉