【图片】回复：网二小和他的【网工家教】网老师。（吧主，别删贴，是自己人【ccna吧】

这个系列贴的目的是促进大家在学习中养成思辨问题的能力。不要只停留在“书上这么说的”或“某某这么说了”。以OSPF为例，intra-area路由的计算是一个典型的图论算法，它的结果是完备的，我们不必对它讨论了。但除它之外，其它类型的OSPF路由究竞是根据什么规则计算的，有什么因素会影响其计算结果呢? 大概只有在回答了这些问题之后，才会从对OSPF的学习上得到些自我满足吧。在此之前只能说是“我记会了OSPF”而不能说“我学会了OSPF”。

Number of Links: 4 Link connected to: another Router (point-to-point)
(Link ID) Neighboring Router ID: 10.0.0.101
(Link Data) Router Interface address: 10.101.102.102
Number of TOS metrics: 0
TOS 0 Metrics: 5 Link connected to: a Stub Network
(Link ID) Network/subnet number: 10.101.102.0
(Link Data) Network Mask: 255.255.255.0
Number of TOS metrics: 0
TOS 0 Metrics: 5
Link connected to: another Router (point-to-point)
(Link ID) Neighboring Router ID: 10.0.0.100
(Link Data) Router Interface address: 10.100.102.102
Number of TOS metrics: 0
TOS 0 Metrics: 1 Link connected to: a Stub Network
(Link ID) Network/subnet number: 10.100.102.0
(Link Data) Network Mask: 255.255.255.0
Number of TOS metrics: 0
TOS 0 Metrics: 1
LS age: 15
Options: (No TOS-capability, DC)
LS Type: Router Links
Link State ID: 10.0.0.108
Advertising Router: 10.0.0.108
LS Seq Number: 80000014
Checksum: 0x5464
Length: 48
Number of Links: 2 Link connected to: a Transit Network
(Link ID) Designated Router address: 10.104.0.101
(Link Data) Router Interface address: 10.104.0.108
Number of TOS metrics: 0
TOS 0 Metrics: 5 Link connected to: a Transit Network
(Link ID) Designated Router address: 10.101.0.100
(Link Data) Router Interface address: 10.101.0.108
Number of TOS metrics: 0
TOS 0 Metrics: 1
Router Link States (Area 2) LS age: 1786
Options: (No TOS-capability, DC)
LS Type: Router Links
Link State ID: 10.0.0.101
Advertising Router: 10.0.0.101
LS Seq Number: 80000011
Checksum: 0xE2B3
Length: 36
Number of Links: 1 Link connected to: a Transit Network
(Link ID) Designated Router address: 10.103.0.101
(Link Data) Router Interface address: 10.103.0.101
Number of TOS metrics: 0
TOS 0 Metrics: 1
LS age: 20
Options: (No TOS-capability, DC)
LS Type: Router Links
Link State ID: 10.0.0.108
Advertising Router: 10.0.0.108
LS Seq Number: 80000014
Checksum: 0xE299
Length: 36
Number of Links: 1 Link connected to: a Transit Network
(Link ID) Designated Router address: 10.100.0.109
(Link Data) Router Interface address: 10.100.0.108
Number of TOS metrics: 0
TOS 0 Metrics: 1
LS age: 28
Options: (No TOS-capability, DC)
LS Type: Router Links
Link State ID: 10.0.0.109
Advertising Router: 10.0.0.109
LS Seq Number: 80000012
Checksum: 0xAE07
Length: 48
Number of Links: 2 Link connected to: a Transit Network
(Link ID) Designated Router address: 10.103.0.101
(Link Data) Router Interface address: 10.103.0.109
Number of TOS metrics: 0
TOS 0 Metrics: 1 Link connected to: a Transit Network
(Link ID) Designated Router address: 10.100.0.109
(Link Data) Router Interface address: 10.100.0.109
Number of TOS metrics: 0
TOS 0 Metrics: 1
R108#

下面是针对实验之一中对l.1.1.1路由在Rl07上LSA类型的输出：
R107#sh ip ospf data external 1.1.1.1 OSPF Router with ID (10.0.0.107) (Process ID 10) Type-5 AS External Link States Routing Bit Set on this LSA
LS age: 736
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 1.1.1.1 (External Network Number )
Advertising Router: 10.0.0.102
LS Seq Number: 80000002
Checksum: 0x1B85
Length: 36
Network Mask: /32
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 1
Forward Address: 10.100.102.100
External Route Tag: 100
R107#

下面是针对你的问题的输出：

R100#sh ip ospf data nssa-external 1.1.1.1

OSPF Router with ID (10.0.0.100) (Process ID 10)

Type-7 AS External Link States (Area 1)

LS age: 622
Options: (No TOS-capability, Type 7/5 translation, DC)
LS Type: AS External Link
Link State ID: 1.1.1.1 (External Network Number )
Advertising Router: 10.0.0.100
LS Seq Number: 80000001
Checksum: 0x9405
Length: 36
Network Mask: /32
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 1
Forward Address: 10.100.102.100
External Route Tag: 100

R100#

读懂LSA是基础功。建议同学们从与拓扑有最直接关系的type-1开始。
举例如下:
R108#sh ip ospf data router
OSPF Router with ID (10.0.0.108) (Process ID 10)
Router Link States (Area 1) <----------- 从这以下是R108知道的有关R100的信息
LS age: 14
Options: (No TOS-capability, DC)
LS Type: Router Links
Link State ID: 10.0.0.100
Advertising Router: 10.0.0.100
LS Seq Number: 80000015
Checksum: 0xF547
Length: 72 Number of Links: 4
<----------- 从这以下是R100每个端口的信息，由此可知R100共有4个Link（未必是4个端口）。
Link connected to: another Router (point-to-point)
<---------- 由此可知R100的第一个端口是OSPF的P-P端口
(Link ID) Neighboring Router ID: 10.0.0.102
<-----------这个P-P端口的另一端是R102
(Link Data) Router Interface address: 10.100.102.100
<-------------R100在这个端口上的IP地址
Number of TOS metrics: 0
TOS 0 Metrics: 1
<-------------R100在这个端口上的花费是1
Link connected to: a Stub Network
<----------- OSPF认为每个P-P端口上的子网对该路由器来说是一个stub net
(Link ID) Network/subnet number: 10.100.102.0
<------------- 并在拓扑中为每个stub net产生一个router link
(Link Data) Network Mask: 255.255.255.0
<------------这个stub link是为上面的P-P端口生产的
Number of TOS metrics: 0
TOS 0 Metrics: 1
<--------------R100到这个stub net 10.100.102.0/24的花费是1
Link connected to: a Transit Network
<----------- 由此可知R100的第二个端口是Transit端口,也就是OSPF的broadcast端口
(Link ID) Designated Router address: 10.102.0.101
<-----------既然是broadcast端口,就应有DR，由此可知R101是这个端口上的DR
(Link Data) Router Interface address: 10.102.0.100
<--------------R100在这个端口上的IP地址
Number of TOS metrics: 0
TOS 0 Metrics: 5
<--------------R100在这个端口上的花费是5
Link connected to: a Transit Network
<------------由此可知R100的第三个端口是Transit端口,也就是OSPF的broadcast端口
(Link ID) Designated Router address: 10.101.0.100
<-----------既然是broadcast端口,就应有DR，由此可知R100是这个端口上的DR
(Link Data) Router Interface address: 10.101.0.100
<----------R100在这个端口上的IP地址
Number of TOS metrics: 0
TOS 0 Metrics: 1
<-------------R100在这个端口上的花费是1
至此我们应能画出围绕R100的拓扑如下:
R100
|||
||\-------P-P--------R102
|\-------Broadcast--------- pseudo router/DR (R101)
\--------Broadcast--------- pseudo router/DR (R100)
要想完成Broadcast link上的细节还要读懂Type-2 LSA （network LSA）

所有输出都是Rl08所持有的Type-1 LSA（Router LSA）信息。
Router Link States (Area 2) LS age: 1786
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
看,这里还是说Router Link State。但是以下是在区域2中的Type-1信息。为什么在R108会有区域1和区域2的Type-1信息呢? 因为Type-1 LSA 的 flooding 范围是在本区域之内，所以Rl08在区域1和区域2中一定都有端口。好了,接着自己完成作业吧。完成之后请贴图。

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回复：网二小和他的【网工家教】网老师。（吧主，别删贴，是自己人

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