RT2收到这条路由，保存到LSDB中，并计算路由，把最优路由安装到全局路由表中：
O*IA 0.0.0.0/0 [110/65] via 10.2.26.2, 00:07:10, Serial0/2
O*IA表示下发的3类缺省路由
度量值为：S0/2+LSA内的开销＝64+1＝65
在RT2上做了单点双向重分布，把OSPF的路由重分布到RIP中，RT4运行RIP协议，学习到路由信息：
RIP数据库中的路由信息为：
0.0.0.0/0
[5] via 172.16.24.1, 00:00:00, Serial0/0
RT4的全局路表：
R* 0.0.0.0/0 [120/5] via 172.16.24.1, 00:00:20, Serial0/0
R表示RIP协议 *表示缺省路由
管理距离为120 度量值为5（重分布时指定为5,默认为15）
至此RT4上就可以去往RT3了！
RT4上的路由传播分析：
RT4上的直连路由:
C 172.16.4.0/24 is directly connected, Ethernet3/0
RT2上通过RIP学习到RT4的路由:
R 172.16.4.0/24 [120/1] via 172.16.24.2, 00:00:01, Serial0/0
在RT2上将RIP路由重分布到OSPF中,同时进行外部路由汇总:
LS age: 271
Options: (No TOS-capability, Type 7/5 translation, DC)
LS Type: AS External Link //AS外部路由
Link State ID: 172.16.0.0 (External Network Number )//LSID172.16.0.0
Advertising Router: 2.2.2.2 //通告路由器ID 2.2.2.2
LS Seq Number: 80000001
Checksum: 0xEC21
Length: 36
Network Mask: /16 //网络掩码16位
Metric Type: 1 (Comparable directly to link state metric)//重发布类型1
TOS: 0
Metric: 1000 //开销为1000,手工指定
Forward Address: 2.2.2.2 //转发地址为2.2.2.2（7类一般为ROUTER-ID）
External Route Tag: 0
RT6收到7类汇总路由LSA后，保存到LSDB中，同时计算路由，选择最优路由安装到全局路由表中，并将7类LSA转化成5类LSA向外通告:
O N1 172.16.0.0/16 [110/1065] via 10.2.26.1, 00:05:03, Serial0/0
N1：NSSA区域为类型1的路由
度量值＝到达转发地址的开销+LSA内开销＝65+1000=1065
LS age: 27
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 172.16.0.0 (External Network Number )
Advertising Router: 6.6.6.6 //通告路由器ID，7转5由ABR通告，当存在多个NSSA ABR时，ROUTER-ID大的做7转5,失效后由另个一个做7转5
LS Seq Number: 80000004
Checksum: 0x302
Length: 36
Network Mask: /16 //网络掩码16位
Metric Type: 1 (Comparable directly to link state metric)
TOS: 0
Metric: 1000 //开销为1000,手工指定
Forward Address: 2.2.2.2 //转发地址2.2.2.2,用来标识去往外部路由下一跳应往哪走
External Route Tag: 0
RT5收到5类LSA后，保存到LSDB中，同时计算路由，择最优路由安装到全局路由表中，并向外洪泛LSA:
O E1 172.16.0.0/16 [110/1129] via 10.0.56.2, 00:04:32, Serial0/1
E1：5类LSA外部路由，开销类型为1
度量值＝到达转发地址的开销+LSA内开销＝S0/1+S0/0+LOOP0+1000=64+64+1+1000=1129
RT5向外洪泛的LSA，不改变任何内容：
Routing Bit Set on this LSA
LS age: 192
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 172.16.0.0 (External Network Number )
Advertising Router: 6.6.6.6
LS Seq Number: 80000004
Checksum: 0x302
Length: 36
Network Mask: /16
Metric Type: 1 (Comparable directly to link state metric)
TOS: 0
Metric: 1000
Forward Address: 2.2.2.2
External Route Tag: 0
到达转发地址的开销，由R6通告，计算外部开销时还要加上到达RT6的开销：
Routing Bit Set on this LSA
LS age: 674
Options: (No TOS-capability, DC, Upward)
LS Type: Summary Links(Network)
Link State ID: 2.2.2.2 (summary Network Number)
Advertising Router: 6.6.6.6
LS Seq Number: 80000001
Checksum: 0x5D6
Length: 28
Network Mask: /32
TOS: 0 Metric: 65
RT1收到RT5洪泛的LSA后，保存到LSDB中，并计算路由，择最优路由安装到全局路由表中，因为RT5做了完全末梢区域，过滤了3类LSA,所以向区域1中下发一条缺省3类LSA，能够让区域1的路由器能够去往RT4:
O E1 172.16.0.0/16 [110/1193] via 10.0.15.2, 00:06:21, Serial0/2
RT1收到的5类LSA，与RT6发出时没任何改变：
Routing Bit Set on this LSA
LS age: 440
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 172.16.0.0 (External Network Number )
Advertising Router: 6.6.6.6
LS Seq Number: 80000004
Checksum: 0x302
Length: 36
Network Mask: /16
Metric Type: 1 (Comparable directly to link state metric)
TOS: 0
Metric: 1000
Forward Address: 2.2.2.2
External Route Tag: 0
RT1向区域1中下发的3类缺省LSA：
LS age: 958
Options: (No TOS-capability, DC, Upward)
LS Type: Summary Links(Network) //网络汇总LSA 3类LSA
Link State ID: 0.0.0.0 (summary Network Number)//LSID 0.0.0.0
Advertising Router: 1.1.1.1 //通告路由器为ABR
LS Seq Number: 80000001
Checksum: 0x93A6
Length: 28
Network Mask: /0 //掩码为0,缺省路由
TOS: 0 Metric: 1 //默认开销为1,default-metric 度量值，可以修改下发缺省路由的开销
RT3收到3类缺省LSA，保存到LSDB中，并计算路由，择最优路由安装到全局路由表中:
O*IA 0.0.0.0/0 [110/65] via 10.1.13.1, 00:16:08, Serial0/0
度量值＝S0/0+LSA内开销＝64+1＝65
RT3 LSDB中保存的LSA
LS age: 958
Options: (No TOS-capability, DC, Upward)
LS Type: Summary Links(Network)
Link State ID: 0.0.0.0 (summary Network Number)
Advertising Router: 1.1.1.1
LS Seq Number: 80000001
Checksum: 0x93A6
Length: 28
Network Mask: /0
TOS: 0 Metric: 1
至些区域1中的路由器可以去往RT4了，也有回来的路由了！分析到此结束！关注下一节实验分析！博客不断更新中！
本文转自 tangfangxiao 51CTO博客，原文链接:http://blog.51cto.com/tangfangxiao/632999
