OSPF 笔记

区域类型对应的LSA:backbone 1 2 3 4 5 no-backbone,no-stub 1 2 3 4 5 stub 1 2 3 and A Default Routetotally stubby 1 2 and A Default Route not-so-stubby 1 2 3 7 nssa no-summary 1 2 7 and A Default Route
调整区域类型:backbone no-backbone,no-stub stub R1(config-router)#area 1 stub totally stubby R1(config-router)#area 1 stub no-summary not-so-stubby R1(config-router)#area 1 nssa nssa no-summary R1(config-router)#area 1 nssa no-summary
查看对应的LSA：1 R1#show ip ospf database router (该区域内的每个路由器产生)2 R1#show ip ospf database network (该区域内DR产生)3 R1#show ip ospf database summary (ABR产生)4 R1#show ip ospf database asbr-summary (ABR产生，描述到ASBR距离)5 R1#show ip ospf database external (ASBR产生,描述到AS外的路由)7 R1#show ip ospf database nssa (ASBR产生，仅在NSSA传递，ABR转换成5内到其他区域)
类型1的LSA ： link-id= router-id类型2的LSA ： link-id=DR的接口IP类型3的LSA ： link-id=目的网络号类型4的LSA ： link-id= ASBR router-id类型5的LSA ： link-id= 外部网络号类型7的LSA ： link-id= 外部网络号
5[/b]类[/b] External [/b]LSA[/b]在LSA5类中的Forward Address:
The value of the forwarding address specified by the autonomous system boundary router (ASBR) (Router 1 in the previous figure) can be either 0.0.0.0 or non-zero. The 0.0.0.0 address indicates that the originating router (the ASBR) is the next hop. The forwarding address is determined by these conditions:
• The forwarding address is set to 0.0.0.0 if the ASBR redistributes routes and OSPF is not enabled on the next hop interface for those routes.
• These conditions set the forwarding address field to a non-zero address:
o OSPF is enabled on the ASBR's next hop interface AND
o ASBR's next hop interface is non-passive under OSPF AND
o ASBR's next hop interface is not point-to-point AND
o ASBR's next hop interface is not point-to-multipoint AND
o ASBR's next hop interface address falls under the network range specified in the router ospf command.
• Any other conditions besides these set the forwarding address to 0.0.0.0.
Type 5Forward != 0.0.0.0外部路由的cost = 到forward address的cost + ASBR通告的type5的metric
Forward = 0.0.0.0外部路由的cost = 到Advertising Router（show ip ospf border-routers）的cost + ASBR通告的type5的metric
OSPF将引入的AS外部路由分为两类：Type1和Type2。第一类外部路由是指接收的是IGP（Interior Gateway Protocol，内部网关协议）路由（例如静态路由和RIP路由）。由于这类路由的可信程度较高，并且和OSPF自身路由的开销具有可比性，所以到第一类外部路由的开销等于本路由器到相应的ASBR的开销与ASBR到该路由目的地址的开销之和。第二类外部路由是指接收的是EGP（Exterior Gateway Protocol，外部网关协议）路由。由于这类路由的可信度比较低，所以OSPF协议认为从ASBR到自治系统之外的开销远远大于在自治系统之内到达ASBR的开销。所以计算路由开销时将主要考虑前者，即到第二类外部路由的开销等于ASBR到该路由目的地址的开销。如果计算出开销值相等的两条路由，再考虑本路由器到相应的ASBR的开销。
Type 3Type的路由 = 到ABR的cost(show ip ospf border-routers) + ABR通告的Type3的路由cost(show ip ospf database summary)

[align=center]4[/b]类[/b] ASBR[/b]汇总[/b]LSA[/b][/align][align=left] [/align][align=left] ASBR汇总LSA通告的是一个区域外部的ASBR路由器，且只能在单个区域中泛洪。由外部路由起源区域的ABR产生，泛洪到起源区域的整个AS中。[/align][align=left] [/align][align=left] LSA传播范围：泛洪到整个AS中，（把ASBR的Router ID传播到其他区域，让其他区域的路由器得知ASBR的位置。）[/align][align=left] LSA通告路由器：ABR的Router ID（经过一个ABR，就会改为这个ABR的Router ID）[/align][align=left] LSA链路状态ID：ASBR的Router ID[/align][align=left] LSA包含的内容：本区域中的路由信息，包括网络号和掩码[/align][align=left] [/align][align=left]注意：[/b]在ASBR直连的区域内，不会产生4类的LSA，因为ASBR会发出1类的LSA，其中会指明自己是ASBR。[/align][align=left]
[/align][align=left]R1(config-if)#do show ip os da router[/align][align=left]
[/align][align=left] OSPF Router with ID (1.1.1.1) (Process ID 100)[/align][align=left]
[/align][align=left] Router Link States (Area 1)[/align][align=left]
[/align][align=left] LS age: 1378[/align][align=left] Options: (No TOS-capability, DC)[/align][align=left] LS Type: Router Links[/align][align=left] Link State ID: 1.1.1.1[/align][align=left] Advertising Router: 1.1.1.1[/align][align=left] LS Seq Number: 8000002E[/align][align=left] Checksum: 0x9872[/align][align=left] Length: 72[/align][align=left] Number of Links: 4[/align][align=left]
[/align][align=left] Link connected to: a Stub Network[/align][align=left] (Link ID) Network/subnet number: 10.10.10.10[/align][align=left] (Link Data) Network Mask: 255.255.255.255[/align][align=left] Number of TOS metrics: 0[/align][align=left] TOS 0 Metrics: 1[/align][align=left]
[/align][align=left] Link connected to: a Stub Network[/align][align=left] (Link ID) Network/subnet number: 1.1.1.1[/align][align=left] (Link Data) Network Mask: 255.255.255.255[/align][align=left] Number of TOS metrics: 0[/align][align=left] TOS 0 Metrics: 1[/align][align=left]
[/align][align=left] Link connected to: a Transit Network[/align][align=left] (Link ID) Designated Router address: 9.9.15.1[/align][align=left] (Link Data) Router Interface address: 9.9.15.1[/align][align=left] Number of TOS metrics: 0[/align][align=left] TOS 0 Metrics: 10[/align][align=left]
[/align][align=left] Link connected to: a Transit Network[/align][align=left] (Link ID) Designated Router address: 9.9.12.1[/align][align=left] (Link Data) Router Interface address: 9.9.12.1[/align][align=left] Number of TOS metrics: 0[/align][align=left] TOS 0 Metrics: 10[/align][align=left]
[/align][align=left]
[/align][align=left] Routing Bit Set on this LSA[/align][align=left] LS age: 1728[/align][align=left] Options: (No TOS-capability, DC)[/align][align=left] LS Type: Router Links[/align][align=left] Link State ID: 2.2.2.2[/align][align=left] Advertising Router: 2.2.2.2[/align][align=left] LS Seq Number: 80000024[/align][align=left] Checksum: 0x397D[/align][align=left] Length: 36[/align][align=left] Area Border Router[/align][align=left] Number of Links: 1[/align][align=left]
[/align][align=left] Link connected to: a Transit Network[/align][align=left] (Link ID) Designated Router address: 9.9.12.1[/align][align=left] (Link Data) Router Interface address: 9.9.12.2[/align][align=left] Number of TOS metrics: 0[/align][align=left] TOS 0 Metrics: 10[/align][align=left]
[/align][align=left]
[/align][align=left] Routing Bit Set on this LSA[/align][align=left] LS age: 1380[/align][align=left] Options: (No TOS-capability, DC)[/align][align=left] LS Type: Router Links[/align][align=left] Link State ID: 5.5.5.5[/align][align=left] Advertising Router: 5.5.5.5[/align][align=left] LS Seq Number: 80000014[/align][align=left] Checksum: 0xE6BC[/align][align=left] Length: 36[/align][align=left] Area Border Router[/align][align=left] AS Boundary Router[/align][align=left] Number of Links: 1[/align][align=left]
[/align][align=left] Link connected to: a Transit Network[/align][align=left] (Link ID) Designated Router address: 9.9.15.1[/align][align=left] (Link Data) Router Interface address: 9.9.15.5[/align][align=left] Number of TOS metrics: 0[/align][align=left] TOS 0 Metrics: 10[/align][align=left]
[/align][align=left]i 5.5.5.5 [10] via 9.9.15.5, FastEthernet0/1, ABR/ASBR, Area 1, SPF 55[/align][align=left]i 2.2.2.2 [10] via 9.9.12.2, FastEthernet0/0, ABR, Area 1, SPF 55[/align][align=left]I 3.3.3.3 [20] via 9.9.15.5, FastEthernet0/1, ASBR, Area 1, SPF 55[/align][align=left]I 3.3.3.3 [20] via 9.9.12.2, FastEthernet0/0, ASBR, Area 1, SPF 55[/align]