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 Route
totally 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类 External LSA
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.
• 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 5
Forward != 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 3
Type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)
4
类
ASBR
汇总
LSA
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。
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。）
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
）
LSA
链路状态
ID
：
ASBR
的
Router ID
LSA
包含的内容：本区域中的路由信息，包括网络号和掩码
注意：
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
。
R1(config-if)#do show ip os da router
OSPF Router with ID (1.1.1.1) (Process ID 100)
Router Link States (Area 1)
LS age: 1378
Options: (No TOS-capability, DC)
LS Type: Router Links
Link State ID: 1.1.1.1
Advertising Router: 1.1.1.1
LS Seq Number: 8000002E
Checksum: 0x9872
Length: 72
Number of Links: 4
Link connected to: a Stub Network
(Link ID) Network/subnet number: 10.10.10.10
(Link Data) Network Mask: 255.255.255.255
Number of TOS metrics: 0
TOS 0 Metrics: 1
Link connected to: a Stub Network
(Link ID) Network/subnet number: 1.1.1.1
(Link Data) Network Mask: 255.255.255.255
Number of TOS metrics: 0
TOS 0 Metrics: 1
Link connected to: a Transit Network
(Link ID) Designated Router address: 9.9.15.1
(Link Data) Router Interface address: 9.9.15.1
Number of TOS metrics: 0
TOS 0 Metrics: 10
Link connected to: a Transit Network
(Link ID) Designated Router address: 9.9.12.1
(Link Data) Router Interface address: 9.9.12.1
Number of TOS metrics: 0
TOS 0 Metrics: 10
Routing Bit Set on this LSA
LS age: 1728
Options: (No TOS-capability, DC)
LS Type: Router Links
Link State ID: 2.2.2.2
Advertising Router: 2.2.2.2
LS Seq Number: 80000024
Checksum: 0x397D
Length: 36
Area Border Router
Number of Links: 1
Link connected to: a Transit Network
(Link ID) Designated Router address: 9.9.12.1
(Link Data) Router Interface address: 9.9.12.2
Number of TOS metrics: 0
TOS 0 Metrics: 10
Routing Bit Set on this LSA
LS age: 1380
Options: (No TOS-capability, DC)
LS Type: Router Links
Link State ID: 5.5.5.5
Advertising Router: 5.5.5.5
LS Seq Number: 80000014
Checksum: 0xE6BC
Length: 36
Area Border Router
AS Boundary Router
Number of Links: 1
Link connected to: a Transit Network
(Link ID) Designated Router address: 9.9.15.1
(Link Data) Router Interface address: 9.9.15.5
Number of TOS metrics: 0
TOS 0 Metrics: 10
i 5.5.5.5 [10] via 9.9.15.5, FastEthernet0/1, ABR/ASBR, Area 1, SPF 55
i 2.2.2.2 [10] via 9.9.12.2, FastEthernet0/0, ABR, Area 1, SPF 55
I 3.3.3.3 [20] via 9.9.15.5, FastEthernet0/1, ASBR, Area 1, SPF 55
I 3.3.3.3 [20] via 9.9.12.2, FastEthernet0/0, ASBR, Area 1, SPF 55