OSPF中 LSA 2的真正用法

2007-07-12 12:33:50

　标签：OSPF LSA2　　　[推送到技术圈]

OSPF中Lsa 2的用法

概述:

----------------------------------------------------------------------------------------

此文档在于描述OSPF中DR始发的LSA2在SPF算法中的作用.

----------------------------------------------------------------------------------------

拓扑:

配置:

--------------------------------------------------------------------------------------------

R1的配置

R1#show run
Building configuration...
!
hostname R1
!
interface Serial2/0
ip address 13.1.1.1 255.255.255.0
serial restart-delay 0
!
router ospf 10

router-id 1.1.1.1
log-adjacency-changes
network 13.1.1.1 0.0.0.0 area 0
!
end

--------------------------------------------------------

R2的配置

R2#show run
Building configuration...
!
hostname R2
!
interface Ethernet0/0
ip address 10.1.1.2 255.255.255.0
!
router ospf 10
router-id 2.2.2.2
log-adjacency-changes
network 10.1.1.2 0.0.0.0 area 0
!
end

---------------------------------------------------------

R3的配置

R3#show run
Building configuration...
!
hostname R3
!
interface Ethernet0/0
ip address 10.1.1.3 255.255.255.0
!
interface Serial1/0
ip address 13.1.1.3 255.255.255.0
serial restart-delay 0
!
router ospf 10
router-id 3.3.3.3
log-adjacency-changes
network 10.1.1.3 0.0.0.0 area 0
network 13.1.1.3 0.0.0.0 area 0
!
end

---------------------------------------------------------

R4的配置

R4#show run
Building configuration...
!
hostname R4
!
interface Ethernet0/0
ip address 10.1.1.4 255.255.255.0
!
router ospf 10
router-id 4.4.4.4
log-adjacency-changes
network 10.1.1.4 0.0.0.0 area 0
!
end

---------------------------------------------------------

R5的配置

R5#show run
Building configuration...

hostname R5
!
interface Ethernet0/0
ip address 10.1.1.5 255.255.255.0
!
router ospf 10
router-id 5.5.5.5
log-adjacency-changes
network 10.1.1.5 0.0.0.0 area 0
!
end

-----------------------------------------------------------

现象:

R3被选举为DR,先看看作为DR的R3通告给R1的LSA1和LSA2

-----------------------------------------------------

R1#show ip ospf data router adv 3.3.3.3

OSPF Router with ID (1.1.1.1) (Process ID 10)

Router Link States (Area 0)

LS age: 791
Options: (No TOS-capability, DC)
LS Type: Router Links
Link State ID: 3.3.3.3
Advertising Router: 3.3.3.3
LS Seq Number: 80000015
Checksum: 0x5BC0
Length: 60
Number of Links: 3

    Link connected to: another Router (point-to-point)
     (Link ID) Neighboring Router ID: 1.1.1.1
     (Link Data) Router Interface address: 13.1.1.3
      Number of TOS metrics: 0
       TOS 0 Metrics: 64

    Link connected to: a Stub Network
     (Link ID) Network/subnet number: 13.1.1.0
     (Link Data) Network Mask: 255.255.255.0
      Number of TOS metrics: 0
       TOS 0 Metrics: 64

    Link connected to: a Transit Network
     (Link ID) Designated Router address: 10.1.1.3
     (Link Data) Router Interface address: 10.1.1.3
      Number of TOS metrics: 0
       TOS 0 Metrics: 10

R3通告给R1的LSA1,里面表现了R3所连接了一个LAN,和LAN中的DR接口个地址

R1#show ip ospf data net adv 3.3.3.3

OSPF Router with ID (1.1.1.1) (Process ID 10)

Net Link States (Area 0)

Routing Bit Set on this LSA
LS age: 972
Options: (No TOS-capability, DC)
LS Type: Network Links
Link State ID: 10.1.1.3 (address of Designated Router)
Advertising Router: 3.3.3.3
LS Seq Number: 80000006
Checksum: 0x3D6
Length: 40
Network Mask: /24
        Attached Router: 3.3.3.3
        Attached Router: 2.2.2.2
        Attached Router: 4.4.4.4
        Attached Router: 5.5.5.5

LSA2里明确的交代了LAN中的网络掩码.

---------------------------------------------------------

接下来看一看R1上面计算到达这个LAN的SPF输出信息

R1#debug ip ospf spf

OSPF: Add Network Route to 10.1.1.0 Mask /24. Metric: 74, Next Hop: 13.1.1.3
*Jul 9 18:38:39.255: OSPF: insert route list LS ID 10.1.1.3, type 2, adv rtr 3.3.3.3
*Jul 9 18:38:39.255: It is a network LSA 10.1.1.3. Router Count 4
*Jul 9 18:38:39.255:   Processing router id 3.3.3.3
*Jul 9 18:38:39.255:   New newdist 74 olddist 64
*Jul 9 18:38:39.255:   Processing router id 2.2.2.2
*Jul 9 18:38:39.255:    Add better path to LSA ID 2.2.2.2, gateway 10.1.1.2, dist 74
*Jul 9 18:38:39.255:    Add path: next-hop 13.1.1.3, interface Serial2/0
*Jul 9 18:38:39.255:   Processing router id 4.4.4.4
*Jul 9 18:38:39.255:    Add better path to LSA ID 4.4.4.4, gateway 10.1.1.4, dist 74
*Jul 9 18:38:39.255:    Add path: next-hop 13.1.1.3, interface Serial2/0
*Jul 9 18:38:39.255:   Processing router id 5.5.5.5
*Jul 9 18:38:39.255:    Add better path to LSA ID 5.5.5.5, gateway 10.1.1.5, dist 74
*Jul 9 18:38:39.255:    Add path: next-hop 13.1.1.3, interface Serial2/0
*Jul 9 18:38:39.255: It is a router LSA 5.5.5.5. Link Count 1
*Jul 9 18:38:39.255:   Processing link 0, id 10.1.1.3, link data 10.1.1.5, type 2
*Jul 9 18:38:39.255:   Ignore newdist 84 olddist 74
*Jul 9 18:38:39.255: It is a router LSA 4.4.4.4. Link Count 1
*Jul 9 18:38:39.255:   Processing link 0, id 10.1.1.3, link data 10.1.1.4, type 2
*Jul 9 18:38:39.255:   Ignore newdist 84 olddist 74
*Jul 9 18:38:39.255: It is a router LSA 2.2.2.2. Link Count 1
*Jul 9 18:38:39.255:   Processing link 0, id 10.1.1.3, link data 10.1.1.2, type 2
*Jul 9 18:38:39.255:   Ignore newdist 84 olddist 74

注意红色部分的link data 10.1.12,type 2 部分...这里我们可以联想一下LSA 1的输出信息.

R1#show ip ospf data router adv 3.3.3.3

OSPF Router with ID (1.1.1.1) (Process ID 10)

Router Link States (Area 0)

LS age: 791
Options: (No TOS-capability, DC)
LS Type: Router Links
Link State ID: 3.3.3.3
Advertising Router: 3.3.3.3
LS Seq Number: 80000015
Checksum: 0x5BC0
Length: 60
Number of Links: 3

    Link connected to: another Router (point-to-point)
     (Link ID) Neighboring Router ID: 1.1.1.1
     (Link Data) Router Interface address: 13.1.1.3
      Number of TOS metrics: 0
       TOS 0 Metrics: 64

    Link connected to: a Stub Network
     (Link ID) Network/subnet number: 13.1.1.0
     (Link Data) Network Mask: 255.255.255.0
      Number of TOS metrics: 0
       TOS 0 Metrics: 64

    Link connected to: a Transit Network
     (Link ID) Designated Router address: 10.1.1.3
     (Link Data) Router Interface address: 10.1.1.3
      Number of TOS metrics: 0
       TOS 0 Metrics: 10

前面输出的type 2在ospfv2中定义的是transit network. 而link Data在LSA1中的表示的是通告此LSA的ADV在LAN中的接口地址.也就是说在R1在SPF计算到达LAN的每一个接口时使用了LSA是类型1的.那么类型2的又有什么用呢?

大家是否发现LSA1包含的信息中并没有包含这个LAN的掩码.而LSA2却带上了掩码

R1#show ip ospf data net adv 3.3.3.3

OSPF Router with ID (1.1.1.1) (Process ID 10)

Net Link States (Area 0)

Routing Bit Set on this LSA
LS age: 972
Options: (No TOS-capability, DC)
LS Type: Network Links
Link State ID: 10.1.1.3 (address of Designated Router)
Advertising Router: 3.3.3.3
LS Seq Number: 80000006
Checksum: 0x3D6
Length: 40
Network Mask: /24
        Attached Router: 3.3.3.3
        Attached Router: 2.2.2.2
        Attached Router: 4.4.4.4
        Attached Router: 5.5.5.5

结论

路由器在SPF运算时,使用LSA1确定如何到达此MAN..再使用LSA2确定到此MAN的掩码.这就是为什么LSA2要求被泛洪到整个区域的原因.也是LSA2最大的一个作用.

更多精华贴请详见:http://www.one-tom.com/bbs

本文出自 “IT傻博士 [技术成就梦想]” 博客，谢绝转载！

上一篇无线接入技术浅析　　下一篇 CISCO发现协议（CDP）理论与实验

类别：汤姆一通ITAA网络技术实验室 ┆ 技术圈() ┆ 阅读() ┆ 评论() ┆推送到技术圈 ┆返回首页

相关文章

文章评论

[匿名]18558

2007-07-12 21:49:08

R3被选举为DR,先看看作为DR的R3通告给R1的LSA1和LSA2

有机会还得再学学这个

昵称：
验证码：		点击图片可刷新验证码　　博客过2级，无需填写验证码
内容：