PSTN 详解 2

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异步拨号备份DDN专线:

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此例主连接采用DDN专线,备份线路为电话拨号。当DDN专线连接正常时,主端口S0状态为up,line protocol亦为up,则备份线路状态为standby,line protocol为down,此时所有通信均通过主接口进行。当主接口连接发生故障时,端口状态为down,则激活备份接口,完成数据通信。此方法不适合为X.25做备份。因为,配置封装为X.25的接口只要和X.25交换机之间的连接正常其接口及line protocol的状态亦为 up,它并不考虑其它地方需与之通信的路由器的状态如何,所以若本地路由器状态正常,而对方路由器连接即使发生故障,本地也不会激活备份线路。例4将会描述如何为X.25做拨号备份。

以下是相关命令:

任务

命令

指定主线路改变后,次线路状态发生改变的延迟时间

backup delay {enable-delay | never} {disable-delay | never}

指定一个接口作为备份接口

backup interface type number

hostname c2522rb

!

enable secret 5 $1$J5vn$ceYDe2FwPhrZi6qsIIz6g0

enable password cisco

!

username c4700 password 0 cisco

ip subnet-zero

chat-script cisco-default "" "AT" TIMEOUT 30 OK "ATDT \T" TIMEOUT 30 CONNECT \c

chat-script reset atz

!

interface Ethernet0

ip address 16.122.51.254 255.255.255.0

no ip mroute-cache

!

interface Serial0

backup delay 10 10

backup interface Serial2

ip address 16.250.123.18 255.255.255.252

no ip mroute-cache

no fair-queue

!

interface Serial1

no ip address

no ip mroute-cache

shutdown

!

interface Serial2

physical-layer async

ip address 16.249.123.18 255.255.255.252

encapsulation ppp

async mode dedicated

dialer in-band

dialer idle-timeout 60

dialer map ip 16.249.123.17 name c4700 6825179

dialer-group 1

ppp authentication chap

!

interface Serial3

no ip address

shutdown

no cdp enable

!

interface Serial4

no ip address

shutdown

no cdp enable

!

interface Serial5

no ip address

no ip mroute-cache

shutdown

!

interface Serial6

no ip address

no ip mroute-cache

shutdown

!

interface Serial7

no ip address

no ip mroute-cache

shutdown

!

interface Serial8

no ip address

no ip mroute-cache

shutdown

!

interface Serial9

no ip address

no ip mroute-cache

shutdown

!

interface BRI0

no ip address

no ip mroute-cache

shutdown

!

router eigrp 200

network 16.0.0.0

!

ip classless

!

dialer-list 1 protocol ip permit

!

line con 0

line 2

script dialer cisco-default

script reset reset

modem InOut

modem autoconfigure discovery

rxspeed 38400

txspeed 38400

flowcontrol hardware

line aux 0

line vty 0 4

password cisco

login

!

end

c2522rb#

4.       异步拨号备份X.25:

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设置X.25的拨号备份,首先X.25连接的端口必须运行动态路由协议,异步拨号口必须使用静态路由.本例选择EIGRP作为路由选择协议,将静态路由的Metric的值设置为200,由于EIGRP的默认Metric为90,所以当同时有两条路径通往同一网段时,其中Metric值小的路径生效,而当X.25连接出现问题时,路由器无法通过路由协议学习到路由表,则此时静态路由生效,访问通过拨号端口实现。当X.25连接恢复正常时,路由器又可以学习到路由表,则由于 Metric值的不同,静态路由自动被动态路由所代替,这样就实现了备份的功能。

路由器Router1配置如下:

hostname router1

!

enable secret 5 $1$UTvD$99YiY2XsRMxHudcYeHn.Y.

enable password cisco

!

username router2 password cisco

ip subnet-zero

chat-script cisco-default "" "AT" TIMEOUT 30 OK "ATDT \T" TIMEOUT 30 CONNECT \c

chat-script reset atz

interface Ethernet0

ip address 202.96.38.100 255.255.255.0

!

interface Serial0

ip address 202.96.0.1 255.255.255.0

encapsulation x25

x25 address 10112227

x25 htc 16

x25 map ip 202.96.0.2 10112225 broadcast

!

interface Serial1

no ip address

shutdown

!

!

interface Async 1

ip address 202.96.1.1 255.255.255.252

encapsulation ppp

dialer in-band

dialer idle-timeout 60

dialer map ip 202.96.1.2 name router2 modem-script cisco-default 2113470

dialer-group 1

ppp authentication chap

!

router eigrp 200

redistribute connected

network 202.96.0.0

!

ip route 202.96.37.0 255.255.255.0 202.96.1.2 200

dialer-list 1 protocol ip permit

line con 0

line aux 0

script dialer cisco-default

script reset reset

modem InOut

modem autoconfigure discovery

transport input all

rxspeed 38400

txspeed 38400

flowcontrol hardware

line vty 0 4

password cisco

login

!

end

路由器Router2配置如下:

hostname router2

!

enable secret 5 $1$T4IU$2cIqak8f/E4Ug6dLT0k.J0

enable password cisco

!

username router1 password cisco

ip subnet-zero

chat-script cisco-default "" "AT" TIMEOUT 30 OK "ATDT \T" TIMEOUT 30 CONNECT \c

chat-script reset atz

!

interface Ethernet0

ip address 202.96.37.100 255.255.255.0

!

interface Serial0

ip address 202.96.0.2 255.255.255.0

no ip mroute-cache

encapsulation x25

x25 address 10112225

x25 htc 16

x25 map ip 202.96.0.1 10112227 broadcast

!

interface Serial1

no ip address

shutdown

!

interface Async1

ip address 202.96.1.2 255.255.255.252

encapsulation ppp

keepalive 30

async default routing

async mode dedicated

dialer in-band

dialer idle-timeout 60

dialer wait-for-carrier-time 120

dialer map ip 202.96.1.1 name router1 modem-script cisco-default 2113469

dialer-group 1

ppp authentication chap

!

router eigrp 200

redistribute static

network 202.96.0.0

!

no ip classless

ip route 202.96.38.0 255.255.255.0 202.96.1.1 200

dialer-list 1 protocol ip permit

!

line con 0

exec-timeout 0 0

line aux 0

script reset reset

modem InOut

modem autoconfigure discovery

transport input all

rxspeed 38400

txspeed 38400

flowcontrol hardware

line vty 0 4

password cisco

login

!

end

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