某交通管理局，各个各地区有若干执法站，各种交通违章处罚单数据放在交管局数据库上，执法站在受理交通处罚时需要连接到交管局查询处罚单，并进行更新。由于每天各个执法站接受出发的人数不定，时间也没有规律，而且非工作时间是绝对不需要连接的。同时各个执法站数据流量都不是很大，采用专线连接成本太高；但是采用modem连接连接速度太慢，通讯带宽也不够。所以，采用ISDN。
拓扑图如下：
配置清单：
中心路由器
!
service timestamps debug uptime
service timestamps log uptime
service password-encryption
no service tcp-small-servers
no service udp-small-servers
!
hostname Cisco2620
! enable password aa
username 1720 password cisco
!
no ip name-server
!
isdn switch-type primary-net5
!
ip subnet-zero
no ip domain-lookup
ip routing
!
controller E1 1/0
framing no-crc4
linecode hdb3
pri-group timeslots 1-31
!
controller E1 1/1
framing no-crc4
linecode hdb3
pri-group timeslots 1-31
!
interface FastEthernet 0/0
ip add 10.1.1.1 255.255.255.0
!
interface loopback 0
ip add 10.1.2.1 255.255.255.0
!
interface Serial 1/0:15
encapsulation ppp
ip unnumbered loopback 0
ppp authentication chap callin
ppp chap host 2620
peer default ip address dhcp dhcp_pool
ppp multi-link
dialer-group 1
!
interface Serial 1/1:15
encapsulation ppp
ip unnumbered loopback 0
ppp authentication chap callin
ppp chap host 2620
peer default ip address dhcp dhcp_pool
ppp multi-link
dialer-group 1
!
dialer-list 1 protocol ip permit
!
router rip
net 10.0.0.0
passive-interface default
no passive-interface fastethernet 0/0
!
ip local pool dhcp_ppol 10.2.1.10 10.1.2.70
ip classless
no ip http server
snmp-server community public RO
no snmp-server location
no snmp-server contact
!
line console 0
exec-timeout 0 0
password hh
login
!
line vty 0 4
password hh
login
!
end
执法站路由器配置
! service timestamps debug uptime
service timestamps log uptime
service password-encryption
no service tcp-small-servers
no service udp-small-servers
!
hostname Cisco1720
!
enable password jjjj
username 2620 password cisco
!
no ip name-server
!
isdn switch-type basic-nwnet3
!
ip subnet-zero
no ip domain-lookup
ip routing
!
!
interface FastEthernet 0
ip add 192.168.0.1 255.255.255.0
ip nat inside
!
interface BRI 0
ip address negotiation
isdn switch-type basic-net3
encapsulation ppp
ppp authentication chap
ppp chap host 1720
dialer string 12345678
ip nat outside
!
dialer-list 1 protocol ip permit
!
ip nat inside source-list 1 interface bri 0 overload
!
access-list 1 permit any
ip classless
no ip http server
snmp-server community public RO
no snmp-server location
no snmp-server contact
!
line console 0
exec-timeout 0 0
password jj
login
!
line vty 0 4
password jj
login
!
end
