利用Internet 出口线路建立×××通道实现总、分公司之间的互联,是目前许多公司热衷的方案。以往要建立这样的×××,需要至少一端使用静态的IP地址。当前很多公司都通过ADSL方式上网,如果要求电信提供静态地址,费用将会大大增加(如深圳512K固定IP的ADSL月租是RMB5000)。现在Cisco IOS 12.3(4)T中新增了根据DNS名称来建立××× peer 的命令,借 助希网(3322.org)、88ip等动态域名解释系统的配合,可以在×××两端都使用动态地址的ADSL线路,节省大笔费用。
     关键命令:
set peer {host-name [dynamic] | ip-address}
    说明:
    host-name 指定IPSec peer的DNS主机名称,如:myhost.example.com。
    dynamic (可选参数) 指定 IPSec peer 的主机名在需要建立IPSec通道的时候才通过DNS服务器解释为IP地址。
    ip-address 直接给出IPSec peer的IP地址(传统的配置方式)。
     实际环境中局域网内应在一台机器上运行动态域名解释客户端程序,以将主机名nbo.3322.org注册到服务器,注册地址是路由器的外网端口地址。
 
配置:
    ×××-1(省略了部分无关配置):

    version 12.3
    !
    hostname ***-1
    !
    aaa new-model
    !
    aaa authentication login authen group radius local
    aaa authorization network author local
    aaa session-id common
    ip subnet-zero
    !
    ip cef
    ip name-server 202.96.134.133
    !
    crypto isakmp policy 10
     authentication pre-share
     group 2
    crypto isakmp key cisco address 0.0.0.0 0.0.0.0
    !
    crypto ipsec transform-set s2s esp-des esp-sha-hmac
    !
    crypto dynamic-map dymap 1
     set transform-set s2s
     match address 110
    !
    crypto map mymap 1 ipsec-isakmp dynamic dymap
    !
    interface FastEthernet0/0
     description ×××
     ip address 202.11.22.11 255.255.255.248
     ip nat outside
     crypto map mymap
    !
    interface FastEthernet0/1
     description INSIDE_GATEWAY
     ip address 172.16.10.110 255.255.0.0
     ip nat inside
    !
    ip nat inside source route-map nonat interface FastEthernet0/0 overload
    ip classless
    ip route 0.0.0.0 0.0.0.0 FastEthernet0/0
    no ip http server
    !
    access-list 110 permit ip 172.16.0.0 0.0.255.255 172.30.1.0 0.0.0.255
    access-list 120 deny   ip 172.16.0.0 0.0.255.255 172.30.1.0 0.0.0.255
    access-list 120 permit ip 172.16.0.0 0.0.255.255 any
    route-map nonat permit 10
     match ip address 120
    !
    end
   
    ×××-2(省略了部分无关配置):
   
    version 12.3
    !
    hostname ***-2
    !
    username mize password 0 [url]http://mize.netbuddy.org[/url]
    no aaa new-model
    ip subnet-zero
    !
    ip cef
    ip name-server 202.96.134.133
    !
    crypto isakmp policy 1
     authentication pre-share
     group 2
    crypto isakmp key cisco hostname nbo.3322.org
    !
    crypto ipsec transform-set s2s esp-des esp-sha-hmac
    !
    crypto map mymap 10 ipsec-isakmp
     set peer nbo.3322.org dynamic
     set transform-set s2s
     match address 110
    !
    interface FastEthernet0/0
     ip address 202.11.22.43 255.255.255.248
     ip nat outside
     crypto map mymap
    !
    interface FastEthernet0/1
     ip address 172.30.1.1 255.255.255.0
     ip nat inside
    !
    ip nat inside source route-map nonat interface FastEthernet0/0 overload
    ip classless
    ip route 0.0.0.0 0.0.0.0 FastEthernet0/0
    !
    access-list 110 permit ip 172.30.1.0 0.0.0.255 172.16.0.0 0.0.255.255
    access-list 120 deny   ip 172.30.1.0 0.0.0.255 172.16.0.0 0.0.255.255
    access-list 120 permit ip 172.30.1.0 0.0.0.255 any
    route-map nonat permit 10
     match ip address 120   
    !
    end

    相关调试命令:
    show cry isa sa
    show cry ipsec sa