R5:
interface Virtual-Template1                     //C、进入模板就和配置PPP一样了，配置IP，和封装。
 ip address 25.0.0.5 255.255.255.0
 ppp authentication chap
!
interface Serial0                                //A、在接口封装FR,并且打开接口（no sh）
 no ip address
 encapsulation frame-relay
 no frame-relay inverse-arp
!
interface Serial0.1 point-to-point          //B、创建子接口，再启用一个模板
 frame-relay interface-dlci 602 ppp Virtual-Template1
 
 R2:
 interface Virtual-Template1
 ip address 25.0.0.2 255.255.255.0
 ppp authentication chap
!
interface Serial0
 no ip address
 encapsulation frame-relay
 no frame-relay inverse-arp
!
interface Serial0.1 point-to-point
 frame-relay interface-dlci 206 ppp Virtual-Template1
!
=======================RIP AUTH==========================
R2:
key chain cisco      //A、定义一个明文的key,
 key 1
  key-string cisco
interface Virtual-Template1
 ip address 25.0.0.2 255.255.255.0
 ip rip authentication key-chain cisco    //调用key，完成rip的认证
 ppp authentication chap
!
router rip   //启动rip路由协议，version 2,(version 1 没有认证)
 version 2
 passive-interface Loopback0
 network 2.0.0.0
 network 25.0.0.0
 neighbor 25.0.0.5
 no auto-summary
R5:
key chain cisco
 key 1
  key-string cisco
interface Virtual-Template1
 ip address 25.0.0.5 255.255.255.0
 ip rip authentication key-chain cisco
 ppp authentication chap
!
router rip
 version 2
 passive-interface Loopback0
 network 5.0.0.0
 network 25.0.0.0
 neighbor 25.0.0.2
 no auto-summary



PS：
    小弟没有尝试rip v2的密文方式认证。下次继续写密文的配置。