CCNA 重新认证：CCNA认证证书的时效性是三年。要重新更新证书，必须通过CCNA的考试(如果通过的下一阶段CCNP的考试，CCNA认证证书会被自动更新)下面是小编整理的关于思科路由器设置VPDN的方法，欢迎大家参考!
1 启用aaa new-model
aaa new-model
2、建立认证方式
aaa authentication ppp mytest local (这里为本地认证)
3、启用VPDN
vpdn enable
4、建立VPDN组
vpdn-group mytest
! Default L2TP VPDN group
accept-dialin
protocol l2tp
virtual-template 1
local name mytest-name
lcp renegotiation always //注意非常重要，否则LCP不会自协商，那么路由器的MTU值一定要和对方LAC发过来的要匹配，否则LCP失败
l2tp tunnel password 7 00090A1201481F
source-ip x.x.x.x
5、建立IP 本地POOL
ip local pool mytest-01 172.23.1.2 172.23.1.254
6、配置虚模板
interface Virtual-Template1
ip address 172.23.1.1 255.255.255.0
peer default ip address pool mytest-01
ppp authentication pap mytest
5200g
domain qh.org
authentication-scheme vpdn_none
accounting-scheme vpdn_none
l2tp-group qh.org
l2tp-group qh.org
tunnel password simple mytest
tunnel name mytest
start l2tp ip x.x.x.x
tunnel source LoopBack0
附：L2TP协议结构
1、IP包头 20字节
2、UDP报头 8字节
3、L2TP报头 12字节：包括：
1)the version and flag fields (2 bytes)
2)the tunnel id and session id fields (2 bytes each)
3)2 bytes of padding offset
4)4 bytes of Point-to-Point Protocol (PPP) encapsulation
//以下是没有启用LCP自协商的DEBUG 连接失败
Jul 25 00:03:48.084: Vi1 VPDN: Virtual interface created for qh@qh.org
Jul 25 00:03:48.084: Vi1 PPP: Phase is DOWN, Setup
Jul 25 00:03:48.084: Vi1 VPDN: Clone from Vtemplate 1 filterPPP=0 blocking
Jul 25 00:03:48.204: %LINK-3-UPDOWN: Interface Virtual-Access1, changed state to up
Jul 25 00:03:48.204: Vi1 PPP: Using set call direction
Jul 25 00:03:48.204: Vi1 PPP: Treating connection as a callin
Jul 25 00:03:48.204: Vi1 PPP: Phase is ESTABLISHING, Passive Open
Jul 25 00:03:48.204: Vi1 LCP: State is Listen
Jul 25 00:03:48.204: Vi1 VPDN: Bind interface direction=2
Jul 25 00:03:48.204: Vi1 LCP: I FORCED CONFREQ len 14
Jul 25 00:03:48.204: Vi1 LCP: MRU 1492 (0x010405D4)
Jul 25 00:03:48.204: Vi1 LCP: AuthProto PAP (0x0304C023)
Jul 25 00:03:48.204: Vi1 LCP: MagicNumber 0x01022143 (0x050601022143)
Jul 25 00:03:48.204: Vi1 VPDN: PPP LCP accepted rcv CONFACK
Jul 25 00:03:48.204: Vi1 LCP: I FORCED CONFACK len 10
Jul 25 00:03:48.204: Vi1 LCP: MRU 1480 (0x010405C8)
Jul 25 00:03:48.204: Vi1 LCP: MagicNumber 0x082D5DCE (0x0506082D5DCE)
Jul 25 00:03:48.204: Vi1 VPDN: PPP LCP not accepting sent CONFACK
Jul 25 00:03:48.204: Vi1 VPDN: Unbind interface
Jul 25 00:03:48.296: Vi1 PPP: No remote authentication for call-in
Jul 25 00:03:48.560: Vi1 PPP: Missed link down notification
Jul 25 00:03:48.560: Vi1 LCP: State is Closed
