MSR36-60 关于PPP计费问题

想要通过在账户里配置access-limit限制L2TP VPN账户使用人数。access-limit需要通过PPP的计费来实现。但是发现如果两个用户用同一个账号拨入，显示的用户数还是只有一个。

配置如下：

#
l2tp-group 1 mode lns
 allow l2tp virtual-template 1
 undo tunnel authentication
#
 l2tp enable

#
interface Virtual-Template1
 ppp authentication-mode chap
 ppp account-statistics enable
 ip address 192.168.200.1 255.255.255.0

#
local-user h3c class network
 password cipher $c$3$6P3rkJeI+koDYSgH/z22BGAoWJKKbQ==
 access-limit 1
 service-type ppp
 authorization-attribute user-role network-admin
 authorization-attribute user-role network-operator
 authorization-attribute ip 192.168.100.2

两台设备同时拨入后信息如下：

<H3C>display ppp access-user username h3c
Basic:
  Interface: VA0
  User ID: 0x28000001
  Username: h3c
  Domain: -
  IP address: 192.168.100.2
  IPv6 address: -
  IPv6 PD prefix: -
  VPN instance: -
  Access type: L2TP
  Authentication type: CHAP

AAA:
  Authentication state: Authenticated
  Authorization state: Authorized
  Realtime accounting switch: Closed
  Realtime accounting interval: -
  Login time: 2017-05-20  21:09:04:388
  Accounting start time: 2017-05-20  21:09:04:394
  Online time(hh:mm:ss): 00:04:00
  Accounting state: Accounting
  Idle cut: 0 sec  0 byte
  Session timeout: -
  Time remained: -
  Byte remained: -
  Redirect WebURL: -

ACL&QoS:
  User profile: -
  User group profile: -
  Inbound CAR: -
  Outbound CAR: -

Flow Statistic:
  IPv4 uplink   packets/bytes: 1674/130615
  IPv4 downlink packets/bytes: 0/0
  IPv6 uplink   packets/bytes: 0/0
  IPv6 downlink packets/bytes: 0/0

Basic:
  Interface: VA1
  User ID: 0x28000002
  Username: h3c
  Domain: -
  IP address: 192.168.100.2
  IPv6 address: -
  IPv6 PD prefix: -
  VPN instance: -
  Access type: L2TP
  Authentication type: CHAP

AAA:
  Authentication state: Authenticated
  Authorization state: Authorized
  Realtime accounting switch: Closed
  Realtime accounting interval: -
  Login time: 2017-05-20  21:12:59:442
  Accounting start time: -
  Online time(hh:mm:ss): 00:00:05
  Accounting state: Stop
  Idle cut: 0 sec  0 byte
  Session timeout: -
  Time remained: -
  Byte remained: -
  Redirect WebURL: -

ACL&QoS:
  User profile: -
  User group profile: -
  Inbound CAR: -
  Outbound CAR: -

Flow Statistic:
  IPv4 uplink   packets/bytes: 0/0
  IPv4 downlink packets/bytes: 0/0
  IPv6 uplink   packets/bytes: 0/0
  IPv6 downlink packets/bytes: 0/0

<H3C>dis local-user user-name h3c class network
Total 1 local users matched.

Network access user h3c:
  State:                     Active
  Service type:              PPP
  Access limit:              Enabled           Max access number: 1
  Current access number:     1
  User group:                system
  Bind attributes:
  Authorization attributes:
    Work directory:          cfa0:
    User role list:          network-admin, network-operator
    IP address:              192.168.100.2

可以看到，一个计费状态是  Accounting state: Stop，一个是Accounting state: Accounting。

如果是因为针对单一IP进行计费导致的，那么如果让两个用户获取到不同地址，效果也是一样的。

<H3C>dis ppp access-user username h3c
Basic:
  Interface: VA0
  User ID: 0x28000001
  Username: h3c
  Domain: -
  IP address: 192.168.100.2
  IPv6 address: -
  IPv6 PD prefix: -
  VPN instance: -
  Access type: L2TP
  Authentication type: CHAP

AAA:
  Authentication state: Authenticated
  Authorization state: Authorized
  Realtime accounting switch: Closed
  Realtime accounting interval: -
  Login time: 2017-05-20  21:25:58:685
  Accounting start time: -
  Online time(hh:mm:ss): 00:00:43
  Accounting state: Stop
  Idle cut: 0 sec  0 byte
  Session timeout: -
  Time remained: -
  Byte remained: -
  Redirect WebURL: -

ACL&QoS:
  User profile: -
  User group profile: -
  Inbound CAR: -
  Outbound CAR: -

Flow Statistic:
  IPv4 uplink   packets/bytes: 0/0
  IPv4 downlink packets/bytes: 0/0
  IPv6 uplink   packets/bytes: 0/0
  IPv6 downlink packets/bytes: 0/0

Basic:
  Interface: VA1
  User ID: 0x28000002
  Username: h3c
  Domain: -
  IP address: 192.168.100.3
  IPv6 address: -
  IPv6 PD prefix: -
  VPN instance: -
  Access type: L2TP
  Authentication type: CHAP

AAA:
  Authentication state: Authenticated
  Authorization state: Authorized
  Realtime accounting switch: Closed
  Realtime accounting interval: -
  Login time: 2017-05-20  21:26:09:502
  Accounting start time: 2017-05-20  21:26:09:511
  Online time(hh:mm:ss): 00:00:33
  Accounting state: Accounting
  Idle cut: 0 sec  0 byte
  Session timeout: -
  Time remained: -
  Byte remained: -
  Redirect WebURL: -

ACL&QoS:
  User profile: -
  User group profile: -
  Inbound CAR: -
  Outbound CAR: -

Flow Statistic:
  IPv4 uplink   packets/bytes: 195/14653
  IPv4 downlink packets/bytes: 0/0
  IPv6 uplink   packets/bytes: 0/0
  IPv6 downlink packets/bytes: 0/0

<H3C>display local-user user-name h3c class network
Total 1 local users matched.

Network access user h3c:
  State:                     Active
  Service type:              PPP
  Access limit:              Enabled           Max access number: 1
  Current access number:     1
  User group:                system
  Bind attributes:
  Authorization attributes:
    Work directory:          cfa0:
    User role list:          network-admin, network-operator

请问一下，这种情况是什么原因？