请教专家：我的VMPS怎么老是无法获得正确的vlan name，百思不解

准备采用动态vlan技术，VMPS服务器用的是linux平台的open vmps 1.3.1，客户端是cisco 2960交换机
在2960上全局配置：
vmps reconfirm 10
vmps retry 10
vmps server 10.96.2.207 primary
在具体端口下配置了：
interface FastEthernet0/1
switchport access vlan dynamic
switchport mode access
spanning-tree portfast
下面是debug vqpc 的信息：
*Mar 1 01:47:41.903: VQPC EVENT: -pm_port_vqp_start: port Fa0/1
*Mar 1 01:47:41.903: VQPC: Master requesting VQP START locally
*Mar 1 01:47:41.903: VQPC: Start everything
*Mar 1 01:47:41.962: VQPC LEARN:
*Mar 1 01:47:41.962: VQPC LEARN: -learning mac 68f7.28df.c082 on vlan 0, port Fa0/1
*Mar 1 01:47:41.962: VQPC LEARN: adding mac 68f7.28df.c082 on vlan 0, port Fa0/1, type = 0x0021
*Mar 1 01:47:41.962: VQPC: allocating transID 0x000000A1
*Mar 1 01:47:41.962: VQPC PAK: xmt transaction ID = 0x000000A1
*Mar 1 01:47:41.962: VQPC PAK: sending query to VMPS
*Mar 1 01:47:41.962: VQPC PAK:
*Mar 1 01:47:41.962: VQPC PAK: rcvd packet from VMPS
*Mar 1 01:47:41.962: VQPC PAK: transaction ID = 0x000000A1
*Mar 1 01:47:41.962: VQPC: rcvd response, transID = 0x000000A1
*Mar 1 01:47:41.962: VQPC PAK: VLAN name TLV, vlanName =
*Mar 1 01:47:43.908: %LINK-3-UPDOWN: Interface FastEthernet0/1, changed state to up
*Mar 1 01:47:44.915: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/1, changed state to up
为什么vlanName为空啊？
在VMPS服务器端可以看到
[root@vmpsd bin]# ./vmpsd -d
VMPSD STARTED. Waiting for requests
ALLOW: 68f728dfc082 -> vlan511, switch 10.96.201.5 port Fa0/1
ALLOW: 68f728dfc082 -> vlan511, switch 10.96.201.5 port Fa0/1
ALLOW: 68f728dfc082 -> vlan511, switch 10.96.201.5 port Fa0/1
证明匹配到了，并已经分配了正确的vlanname，我通过wireshark分析vmps返回的数据包，也在其中发现了vlan的name，为什么在交换机上就无法正确解析呢？
哪位高手帮助解决，谢谢！