S7503E DHCP回复出现错误

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手机从vlan23上来后一直获取不到地址，但是该vlan下别的终端可以正常拿到地址，故障终端的MAC地址是f0db-e2a5-c235

根据现场的故障现象，我们怀疑是DHCP的问题，在设备上debugging dhcp server all，我们看到  

*Nov 22 16:07:07:457 2018 core_7503E DHCPS/7/PACKET:

From 0.0.0.0 port 68, interface Vlan-interface23

    Message type: REQUEST (1)

    Hardware type: 1, Hardware address length: 6

    Hops: 0, Transaction ID: 3566393750

    Seconds: 0, Broadcast flag: 0

    Client IP address: 0.0.0.0   Your IP address: 0.0.0.0

    Server IP address: 0.0.0.0   Relay agent IP address: 0.0.0.0

    Client hardware address: f0db-e2a5-c235

    Server host name: not configured

    Boot file name: not configured

    DHCP message type: DHCPDISCOVER (1)

*Nov 22 16:07:08:040 2018 core_7503E DHCPS/7/PACKET:

To 10.74.104.221 port 68, interface Vlan-interface23

    Message type: REPLY (2)

    Hardware type: 1, Hardware address length: 6

    Hops: 0, Transaction ID: 3566393750

    Seconds: 0, Broadcast flag: 0

    Client IP address: 0.0.0.0   Your IP address: 10.74.104.221   //VLAN27

    Server IP address: 0.0.0.0   Relay agent IP address: 0.0.0.0

    Client hardware address: f0db-e2a5-c235

    Server host name: not configured

    Boot file name: not configured

    DHCP message type: DHCPOFFER (2)

*Nov 22 16:07:09:098 2018 core_7503E DHCPS/7/PACKET:

From 0.0.0.0 port 68, interface Vlan-interface23

    Message type: REQUEST (1)

    Hardware type: 1, Hardware address length: 6

    Hops: 0, Transaction ID: 3566393750

    Seconds: 2, Broadcast flag: 0

    Client IP address: 0.0.0.0   Your IP address: 0.0.0.0

    Server IP address: 0.0.0.0   Relay agent IP address: 0.0.0.0

    Client hardware address: f0db-e2a5-c235

    Server host name: not configured

    Boot file name: not configured

    DHCP message type: DHCPREQUEST (3)

*Nov 22 16:07:09:099 2018 core_7503E DHCPS/7/PACKET:

To 255.255.255.255 port 68, interface Vlan-interface23

    Message type: REPLY (2)

    Hardware type: 1, Hardware address length: 6

    Hops: 0, Transaction ID: 3566393750

    Seconds: 2, Broadcast flag: 1

    Client IP address: 0.0.0.0   Your IP address: 0.0.0.0

    Server IP address: 10.74.102.126   Relay agent IP address: 0.0.0.0

    Client hardware address: f0db-e2a5-c235

    Server host name: not configured

    Boot file name: not configured

 查看75E上DHCP的交互过程，终端从VLAN 23 上请求DHCPDISCOVER (1) ，设备侧给终端回复的地址也是从VLAN 23 下发的，但是回复的地址确是VLAN 27的地址，这就导致终端获取不到地址，从而关联失败。 通过命令dis dhcp server free-ip查看，地址池中还有剩余地址。

后续研究得知，当终端上线的VLAN上的IP超期后，如果其他VLAN上有address range配置，并且有租约记录，那么会分配其他VLAN的租约地址。

如果VLAN都配置了address range或都没有配置，则不会触发这个问题。

这种属于软件问题，在7568P01及之后的版本解决, 升级到7577P02版本。