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某局点无线终端无法获取地址问题处理经验案例

2015-06-11 发表

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陈铮

陈铮八段

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某用户反馈WX3540E上划分多个地址池，唯独VLAN40对应的地址池拿不到地址，尝试换过多个终端无果。

首先要判断拿不到地址是无线的问题还是DHCP的问题，将终端有线连接交换机的vlan40口，发现依旧拿不到地址，所以怀疑是DHCP的问题。

在AC上打开日志和debug，发现如下：

%Jun 8 22:28:54:713 2015 AC-WX3510E WMAC/6/WMAC_CLIENT_JOIN_WLAN: Client acf7-f3bf-9f73 successfully joins WLAN CNEC24-guest, on APID 40 with BSSID 586a-b1fb-05b1.//客户端正常关联AP

*Jun 8 22:28:54:832 2015 AC-WX3510E DHCPS/7/DHCPS_EVENT:

DHCPServer: Receive DHCPREQUEST from ACF7-F3BF-9F73.

*Jun 8 22:28:54:832 2015 AC-WX3510E DHCPS/7/DHCPS_PACKET:

Rx, interface Vlan-interface40

Message type: request

Hardware type: 1, Hardware address length: 6

Hops: 0, Transaction ID: 2556899216

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: acf7-f3bf-9f73

Server host name: Not Configured, Boot file name: Not Configured

DHCP message type: DHCP Request

Requested IP: 10.1.30.25, Sever identifier: 0.0.0.0

*Jun 8 22:28:54:832 2015 AC-WX3510E DHCPS/7/DHCPS_EVENT:

DHCPServer: Deny DHCPREQUEST message for client has moved to a new subnet.//这里是因为客户端第一个请求报文携带的地址和地址池分配的地址不在一个网段而被拒绝，

*Jun 8 22:28:54:833 2015 AC-WX3510E DHCPS/7/DHCPS_PACKET:

Tx, interface Vlan-interface40

Message type: reply

Hardware type: 1, Hardware address length: 6

Hops: 0, Transaction ID: 2556899216

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: acf7-f3bf-9f73

Server host name: Not Configured, Boot file name: Not Configured

DHCP message type: DHCP Nak

*Jun 8 22:28:54:833 2015 AC-WX3510E DHCPS/7/DHCPS_EVENT:

DHCPServer: Send DHCPNAK to ACF7-F3BF-9F73. //发送NAK之后客户端会重新广播发现

*Jun 8 22:28:55:953 2015 AC-WX3510E DHCPS/7/DHCPS_EVENT:

DHCPServer: Receive DHCPDISCOVER from ACF7-F3BF-9F73.

*Jun 8 22:28:55:954 2015 AC-WX3510E DHCPS/7/DHCPS_PACKET:

Rx, interface Vlan-interface40

Message type: request

Hardware type: 1, Hardware address length: 6

Hops: 0, Transaction ID: 2338424837

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: acf7-f3bf-9f73

Server host name: Not Configured, Boot file name: Not Configured

DHCP message type: DHCP Discover

*Jun 8 22:28:55:954 2015 AC-WX3510E DHCPS/7/DHCPS_EVENT:

DHCPServer: Failed to get an available IP address from the corresponding address pool that includes the IP address 10.1.40.254.//这里说分配地址失败了

*Jun 8 22:28:55:954 2015 AC-WX3510E DHCPS/7/DHCPS_EVENT:

DHCPServer: Lease is exhausted.//地址池耗尽

查看DHCP地址池利用率：

[AC-WX3510E]display dhcp server ip-in-use all

Pool utilization: 22.41%//地址利用率还没有超过90%

查看DHCP可用地址：

[AC-WX3510E]display dhcp server free-ip

IP Range from 10.1.30.60 to 10.1.30.254

IP Range from 10.1.33.243 to 10.1.33.254

IP Range from 10.1.34.160 to 10.1.34.160

IP Range from 10.1.34.200 to 10.1.34.214

IP Range from 10.1.34.216 to 10.1.34.254

IP Range from 10.1.36.223 to 10.1.36.254

IP Range from 10.1.37.68 to 10.1.37.94

IP Range from 10.1.37.96 to 10.1.37.252

发现没有10.1.40.0/24（vlan40）对应网段，检查配置发现问题所在：

dhcp server forbidden-ip 10.1.37.254 255.255.255.0

dhcp server forbidden-ip 10.1.37.253 255.255.255.0

删除配置dhcp server forbidden-ip命令后，vlan40下的客户端正常拿地址。这里要强调下dhcp server forbidden-ip命令后面跟着的是由低到高的地址范围而不是网段，误配置后，导致10.1.37.243到255.255.255.0全部不能分配，vlan40的网段10.1.40.0/24碰巧在这个范围内，所以出现了以上故障现象。