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ac的dhcp池里option43配错导致ap无法上线问题排查过程

news 2026/2/8 20:09:02

dhcp池里ac地址配错，导致ap无法上线问题排查过程

问题：ap手动设置ac的ip正常注册在线，但dhcp获得ip和ac地址发现无法在ac上注册成功。

组网：

ac旁路结构，路由器lan口地址172.16.1.1，开dhcp服务，option43提供ac的地址172.16.1.206，地址池172.16.100-200，网关ip172.16.1.1。

解决过程：

如上图，路由器上开dhcp服务，给ap提供dhcp服务，dhcp池设置ip范围是172.16.1.100-172.16.1.200，掩码24，gw是172.16.1.1，ac的地址是172.16.1.206

ap1上电后，查看dhcp分配情况，发现分配地址是172.16.1.200，但在ac172.16.1.206上看不到ap1上线

路由器上

ac上

ap1 ping正常

登录ap，设置ac地址为手动配置172.16.1.206，并在路由器4口抓包

发现ac上，看到ap上线了

抓包tcpdump -i eth4 -nnev udp port 5246 -c 20 抓ap的capwap消息，udp port是5246，并抓20包自动退出-c 20，-nnev是关闭dns查询，数字化显示，显示mac地址，并显示详情

tcpdump: listening on eth4, link-type EN10MB (Ethernet), capture size 262144 bytes

17:29:35.427300 6c:ef:c6:65:ab:c0 > 64:c3:41:b2:18:21, ethertype IPv4 (0x0800), length 567: (tos 0x7,CE, ttl 64, id 43379, offset 0, flags [DF], proto UDP (17), length 553)

172.16.1.200.5246 > 172.16.1.206.5246: UDP, length 525

17:29:35.427579 64:c3:41:b2:18:21 > 6c:ef:c6:65:ab:c0, ethertype IPv4 (0x0800), length 277: (tos 0x7,CE, ttl 64, id 0, offset 0, flags [DF], proto UDP (17), length 263)

172.16.1.206.5246 > 172.16.1.200.5246: UDP, length 235

17:29:40.429262 6c:ef:c6:65:ab:c0 > 64:c3:41:b2:18:21, ethertype IPv4 (0x0800), length 825: (tos 0x7,CE, ttl 64, id 43559, offset 0, flags [DF], proto UDP (17), length 811)

172.16.1.200.5246 > 172.16.1.206.5246: UDP, length 783

17:29:40.429650 64:c3:41:b2:18:21 > 6c:ef:c6:65:ab:c0, ethertype IPv4 (0x0800), length 277: (tos 0x7,CE, ttl 64, id 0, offset 0, flags [DF], proto UDP (17), length 263)

172.16.1.206.5246 > 172.16.1.200.5246: UDP, length 235

17:29:40.431498 6c:ef:c6:65:ab:c0 > 64:c3:41:b2:18:21, ethertype IPv4 (0x0800), length 603: (tos 0x7,CE, ttl 64, id 43560, offset 0, flags [DF], proto UDP (17), length 589)

172.16.1.200.5246 > 172.16.1.206.5246: UDP, length 561

17:29:40.432161 64:c3:41:b2:18:21 > 6c:ef:c6:65:ab:c0, ethertype IPv4 (0x0800), length 1050: (tos 0x7,CE, ttl 64, id 0, offset 0, flags [DF], proto UDP (17), length 1036)

172.16.1.206.5246 > 172.16.1.200.5246: UDP, length 1008

17:29:40.616124 6c:ef:c6:65:ab:c0 > 64:c3:41:b2:18:21, ethertype IPv4 (0x0800), length 80: (tos 0x7,CE, ttl 64, id 43564, offset 0, flags [DF], proto UDP (17), length 66)

172.16.1.200.5246 > 172.16.1.206.5246: UDP, length 38

17:29:40.616458 64:c3:41:b2:18:21 > 6c:ef:c6:65:ab:c0, ethertype IPv4 (0x0800), length 60: (tos 0x7,CE, ttl 64, id 0, offset 0, flags [DF], proto UDP (17), length 44)

发现ap的mac是6c:ef:c6:65:ab:c0，ip是172.16.1.200，ac的ip是172.168.1.206，mac地址是64:c3:41:b2:18:21，2毫秒后，开始有响应。

root@IIIoT:~# arp -n   ap上执行命令arp -n
IP address       HW type     Flags       HW address            Mask     Device
172.16.1.1       0x1         0x2         20:1f:54:f5:36:61     *        br-wan
172.16.1.206     0x1         0x2         64:c3:41:b2:18:21     *        br-wan

ap的banner显示mac地址

NAME: WAP6240-IE
MAC: 6c:ef:c6:65:ab:c0

奇怪，删除ap上手动配置ac地址，改成从dhcp的option43里获取ac地址，重启ap，在路由器上再次抓包

~ # tcpdump -i eth4 -nnev udp port 5246 -c 20

tcpdump: listening on eth4, link-type EN10MB (Ethernet), capture size 262144 bytes

17:58:51.777366 6c:ef:c6:65:ab:c0 > 20:1f:54:f5:36:61, ethertype IPv4 (0x0800), length 567: (tos 0x7,CE, ttl 64, id 52870, offset 0, flags [DF], proto UDP (17), length 553)发给了这个mac地址

172.16.1.200.5246 > 17.16.1.206.5246: UDP, length 525 发出的目的ip 是17.16.1.206，好像ip错了，正确的ip是172.16.1.206，ip第一段错了

17:58:58.793246 6c:ef:c6:65:ab:c0 > 20:1f:54:f5:36:61, ethertype IPv4 (0x0800), length 567: (tos 0x7,CE, ttl 64, id 53510, offset 0, flags [DF], proto UDP (17), length 553)