初始组网:
变更后组网:
终端设备通过初始组网图向DHCP服务器请求地址,获取速度较慢。后客户变更组网,终端直连DHCP服务器,现象依旧。
第一步:故障时在连接PC的端口上进行抓包以及debug分析。
抓包截图如下,可以看出终端设备向dhcp服务器发送了许多DHCP Discover报文,但交换机未应答。
从debug信息看,设备收到如下discover报文时,有时会不回复offer报文,从报文方面来看,未见明显异常。
*Sep 30 15:10:52:411 2021 core-1F DHCPS/7/PACKET: From 0.0.0.0 port 68, interface Vlan-interface4
Message type: REQUEST (1)
Hardware type: 1, Hardware address length: 6
Hops: 0, Transaction ID: 2001877267
Seconds: 8, 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: 0c38-3e19-a2b0
Server host name: not configured
Boot file name: not configured
DHCP message type: DHCPDISCOVER (1)
第二步:查看设备的logbuffer,从logbuff中看到设备有收到比较频繁的TC消息,收到TC后会删除mac地址表项,报文上送时会检查有没有mac地址,如果没有就被丢掉了,故让客户把连接终端的端口配置成边缘端口进行测试。
%Sep 29 22:41:04:772 2021 core-1F STP/6/STP_NOTIFIED_TC: Instance 0's port Ten-GigabitEthernet1/0/4 was notified a topology change.
%Sep 29 22:41:46:801 2021 core-1F STP/6/STP_NOTIFIED_TC: Instance 0's port Ten-GigabitEthernet1/0/4 was notified a topology change.
从平台的debugging信息中搜收和发,数量是一致的,说明平台收到的报文基本都回复了,大部分都是回复offer和ack,有时会回复icmp echo。
Search "DHCPS/7/EVENT: R" (1490 hits in 1 file)
Line 38: *Sep 30 15:10:05:496 2021 core-1F DHCPS/7/EVENT: Receive a DHCPINFORM message from Vlan-interface5.
Line 62: *Sep 30 15:10:05:497 2021 core-1F DHCPS/7/EVENT: Receive a DHCPINFORM message from Vlan-interface5.
Line 86: *Sep 30 15:10:08:487 2021 core-1F DHCPS/7/EVENT: Receive a DHCPINFORM message from Vlan-interface5.
Line 99: *Sep 30 15:10:08:488 2021 core-1F DHCPS/7/EVENT: Receive a DHCPINFORM message from Vlan-interface5.
… …
Search "DHCPS/7/EVENT: S" (1490 hits in 1 file).
Line 520: *Sep 30 15:10:43:389 2021 core-1F DHCPS/7/EVENT: Sent DHCPACK to 192.168.2.90.
Line 544: *Sep 30 15:10:43:390 2021 core-1F DHCPS/7/EVENT: Sent DHCPACK to 192.168.2.90.
Line 568: *Sep 30 15:10:43:554 2021 core-1F DHCPS/7/EVENT: Sent DHCPACK to 192.168.51.79.
Line 592: *Sep 30 15:10:43:555 2021 core-1F DHCPS/7/EVENT: Sent DHCPACK to 192.168.51.79.
Line 620: *Sep 30 15:10:44:414 2021 core-1F DHCPS/7/EVENT: Send an ICMP echo request to 192.168.4.60.
Line 637: *Sep 30 15:10:44:988 2021 core-1F DHCPS/7/EVENT: Send a DHCPOFFER message on Vlan-interface4.
Line 665: *Sep 30 15:10:48:412 2021 core-1F DHCPS/7/EVENT: Send an ICMP echo request to 192.168.4.60.
Line 694: *Sep 30 15:10:48:767 2021 core-1F DHCPS/7/EVENT: Sent DHCPACK to 192.168.3.36.
第三步:配置完成边缘端口后,仍有故障现象。经远程排查,发现核心下连的AC会反弹报文给交换机,导致交换机MAC地址漂移,进而导致终端获取地址慢的问题。
注:知了社区有报文回弹导致MAC地址漂移问题案例,
链接为:https://zhiliao.h3c.com/Theme/details/66426
第四步:无线侧进行分析后发现AC 开启了dhcp snooping的功能,R5441P02版本以前不支持AC与交换机上同时开启dhcp snooping功能,原因为交换机1口收到dhcp discovery转发到2口给ac,此时ac会把这个报文复制一份从有线口原路发回去,从而导致交换机的mac地址学习出现错误引起mac漂移。
将AC侧的DHCP Snooping功能关闭
升级AC版本
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