1、现象
局域网的用户上网慢；
2、处理过程
1）局域网出口链路查看无问题；
2）查看核心交换机的日志
*Jun 19 10:19:43: %NFPP_ARP_GUARD-4-DOS_DETECTED: Host<IP=192.168.1.235,MAC=N/A,port=Gi0/22,VLAN=1> was detected.(2015-6-19 10:19:43)
*Jun 19 10:53:44: %NFPP_ARP_GUARD-4-DOS_DETECTED: Host<IP=192.168.1.96,MAC=N/A,port=Gi0/24,VLAN=1> was detected.(2015-6-19 10:19:44)
*Jun 19 10:54:14: %NFPP_ARP_GUARD-4-DOS_DETECTED: Host<IP=N/A,MAC=001e.904a.eccd,port=Gi0/24,VLAN=1> was detected.(2015-6-19 10:19:44)
*Jun 19 10:54:44: %NFPP_ARP_GUARD-4-DOS_DETECTED: Host<IP=192.168.1.174,MAC=N/A,port=Gi0/24,VLAN=1> was detected.(2015-6-19 10:19:44)
*Jun 19 10:55:14: %NFPP_ARP_GUARD-4-DOS_DETECTED: Host<IP=N/A,MAC=001e.904a.2fa0,port=Gi0/24,VLAN=1> was detected.(2015-6-19 10:19:44)
*Jun 19 10:55:44: %NFPP_ARP_GUARD-4-DOS_DETECTED: Host<IP=192.168.1.174,MAC=N/A,port=Gi0/22,VLAN=1> was detected.(2015-6-19 10:19:44)
初步判断是环路问题。
3）通过在交换机配置开启环路检测命令，发现
*Jun 19 10:55:01: %PORT_SECURITY-4-ERR_RECOVER: Interface GigabitEthernet 0/22 recover from an error.
*Jun 19 10:55:01: %RLDP-3-LINK_DETECT_RECOVER: rldp recover interface GigabitEthernet 0/22 from loop error
*Jun 19 10:55:03: %LINK-3-UPDOWN: Interface GigabitEthernet 0/22, changed state
to up.
*Jun 19 10:55:03: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet 0/22, changed state to up.
*Jun 19 10:55:03: %RLDP-3-LINK_DETECT_ERROR: loop detection error detect on interface GigabitEthernet 0/24.set this interface errordisable!
*Jun 19 10:55:05: %LINK-3-UPDOWN: Interface GigabitEthernet 0/24, changed stateto down.
*Jun 19 10:55:05: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEtherne
t 0/24, changed state to down.
发现在GigabitEthernet 0/22和GigabitEthernet 0/24端口下存在环路问题，具体处理一下该端口下的问题。
