描述

协助一场网络排查，现场反馈无线网络访问无线网关延迟较大，部分区域延迟超过 400ms，并伴随不同程度的网络卡顿、掉线现象；路由器、AC 上都没有异常，CPU、RAM 都正常。

排查

了解现场，核心交换机同时承担有线网关和无线网关功能，VLAN 网关均配置在核心交换机上；AC 为旁路部署，非无线终端网关；同时反馈。
对 AC、防火墙、路由器等设备的内网 IP 进行 ping 测试，延迟均正常。
由于无线终端到无线网关的延迟异常，而其他设备延迟正常，初步判断问题可能与核心交换机或其下联链路有关。
登录核心交换机，查看 cpu 使用信息、无明显占用，非设备硬件瓶颈；
检查 stp 情况，发现 GigabitEthernet1/0/12 接口处于 DISCARDING 状态，查看该接口的 LLDP 邻居信息为核心交换机自身，存在环路表象；
验证，使用其他终端持续 ping 核心交换机网关 IP，同时拔掉 GigabitEthernet1/0/12 接口网线，拔线后，ping 延迟立即恢复正常，询问现场网络卡顿现象同步缓解，确定该故障为环路导致。

相关命令

<HX-S5500V3-54S-SI>disp cpu-u
Slot 1 CPU 0 CPU usage:
       5% in last 5 seconds
       5% in last 1 minute
       5% in last 5 minutes
<HX-S5500V3-54S-SI>disp int brie
Brief information on interfaces in route mode:
Link: ADM - administratively down; Stby - standby
Protocol: (s) - spoofing
Interface            Link Protocol Primary IP        Description              
InLoop0              UP   UP(s)    --                
NULL0                UP   UP(s)    --                
REG0                 UP   --       --                
Vlan10               UP   UP       172.16.0.1        
Vlan20               UP   UP       172.16.20.1       
Vlan100              UP   UP       10.10.10.3        manage
...
<HX-S5500V3-54S-SI>display stp brief
 MST ID   Port                                Role  STP State   Protection
 0        GigabitEthernet1/0/3                DESI  FORWARDING  NONE
 0        GigabitEthernet1/0/4                DESI  FORWARDING  NONE
 0        GigabitEthernet1/0/6                DESI  FORWARDING  NONE
 0        GigabitEthernet1/0/7                DESI  FORWARDING  NONE
 0        GigabitEthernet1/0/11               DESI  FORWARDING  NONE
 0        GigabitEthernet1/0/12               DESI  DISCARDING  NONE
 0        GigabitEthernet1/0/13               DESI  FORWARDING  NONE
...
<HX-S5500V3-54S-SI>display lldp neighbor-information interface GigabitEthernet 1/0/12 verbose
LLDP neighbor-information of port 12[GigabitEthernet1/0/12]:
LLDP agent nearest-bridge:
 LLDP neighbor index : 1
 Update time         : 223 days, 18 hours, 31 minutes, 45 seconds
 Chassis type        : MAC address
 Chassis ID          : 58b3-8f6f-f9f0
 Port ID type        : Interface name
 Port ID             : GigabitEthernet1/0/12
 Time to live        : 121
 Port description    : GigabitEthernet1/0/12 Interface
 System name         : HX-S5500V3-54S-SI
 System description  : 
   H3C Comware Platform Software, Software Version 7.1.070, Release 1107
   H3C S5500V3-54S-SI
   Copyright (c) 2004-2022 New H3C Technologies Co., Ltd. All rights reserved.
 System capabilities supported : Bridge, Router, Customer Bridge, Service Bridge
 System capabilities enabled   : Bridge, Router, Customer Bridge
 Management address type           : IPv4
 Management address                : 172.16.0.1
 Management address interface type : IfIndex
 Management address interface ID   : 636
 Management address OID            : 0
 Port VLAN ID(PVID)  : 10
 Link aggregation supported : Yes