CISCO / BushNET Troubleshooting Guide¶
Common issues and solutions for the CISCO / BushNET.
Table of Contents¶
- Connection Issues
- Interface Problems
- VLAN Issues
- Spanning Tree Issues
- Routing Issues
- Performance Problems
- Security Issues
- Environmental Issues
- Recovery Procedures
Connection Issues¶
Cannot Connect to Console Port¶
Symptoms:
- No output in terminal
- Garbled characters
- No response to keystrokes
Solutions:
- Verify cable connections
- Verify terminal settings
- Check COM port assignment
# Linux
ls /dev/ttyUSB* /dev/ttyACM*
dmesg | tail -20
# Windows
# Device Manager → Ports (COM & LPT)
- Linux permission issue
Cannot SSH to Switch¶
Symptoms:
- Connection refused
- Connection timeout
- Authentication failure
Diagnostic Commands:
Solutions:
- Verify IP connectivity
- Verify SSH is enabled
show ip ssh
# If not enabled:
ip domain-name company.local
crypto key generate rsa modulus 2048
ip ssh version 2
- Verify VTY configuration
- Check ACL blocking SSH
- Verify user credentials
Interface Problems¶
Interface Down¶
Diagnostic Commands:
Common Causes & Solutions:
- Administratively Down
- No Link (down/down)
- Check cable connection
- Verify remote device is powered
- Check cable type (straight vs crossover)
-
Try different port
-
Speed/Duplex Mismatch
show interfaces GigabitEthernet1/1 | include duplex
# Fix - set to auto:
interface GigabitEthernet1/1
speed auto
duplex auto
- err-disabled State
show interfaces status err-disabled
show errdisable recovery
# View cause:
show logging | include err-disable
# Re-enable:
interface GigabitEthernet1/1
shutdown
no shutdown
# Enable auto-recovery:
errdisable recovery cause all
errdisable recovery interval 300
High Interface Errors¶
Diagnostic Commands:
Common Causes:
| Error Type | Cause | Solution |
|---|---|---|
| CRC errors | Bad cable, EMI | Replace cable, check routing |
| Collisions | Duplex mismatch | Set duplex auto/full |
| Input errors | Various | Check cable, speed/duplex |
| Output drops | Congestion | Check QoS, upgrade link |
| Giants | MTU mismatch | Match MTU settings |
| Runts | Collisions/bad NIC | Check duplex, replace NIC |
Clear Counters (for testing):
VLAN Issues¶
Device Cannot Reach Other VLAN¶
Diagnostic Commands:
Solutions:
- Verify VLAN exists
- Verify port VLAN assignment
show interfaces GigabitEthernet1/1 switchport
# Fix:
interface GigabitEthernet1/1
switchport access vlan 10
- Verify trunk allows VLAN
- Verify routing between VLANs
Native VLAN Mismatch¶
Symptoms:
- CDP/LLDP shows native VLAN mismatch
- Intermittent connectivity
Diagnostic:
Solution:
Spanning Tree Issues¶
Unexpected Topology Changes¶
Diagnostic Commands:
Solutions:
- Enable PortFast on access ports
- Enable BPDU Guard
- Verify root bridge
Port in Blocking State¶
Diagnostic:
Solutions:
- Expected behavior - STP blocks redundant paths
- Incorrect root bridge - Set proper root priorities
- Loop detected - Check physical cabling
Routing Issues¶
No Route to Destination¶
Diagnostic Commands:
show ip route
show ip route <destination>
show ip protocols
ping <destination>
traceroute <destination>
Solutions:
- Missing default gateway
- Missing static route
- OSPF neighbor not forming
show ip ospf neighbor
show ip ospf interface
# Check:
# - Matching area IDs
# - Matching network types
# - Hello/dead timers
# - Authentication
Performance Problems¶
High CPU Usage¶
Diagnostic Commands:
Common Causes:
| Process | Cause | Solution |
|---|---|---|
| IP Input | High traffic, ACL | Optimize ACLs |
| Hulc LED | Normal | Usually OK |
| Spanning Tree | Topology changes | Stabilize STP |
| SNMP Engine | Polling | Reduce poll frequency |
| Logger | Excessive logging | Tune logging levels |
High Memory Usage¶
Diagnostic:
Solutions:
- Clear unused sessions
- Reduce logging buffer
- Upgrade IOS if memory leak
Slow Network Performance¶
Diagnostic:
Solutions:
- Check for errors
- Check QoS
- Check for congestion
Security Issues¶
Port Security Violation¶
Diagnostic:
Recovery:
Or enable auto-recovery:
Locked Out of Switch¶
Solutions:
- Console access available:
- Connect via console
-
Reset password (see Recovery Procedures)
-
No console access:
- Physical access to switch required
- Follow password recovery procedure
Environmental Issues¶
Temperature Warnings¶
Diagnostic:
Solutions:
- Check ambient temperature
- Verify ventilation
- Check fan operation
- Clean dust from vents
Power Supply Issues¶
Diagnostic:
Solutions:
- Verify power connections
- Check power supply LED
- Verify input voltage
Recovery Procedures¶
Password Recovery¶
- Connect via console
- Power cycle switch
- Press MODE button for 15 seconds during boot
- Follow prompts in ROMMON:
switch: flash_init
switch: dir flash:
switch: rename flash:config.text flash:config.bak
switch: boot
- After boot:
Switch> enable
Switch# rename flash:config.bak flash:config.text
Switch# copy flash:config.text running-config
Switch# configure terminal
Switch(config)# enable secret NewPassword
Switch(config)# end
Switch# write memory
Factory Reset¶
IOS Recovery via TFTP¶
From ROMMON:
rommon 1 > set IP_ADDRESS=192.168.1.10
rommon 2 > set IP_SUBNET_MASK=255.255.255.0
rommon 3 > set DEFAULT_GATEWAY=192.168.1.1
rommon 4 > set TFTP_SERVER=192.168.1.100
rommon 5 > set TFTP_FILE=ie3300-universalk9.bin
rommon 6 > tftpdnld
rommon 7 > boot
Emergency Installation¶
See: Emergency Recovery Installation
Diagnostic Command Summary¶
| Issue | Commands |
|---|---|
| General health | show version, show environment all |
| Interfaces | show interfaces status, show interfaces counters errors |
| VLANs | show vlan brief, show interfaces trunk |
| Spanning Tree | show spanning-tree, show spanning-tree root |
| Routing | show ip route, show ip interface brief |
| MAC addresses | show mac address-table |
| CDP/LLDP | show cdp neighbors, show lldp neighbors |
| Logs | show logging, show logging | include error |
| CPU/Memory | show processes cpu sorted, show memory statistics |