Cisco Troubleshooting Notes

Cisco's lifecycle: Preparation, planning, design, implementation, operation, optimization
Fault Management
Configuration Management
Bookkeeping Management
Performance management
Security management

Logging console warnings only log messages below level 4 are displayed to the console, and all log information is logged by default

Troubleshooting: 1, define the fault 2, information collection 3, analysis information 4, infer the cause of the failure 5, troubleshoot the potential cause of the failure 6, verification 7, troubleshooting
Classification inquiry information confirming escalation coordination Update report

Troubleshooting methods: 1, from the top and 2, bottom-up Method 3, divide and conquer 4, Tracking flow path method 5, Contrast configuration Method 6, Component replacement method

1. Report fault 2, verify fault 3, define fault 4, allocate fault 5, collect fault 6, escalate fault

1, the elimination of potential failure cause 2, the collection of information 3, the determination of responsibility 4, verification inference 5, escalation failure

Installing devices, adding, removing, changing performance monitoring security audit backup capacity Planning response planning Support User Performance Tuning application software patching network document disaster recovery backup

Define the fault: What do you mean by the fault? Do you have any changes before the fault occurs? Did you find anything unusual before the fault occurred? What is the last time of normal work?

Unassigned section specific paragraphs are stricter than begin

Cisco command failure: Hardware failure, software failure, configuration error
Ping U: Network unreachable M: Destination too busy?: Unknown packet type &: Package lifetime time-out
Show controllers packet and error statistics for hardware interface types
Show Inventory View Cisco's SN number

VLAN 100
Remote-span
Monitor Session 3 Source interface F0/2
Monitor session 3 destination remote VLAN 100

VLAN 100
Remote-span
Monitor session 3 Destination interface F0/1
Monitor session 3 Source remote VLAN 100

Two-layer communication failure reason
Data frame not received on the correct VLAN: The problem may be due to a VLAN or trunk configuration error
Data frame not received on expected port: possible physical failure, spanning tree problem
The MAC address is not registered in the MAC Address table:
Show Mac-address-table
Show VLAN
Show interface Trunk
Show Interface Switchport
Show platform Forward

EtherChannel Fault Point
1. Multiple physical interface configurations that belong to the same channel are inconsistent
2. Inconsistent port configuration on EtherChannel link-to-end
3, EtherChannel bound link traffic imbalance

Two-tier port, three-layer interface
A routed interface does not enable regular two-layer protocols, such as STP and DTP, by default

show ip Route IP mask
Show IP EIGRP Interface View interface table
Show ip eigrp neighbour view Neighbor table

Ospf
1. Hello Timer
2. OSPF area number
3. OSPF area type
4. IP Subnet and subnet mask
5. Authentication type and authentication data

Init: Hello packet not received by neighbor
2-way:other Dr Final State
Exstart
Exchange
LOADING:MTU inconsistent, indicating that the packet could be corrupted or that the router has a memory corruption problem
Full

Redistribute meet the conditions:
1. The route must be in the routing table
2. You need to assign the correct seed metric to the route being redistributed

Disadvantages of NAT: Address translation introduces processing delay, loss of end-to-end IP accessibility, some applications do not support NAT,

Many considerations to consider when working with VPNs
1. Routing
2. Access control list, subnet mask
3. Configuration Error
Show ip NAT Translations
Clear IP Nat Translations

Dhcp
Discover Source Destination 67
Offer Source Destination 68
Request
Ack

Show ip DHCP conflict detects address conflicts

Switch Performance detection
1. Assess whether the nature of the problem is a technical issue
2. Isolate the performance fault to the device, link, or component
3. Diagnose and resolve performance degradation faults at the component level

interface, hardware forwarding, control plane hardware
Show interface f0/0 counters errors

Cisco Troubleshooting Notes