Commands

Modules: | 1 | 2 | 3 | 4 | 5 | 6 | 7 | All |

Module 1-7 and Case Study

Module 1: Documenting and Baselining the Network

1.2.4

Discovering network configuration information

> Router#show version
> Router#show ip interface [type number][brief]
> Switch#show interface [interface-id | vlan vlan-
> id] [pruning | status [err-disabled] | switchport [allowed-vlan | prune-elig | native-vlan]] | trunk] [ | {begin | exclude | include} expression]
> Router#show ip protocols
> Router#show spanning-tree [bridge-group] [active | backbonefast | blockedports | bridge | brief | inconsistentports | interface interface-id | pathcost method | root | summary [totals] | uplinkfast | vlan vlan-id] [ | {begin | exclude | include} expression]
> Router#show cdp neighbors [interface] [detail]
> Router#show cdp entry {* | device-name[*] [protocol | version]}
> Switch#show etherchannel [channel-group-number] {brief | detail | load-balance | port | port-channel | summary} [ | {begin | exclude | include} expression]
> Router#show tech-support [page] [password]

Module 2: Troubleshooting Methodologies and Tools

2.2.2

Bottom-up

> ping
> traceroute

Module 3: Troubleshooting at the Physical Layer

3.1.5

Noncritical characteristics - console messages

> Router#show interface
> Router(config-if)#no keepalive

3.3.1

End-system commands - common commands

> ping {host | ip-address}
> arp -a
> netstat -r
> netstat -n

3.3.2

End-system commands - Windows only

> ipconfig /all (Windows NT/2000/XP)
> tracert [destination]
> winipcfg (Windows 9x)

3.3.3

End-system commands - UNIX/Mac OS

> ifconfig -a
> traceroute

3.3.4

Common Cisco IOS commands

> Router#clear counters
> Router#debug {option}
> Router#diag [slot]
> Router#ping {host | ip-address}
> Router#traceroute {host | ip-address}
> Router#undebug all

3.3.5

Cisco IOS show commands

> Router#show arp
> Router#show buffers
> Router#show cdp neighbors
> Router#show context
> Router#show controllers
> Router#show diag [slot]
> Router#show diagbus [slot]
> Router#show environment
> Router#show interface
> Router#show ip interface [brief]
> Router#show logging
> Router#show mac-address table {module/port}
> Router#show memory
> Router#show module
> Router#show port {module/port}
> Router#show port status
> Router#show processes cpu
> Router#show processes memory
> Router#show running-config
> Router#show stacks
> Router#show tech-support
> Router#show version

3.4.2

Cabling faults - CAT5

> ipconfig /all (Windows NT/2000/XP)
> ifconfig -a (UNIX/Mac OS)

3.5.5

Interface configuration

> Switch#no switchport

3.6.2

ARP Command

> Router#arp -s ip-address mac address
> Router#arp -d ip address

3.6.3

Solving common problems - Windows, UNIX/Mac OS end-system commands

> For Windows 2000 and XP:
> ipconfig
> ipconfig /release
> ipconfig /renew

> For UNIX and Mac OS:
> ifconfig -a

3.6.4

Solving common problems - Cisco IOS commands

> Router#clock rate {value}
> Router#configure terminal
> Router#copy running-config starting-config
> Router#disable
> Router>enable
> Router(config-if)#encapsulation {options}
> Router(config)#exit
> Router(config)#interface {type} {slot/number}
> Router(cnofig-if)#no shutdown
> Router(cnofig-if)#shutdown

Module 4: Layer 2 Troubleshooting

4.1.2

No component above the data link layer is functional

> Router#show cdp neighbor
> Router#ping
> Router#show interfaces

4.1.6

Layer 2 to Layer 3 address mapping errors

> Router#show arp
> Router(config-if)#no frame-relay inverse-arp
> Router#clear arp-cache
> Router#show cdp neighbor detail
> Router#show frame-relay map

4.2.2

Microsoft Windows end-system commands

> winipcfg
> ipconfig /all
> tracert
> netstat -r
> netstat -n
> arp -a

4.2.3

UNIX/Mac operating systems end-system commands

> ifconfig -a
> traceroute

4.2.4

General Cisco IOS commands

> Router#ping {host | ip-address}
> Router#trace [destination]
> Router#clear counter
> Router#debug ?
> Router#debug {option}
> Router#undebug all

4.2.6

The show cdp neighbor command

> Router(config)#show cdp neighbors
> Router(config)#cdp run
> Router(config-if)#cdp enable

4.3.2

Troubleshooting STP loops

> Switch(config)#spanning-tree vlan vlan-ID
> Switch#show spanning-tree [vlan vlan-ID]

4.3.3

Preventing STP loops

> Switch#show udld [interface-ID]
> Switch(config)#udld enable
> Switch(config-if)#udld enable

4.3.6

Troubleshooting Ethernet switch flooding

> Switch(config-if)#switchport port-security
> Switch(config-if)#switchport port-security maximum maximum
> Switch#show spanning-tree [vlan vlan-ID]
> Switch#show mac-address-table

4.3.7

Troubleshooting VTP misconfiguration

> Switch#show vtp status

4.3.8

Troubleshooting EtherChannel

> Switch(config)#port-channel load-balance [dst-mac | src-mac]

4.4.1

T1 Framing errors

> Router#show controllers t1 [slot/port]
> Router(config-controller)#clock source {line {primary | secondary} | internal}
> Router(config-controller)#framing {sf | esf }
> Router(config-controller)#cablelength long [dbgain-value dbloss-value]
> Router(config-controller)#cablelength short {133 | 266 | 399 | 533 | 655}
> Router(config-controller)#linecode {ami | b8zs | hdb3}

4.4.2

Troubleshooting ISDN primary rate switch types

> Router(config)#isdn switch-type switch-type
> Router(config-if)#isdn switch-type switch-type
> Router(config-controller)#pri-group timeslots range

4.4.3

Troubleshooting ISDN BRI to telco communications

> Router#show isdn status
> Router(config-if)#isdn twait-disable
> Router#debug isdn q921

4.4.4

Troubleshooting ISDN BRI to dialer problems

> Router#debug dialer events

4.4.5

Debugging ISDN call setup failures

> Router#debug isdn q931

4.5.1

Steps for troubleshooting Frame Relay

> Router#show interfaces [type number] [first] [last] [accounting]
> Router#show frame-relay lmi [type number]
> Router#show frame-relay pvc
> Router#show frame-relay map
> Router#debug frame-relay lmi [interface name]
> Router#debug frame-relay events
> Router#debug frame-relay packet [interface name [dlci value]]

4.6.1

Link Control Protocol

> Router#debug ppp negotiation

4.6.2

Troubleshooting PPP authentication PAP

> Router(config)#username name {nopassword | password password | password encryption-type encrypted-password}
> Router(config-if)#ppp pap sent-username username password password
> Router#debug ppp authentication
> Router(config-if)#ppp authentication {protocol1 [protocol2...]} [if-needed] [list-name | default] [callin] [one-time]
> Router(config-if)#ppp chap refuse [callin]

4.6.5

OSPF in an NBMA environment

> Router(config-if)#ip ospf network {broadcast | non-broadcast | {point-to-multipoint [non-broadcast] | point-to-point}}

4.6.6

The keyword broadcast

> Router(config-if)#frame-relay map protocol protocol-address dlci [broadcast] [ietf | cisco]
> Router(config-router)#neighbor ip-address [priority number] [poll-interval seconds] [cost number] [database-filter [all]]
> Router(config-if)#ip ospf network {broadcast | non-broadcast | {point-to-multipoint [non-broadcast] | point-to-point}}

Module 5: Layer 3 Troubleshooting

5.1.2

Isolating the problem methodology

> Router#ping
> Router#traceroute
> Router#show interface
> Router#show ip interface
> Router#debug

5.2.1

Static routes and classful lookups

> Router#ip classless
> Router#show ip route
> Router#debug ip routing

5.3.2

Missing or incorrect network or neighbor statement

> Router#show ip protocols
> Router#show ip interface
> Router#show ip interface brief
> Router#show ip eigrp interfaces
> Router#show ip eigrp neighbors
> Router#show ip ospf neighbor
> Router#show ip ospf interface
> Router#debug ip routing
> Router#debug ip rip
> Router#debug ip eigrp
> Router#debug ip igrp events [ip-address]
> Router#debug ip igrp transactions [ip-address]
> Router#debug ip ospf events
> Router#debug isis adj packets
> Router#debug isis update-packets

5.3.5

Access list blocking

> Router(config)#ip access-group {access-list-number | access-list-name}{in | out}
> Router(config)#debug ip packet

5.3.7

Passive interface

> Router(config-router)#passive-interface {interface-type interface-number}

5.4.7

Large routing tables

> Router(config-router)#ip summary-address rip ip-address ip-network-mask

5.5.5

Candidate default

> Router(config-router)#default-information originate
> Router(config)#redistribute static
> Router(config)#ip default-network

5.6.1

Mismatched K values

> Router(config-router)#metric weights qos k1 k2 k3 k4 k5

5.6.3

Stuck in active-determining the problem

> Router#show ip eigrp topology [active | pending | zero-successors]

5.7.1

Mismatched parameters

> Router#debug ip ospf adj

5.7.5

Forwarding address is not know through the intra-area or inter-area route

> Router(config-router)#area area-id range ip-address mask [advertise | not-advertise] [cost cost]
> Router#show ip ospf database [external]
> Router#debug ip route
> Router(config)#route-map map-tag [permit | deny] [sequence-number]

5.7.6

Route summarization problems

> Router#show ip ospf [process-id] summary-address

5.7.8

SPF Calculation and route flapping

> Router#debug ip ospf monitor
> Router#show log

5.8.1

IS-IS adjacency problems

> Router#show clns area-tag is-neighbors [type number] [detail]
> Router#debug isis adj-packets
> Router#show clns neighbors [detail]

5.8.2

Some or all of the adjacencies are not coming up

> Router(config-router)#is-type [level-1 | level-1-2 | level-2-only]
> Router#debug isis adj-packet

5.8.3

Adjacency is stuck in INIT state

> Router#show clns area-tag is-neighbors [type number] [detail]
> Router#show clns interface
> Router#debug isis adj-packet

5.8.6

Route flapping problem

> Router#show isis area-tag spf-log
> Router#debug isis spf-events
> Router#debug isis spf-triggers
> Router#debug isis spf-statistics
> Router#debug isis update-packet
> Router#debug isis adj-packet

5.9.1

Troubleshooting BGP neighbor relationships

> Router#show ip bpg summary
> Router#show ip bgp neighbors
> Router#debug ip bgp

5.10.2

Redistribution problems with IGRP/EIGRP

> Router(config-router)#neighbor {ip-address | peer-group-name} default-originate [route-map map-name]
> Router(config-router)#default-metric
> Router(config-router)#neighbor {ip-address | peer-group-name} distribute-list {access-list-number | expanded-list-number | access-list-name| prefix-list-name} {in | out}

Module 6: Layer 4 Troubleshooting

6.2.2

Gathering information on ACL operation

> Router#show logging [history | slot slot-number | summary]
> Router#show ip access-list [access-list-number | access-list-name]
> Router#clear access-list counters {access-list-number | access-list-name}

6.2.5

Gathering information on NAT configuration and operation

> Router#show ip nat statistics
> Router#show ip nat translations [verbose]
> Router#debug ip nat [access-list | detailed | h323 | pptp]
> Router#clear ip nat translation {* | [inside global-ip local-ip] [outside local-ip global-ip]}

6.2.6

Other useful information

> Router(config)#logging on
> Router(config)#logging buffered [buffer-size | level] Router#clock set hh:mm:ss day month year
> Router#clock set hh:mm:ss month day year
> Router(config)#ntp peer ip-address [version number] [key keyid] [source interface] [prefer] Router(config)#clock timezone zone hours-offset [minutes-offset]
> Router(config)#service timestamps message-type [uptime]
> Router(config)#service timestamps message-type datetime [msec] [localtime] [show-timezone]

6.3.3

Gathering transport layer information on UNIX machines

> man [tool_name]
> ipfwadm (UNIX kernel version 2.0)
> ipchains (UNIX kernel version 2.2)
> iptables (UNIX kernel version 2.4)
> ifconfig
> netstat
> route
> ip
> netcat

6.3.4

Common issues with NetBIOS networks

> netbios-name-server name-server-address
> netbios-node-type type

6.3.5

Gathering NetBIOS information

> netstat
> nbstat

6.4.3

Solving the component problems

> router(config-ext-nacl)#deny protocol source source-wildcard destination destination-wildcard [precedence precedence] [tos tos] [log] [time-range time-range-name]
> Router(config)#ip nat translation [max-entries] {timeout | udp-timeout | dns-timeout | tcp-timeout | finrst-timeout | icmp-timeout | syn-timeout | port-timeout} seconds

6.4.4

Dynamic NAT and extended ACLs

> Router(config)#ip nat translation timeout seconds
> Router(config)#ip nat translation udp-timeout seconds
> Router(config)#ip nat translation dns-timeout seconds
> Router(config)#ip nat translation tcp-timeout seconds
> Router(config)#ip nat translation finret-timeout seconds

Module 7: Layer 1-7 Troubleshooting

7.1.3

Eliminating Layer 4

> Router#show access-lists [access-list-number | access-list-name]

7.2.2

Common TCP/IP Commands

> Router> ping [protocol] {host-name | system-address}
> Router> trace [protocol] [destination]

7.2.5

System logs

> Router#show stacks
> Router(config)#service timestamps message-type datetime [msec] [localtime] [show-timezone]

7.2.6

Syslog destinations

> Router(config)#logging monitor severity-level
> Router#clear logging
> Router#logging synchronous [level severity-level | all] [limit number-of-buffers] Router#terminal monitor
> Router(config)#logging console level
> Router(config)#logging host-name
> Router(config)#logging trap level

7.3. 3

Terminals and consoles (TELNET, Terminal Services)

> Router#telnet host [port] [keyword]
> Router#debug telnet
> Router(config)#ip telnet source-interface interface

7.3.4

Web traffic

> Router#debug http client {all | api | background | cache | error | main | msg | socket}

7.3.6

File transfer

> Router#copy tftp destination Router#debug tftp

7.3.7

Network Management and Time protocols

> Router(config)#ntp server ip-address [version number] [key keyid] [source interface] [prefer]
> Router(config)#ntp source type number
> Router#show ntp associations [detail]
> Router#show ntp status
> Router#debug snmp packet
> Router#debug ntp {adjust | authentication | events | loopfilter | packets | params | refclock | select | sync | validity}
> Router(config)#snmp-server enable traps [notification-type]
> Router(config)#snmp-server community string [view view-name] [ro | rw] [number] Router(config)#snmp-server host host-addr [traps | informs] [version {1 | 2c | 3 [auth | noauth | priv]}] community-string [udp-port port] [notification-type]
> Router(config)#ntp peer ip-address [version number] [key keyid] [source interface] [prefer]

7.3.8

Name resolution

> Router(config)#ip domain-lookup
> Router(config)#ip name-server server-address1 [server-address2...server-address6] Router(config)#ip domain-list name
> Router(config)#ip domain-name name

7.3.9

Dynamic Host Configuration Protocol (DHCP)

> Router(config)#show ip dhcp binding [ip-address]
> Router(config)#show dhcp {server | lease [interface async [number]]}
> Router(config)#debug ip dhcp server events

7.4.1

Troubleshooting Telnet problems

> Router#show clock [detail]

7.4.2

Troubleshooting HTTP problems

> Router(config-if)#ip http authentication {aaa | enable | local | tacacs}
> Router(config-if)#ip http port port-number
> Router(config-if)#ip http server

7.4.4

Troubleshooting FTP problems

> rommon >?
> rommon >boot
> rommon >reset
> rommon >dir
> rommon >dir flash:
> rommon >tftpdnld
> rommon >IP_ADDRESS= ip-address
> rommon >IP_SUBNET_MASK= subnet-mask
> rommon >DEFAULT_GATEWAY= default-gateway
> rommon >TFTP_SERVER= server-address
> rommon >TFTP_FILE=filename
> Router(config)#ip subnet-zero

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