Cisco IOS Command Tips and Tricks – Part 1

7. Basic Commands to Enable Telnet/SSH on Cisco Devices

a. Telnet Access

no aaa new-model
username test privilege 15 secret test
line vty 0 15
login local
no password
transport input telnet

b. SSH Access:

hostname Switch1
ip domain-name test.com
crypto key generate rsa general-usage modulus 2048
ip ssh time-out 60
ip ssh version 2
line vty 0 15
transport input ssh

c. Console Access with username/password:

line con 0
login local
exit

 cli write

Another example to run TCL script script.tcl with specific user jonny:kron occurrence tcl_occur user jonny in 12:0 recurring
policy-list tclpol
kron policy-list tclpol
tclsh flash:/script.tcl

10. Enable IP Accounting on interface

IP accounting doesn’t quite provide much functionality, but it certainly provides a summary of traffic passing through a router. The router will only record packets that goes through the router. Any connections initiated from the router or terminates to the router are not counted.

interface GigabitEthernet0/1
ip address 100.199.48.15 255.255.255.0
ip accounting output-packets
duplex full
speed 100
end

R1#sh ip accounting
Source Destination Packets Bytes
100.199.48.10 100.199.3853 6 241
100.199.38.53 100.199.48.10 4 183
138.11.117.16 166.6.23.14 1 104

Accounting data age is 3w0d

11. Show configuration without break/pause @Cisco Router/Switch
terminal length 0

@ASA Firewall
terminal pager 0

12. Debug commands at Cisco ASA 9.1(2)

debug crypto ipsec 127
debug crypto ikev1 127

13. Display Cisco IOS Device Opened Ports

R#show control-plane host open-ports
Active internet connections (servers and established)
Prot               Local Address             Foreign Address                  Service    State
 tcp                        *:22                         *:0               SSH-Server   LISTEN
 tcp                        *:23                         *:0                   Telnet   LISTEN
 udp                       *:161                         *:0                  IP SNMP   LISTEN
 udp                       *:162                         *:0                  IP SNMP   LISTEN
 udp                     *:65110                         *:0                  IP SNMP   LISTEN
 udp                      *:1975                         *:0                      IPC   LISTEN

The method how to close ports 23 from external scan is in my post: Close Cisco IOS TCP Ports 23, 2002, 4002, 6002, and 9002 from Network Ports Scanning

14. Native VLAN mismatch

062275: May 12 00:09:37.207 EDT: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on GigabitEthernet0/3 (1), with Swtch1 GigabitEthernet0/5 (56).

although both ports are set as access port and set to different vlan 56 and 1, it should not have this mismatch info.   Solution would be one global command :

no cdp advertise-v2

Or

This solution: using different vtp domain name on those switches:

Switch(config)# vtp mode transparent
Switch(config)# vtp domain a_unique_name

15. IOS Password Recovery Procedures

• Shut down the router then Power on the router
• Press Break on the terminal keyboard within 60 seconds of power up in order to put the router into Rommon. (In some Keyboards, Pause key is used to enter into Rommon mode. You may not need Fn+Pause, or CTRL+ Break)
• Once the Rommon1> prompt appears, enter this command: confreg 0x2142
  Then type reset to reboot Cisco device.
• When you are prompted to enter the initial configuration, type No, and press Enter.
  At the Router> prompt, type enable.
• At the Router# prompt, enter the configure memory command, and press Enter in order to copy the startup configuration to the running configuration.
• Use the config t command in order to enter global configuration mode.
• Use this command in order to create a new user name and password:
  router(config)#username test privilege 15 password test
• Use this command in order to change the boot statement: config-register 0x2102
• Use this command in order to save the configuration: write memory

16. Reload Device in xx minutes 

It is helpful for your remote work just in case you lost connection by mis-configuration

By default, the IOS calculate statistics by interval 5 minutes. The minimal interval is 30 seconds you can set.

interface GigabitEthernet0/0
 ip flow ingress
 load-interval 30
 duplex auto
 speed auto
end

Router#sh interfaces g0/0
GigabitEthernet0/0 is up, line protocol is up
  Hardware is PQ3_TSEC, address is c464.139b.ee00 (bia c464.139b.ee00)
  Description:
  Internet address is
  MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
     reliability 255/255, txload 1/255, rxload 3/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full Duplex, 1Gbps, media type is RJ45
  output flow-control is XON, input flow-control is XON
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:00, output 00:00:00, output hang never
  Last clearing of “show interface” counters never
  Input queue: 0/75/149/0 (size/max/drops/flushes); Total output drops: 15
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  30 second input rate 12706000 bits/sec, 1423 packets/sec  30 second output rate 966000 bits/sec, 957 packets/sec     7877466781 packets input, 4315500899841 bytes, 1023 no buffer
     Received 345354184 broadcasts (0 IP multicasts)
     0 runts, 0 giants, 13 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 520835 multicast, 2112 pause input
     7120190572 packets output, 2103538386166 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     121793930 unknown protocol drops
     0 babbles, 0 late collision, 0 deferred
     4 lost carrier, 0 no carrier, 58519 pause output
     0 output buffer failures, 0 output buffers swapped out

18. Turn off IP Spoof Protection

ip verify reverse-path interface outside
“Deny IP spoof from (10.245.6.1) to 192.168.6.25 on interface inside”

19. Create Read only Account

method one.

username local1 secret Cisco1234
username local1 privilege 15 autocommand show running

aaa new-model
aaa authentication login default local
aaa authorization exec default local
aaa authorization console

method two.

aaa new-model
aaa authentication login default local
aaa authorization exec default local
aaa authorization console

username local2 privilege 7 password Cisco1234
privilege exec level 7 show config

The list is getting longer , and I am splitting it to two posts:

• Cisco IOS Command Tips and Tricks – Part 1
• Cisco IOS Command Tips and Tricks – Part 2

Cisco My Device Page

Reference:

• The Cisco Support Community
• How to Buy – Cisco Commerce Tools
• Cisco Tool – Check Device Coverage
• Cisco Tools and Resources
• Cisco Tool – My Devices
• Cisco Active Advisory