IP subnetting

IPv4 subnetting calculator

IPv4 subnetting questions

Videos

CCENT Subnetting Part 1 of 2

CCENT Subnetting Part 2 of 2

Solve a VLSM subnet problem Cisco CCNA

Subnetting made easy subnet 101 Only 16 minutes to become Subnet Guru!

IP Subnetting – Cheatsheet

Quick Subnetting Review

Subnetting Table 
Network Bits Subnet Mask Number of Subnets Number of Hosts
 /8  255.0.0.0  0  16777214
 /9  255.128.0.0  2 (0)  8388606
 /10  255.192.0.0  4 (2)  4194302
 /11  255.224.0.0  8 (6) 2097150
 /12  255.240.0.0  16 (14)  1048574
 /13  255.248.0.0  32 (30)  524286
 /14  255.252.0.0  64 (62)  262142
 /15  255.254.0.0  128 (126)  131070
 /16  255.255.0.0  256 (254)  65534
 /17  255.255.128.0  512 (510)  32766
 /18  255.255.192.0  1024 (1022)  16382
 /19  255.255.224.0  2048 (2046)  8190
 /20  255.255.240.0  4096 (4094)  4094
 /21  255.255.248.0  8192 (8190)  2046
 /22  255.255.252.0  16384 (16382)  1022
 /23  255.255.254.0  32768 (32766)  510
 /24  255.255.255.0  65536 (65534)  254
 /25  255.255.255.128  131072 (131070)  126
 /26  255.255.255.192 262144 (262142)  62
 /27  255.255.255.224  524288 (52486)  30
 /28  255.255.255.240  1048576 (1048574)  14
 /29  255.255.255.248  2097152 (2097150)  6
 /30  255.255.255.252  4194304 (4194302)  2

a

Cisco AAA, TACACS+, and SSH

conf term
enable secret Veryd!fficult
!
username admin privilege 15 secret hard-passw0rd
! Turn on SSH
ip domain-name ipvanquish.com
crypto key generate rsa modulus 1024
!
! Enable AAA
aaa new-model
!
tacacs-server 10.1.1.222
tacacs-server ipvanquish293
!
aaa authen login default group tacacs+ local
!
management-interface fastethernet0/1 allow ssh
!
do debug AAA authentication
!
do show run | inc user
!

MicroNugget: AAA, TACACS+, and SSH

How to install tacacs+ on Linux Centos

Cisco Automation Backup Script With Python Telnet and SSH

Python automation scripts ciscoBy Kirk Byers

https://www.oreilly.com/ideas/practical-network-automation-using-python-and-ansible + Netmiko

https://rootbridge.wordpress.com/2015/08/14/linux-python-cisco-backup-script/
Cisco Router Backup Script With Python and Telnet

Network Automation 4 (Python + Ansible + Paramiko on Cisco Switcher)

Automating Cisco commands with C.R.A.SSH
Automating Cisco Switch Interactions

Automation scripts to control Cisco devices

https://pynet.twb-tech.com/blog/automation/netmiko.html

https://gns3.com/news/article/network-automation-using-python-

Automate SSH connections with netmiko

https://codingnetworker.com/2016/03/automate-ssh-connections-with-netmiko/

http://rapidtechguide.blogspot.co.nz/2013/03/telnet-automation-using-python-copy.html

aaa

Cisco access ROMMON mode with reverse telnet aux.

If you are using putty with serial port. To access rommon mode press

Ctrl + Shift + Break or Pause.

And if you are using Terra Term with serial port press

Alt + B

Configure aux 0 for reverse telnet.

conf term
line aux 0
 modem InOut
 transport input all
 exit
!

How to find line number for aux 0

R01#show line
   Tty Line Typ     Tx/Rx    A Modem  Roty AccO AccI  Uses  Noise Overruns  Int
      0    0 CTY              -    -      -    -    -     0      0    0/0      -
*     1    1 AUX   9600/9600  - inout     -    -    -     0      0    0/0      -
*   514  514 VTY              -    -      -    -   50     1      0    0/0      -
    515  515 VTY              -    -      -    -   50     0      0    0/0      -
!

Now that found line number for aux 0 is line number 1.
IP address of the router 2000 + line number 1
Is telnet 10.1.1.1 2001

R01#telnet 10.1.1.1 2001
Trying 10.1.1.1, 2001 ...
% Connection refused by remote host

R01#clear line 1
[confirm]
 [OK]
R01#telnet 10.1.1.1 2001
Trying 10.1.1.1, 2001 ... Open

User Access Verification

Username: admin
Password:
PPPOE#
PPPOE#
PPPOE#


Then what to do with reverse telnet how to access rommon mode ?

( Ctrl + Shift + 6 ) release and then press B

System Bootstrap, Version 12.4(13r)T11, RELEASE SOFTWARE (fc1)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 2009 by cisco Systems, Inc.

Initializing memory for ECC
.
c2811 platform with 262144 Kbytes of main memory
Main memory is configured to 64 bit mode with ECC enabled


Upgrade ROMMON initialized
PC = 0xbfcd0d54, Cause = 0x2000, Status Reg = 0x3040a803

monitor: command "boot" aborted due to user interrupt
rommon 1 >
rommon 1 >
rommon 1 >
rommon 1 > confreg 0x2142


You must reset or power cycle for new config to take effect
rommon 2 > reset

After reset.


Router>en
Router#copy start running-config
Destination filename [running-config]?

2991 bytes copied in 12.400 secs (241 bytes/sec)
PPPOE#
PPPOE#conf term
Enter configuration commands, one per line.  End with CNTL/Z.
PPPOE(config)#config 0x2102
PPPOE(config)#end
PPPOE#
*Apr 30 04:55:47.419: %SYS-5-CONFIG_I: Configured from console by console
PPPOE#show version

Configuration register is 0x2142 (will be 0x2102 at next reload)

PPPOE#

Then to exit reverse telnet.

( Ctrl + Shift + 6) release and then press X

https://supportforums.cisco.com/discussion/11390416/how-do-you-send-break-putty-cisco-2600-terminal-server

http://www.cisco.com/c/en/us/td/docs/ios/termserv/configuration/guide/15-mt/tsv-15-MT-book/tsv_dialin_term_svcs.html

https://networklessons.com/network-services/cisco-terminal-server-configuration-example/

http://ciscofaq.blogspot.com/2005/05/how-to-i-reverse-telnet-out-my-aux.html

https://supportforums.cisco.com/discussion/10680346/me-3400-password-recovery