login on-failure log - not logging?

Recently I needed to enable logging of failed logon attempts in Cisco IOS. There is a "login on-failure log" configuration command which helped me accomplish my goal. While testing I noticed that enabling it on its own didn't produce expected results. Basically failed login attempts didn't show up in the log upon enabling it. In the end I found out that it must be used in conjunction with "login block-for" command to actually log logon attempts.

R3#show login failures
*** No logged failed login attempts with the device.***

This the defualt configuration:

R4#sh login
No login delay has been applied.
No Quiet-Mode access list has been configured.

Router NOT enabled to watch for login Attacks

This is what we see after enabling "login on-failure log":

R3#sh login
No login delay has been applied.
No Quiet-Mode access list has been configured.
All failed login is logged.

Router NOT enabled to watch for login Attacks

This is configuration that we need in order for the router to actually log failed attempts:

R3#sh login
A default login delay of 1 seconds is applied.
No Quiet-Mode access list has been configured.
All failed login is logged.

Router enabled to watch for login Attacks.
If more than 3 login failures occur in 60 seconds or less,
logins will be disabled for 10 seconds.

Router presently in Normal-Mode.
Current Watch Window
Time remaining: 27 seconds.

To set it up we need to do the following:

1. Create local user:

username test privilege 1 password cisco

2. Force use of local authentication database for vty lines:

line vty 0 4
login local

3. Enable logging of failed attempts:

login on-failure log

4. Enable block-for feature:

login block-for 10 attempts 3 within 60

Now the router will log failures:

R3#show login failures
Total failed logins: 1
Detailed information about last 50 failures

Username SourceIPAddr lPort Count TimeStamp
test 10.0.0.2 23 1 00:08:40 UTC Fri Mar 1 2002

R3#sh login
A default login delay of 1 seconds is applied.
No Quiet-Mode access list has been configured.
All failed login is logged.

Router enabled to watch for login Attacks.
If more than 3 login failures occur in 60 seconds or less,
logins will be disabled for 10 seconds.

Router presently in Normal-Mode.
Current Watch Window
Time remaining: 27 seconds.
Login failures for current window: 0.
Total login failures: 1.

More details on Cisco site: https://www.cisco.com/en/US/docs/ios/sec_user_services/configuration/guide/sec_login_enhance.html

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