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Cisco Bug: CSCvs40645 - CLI alias for "exit" command increases time to save running-configuration and may cause timeout

Last Modified

Jan 13, 2020

Products (61)

  • Cisco Nexus 9000 Series Switches
  • Cisco Nexus 3548-X Switch
  • Cisco Nexus 92348GC-X Switch
  • Cisco Nexus 9516 Switch
  • Cisco Nexus 3548 Switch
  • Cisco Nexus 3636C-R Switch
  • Cisco Nexus 9396TX Switch
  • Cisco Nexus 92304QC Switch
  • Cisco Nexus 9396PX Switch
  • Cisco Nexus 92160YC-X Switch
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Known Affected Releases

9.3(2)

Description (partial)

Symptom:
A Nexus device configured with a CLI alias named with a single letter (such as "q") mapped to a command will cause the device to take exponentially longer to save its running-configuration to the startup-configuration, depending upon the number of lines present in the running-configuration. This is only observed when the single case-insensitive letter used for the CLI alias is also used as the delimiting character for the device's MOTD banner.

For example, consider a Nexus 93180YC-FX with 461 lines of configuration, but no CLI aliases configured.

N9K# show running-config | count
461

N9K# show running-config | include alias
N9K# 

The device also has an MOTD banner configured using a single letter as the delimiting character, such as "Q"

N9K# show running-config | section banner
banner motd Q
##################################
# This is an example MOTD banner #
##################################
Q

With this configuration, the device will take approximately 5 seconds to save its configuration.

N9K# show clock ; copy running-config startup-config ; show clock
16:17:49.222 UTC Tue Dec 10 2019
Time source is NTP
[########################################] 100%
Copy complete, now saving to disk (please wait)...
Copy complete.
16:17:55.113 UTC Tue Dec 10 2019
Time source is NTP

Now, with a CLI alias named "q" mapping to the "exit" command configured, the device will take approximately 30 seconds to save its configuration.

N9K# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
N9K(config)# cli alias name q exit
N9K(config)# end
N9K# show running-config | include cli
cli alias name q exit
N9K# show running-config | count
462
N9K# show clock ; copy running-config startup-config ; show clock
17:15:38.417 UTC Tue Dec 10 2019
Time source is NTP
[########################################] 100%
Copy complete, now saving to disk (please wait)...
Copy complete.
17:16:06.682 UTC Tue Dec 10 2019
Time source is NTP

This delay scales exponentially with the lines of configuration present in the device's running-configuration. When the configuration reaches a certain size, the device will fail to save the running-configuration to the startup-configuration entirely. For example, consider a device with 5,672 lines of configuration (including the CLI alias) in the running-configuration

N9K# sh run | count
5672

N9K# sh run | i cli
cli alias name q exit

When attempting to save the configuration, the process eventually aborts after about eight minutes.

N9K# show clock ; copy r s ; show clock
17:46:49.656 UTC Tue Dec 10 2019
Time source is NTP
[########################################]  99%Configuration update aborted: timed out
17:54:51.020 UTC Tue Dec 10 2019
Time source is NTP

When this issue occurs, the following syslogs may be observed:

N9K# show logging logfile | last 3
2019 Dec 10 17:54:50 N9K %SYSMGR-3-CFGWRITE_SRVTIMEOUT: Service "ascii-cfg" failed to store its configuration in the timeout period
2019 Dec 10 17:54:50 N9K %SYSMGR-2-CFGWRITE_ABORTED: Configuration copy aborted.
2019 Dec 10 17:54:50 N9K %SYSMGR-3-CFGWRITE_FAILED: Configuration copy failed (error-id 0x401E0045).

Conditions:
1. Nexus device with a CLI alias using a single-letter case-insensitive character mapping to a command configured, as shown below:

N9K# show running-config | include cli
cli alias name q exit

2. Nexus device also has an MOTD banner configured that utilizes the same character as the delimiting character.

N9K# show running-config | section banner
banner motd Q
##################################
# This is an example MOTD banner #
##################################
Q
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