Cisco Catalyst 9400 Series Hardware Installation Manual page 147

Troubleshooting
Possible BAUD Mismatch Scenario 1
Description—When you started off, the BAUD variable, start-up configuration and console port speed were
all set to 115200. After this, if you unset the BAUD parameter at some point...
1. This is an implicit change in the BAUD variable to 9600 and not an explicit setting in the ROMMON.
Further, the current console port session speed is still set to 115200 and you still have access.
2. Boot the image—Cisco IOS boots the image normally. The line console speed is initially retrieved from
BAUD (9600), but Cisco IOS parses the startup-configuration, and the speed is changed to 115200. This
matches the current console port speed.
3. Reload or power cycle the switch—Setup goes back to ROMMON mode and console access is lost because
the default BAUD speed of 9600 is effective and mismatched with the console port speed. Set console
port speed to 9600 to restore access.
4. Boot the image—Console port access is lost because the line console speed is initially retrieved from
BAUD (9600), Cisco IOS parses the startup-configuration, where the speed is set to 115200 and not in
sync with console port 9600 speed, and console port access is lost. Access is restored once console port
speed is set to 115200.
5. Reload or power cycle the switch—Setup goes back to ROMMON mode, but console access is lost again
due to mismatched BAUD of 9600.
In the above scenario, note the difference between an unset BAUD in step no.1 (where the implicit speed is
9600) and a set BAUD=9600 command (where the speed is explicitly set using the "set" command in
ROMMON). You are able to access the console until step no.4 because the BAUD has an unset, implicit speed
of 9600, but the speed was not actually changed from 115200. Once you reloaded or power cycled in step
no.5, the speed was set to 9600.
Solution 1—If you save running configuration to start-up configuration (copy system:running-config
nvram:startup-config) at step no. 2 then BAUD and the startup-configuration are synchronized with speeds
at 115200, and subsequent reloads will not interrupt access.
Solution 2—(Instead of performing the above steps) Configure the line console speed to 9600, change the
console port speed to 9600, and then save running configuration to start-up configuration, then BAUD in
ROMMON and startup-configuration will be synchronized with speeds at 9600.
Possible BAUD Mismatch Scenario 2
Description—When you started off, the BAUD environment variable, startup-configuration speed and console
port speed were all 9600. (The BAUD and startup configuration speeds have not been set explicitly). After
this, at some point you explicitly set the BAUD variable to 115200...
1. You lose console access immediately. Set the console port speed to 115200 to restore access.
2. Boot the image—Line console speed is initially retrieved from BAUD (115200). While booting, the
system parses the startup-configuration, but even though the configured speed is 9600, this is the value
that the system defaults to, and the "speed 9600" line is not actually present in startup-configuration. Since
the speed configuration is not present, it is not explicitly parsed and applied, so the speed retrieved from
BAUD previously (115200) is used.
In this state, the line console speed is set to 115200, matching BAUD, while the startup-configuration has
line console speed as default (9600). The system is useable since the speed was not changed to 9600, even
with the BAUD and startup-configuration mismatch. If you save running configuration to start-up
configuration, then BAUD and startup-config will be in sync with speeds explicitly set to 115200.
Cannot Connect to a Switch Through the Console Port
Cisco Catalyst 9400 Series Switches Hardware Installation Guide
141