1. Restoring the BIG-IP configuration to the factory default setting

Impact of procedure: This procedure removes all BIG-IP local traffic objects, network configuration, and BIG-IP module data. Admin and Root password will be reset to default. Your MGMT interface ip address will be kept.

1.1 Log in to the Traffic Management Shell (tmsh) by typing the following command:
tmsh

1.2 To restore the configuration to the factory default setting, type the following command:
load sys config default

1.3 You are prompted with the following confirmation:
Reset the system configuration to factory defaults? (y/n)

To confirm that you want to restore factory default values, press the following key:
y

1.4 Save the change by typing the following command:
save sys config partitions all

1.5 Reboot the BIG-IP device
reboot


2. Upgrade F5 TMOS

2.1 Download the ISO File from F5 Downloads site.
File name is BIGIP-12.1.2.0.0.249.iso. Make shre verify file’s MD5 value

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2.2 Go to F5 device’s System /Software Management page

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2.3 Import the new download IOS file BIGIP-12.1.2.0.0.249.iso 
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2.4 Install new imported file into HD1.1 partition.
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2.5 Active new software
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Make sure you install configuration from right Source Volume. Else you will lose all configuration in your new software.
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2.6 verify

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Reference: