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JUNOS High Availability by Orin Blomberg, Senad Palislamovic, Kieran Milne, James Sonderegger

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CLI Configuration Automation

In the realm of network engineers and technicians, it is a badge of honor to be a “CLI guy,” someone who is never seen to use a GUI. With some of the legacy operating systems on network devices, this virtue can quickly become a pitfall. Because the operating systems of many network devices apply changes to their active, or running, configuration, simple typos or poorly planned configuration sequences can lead to network downtime. Because these operating systems use instant activation, they lack a way to validate the full command sequence to ensure that all requirements for the configuration are met; instead, they validate only the syntax of individual lines as entered.

Senior network engineers have developed all forms of voodoo rituals, ranging from copying and pasting complete configurations at once to having possibly insecure back doors into equipment, to mitigate the ramifications of errors introduced into the configuration. Although these tricks are often effective, sometimes they themselves cause network downtime or force the engineer to take a trip across the city to reboot a device that is not responding.

Note

In some networks, the engineers believe the only way to ensure that a major configuration change is implemented properly is to erase the startup configuration, reboot the device, and then cut and paste the whole configuration in one fell swoop. Although this process may ensure that the whole new configuration is applied in order, it results ...

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