I work in an enterprise with tens of thousands of devices owned by dozens of offices and groups. I’m also one of the people tasked with pushing IPv6 adoption inside of that enterprise! A lot went into planning our IPv6 scheme, but that’s outside of the focus of this blog post. Instead, I’ll be writing about some PowerShell I wrote to make sure all of these disparate system owners use our planned scheme correctly:<\/p>\n\n\n\n
PowerShell was chosen for the original cmdlet because I wanted anyone and everyone in my organization to be able to take an IPv4 address and quickly be able to determine what the “matching” IPv6 address should be, without any outside dependencies. This original cmdlet became the core for a project to speed up the process of replicating IPv4 access to IPv6 on our firewalls.<\/p>\n\n\n\n
We planned out our IPv6 scheme to include address bits for the physical site, for the VLAN (this is just the VLAN number translated DEC:HEX), for the last octet of the original address, and a few other bits in the same vein – gotta keep this a little vague for security reasons! After the general scheme was drawn up our network team created a master Excel “lookup” workbook with data reference tables for all of those address bits. For example, VLAN 100 could be the San Franciso office, with the site ID arbitrarily set to 0E3.<\/p>\n\n\n\n
The Excel sheet was useful – as long as you knew the site and the VLAN it was simple enough to enter the original IPv4 address, the VLAN ID, and the human readable site name and have a cell on the first sheet calculate the full IPv6 address. A little cumbersome if you have to do several addresses, but completely useable.<\/p>\n\n\n\n
After a few days of heavy use of the spreadsheet, I got fed up with manually clicking the dropdowns and copying and pasting. I recalled how at a previous job I assisted the accounting team with end-of-month paperwork by using MSWord COM objects to open up their prebills and work some regex magic to extract client names and IDs and how much we were billing them, thereby replacing their manual process. What I can do in Word, I can do in Excel, right? The idea was born: write a PowerShell script that opens up Excel in the background, passes arguments into the correct cells, and then extracts the resulting address and puts it right back into the command line.<\/p>\n\n\n\n
The PowerShell to open up and utilize an Office application is actually pretty simple, it looks something like this:<\/p>\n\n\n\n