Where do we use Cisco Wildcard Masks?

People might still be interested in about Cisco Wildcard Masks. I try to summarize interesting information about Wildcard Masks in this post.

Use Case 1: IPv4 Access Control Lists on Cisco IOS, IOS XE, and IOS XR

Wildcard masks are for us to select only subsets of IPv4 addresses.

Revised post: Covering Subnet Calculator to understand more about Wildcard Mask

This tool is an update to my previous post:

Simple visual tool to calculate Cisco IOS Wildcard Mask

Notes for Cisco IOS Wildcard Mask

You can simply assume Cisco IOS Wildcard Mask are derived by mapping 1s to 0s and 0s to 1s of equivalent subnet mask in binary notation.

Global BGP IPv4 table is around 800K in size

This week the global BGP IPv4 table is around 800,000 entries in size. I bring this up just to give you a head-up and say a “Wow”. I don’t want to make you worry about the number. This is not my intention.

I still remember the “old good time” when I had installed a BGP router (Cisco 3660) with 256 Megabytes of DRAM memory in year 2001. At that time, the BGP table is below 150,000 entries so that router worked well.