May I Borrow your IPv4?

Junxiao Shi

2023-09-09

With the rise of IPv4 costs, IPv6-only servers are becoming more popular in low end hosting world. In one occasion, I acquired an IPv6-only server, but wanted to have IPv4 on it. Somewhere else, I have a dual-stack IPv4+IPv6 server, idling away. Can I "borrow" the IPv4 of that dual-stack server, to use on the IPv6-only server? I tried several methods, and found a way to make this work.

Situation / Assumption / Requirement

In this case, both servers have KVM virtualization and are running Debian 12 operating system. Server A is a dual-stack server, with IPv4 address 192.0.2.158 and IPv6 address 2001:db8:aefc::2. Server B is an IPv6-only server, with IPv6 address 2001:db8:eec0::2. At server A, both IPv4 and IPv6 service are delivered on the same network interface.

My goal is to somehow "move" the IPv4 address from server A to server B. In particular, I want all IPv4 traffic to the 192.0.2.158 destination address to reach server B, and allow server B to send any IPv4 traffic with 192.0.2.158 source address. This shall include all TCP and UDP ports, as well as other IPv4 traffic such as ICMP ping. A "port forwarding" solution would be insufficient, as it cannot deliver non-TCP/UDP traffic.

Tunnel + Ethernet Bridge (does not work)

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Mom Calendar with Adafruit MagTag

Junxiao Shi

2023-06-02

I bought an Adafruit MagTag last year, wanting to play with E-Ink technology. E-Ink, also known as "electronic paper", is a display device that mimics the appearance of paper. A special property of E-Ink is that, it only consumes electricity for changing the displayed content, but does not need electricity to retain the text and images it's already showing. This type of display is often found on E-Readers such as the Amazon Kindle (paid link), where the content doesn't change rapidly and the user would be looking at the same content for several minutes or longer.

After three years of pandemic flight restrictions, my mother was finally able to come from Shanghai and visit me in Maryland. She was here for 70 days, arriving on March 08 and departing on May 17. When I was cleaning the apartment prior to her arrival, I noticed the blank E-Ink display on my wall, and decided to build a calendar that counts mom's visit.

Mom Calendar - Features

The mom calendar shall display number of days since mom's arrival. The day counter starts from 0 on March 08, increments by 1 on each day, and reaches 70 on May 17.

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