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Sunday, December 16, 2018

3D printed jet engine

I 3D printed a jet engine. It's not a scale of any particular engine, and the mixer is wacky, but it has all of the major components and was free, so I can't complain too much. Definitely the most complicated thing I've printed to date.

Took a few months of off and on printing to finish all of the parts. Most parts had to be printed multiple times to get them to come out nicely. It took about 5 hours to assemble, much of which was spent trying to get it to turn smoothly without any rubbing. The final product is pretty nice.

I also printed a bunch of other things recently, and updated this post with them.

Friday, December 14, 2018

Internet Upgrade

We recently upgraded from BT 50Mbps internet to Virgin 105Mbps internet. Twice the speed for exactly half the cost. Virgin's customer service is worse, and the wifi router built into their modem was much worse than BT's "Smarthub", but it is much faster internet. The virgin quickstart kit is bullshit by the way: unless that property has had virgin internet recently, you'll have to have an engineer come out to get everything working: I think you can select that you don't have the right ports at checkout on their website in order to schedule the engineer. Their customer service agents are all in India and useless.

Anyways, I purchased a TPLink C1200 router to solve the poor range problem. You have to be careful buying routers: there are still many out there with 100Mbps ethernet ports. I'd consider modern to be 4x 1Gbe ports and AC wifi, and the C1200 seemed to have the best range/cost ratio with those options. It works great. I later noticed that there was a cable hook up right behind the server cabinet, so I moved the modem and router to the shelf above my homelab.

Originally, the headnode was connected to the wifi via a usb wifi adapter. This worked ok, but obviously wasn't ideal.

Network diagram drawn with
Now that I have the router close to the homelab, it just makes sense to use a wired ethernet connection for internet. However, I'm out of ethernet ports on the headnode's motherboard. As a reminder, there are two ethernet ports on the motherboard, each connects to one 8 port unmanaged switch and has a static IP assigned. The ethernet ports/switches are on different subnets. One switch is connected to the management ports on all four SM compute nodes for IPMI (administration). The other switch is connected to an ethernet port on all four compute nodes (for MPI, ssh, data transfer, etc). This works well: the headnode can talk to the management controllers over the ipmi interface and ssh to the compute nodes' OSs' over the intranet interface.

I'd like to replace the wifi link with an ethernet link. Since the IPMI network usage is tiny, and I have extra ports on that switch, I realized I could connect the router to that switch without a performance hit. Doing that means that the ethernet adapter on the motherboard connected to the ipmi switch has to have two different static IP addresses and subnets: one for the original ipmi, and one for the router. Turns out this is fairly simple to do using nmtui. Just edit the connection you want to add an IP address to, go to add address, add in the new IP address and subnet mask, e.g., put the router's internal network gateway (usually just the router's IP, which is usually XXX.XXX.XXX.1) as the "gateway" and "dns", then make sure "never use this network for default route" is unchecked, bring the interface up and down, and you should now be able to access both networks from one interface. The route command is useful for troubleshooting. Here are some links I found useful: 1 2 3 4 . And if you need to cross the router between subnets: 1. I also set the static IP for the headnode in the router using the router's administration page (accessed by typing the router's IP into a browser and entering the administrative password) so that the router's DHCP wouldn't try to double assign the headnode's IP.

I also: 1. edited my firewall and moved the ipmi interface to the public zone, 2. updated the ddns (router) and noip settings so I can access it remotely, 3. got all of the wireless devices on the new wifi network.

Yay for more stable internet.