why = WHY_NOT; (Posts about networking)

Configuring a VXLAN interface on a Linux machine

Svedrin — Sun, 23 Jun 2024 10:04:03 GMT

Sometimes you’d like to span a layer2 network across two locations, but you don’t want to (or can’t) use VLANs. An excellent alternative in this situation is VXLAN, which transports the payload traffic via standard ole UDP packets on port 4789. This works easily with unmanaged switches (or switches you don’t have admin access to), and can even be routed across other networks or VPNs. Here’s how to set things up between two Linux boxes, and a FortiGate firewall to top it off.

Running Path MTU Discovery from Windows

Svedrin — Thu, 18 Apr 2024 08:49:25 GMT

When debugging network connectivity issues, sometimes it would be helpful to know what’s the largest packet that can be transferred from one host to another without being fragmented. This is especially helpful when Jumbo Frames or VPNs are involved. The method to find this size is called Path MTU Discovery (PMTUD). It is performed by your OS of choice in the background, but you can also do it manually. In Linux this is easily done, but it’s also possible from Windows. Here’s how.

Sysadmin Life Hack: Syslog and NodeRed, a match made in heaven

Svedrin — Sat, 24 Feb 2024 20:18:15 GMT

I recently wanted to react to events detected by some obscure hardware monitoring device, using NodeRED. I was not exactly sure how to achieve this, because the device doesn’t really offer any method of accessing it via an API or something. Of course these devices often can send mail or SNMP traps, but I didn’t want to involve a mail server or deal with OIDs, so I kept looking for a different solution.

Another protocol that is actually quite widely supported is syslog. Since I had a syslog-ng instance running to send logs to Loki, I wondered if it would be possible to also send the logs to MQTT. Indeed this works, and it allowed me to implement my use-case quite easily. But ever since, I kept finding new applications for this: The syslog protocol is ubiquitous, and even the cheapest routers support it.

I’m going to lay out a few details on how it works.

HKP port number

Svedrin — Tue, 07 Jul 2020 21:06:22 GMT

The port number used by GnuPG’s HKP protocol is 11371.

Just saying.

Fun with dhcpd hooks

Svedrin — Sat, 05 Sep 2015 20:15:18 GMT

Today, I found out one of my switches had a hiccup and caused a packet loss of about 80%. This triggered me to build meshping, a distributed ping service that I'm going to integrate with FluxMon in order to notice such stuff more quickly in the future. Of course, I could just use any monitoring tool, but I just can't be arsed to configure one. I need something that configures itself.

Why every (hardware) box on the planet should support LLDP

Svedrin — Fri, 26 Sep 2014 08:04:09 GMT

Recently, I ran across ladvd, an LLDP packet emitter for Linux-based systems. Essentially, it's a little daemon that sits around looking for active network interfaces, and then starts sending out LLDP and/or CDP packets on those interfaces, thereby telling the switches what's connected to them.