Tim Spurling

new year, new network

The new year has arrived amidst a wave of upgrades to the office environment, mostly in the human world of furniture, lighting, paint and so on…

But one of the more subtle changes has come from Chris‘s recent obsession with cables. Ripping out unnecessary ones. Being enthusiastic about proper trunking. Expressing incredible annoyance with the crap phone lines. As another cable-obsession-prone individual I have now gotten slightly involved, and wanted to document some of the excitement.

The building has now been equipped with a solid trunk of five Cat6 links between each adjacent pair of floors; allowing for fast (aggregated) connections between each floor’s new managed switch(!), easy connection to the basement cabinet containing ISP equipment, and a bit of room for future expansion.

Diagram of trunks

tv over (some of) the network

MetaBroadcast has also recently acquired some new equipment along with the aforementioned managed Ethernet switches, as a solution to our continual dashboard-displaying problems: some small hardware for sending compressed streams between HDMI ports over Ethernet.

These devices work pretty well but due to their simplicity (using a broadcast MAC address, layer 2, below IP—the same mechanism ARP relies upon), had a nasty habit of spamming every device with a huge stream of unwanted video; making all the activity lights useless, wasting power, and occasionally stuttering when other traffic took over—although at least the packets didn’t make it onto the WiFi.

Fortunately the same simplicity, and the capability of the new switches, meant the problem could be solved with a VLAN. This is basically the allocation of some ports on the switch to a separate network, i.e. a separate broadcast domain.

Ethernet frames arriving at a port assigned to vlan2 (the ones we patch to the HDMI boxes) are “tagged” with an extra field as they go between switches, and then sent only to the assigned ports (with the tags again removed) on each floor. All other links remain silent apart from the traffic they need, providing probably at least a slight improvement to average latency, as well as of course restoring the purpose of the blinkenlights, and solving all the other problems.


Obviously this kind of special behaviour has great potential to confuse anyone who might want to do a bit of rewiring—so we’ve established a grand unified LAN Googledoc to explain everything:

  • The purposes of the trunks (the diagram from above)
  • The allocation of switch ports (the diagram below—helpful when monitoring traffic or looking at wiring)
  • A list of allocated cable colours for each purpose (a nice idea of Tom‘s)
  • Information about routers, DHCP allocations, passwords, etc., etc.

Diagram of switches

So far, I can wholeheartedly recommend this approach.

Happy new year and I hope it has brought comparable excitement to all readers of the blog!

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