May 2018 – SDN Clinic

Topology of a Freifunk network

This post is part of the series Building your own Software Defined Network with Linux and Open Source Tools and covers the re-designed topology of the distributed infrastructure.

From a birds eye perspective, the Freifunk Hochstift infrastructure mainly consists of three building blocks:

Distributed servers hosted in data centers in Paderborn as remotely in Germany providing infrastructure services
Wireless backbones within the city centers of Paderborn, Warburg, etc.
Freifunk nodes at homes, shops, enterprises, or elsewhere

This post will focus on the distributed servers as well as the wireless backbones and will only cover the around 1.000 client nodes from the perspective of connecting them to the backbone (“gateways“).

With all the things mentions in Specifics and history of a Freifunk network in mind I got back to the drawing board and thought about a new design.

Continue reading Topology of a Freifunk network

GulaschProgrammierNacht 2018 – Awesome talks, fiber cuts and a lot of fun

As every year some weeks after the EasterHegg, the GulaschProgrammierNacht (GPN18) took place at Hochschule für Gestaltung (HFG) and Zentrum für Kunst und Medien (ZKM) in Karlsruhe. It’s a four day event with a lot of lectures, workshops, Gulasch, a lounge and other amazing things; like any chaos event. As usual the C3VOC did an amazing job streaming and recording (nearly) all sessions!

Awesome talks

The GPN had a huge programm with so many technical, cultural, social, … sessions. I would like to especially highlight Alles was ihr schon immer über Glasfasern wissen wolltet (de) by Marc & Momo, Moderne Kommandozeilen-Werkzeuge (de) + Standards – Gut, dass so Viele zur Auswahl stehen (de) by Martin as well as One Brain, One Keyboard, One Editor (en) by Miro.

The network

At the NOC – as always – we had some fun with shiny hardware and running a 4,5 day conference ISP for fun and Tschunk. This year Juniper and Arista provided some nice boxes which made up the core of the GPN network. An Arista DCS-7280SR was the core and border router and connected the GPN18 to the world with 120Gbit/s, a Juniper QFX5100 distributed all that bandwidth within the building, which appeared to be a setup we might want to adopt for future GPNs. As it turns out Aristas Cisco-like CLI is not quite cisco, but better 🙂

As it happens, not everything went after plan and we have a major downtime in the middle of the night due to a fiber cut and a misconfiguration coming together – Murphy must have been at the GPN, too. We had built a 2x40Gb/s LAG with two redundant paths from core to distribution, but one interfaces was in 4x10G mode instead of 1x40G and therefor not part ofthe LAG (so check your ports kids!) and one fiber patch of the active path was taped to the wall and broken by accident. Luckily it was in the middle of the night.

Arista’s not Cisco – Nifty CLI features

At GPN18 we had an Arista DCS-7280SR as our core and border router. The Cisco-like CLI made it easy to configure the system as I know my way around IOS*.

While setting up the final BGP sessions to our upstreams at the GPN18 we by accident found out that Arista supports watch on their CLI which is quite awesome when you want to see if your peering are coming up.

router> watch sh ip bgp summary

The next thing Arista can do which Cisco can’t is show active. When you are in a config stanza like an interface, access-list or router bgp 13020, you can print the current configuration of this sub-tree; in configure mode! This is something every Cisco admin would love to have as it’s not possible to do a show running-config <thingy> for most parts of the config tree and you have to fiddle around with show running-config | section <something>.

As we grew fond of show active really fast we wanted to use it to verify our access-list changes etc. and were wondering why they didn’t show up in show active directly after attemping the chance.

core-hfg#sh ip access-lists bgp
IP Access List bgp
 10 permit tcp host 1.2.3.4 any eq bgp
 20 permit tcp host 2.3.4.5 any eq bgp
 30 permit tcp host 3.4.5.6 any eq bgp

core-hfg#conf t
core-hfg(config)#ip access-list bgp
core-hfg(config-acl-bgp)#40 permit tcp host 9.8.7.6 any eq bgp
core-hfg(config-acl-bgp)#show active 
ip Access List bgp
 10 permit tcp host 1.2.3.4 any eq bgp
 20 permit tcp host 2.3.4.5 any eq bgp
 30 permit tcp host 3.4.5.6 any eq bgp

It turns out some config changes only get active when you leave the block you were editing, which is another subtle difference to Ciscos behavior!

core-hfg(config-acl-bgp)#exit
core-hfg(config)#ip access-list bgp
core-hfg(config-acl-bgp)#show active 
ip Access List bgp
 10 permit tcp host 1.2.3.4 any eq bgp
 20 permit tcp host 2.3.4.5 any eq bgp
 30 permit tcp host 3.4.5.6 any eq bgp
 40 permit tcp host 9.8.7.6 any eq bgp

Update:

Some changes are applied immediately on interface level, for example (no) shut, VLAN changes, … These are visible in show active as expected. Thanks for Nico for the clarification!