Another must-read masterpiece by Julia Evans: how to get useful answers to your questions.

After a brief coverage of the theoretical aspects of network addressing, it’s time to pay a brief visit to the early data-link-layer addressing solutions, from one address per datagram/frame (SDLC, HDLC) and ignore this address (PPP) to no address on P2P links (SLIP).

One of my readers sent me this age-old question:

Is there a real difference in the underlying hardware of switches and routers in terms of the traffic processing chips and their capabilities in terms of routing and switching (or should I say only switching)?

Let’s get the terminology straight. Router is a technical term for a device that forwards packets based on network layer information. Switch is a marketing term for a device that does something with packets.

Rephrasing the question: is there a hardware difference between a box marketed as a router and another box marketed as a layer-3 switch?

TL&DR: Yes.

I stumbled upon an article praising the beauties of SR-MPLS that claimed:

Yet MPLS, until recently, was deprived of anycast routing. This is because MPLS is not a pure packet switching technology, but has a control plane based on virtual circuit switching.

My first reaction was “that’s not how MPLS works,”¹ followed by “that would be fun to test” a few seconds later.

I don’t think I’ve ever met someone saying “I wish my web application would run slower.” Everyone wants their stuff to run faster, but most environments are not willing to pay the cost (rearchitecting the application). Welcome to the wonderful world of PowerPoint “solutions”.

The obvious answer: The Cloud. Let’s move our web servers closer to the clients – deploy them in various cloud regions around the world. Mission accomplished.

Not really; the laws of physics (latency in particular) will kill your wonderful idea. I wrote about the underlying problems years ago, wrote another blog post focused on the misconceptions of cloudbursting, but I’m still getting the questions along the same lines. Time for another blog post, this time with even more diagrams.

One of ipSpace.net subscribers wanted to see a real-life examples in the Overlay Virtual Networking webinar:

I would be nice to have real world examples. The webinar lacks of contents about how to obtain a fully working L3 fabric overlay network, including gateways, vrfs, security zones, etc… I know there is not only one “design for all” but a few complete architectures from L2 to L7 will be appreciated over deep-dives about specific protocols or technologies.

Most ipSpace.net webinars are bits of a larger puzzle. In this particular case:

Vincent Bernat and his team open-sourced Jerikan, a production-grade network configuration management system.

It might not be immediately applicable to your network, but I’m positive you could find tons of good ideas in it.

I read tons of articles debunking the blockchain hype, and the stupidity of waisting CPU cycles and electricity on calculating meaningless hashes; here’s a totally different take on the subject by Avery Pennarun (an update written ten years later).

TL&DR: Bitcoin is a return to gold standard, and people who know more about economy than GPUs and hash functions have figured out that’s a bad idea long time ago.

After Non-Stop Forwarding, Stateful Switchover and Graceful Restart, it’s time for the pinnacle of high-availability switching: Non-Stop Routing (NSR)¹.

The PowerPoint-level description of this idea sounds fantastic:

• A device runs two active copies of its control plane.
• There is no cold/warm start of the backup control plane. The failover is almost instantaneous.
• The state of all control plane protocols is continuously synchronized between the two control plane instances. If one of them fails, the other one continues running.
• A failure of a control plane instance is thus invisible from the outside.

If this sounds an awful lot like VMware Fault Tolerance, you’re not too far off the mark.

One of my readers sent me an age-old question:

I have my current guest network built on top of my production network. The separation between guest- and corporate network is done using a VLAN – once you connect to the wireless guest network, you’re in guest VLAN that forwards your packets to a guest router and off toward the Internet.

Our security team claims that this design is not secure enough. They claim a user would be able to attach somehow to the switch and jump between VLANs, suggesting that it would be better to run guest access over a separate physical network.

Decades ago, VLAN implementations were buggy, and it was possible (using a carefully crafted stack of VLAN tags) to insert packets from one VLAN to another (see also: VLAN hopping).