Anycast Fundamentals

I got into an interesting debate after I published the Anycast Works Just Fine with MPLS/LDP blog post, and after a while it turned out we have a slightly different understanding what anycast means. Time to fall back to a Wikipedia definition:

Anycast is a network addressing and routing methodology in which a single destination IP address is shared by devices (generally servers) in multiple locations. Routers direct packets addressed to this destination to the location nearest the sender, using their normal decision-making algorithms, typically the lowest number of BGP network hops.

Based on that definition, any transport technology that allows the same IP address or prefix to be announced from several locations supports anycast. To make it a bit more challenging, I would add “and if there are multiple paths to the anycast destination that could be used for multipath forwarding¹, they should all be used”.

Multi-Threaded Routing Daemons

When I wrote the Why Does Internet Keep Breaking? blog post a few weeks ago, I claimed that FRR still uses single-threaded routing daemons (after a too-cursory read of their documentation).

Donald Sharp and Quentin Young politely told me I was an idiot I should get my facts straight, I removed the offending part of the blog post, promised to write another one going into the details, and Quentin improved the documentation in the meantime, so here we are…

Multi-Threaded Routing Daemons

When I wrote the Why Does Internet Keep Breaking? blog post a few weeks ago, I claimed that FRR still uses single-threaded routing daemons (after a too-cursory read of their documentation).

Donald Sharp and Quentin Young politely told me I was an idiot I should get my facts straight, I removed the offending part of the blog post, promised to write another one going into the details, and Quentin improved the documentation in the meantime, so here we are…

Custom Groups and Deployment Templates in netsim-tools

Using custom templates to test IP anycast with MPLS was fun, but as I got into interesting discussions focusing on convoluted details, I found myself going through the same set of steps too many times.

It started with the need to specify individual devices in netlab config command to create new loopback interfaces on anycast servers but not on any other device in the lab. Wouldn’t it be nice to have a group of devices (similar to Ansible groups) that one could use in the limit parameter of netlab config?

netlab Custom Groups and Deployment Templates

Using custom templates to test IP anycast with MPLS was fun, but as I got into interesting discussions focusing on convoluted details, I found myself going through the same set of steps too many times.

It started with the need to specify individual devices in netlab config command to create new loopback interfaces on anycast servers but not on any other device in the lab. Wouldn’t it be nice to have a group of devices (similar to Ansible groups) that one could use in the limit parameter of netlab config?

RFC 9098: Operational Implications of IPv6 Extension Headers

It took more than seven years to publish an obvious fact as an RFC: IPv6 extension headers are a bad idea (RFC 9098 has a much more polite title or it would never get published).

RFC 9098: Operational Implications of IPv6 Extension Headers

It took more than seven years to publish an obvious fact as an RFC: IPv6 extension headers are a bad idea (RFC 9098 has a much more polite title or it would never get published).

Worth Reading: How to Get Useful Answers to Your Questions

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

Worth Reading: How to Get Useful Answers to Your Questions

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

Video: Early Data-Link-Layer Addressing

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).

Video: Early Data-Link-Layer Addressing

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).

Hardware Differences between Routers and Switches

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.

Doing packet forwarding at high speeds is expensive, and simpler forwarding pipeline results in cheaper (or faster) silicon.

If you don’t need complex high-speed functionality (like a thousand interface output queues with per-flow classifier), you create a simpler ASIC and call the device a switch. If you thrive on overpriced products, you create as complex an ASIC as you can make it and call the device using it a router. EX9200 is an obvious counterexample, but then Juniper always looked like DEC of networking to me.

There’s even a difference in capabilities between spine- and leaf data Continue reading

Hardware Differences between Routers and Switches

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.

Anycast Works Just Fine with MPLS/LDP

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.

Anycast Works Just Fine with MPLS/LDP

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.

Optimizing the Time-to-First-Byte

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.

Optimizing the Time-to-First-Byte

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.

Overlay Virtual Networking Examples

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:

Overlay Virtual Networking Examples

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:

Jerikan+Ansible: a Configuration Management System

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.