Category: Segment Routing

We’re starting the SR-MPLS workshop @ ITNOG 10 in Bologna in a few hours. Hope you’ll make it, but if you happen to be too far away, here’s the slide deck, the lab topologies, and the usage guidelines.

The we should give different applications different paths across the network idea never dies (even though in many places the residential Internet gives you enough bandwidth to watch 4K videos), and the Leveraging Intent-Based Networking and SRv6 for Dynamic End-to-End Traffic Steering (video) by Severin Dellsperger was an interesting new riff on that ancient grailhunt.

Their solution uses SRv6 for traffic steering¹, an Intent-Based System² that figures out paths across the network, and eBPF on client hosts³ to add per-application SRv6 headers to outgoing traffic.

I love bashing SRv6, so it’s only fair to post a (technical) counterview, this time coming as a comment from Henk Smit.

There are several benefits of SRv6 that I’ve heard of.

Daniel Dib asked an interesting question on LinkedIn when considering an RT5-only EVPN design:

I’m curious what EVPN provides if all you need is L3. For example, you could run pure L3 BGP fabric if you don’t need VRFs or a limited amount of them. If many VRFs are needed, there is MPLS/VPN, SR-MPLS, and SRv6.

I received a similar question numerous times in my previous life as a consultant. It’s usually caused by vendor marketing polluting PowerPoint slide decks with acronyms without explaining the fundamentals¹. Let’s fix that.

Dmytro Shypovalov wrote a fantastic article explaining the basics of MPLS-based Segment Routing. It’s pretty much equivalent to everything I ever wrote about SR-MPLS but in a much nicer package. Definitely a must-read.

A long-time friend sent me this question:

I would like your advice or a reference to a security framework I must consider when building a green field backbone in SR/MPLS.

Before going into the details, keep in mind that the core SR/MPLS functionality is not much different than the traditional MPLS:

Want to explore SRv6? Cisco engineers put together a repository containing scripts and configs for building SRv6 test topologies. It works with Containerlab and FRR (unless you want to beg a Cisco account team for a Cisco 8000 image or make a sandwich while the IOS XRd image is booting).

Want to use netlab? Jeroen van Bemmel implemented baseline SRv6 support for Nokia SR OS.

One of my readers successfully deployed LDPv6 in their production network:

We are using LDPv6 since we started using MPLS with IPv6 because I was used to OSPF/OSPFv3 in dual-stack deployments, and it simply worked.

Not everyone seems to be sharing his enthusiasm:

Now some consultants tell me that they know no-one else that is using LDPv6. According to them “everyone” is using 6PE and the future of LDPv6 is not certain.

During the discussion of the On Applicability of MPLS Segment Routing (SR-MPLS) blog post on LinkedIn someone made an off-the-cuff remark that…

SRv6 as an host2host overlay - in some cases not a bad idea

It’s probably just my myopic view, but I fail to see the above idea as anything else but another tiny chapter in the “Solution in Search of a Problem” SRv6 saga¹.

Henk Smit left a wonderful comment discussing various scalability aspects of SR-MPLS. Let’s go through the points he made:

When you have a thousand routers in your networks, you can put all of them in one (IS-IS) area. Maybe with 2k routers as well. But when you have several thousand routers, you want to use areas, if only to limit the blast-radius.

Absolutely agree, and as RFC 3439 explained in more eloquent terms than I ever could: