BGP Labs: EBGP Sessions over IPv6 LLA Interfaces

If you insist on building your network with EBGP as a better IGP, make sure your implementation supports running IPv4 and IPv6 address families over EBGP sessions established between IPv6 link-local addresses (the functionality lovingly called unnumbered EBGP sessions).

Want to practice that neat trick? Check out the EBGP Sessions over IPv6 LLA Interfaces lab exercise.

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Repost: The Real LISP Mobility Use Case

Béla Várkonyi is working on an interesting challenge: building ground-to-airplane(s) networks providing multilink mobility. Due to its relative simplicity, he claims LISP works much better than BGP in that environment.

In some newer routers BGP would not be such a big bottleneck, but you need a lot of knob turning in BGP to get it right, while in LISP it is quite simple.

If you have many thousands concurrent airplanes with multi-link and max. 16 subnets with different routing policies on each, and the radio links are going up and down, then you have a large number of mobility events.

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netlab: Global and Node VRFs

When designing the netlab VRF configuration module, I tried to make it as flexible as possible while using the minimum number of awkward nerd knobs. As is often the case1, the results could be hard to grasp, so let’s walk through the various scenarios of using global and node VRFs.

netlab allows you to define a VRF in the lab topology vrfs dictionary (global VRF) or in a node vrfs dictionary (node VRF). In most cases, you’d define a few global VRFs and move on.

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Repost: Think About the 99% of the Users

Daniel left a very relevant comment on my Data Center Fabric Designs: Size Matters blog post, describing how everyone rushes to sell the newest gizmos and technologies to the unsuspecting (and sometimes too-awed) users1:

Absolutely right. I’m working at an MSP, and we do a lot of project work for enterprises with between 500 and 2000 people. That means the IT department is not that big; it’s usually just a cost center for them.

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Stop the Network-Based Application Recognition Nonsense

One of my readers sent me an interesting update on the post-QUIC round of NBAR whack-a-mole (TL&DR: everything is better with Bluetooth AI):

Cloudflare (and the other hyperscalers) are full into QUIC, as it gives them lots of E2E control, taking a lot of choice away from the service providers on how they handle traffic and congestion. It is quite well outlined by Geoff Huston in an APNIC podcast.

So far, so good. However, whenever there’s a change, there’s an opportunity for marketing FUD, coming from the usual direction.

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Repost: Campus-Wide Wireless Roaming with EVPN

As a response to my LISP vs EVPN: Mobility in Campus Networks blog post, Route Abel provided interesting real-life details of a large-scale campus wireless testing using EVPN and VXLAN tunnels to a central aggregation point (slightly edited):

I was arguing for VxLAN EVPN with some of my peers, but I had no direct hands-on knowledge of how it would actually perform and very limited ability to lab it on hardware. My client was considering deploying Campus VxLAN, and they have one of the largest campuses in North America.

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Unintended Consequences of IPv6 SLAAC

One of my friends is running a large IPv6 network and has already experienced a shortage of IPv6 neighbor cache on some of his switches. Digging deeper into the root causes, he discovered:

In my larger environments, I see significant neighbor table cache entries, especially on network segments with hosts that make many long-term connections. These hosts have 10 to 20 addresses that maintain state over days or weeks to accomplish their processes.

What’s going on? A perfect storm of numerous unrelated annoyances:

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Explore: Why No IPv6? (IPv6 SaaS)

Lasse Haugen had enough of the never-ending “we can’t possibly deploy IPv6” excuses and decided to start the IPv6 Shame-as-a-Service website, documenting top websites that still don’t offer IPv6 connectivity.

His list includes well-known entries like,, and plus a few unexpected ones. I find not having an AAAA DNS record truly hilarious. Someone within the company that flawlessly provided my website with IPv6 connectivity for years obviously still has some reservations about their own dogfood ;)

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