Category: Bridging

I started January 2018 blogging with a major service provider failure. Why should 2019 be any different? Here’s what Century Link claimed was causing two-day outage (more comments here).

Supposedly it was a problem with the management network used by their optical gear, but it looks a lot like a layer-2 network spanning 15 data centers and no control-plane policing on the managed devices… proving yet again that large-scale layer-2 networks are a really bad idea.

Evil CCIE concluded his long list of leaf-and-spine fabric myths (more in part 1 and part 2) with a layer-2 fabric myth:

Layer 2 Fabrics can't be extended beyond 2 Spine switches. I had a long argument with a $vendor guys on this. They don't even count SPB as Layer 2 fabric and so forth.

The root cause of this myth is the lack of understanding of what layer-2, layer-3, bridging and routing means. You might want to revisit a few of my very old blog posts before moving on: part 1, part 2, what is switching, layer-3 switches and routers.

Got this response to my Stretched Layer-2 Revisited blog post. It’s too good not to turn it into a blog post ;)

Recently I feel like it's really vendors pushing layer 2 solutions, rather than us (enterprise customer) demanding it.

I had that feeling for years. Yes, there are environment with legacy challenges (running COBOL applications on OS/370 with emulated TN3270 terminals comes to mind), but in most cases it’s the vendors trying to peddle unique high-priced non-interoperable warez.

One of my friends sent me this question:

Do you remember if VLANs came first or was it VRFs?

I remember VLANs using ISL (pre-802.1q encapsulation) on early Cisco Ethernet switches (mid 90s), the earliest reference I could track down on Wikipedia is from 1988.

One of my readers was wondering about the stability and scalability of large layer-2 domains implemented with VXLAN. He wrote:

If common BUM traffic (e.g. ARP) is being handled/localized by the network (e.g. NSX or ACI), and if we are managing what traffic hosts can send with micro-segmentation style filtering blocking broadcast/multicast, are large layer-2 domains still a recipe for disaster?

There are three major (fundamental) problems with large L2 domains:

There are two reasonable ways of building a layer-2 leaf-and-spine fabric: use VXLAN (the direction almost everyone in the industry is taking at the moment), or routing-on-layer-2 technology like TRILL or SPB.

Got this comment to one of my L2-over-VXLAN blog posts:

I found the Avaya SPBM solution "right on the money" to build that L2+ fabric. Would you deploy Avaya SPBM?

Interestingly, I got that same question during one of the ExpertExpress engagements and here’s what I told that customer:

One of my readers sent me a lengthy email asking my opinion about his ideas for new data center design (yep, I pointed out there’s a service for that while replying to his email ;). He started with:

I have to design a DR solution for a large enterprise. They have two data centers connected via Fabric Path.

There’s a red flag right there…

Mark Baker left this comment on my Stretched Firewalls across Layer-3 DCI blog post:

Strange how inter-DC clustering failure is considered a certainty in this blog.

Call it experience or exposure to a larger dataset. Anything you build will eventually fail; just because you haven’t experienced the failure yet doesn’t mean that the system will never fail but only that you were lucky so far.

A few months ago I met a number of great engineers from Avaya and they explained to me how they creatively use Shortest Path Bridging (SPB) to create layer-2, layer-3, L2VPN, L3VPN and even IP Multicast fabrics – it was clearly time for another deep dive into SPB.

It took me a while to meet again with Roger Lapuh, but finally we started exploring the intricacies of SPB, and even compared it to MPLS for engineers more familiar with MPLS/VPN. Interested? Listen to Episode 54 of Software Gone Wild.