Mar 26, 2013
“Imagine there’s no spanning tree, it’s easy if you try,
No multi-tiers below us, just a flat network like the sky,
Imagine all the users, living for the apps…”
I recently spoke at Avaya’s Technology Forum, the company’s data networking event (yes, Avaya does networking). After my presentation, Avaya’s Jean Turgeon did a presentation where he asked the audience to “imagine” a world without Spanning Tree. The presentation got me thinking about Imagine — one of my all time favorite Lennon songs — and, more importantly, about all the reasons why it’s important that companies look to move past Spanning Tree Protocol (STP) today.
The tried and true STP has been under significant fire since data center networking vendors have started to tout “fabric” solutions based primarily on TRILL or Shortest Path Bridging (SPB), both of which are being positioned as replacements for STP. As a network engineer I relied heavily on STP but I have to admit it’s time to move on, and I’d like to share the reasons why I think that’s the case.
First, I know not everyone is fluent in networking speak, so I’ll define STP first. STP is protocol that operates at layer 2 of the OSI stack. The protocol prevents routing loops and broadcast storms from occurring by creating a “spanning tree” within a mesh Ethernet network. The protocol disables all links that are not part of the active tree resulting in a single, active path between any two points in a network. The disabled link becomes active when one of the active links fails.
As an analogy, consider the highway system between San Francisco and San Jose. There are multiple paths between the two. One could take 280, 101, 880, 580 to 680 or another combination. If STP were to manage the traffic on this route, all links would be disable except for one, let’s use 101 for example. The only way another route would be opened up is if 101 were to be closed. This analogy should let you see the inherent inefficiency of STP.
Specifically, STP has the following limitations:
SPB and TRILL are competing standards to replace STP. Both protocols use some form of shortest path, multi-hop routing to overcome the slow network convergence times associated with STP. In a TRILL- or SPB-based network, all paths are equally valid and every path is active, which can up to double the total bandwidth available on a network while using fewer physical ports. This “active-active” configuration is the reason why these new networks are considered “fabrics” more so than a legacy network.
Any company looking to expand the use of virtualization should look to drop STP and investigate a TRILL or SPB based fabric to meet the new demands created by cloud and virtualization.
Image credit: archer10 (Dennis) (flickr)