Lots of talk about simplicity recently and the fact that networking is too complicated and inflexible. There are a number of choices that you deliver simplicity in Overlay Networks.
Least Functionality - One choice is to reduce the network to most minimal and least functionality. But we tried that with L2 ECMP protocols like TRILL which would deliver VLANs everywhere. What we ended up with is overly complex protocols and hardware complexity to have this least amount of functionality.
Maximum Features – Another choice would be to have a device have maximum functionality provides simplicity to the server & applications by offering transparent services. Today we have massive switches from the vendors that have thousands of features and is exemplified by the Nexus 7000 family of products which has technology like OTV, LISP, MPLS, QoS, VPC/MLAG, FEX, FCoE, a kitchen sink and a partridge in a pear tree. This applies equally to Brocade VDX and HP A-Series. This isn’t working well because the complexity of the hardware and software means long lead times, massive cost and poor reliability.
Abstraction - the solution that the network industry is taking is abstraction. Abstraction is a well-known computer science topic and applies equally to networking.
In computer science, abstraction is the process by which data and programs are defined with a representation similar in form to its meaning (semantics), while hiding away the implementation details. Abstraction tries to reduce and factor out details so that the programmer can focus on a few concepts at a time. A system can have several abstraction layers whereby different meanings and amounts of detail are exposed to the programmer. For example, low-level abstraction layers expose details of the computer hardware where the program run, while high-level layers deal with the business logic of the program.
Overlay networking in simple computer abstraction. Simplicity is delivered by using the abstracting essence of physical network functionality by using tunnel networking.
The purpose of the overlay to to allow focus onto the overlay network and closer scrutiny of the tunnel fabric.
Coupling - The question that I find unresolved is whether tight coupling or loose coupling of the overlay/underlay is desired.Coupling is an engineering concept that describe how much “interconnectedness” happens between the abstraction layers. Simple abstraction is towards more complete isolation of the layers. Complex abstraction is achieved by having multiple points of interdependence between the physical and logical network.
Today, most SDN vendors (such as Cisco ACI or VMware NSX) are using a concept of inference to derive state about the physical network. That is, their SDN abstraction tools have different methods of finding state in the network by using out-of-band methods. The Cisco ACI chip in the Nexus 9000 appears to use feedback from the Trident chipset. VMware NSX appears to promote the idea of using traffic monitoring to detect network failures or packet loss. The other method of coupling is using OpenFlow which uses flow masking in the switch itself to provide the highest level of coupling.
The EtherealMind View
This is part of series of articles that explores the nature of overlay networking and how it integrates with the physical networks. I’m looking to identify what are the criteria for the claims from SDN vendors who indicate that isolation or integration is the best method. I’ll continue to explore this topic in future posts.
I’ve started an email list where you can subscribe to receive weekly updates if you would like to receive notification of future articles.Look at the footer for subscription details.
Other Posts in A Series On The Same Topic
- ◎ Blessay: Overlay Networking Simplicity is Abstraction, Coupling and Integration (10th December 2013)
- Integrating Overlay Networking and the Physical Network (21st June 2013)
- ◎ Introduction to How Overlay Networking and Tunnel Fabrics Work (10th June 2013)
- ◎ Overlay Networking is More and Better while Ditching the Toxic Sludge. (7th June 2013)