Category: Switching

A comment by Pieter E. Smit on my vSphere Does Not Need LAG Bandaids post opened yet another can of worms: vSphere behavior on uplink recovery.

Short summary: vSphere starts using an uplink as soon as its physical layer becomes operational, which might happen during ToR switch startup phase, or before a ToR switch port enters forwarding state.

When describing Hyper-V Network Virtualization packet forwarding I briefly mentioned that the hypervisor switches create (an equivalent of) a host route for every VM they need to know about, prompting some readers to question the scalability of such an approach. As it turns out, layer-3 switches did the same thing under the hood for years.

The SDN industry probably considers me an old and grumpy naysayer (and I’m positive Mrs Y has a special place in their hearts after her recent blog post), so I tried really hard to find a real-life example where OpenFlow could be used to solve mid-market innovator’s dilemma to balance my usual OpenFlow and SDN presentation.

It took years before the rumored Cisco vSwitch materialized (in the form of Nexus 1000v), several more years before there was the first competitor (IBM Distributed Virtual Switch), and who knows how long before the third entrant (recently announced HP vSwitch) jumps out of PowerPoint slides and whitepapers into the real world.

Compare that to the Hyper-V environment, where we have at least two virtual switches (Nexus 1000V and NEC's PF1000) mere months after Hyper-V's general availability.

I’m probably flogging a fossilized skeleton of a long-dead horse, but it seems I never wrote about this topic before, so here it is (and you might want to read this book for more details).

Process switching is the oldest, simplest and slowest packet forwarding mechanism. Packets received on an interface trigger an interrupt, the interrupt handler identifies the layer-3 protocol based on layer-2 packet headers (example: Ethertype in Ethernet packets) and queues the packets to (user mode) packet forwarding processes (IP Input and IPv6 Input processes in Cisco IOS).

Autumn must be a perfect time for data center product launches: last week Brocade launched its core VDX switch and yesterday Arista and Cisco launched their new low-latency switches (yeah, the simultaneous launch must have been pure coincidence).

I had the opportunity to listen to Cisco’s and Arista’s product briefings, continuously experiencing a weird feeling of déjà vu. The two switches look like twin brothers … but there are some significant differences between the two:

Arista is launching a new product line today shrouded in mists of SDN and cloud buzzwords: the 7150 series top-of-rack switches. As expected, the switches offer up to 64 10GE ports with wire speed L2 and L3 forwarding and 400 nanosecond(!) latency.

Also expected from Arista: unexpected creativity. Instead of providing a 40GE port on the switch that can be split into four 10GE ports with a breakout cable (like everyone else is doing), these switches group four physical 10GE SFP+ ports into a native 40GE (not 4x10GE LAG) interface.

But wait, there’s more...

The Nexus-focused Packet Pushers were discussing a great question during Cisco Nexus Deep Dive part 2 podcast: do we need LACP on top of UDLD?

Short answer: absolutely.

A few days ago Kurt Bales and Cooper Lees gave me access to a test QFabric environment. I always wanted to know what was really going on behind the QFabric curtain and the moment Kurt mentioned he was able to see some of those details, I was totally hooked.

Short summary: QFabric works exactly as I’d predicted three months before the user-facing documentation became publicly available (the behind-the-scenes view described in this blog post is probably still hard to find).

Very short answer: no.

You might think that layer-3 switches perform bridging and routing, while routers do only routing. That hasn’t been the case at least since Cisco introduced Integrated Routing and Bridging in IOS release 11.2 more than 15 years ago. However, Simon Gordon raised an interesting point in a tweet: “I thought IP L3 switching includes switching within subnet based on IP address, routing is between subnets only.”

Layer-3 switches and routers definitely have to perform some intra-subnet layer-3 functions, but they’re usually not performing any intra-subnet L3 forwarding.