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).

The ProgrammableFlow Principles of Operations section of the ProgrammableFlow Technical Deep Dive webinar generated tens of questions from the audience – it took us almost 20 minutes to answer all of them (note: you might watch the answers after watching the section that triggered the questions).

The second part of ProgrammableFlow Technical Deep Dive webinar describes ProgrammableFlow principles – physical networks (control, data, HA cluster, management), edge and core switches, topology discovery and end-to-end routing and path setup procedure.

Matt Thompson provided a really good answer to the “what’s acceptable oversubscription ratio in a ToR switch” when he wrote “I’m expecting a ‘how long is a piece of string’ answer” (note: do watch the BBC video answering that one).

There’s the 3:1 rule-of-thumb recipe, with a more realistic answer being “it depends”. Now let’s see if we can go beyond that without a deep dive into scholastic waters.

Matthew Stone encountered another unintended consequence of full Internet routing in a VRF design: the TCAM on his 6500 was 80% utilized even though he has the new Sup modules with one million IPv4 routes.

A closer look revealed the first clue: L3 forwarding resources on a Cat6500 are shared between IPv4 routes and MPLS labels (I don’t know about you, but I was not aware of that), and half the entries were consumed by MPLS labels:

Mark Berly spent plenty of time explaining the in-depth intricacies of VXLAN-to-VLAN gateways during our VXLAN Technical Deep Dive webinar. He’s obviously heavily immersed in this challenge and hits 9+ on the Nerd Meter, so you might have to watch the video a few times to get all the nuances. What can I say – we’ll have fun times in the coming years ;)

... in a VXLAN segment (over UDP-over-IP-over-EoMPLS-over-MPLS-over-GRE-over-IPsec-over-IP-over-MPLS/VPN-over-MPLS-over-PPPoE-over-ATM-over-ATOM-over ...)

Source: DevOps reactions

Here’s the first video from the ProgrammableFlow webinar. Don’t get too excited, it’s yet another introduction to OpenFlow and control/data plane separation (but it is an animated one ;). More goodies to follow ...

I had an interesting conversation with Doug Hanks (@douglashanksjr) about the need for intra-spine links in leaf-and-spine fabric designs. You clearly don’t need links between spine switches when every leaf node (switch or router/firewall/load balancer) is connected to all spine switches ... but what happens when one of the leaf-to-spine links fails? Will other leaf switches know that they have to avoid the spine switch with the failed link?

Cisco launched two new data center switches on Monday: Nexus 6001, a 1RU ToR switch with the exact same port configuration as any other ToR switch on the market (48 x 10GE, 4 x 40GE usable as 16 x 10GE) and Nexus 6004, a monster spine switch with 96 40GE ports (it has the same bandwidth as Arista’s 7508 in a 4RU form factor and three times as many 40GE ports as Dell Force10 Z9000).

Apart from slightly higher port density, Nexus 6001 looks almost like Nexus 5548 (which has 48 10GE ports) or Nexus 3064X. So where’s the beef?