Fabric versus Network: What’s the Difference?

17 October 2016 |

We often hear about fabrics, and we often hear about networks—but on paper, an in practice, they often seem to be the same thing. Leaving aside the many realms of vendor hype, what’s really the difference? Poking around on the ‘net, I came across a couple of definitions that seemed useful, at least at first…

Enough with “firewalls”

14 September 2016 | Comments Off on Enough with “firewalls”

A mythical conversation on firewalls, and some observations “Let’s put the firewall here, so it can protect the servers in this part of the network.” “How would you define a firewall?” “You know, the appliance that, well, protects servers and other machines from outside threats…” “And how does it do this?” “By filtering the traffic…

DC Fabric Segment Routing Use Case (5)

7 September 2016 | Comments Off on DC Fabric Segment Routing Use Case (5)

In this, the last post on DC fabrics as a Segment Routing use case, I mostly want to tie up some final loose ends. I will probably return to SR in the future to discuss other ideas and technical details. Anycast Anyone who keeps up with LinkedIn knows anycast plays a major role in many…

DC Fabric Segment Routing Use Case (4)

22 August 2016 |

In the last post in this series, I discussed using SR labels to direct traffic from one flow onto, and from other flows off of, a particular path through a DC fabric. Throughout this series, though, I’ve been using node (or prefix) SIDs to direct the traffic. There is another kind of SID in SR…

DC Fabric Segment Routing Use Case (3)

10 August 2016 | Comments Off on DC Fabric Segment Routing Use Case (3)

In the second post in this series, we considered the use of IGP-Prefix segments to carry a flow along a specific path in a data center fabric. Specifically, we looked at pulling the green flow in this diagram— —along the path [A,F,G,D,E]. Let’s assume this single flow is an elephant flow that we’re trying to…

DC Fabric Segment Routing Use Case (2)

28 July 2016 |

In the first post we covered a bit of the basics around segment routing in the data center. Let’s return to the first use case to see if we can figure out how we’d actually implement the type of traffic steering needed to segregate mouse and elephant flows. Let’s return to our fabric and traffic…

DC Fabric Segment Routing Use Case (1)

11 July 2016 |

A couple of weeks ago, I attended a special segment routing Networking Field Day. This set me to thinking about how I would actually use segment routing in a live data center. As always, I’m not so concerned about the configuration aspects, but rather with what bits and pieces I would (or could) put together…

Getting to the point of dual homing

20 June 2016 |

I wonder how many times I’ve seen this sort of diagram across the many years I’ve been doing network design? It’s usually held up as an example of how clever the engineer running the network is about resilience. “You see,” the diagram asserts, “I’m smart enough to purchase connectivity from two providers, rather than one.”…

When prepend fails, what next? (3)

13 June 2016 |

We began this short series with a simple problem—what do you do if your inbound traffic across two Internet facing links is imbalanced? In other words, how do you do BGP load balancing? The first post looked at problems with AS Path prepend, while the second looked at de-aggregating and using communities to modify the…

When prepend fails, what next? (2)

6 June 2016 |

This week’s post was written by Johnny Britt over at FreedomPay. I’ve edited in some small places to add more information, etc., but I think Johnny needs to start blogging… Once you have determined that AS-Path prepending can no longer help us what are our next steps? Routing is based on the longest matched prefix,…