Running BGP between Virtual Machines and Data Center Fabric
Got this question from one of my readers:
When adopting the BGP on the VM model (say, a Kubernetes worker node on top of vSphere or KVM or Openstack), how do you deal with VM migration to another host (same data center, of course) for maintenance purposes? Do you keep peering with the old ToR even after the migration, or do you use some BGP trickery to allow the VM to peer with whatever ToR it’s closest to?
Short answer: you don’t.
Kubernetes was designed in a way that made worker nodes expendable. The Kubernetes cluster (and all properly designed applications) should recover automatically after a worker node restart. From the purely academic perspective, there’s no reason to migrate VMs running Kubernetes.
Optimizing the Time-to-First-Byte
I don’t think I’ve ever met someone saying “I wish my web application would run slower.” Everyone wants their stuff to run faster, but most environments are not willing to pay the cost (rearchitecting the application). Welcome to the wonderful world of PowerPoint “solutions”.
The obvious answer: The Cloud. Let’s move our web servers closer to the clients – deploy them in various cloud regions around the world. Mission accomplished.
Not really; the laws of physics (latency in particular) will kill your wonderful idea. I wrote about the underlying problems years ago, wrote another blog post focused on the misconceptions of cloudbursting, but I’m still getting the questions along the same lines. Time for another blog post, this time with even more diagrams.
Circular Dependencies Considered Harmful
A while ago my friend Nicola Modena sent me another intriguing curveball:
Imagine a CTO who has invested millions in a super-secure data center and wants to consolidate all compute workloads. If you were asked to run a BGP Route Reflector as a VM in that environment, and would like to bring OSPF or ISIS to that box to enable BGP ORR, would you use a GRE tunnel to avoid a dedicated VLAN or boring other hosts with routing protocol hello messages?
While there might be good reasons for doing that, my first knee-jerk reaction was:
… updated on Thursday, September 30, 2021 16:19 UTC
Reusing Underlay Network for Infrastructure Services
Boris Lazarov sent me an excellent question:
Does it make sense and are there any inherent problems from design perspective to use the underlay not only for transport of overlay packets, but also for some services. For example: VMWare cluster, vMotion, VXLAN traffic, and some basic infrastructure services that are prerequisite for the rest (DNS).
Before answering it, let’s define some terminology which will inevitably lead us to the it’s tunnels all the way down endstate.
Building a Small Data Center Fabric with Four Switches
One of my subscribers has to build a small data center fabric that’s just a tad too big for two switch design.
For my datacenter I would need two 48 ports 10GBASE-T switches and two 48 port 10/25G fibber switches. So I was watching the Small Fabrics and Lower-Speed Interfaces part of Physical Fabric Design to make up my mind. There you talk about the possibility to do a leaf and spine with 4 switches and connect servers to the spine.
A picture is worth a thousand words, so here’s the diagram of what I had in mind:
New: ipSpace.net Design Clinic
In early September, I started yet another project that’s been on the back burner for over a year: ipSpace.net Design Clinic (aka Ask Me Anything Reasonable in a more structured format). Instead of collecting questions and answering them in a podcast (example: Deep Questions podcast), I decided to make it more interactive with a live audience and real-time discussions. I also wanted to keep it valuable to anyone interested in watching the recordings, so we won’t discuss obscure failures of broken designs or dirty tricks that should have remained in CCIE lab exams.
Worth Reading: Simplifying Networks
Justin Pietsch wrote another fantastic blog post, this time describing how they simplified Amazon’s internal network, got rid of large-scale VLANs and multi-NIC hosts, moved load balancing functionality into a proxy layer managed by application teams, and finally introduced merchant silicon routers.
Designing Networks: From Tricycles to Aircraft Carriers
I planned to take my summer break seriously and stop blogging until late August, but then I shouldn’t have looked at my Twitter feed (my bad), where the AI algorithms selected just the right morsel to trigger the maximum rantiness. I would strongly recommend you read the original tweet and all the responses first – it looks like it was a serious suggestion, not a trolling exercise (here’s a copy of the original idea in case the tweets get lost in the mists of time).
Stretched VLANs: What Problem Are You Trying to Solve?
One of ipSpace.net subscribers sent me this interesting question:
I am the network administrator of a small data center network that spans 2 buildings. The main building has a pair of L2/L3 10G core switches. The second building has a stack of access switches connected to the main building with 10G uplinks. This secondary datacenter has got some ESX hosts and NAS for remote backup and some VM for development and testing, but all the Internet connection, firewall and server are in the main building.
There is no routing in the secondary building and most of the VLANs are stretched. Do you think I must change that (bringing routing to the secondary datacenter), or keep it simple like it is now?
As always, it depends, this time on what problem are you trying to solve?
Questions about BGP in the Data Center (with a Whiff of SRv6)
Henk Smit left numerous questions in a comment referring to the Rethinking BGP in the Data Center presentation by Russ White:
In Russ White’s presentation, he listed a few requirements to compare BGP, IS-IS and OSPF. Prefix distribution, filtering, TE, tagging, vendor-support, autoconfig and topology visibility. The one thing I was missing was: scalability.
I noticed the same thing. We kept hearing how BGP scales better than link-state protocols (no doubt about that) and how you couldn’t possibly build a large data center fabric with a link-state protocol… and yet this aspect wasn’t even mentioned.
Worth Reading: Switching to IP fabrics
Namex, an Italian IXP, decided to replace their existing peering fabric with a fully automated leaf-and-spine fabric using VXLAN and EVPN running on Cumulus Linux.
They documented the design, deployment process, and automation scripts they developed in an extensive blog post that’s well worth reading. Enjoy ;)
Worth Reading: Running BGP in Large-Scale Data Centers
Here’s one of the major differences between Facebook and Google: one of them publishes research papers with helpful and actionable information, the other uses publications as recruitment drive full of we’re so awesome but you have to trust us – we’re not sharing the crucial details.
Recent data point: Facebook published an interesting paper describing their data center BGP design. Absolutely worth reading.
Just in case you haven’t realized: Petr Lapukhov of the RFC 7938 fame moved from Microsoft to Facebook a few years ago. Coincidence? I think not.
Worth Watching: Rethinking BGP in the Data Center
Ever since draft-lapukhov was first published almost a decade ago, we all knew BGP was the only routing protocol suitable for data center networking… or at least Thought Leaders and vendor marketers seem to be of that persuasion.
Worth Reading: Rethinking Internet Backbone Architectures
Johan Gustawsson wrote a lengthy blog post describing Telia’s approach to next-generation Internet backbone architecture… and it’s so refreshing seeing someone bringing to life what some of us have been preaching for ages:
- Simplify the network;
- Stop cramming ever-more-complex services into the network;
- Bloated major vendor NPUs implementing every magic ever envisioned are overpriced – platforms like Broadcom Jericho2 are good enough for most use cases.
- Return from large chassis-based stupidities to network-centric high availability.
I don’t know enough about optics to have an opinion on what they did there, but it looks as good as the routing part. It would be great to hear your opinion on the topic – write a comment.
Video: Cisco SD-WAN Site Design
In the Site Design part of Cisco SD-WAN webinar, David Penaloza described capabilities you can use when designing complex sites, like extending SD-WAN transport between SD-WAN edge nodes, or implementing high availability between them. He also explained how to track an Internet-facing interface and a service beyond its next hop.