Suspending Devices in netlab Labs

A networking engineer tired of waiting for network devices to start sent me this question:

Can you suspend VMs in netlab? I use this trick in vSphere with CSR1Kv.

TL&DR: Maybe. Probably not.

netlab tries to stay as far away from reinventing the wheels as possible1 and offloads all the virtualization and orchestration tasks to other tools like KVM/libvirt and Vagrant. With that in mind, let’s rephrase the question as “can you use Vagrant to suspend/resume a network device VM in KVM/libvirt environment and what would be the impact of doing that on netlab?

In theory, the answer is “yeah, why not.” In practice, my very first test failed2.

I decided to use the simplest possible topology: two Arista vEOS devices running OSPF to check whether they could exchange control-plane traffic over a Vagrant-provisioned connection.

defaults.device: eos
nodes: [ r1, r2 ]
module: [ ospf ]
links: [ r1, r2, r1-r2 ]

I started the lab with netlab up, which configured the management bridge and executed vagrant up to start the lab followed by an Ansible playbook to configure the devices.

Next, I executed vagrant suspend. No errors, the VMs were suspended. I checked the list of virtual networks with virsh net-list and they were still there. So far, so good.

Finally, I tried to resurrect the VMs with vagrant resume. One of them came up immediately, the other one got totally bricked – SSH didn’t work and I wasn’t able to access it with virsh console which connects to the virtual console serial port.

The same procedure might work with other network devices, but I’m not sure whether saving a minute or two is worth the hassle. I prefer to start my labs from scratch with freshly-minted configuration (hint: you can use netlab restart to do it).

Getting Started

Want to know more about netlab? Start with the Getting Started document and the installation guide. You might also want to watch the Using netlab to Build Networking Labs section of Network Automation Tools webinar.

  1. … although it does have to configure virtual plumbing when mixing virtual machines and containers↩︎

  2. … proving yet again the existence of the theory-practice gap. ↩︎

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