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I need to refresh ARP frequently. [message #52468] Thu, 14 July 2016 13:36
kylerlaird is currently offline  kylerlaird
Messages: 1
Registered: July 2016
Junior Member
I've been using OpenVZ for several years both personally and at work. It's been a big part of my daily life but I have not kept up with changes over the years; it's been so robust that I just depend on it working. Recently, however, it all fell apart.

I use tinc at work to make a campus network available to my OpenVZ servers at Amazon (AWS). This has worked for a year or so with occasional network drops to individual VEs. I usually just restart them and they work again for quite awhile.

Last weekend there was a network hardware upgrade on campus. There were lots of disruptions and suddenly my VE connectivity was up and down constantly. It was a nightmare.

Restarting VEs helped but only momentarily; there were always several VEs offline. I dug into the startup sequence to see what it was that seemed to fix (for a moment) the situation. The key was periodically sending ARP updates to my neighbors on the tinc interface using arpsend. I have attached the Python script I kludged together to do this once a minute.

This script seems to solve the problem for me. I hope that it helps someone else. But I would also be delighted to hear that all I needed to do was set some sysctl value so that my neighbors don't lose my ARP entries. I suspect it's a bit more complicated, though.

(I am using 2.6.32-openvz-042stab112.15-amd64.)

Thank you for OpenVZ!

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