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Improve gratuitous ARP compatibility #172

danderson opened this Issue Feb 28, 2018 · 0 comments


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danderson commented Feb 28, 2018

In #123, @mleklund pointed to , a blog series from OpenStack folks on debugging problems with their ARP-based failover implementation. They found a whole bunch of things, and some of them are relevant to our interests.

Short version: Linux kernels before ~4.11 have a whole set of different bugs that break gratuitous ARP in various ways. Kernels after that have been fixed, so the gratuitous ARP that MetalLB is doing right now should work perfectly, and update all ARP cache entries within 1-2s of failover.

To improve compatibility in the face of buggy kernels, we can do 2 things

  • Broadcast gratuitous ARP requests in addition to responses, so that buggy clients with arp_accept=1 correctly update, and non-linux kernels that selectively implement the RFC update as well.
  • Set the inter-frame broadcast delay to 1.1s, so that if packet 1 lands in the middle of the ARP cache's locktime, subsequent packets only arrive after the locktime expires.

This bug is to track those changes.

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