Multicast GRE changed behaviour
From: Marc St-Onge <hidden>
Date: 2015-02-17 01:24:54
I'm not 100% sure if the issue we are facing is related to recent changes in ip_gre.c but while I was reading through the code I came about the comment on line 341 and suspect some changes may have been introduced in ip_gre.c. We have been using Multicast GRE tunnels in our organisation (we actually call it Broadcast GRE and have given it the BGRE acronym) but essentially, we successfully setup the tunnels exactly as described in the example. The recent Ubuntu upgrade has caused an backward compatibility issue somewhere between kernel 3.8 and 3.13. The previous kernel would use Multicast to do the ARP and discovery as well as encapsulation of Multicast user traffic and would use the end-point Unicast address to encapsulate the Unicast user traffic between the remote nodes. In Kernel 3.13 we are observing that the Unicast traffic is also encapsulated in a Multicast datagram. Marc St-Onge