On Tue, 3 Nov 2020 13:05:59 -0800 Jakub Kicinski wrote: > On Mon, 2 Nov 2020 15:56:43 +0800 LIU Yulong wrote: > > According to the RFC 2464 [1] the prefix "33:33:xx:xx:xx:xx" is defined to > > construct the multicast destination MAC address for IPv6 multicast traffic. > > The NDP (Neighbor Discovery Protocol for IPv6)[2] will comply with such > > rule. The work steps [6] are: > > *) Let's assume a destination address of 2001:db8:1:1::1. > > *) This is mapped into the "Solicited Node Multicast Address" (SNMA) > > format of ff02::1:ffXX:XXXX. > > *) The XX:XXXX represent the last 24 bits of the SNMA, and are derived > > directly from the last 24 bits of the destination address. > > *) Resulting in a SNMA ff02::1:ff00:0001, or ff02::1:ff00:1. > > *) This, being a multicast address, can be mapped to a multicast MAC > > address, using the format 33-33-XX-XX-XX-XX > > *) Resulting in 33-33-ff-00-00-01. > > *) This is a MAC address that is only being listened for by nodes > > sharing the same last 24 bits. > > *) In other words, while there is a chance for a "address collision", > > it is a vast improvement over ARP's guaranteed "collision". > > Kernel related code can be found at [3][4][5]. > > Please make sure you keep maintainers CCed on your postings, adding bond > maintainers now.
Looks like no reviews are coming in, so I had a closer look. It's concerning that we'll disable load balancing for all IPv6 multicast addresses now. AFAIU you're only concerned about 33:33:ff:00:00:01, can we not compare against that? The way the comparison is written now it does a single 64bit comparison per address, so it's the same number of instructions to compare the top two bytes or two full addresses.
