Re: [patch v2 02/37] add opcodes to ib_pack.h

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On Sat, Aug 20, 2011 at 4:47 PM, Bart Van Assche <bvanassche@xxxxxxx> wrote:
> On Mon, Aug 15, 2011 at 6:15 PM, Bob Pearson
> <rpearson@xxxxxxxxxxxxxxxxxxxxx> wrote:
> > I want to eventually complete the IB transport parts of the driver although
> > they are not used by RoCE. They would be useful for a soft IB implementation
> > with say an FPGA based MAC/PHY. The long term goal is to have a complete
> > reference implementation of the IB Architecture.
> Having a complete reference implementation of the IB architecture
> available would be great. IMHO at least the following should be added
> to ib_rxe (not necessarily in the first version) before it can called
> a reference implementation:
> - Support for secondary GIDs. These make it easy to implement
> fail-over in a H.A. cluster.
> - Support for multicast.

More in detail, my comments with regard to multicast support in ib_rxe are:
1. Using ipv6_eth_mc_map() for mapping multicast GIDs seems an
unfortunate choice to me. That choice will cause multicast GIDs to be
mapped to the 33-33-xx-xx-xx-xx Ethernet address range that has been
reserved by RFC 2464 for IPv6 multicast addresses. If a collision with
an IPv6 multicast address occurs and IPv6 MLD snooping has enabled on
the switches in the involved network then RoCE multicast won't work
properly. IMHO we need a separate Ethernet address range for RoCE
multicast purposes, next to the existing ranges for IPv4 and IPv6.
2. We need a way to limit multicast traffic to those switch ports on
which receivers are listening. The InfiniBand architecture has such a
protocol but it relies on the subnet manager, a component that does
not exist in RoCE networks. And since IGMP and MLD are IPv4/IPv6
specific we need a new (IBTA-approved) protocol.
3. RFC 4541, in which IGMP and MLD snooping has been defined, will
have to be extended with a paragraph about snooping the protocol
defined in (2).
4. Switch vendors will have to implement the protocol item (3) refers to.

Shouldn't a RoCE multicast implementation be postponed until the IEEE
has assigned an Ethernet address range for mapping RoCE multicast GIDs

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