[dat-discussions] RE: [openib-general] Re: iWARP emulationprotocol

[Sean Hefty]

Kanevsky, Arkady wrote:
> if look at the proposal it shows 2 ways to address this.

I did notice this.

> 1. Have 2 protocols.
> One just send SRC IP address and port, and provdie 64 bytes to ULP.
> Another one send both SRC and DEST info and leaves 48(+-) bytes of
> private data for ULP.

If the goal is to make the mapping from IP address to IB address transparent, 
then I think we want a single protocol.  Ideally, the application shouldn't need 
to know if they're connecting over iWarp, IB, or any other RDMA NIC.  Any 
solution that makes IB appear different than iWarp makes this more difficult to 
accomplish.

> 2. Have 2 protocols.
> Split IPv4 and IPv6 methods.

Same issue as above.  This makes IB connections appear differently than an iWarp 
connection.  This is why I asked if the destination address is required.  If it 
is, then the applications need to make do with less private data.

> For IPv4 send SRC and DST addressing and 64 bytes of ULP private data.
> For IPv6 we have several options.
> a. GID=IPv6 address

Unless an IP packet can be sent to a GID and be processed, I don't consider a 
GID equal to an IPv6 address.  I also don't think that we should require system 
administrators to add GIDs to IB ports just because they want to add an IP 
address to a system.

> b. use second CM frame to have carry ULP private data.

An application can make due with no private data.  They can transfer whatever 
data that need once the connection has been established, like all TCP 
applications do.  Adding more CM messages to pass the same data that should be 
passed over the user's QP is the wrong approach.

In fact another alternative is to make all CM private data reserved.

- Sean