[openib-general] Problem is routing CM REQ

[Michael Krause]

At 01:14 PM 2/13/2007, Sean Hefty wrote:
>>It does not need to comprehend the remote subnet(s) LID.
>>That is the router protocol to determine.  CM also must understand the 
>>GIDs involved which the router will process to figure out its LID mapping 
>>to the next hop.
>
>The CM REQ carries the remote router LID (primary local port lid - 
>12.7.11) and remote endpoint LID (primary remote port lid - 12.7.21).

Let me clarify what the specification is saying which is what I'm saying.

A LID is subnet local on that we can all agree.   The CM Req contains 
either the LID of a local subnet CA or the LID a local router which will 
move the packet to the next hop to the destination.   12.7.11 is basically 
saying that the remote LID is the router's LID of the local subnet's router 
Port.   12.7.21 also refers to the remote LID but in each subnet that is 
either the router Port's LID or the destination CA.

 From an operational flow perspective, CM would:

Query to see if the destination CA is on the local subnet
If yes, then obtain the associated records to find the local LID
If no, then obtain the set of records that contain the local addressing to 
a router Port that will progress connection establishment to the next hop 
on the way to the destination.

While there isn't a router specification any longer, the basic operation is 
very much like that of an IP subnet.   The router protocol establishes a 
set of routes for given subnet prefix and then communicates that to each 
SM/SA so that queries will resolve the optimal router Port.   Chapter 8 
provides clear guidance in this regard.  Chapter 12 is basically stating 
what to plug into various fields with all LIDs being only local to the 
subnet where they are managed.   The primary global knowledge that one must 
have across subnets are to establish a connection or communication flow.

- SGID
- DGID
- P_Key
- Q_Key

There really isn't much more than this to comprehend.  The TClass and Flow 
Labels were expected to be provided via the router protocol so the 
management requirements are really query look up.

Mike