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<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'> Amar Mudrankit<br>
<br>
</span></font></p>
<p class=MsoNormal style='margin-bottom:12.0pt'><font size=3
face="Times New Roman"><span style='font-size:12.0pt'>Michael,<br>
thanks for your reply. But, this gives rise to couple of questions..<br>
<br>
1] If such multicast routing protocol for IB routers is not yet specifid by
IBTA or IETF, then current implementation have IP subnet restricted within a IB
subnet. According to RFC 4391, section 9.1.1, the link layer address is formed
through combination of GID + QPN. If we are not spanning across IB subnets what
is the use of GID as we need to get LID from GID? Probably, in that case ARP
reply with LID,Q_Key and other path information would be helpful which resolves
path in 1 loop than 2 loops in case of GID(first to resolve GID and then to get
LID). <font color=navy><span style='color:navy'><o:p></o:p></span></font></span></font></p>
<p class=MsoNormal style='margin-bottom:12.0pt'><b><i><font size=2 color=navy
face=Arial><span style='font-size:10.0pt;font-family:Arial;color:navy;
font-weight:bold;font-style:italic'>[Todd Rimmer] Basing IPoIB on the GID keeps
open the opportunity for IPoIB to span IB subnets in the future. Also
this permits the SM to manage the paths and PathRecord parameters appropriately
even in non-routed IB networks. For example, if multi-pathing is used
(LMC!=0, hence giving multiple LIDs per port), the SM may respond to PathRecord
requests for a given Destination GID with a different LID depending on Source
GID. Such a mechanism can be used to manage routes in the fabric, etc.
That is just a simple example, since the PathRecord includes lots of other
information as well (QOS, routing info, MTU, etc). The SM can provide
different PathRecord values for each Source GID talking to a given Destination
GID.<o:p></o:p></span></font></i></b></p>
<p class=MsoNormal style='margin-bottom:12.0pt'><b><i><font size=2 color=navy
face=Arial><span style='font-size:10.0pt;font-family:Arial;color:navy;
font-weight:bold;font-style:italic'>The IETF needed a “MAC Address”
for IPoIB. GID+QPN gave them a unique endpoint with the potential to work
through routers and still support the full intentions of IB’s QOS and
routing options. LID+QPN would severely limit those capabilities.<o:p></o:p></span></font></i></b></p>
<p class=MsoNormal style='margin-bottom:12.0pt'><b><i><font size=2 color=navy
face=Arial><span style='font-size:10.0pt;font-family:Arial;color:navy;
font-weight:bold;font-style:italic'>In general it’s a bad idea for end
nodes to simply exchange LIDs as it bypasses many of the intentions of the IB
spec. Such applications will break in fabrics which use the more advanced
IB QOS, routing, etc options.<o:p></o:p></span></font></i></b></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Todd Rimmer<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New";color:navy'>Chief
Architect </span></font><font color=navy><span style='color:navy'><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New";color:navy'>QLogic System
Interconnect Group</span></font><font color=navy><span style='color:navy'><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New";color:navy'>Voice:
610-233-4852 Fax: 610-233-4777<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><a href="mailto:Todd.Rimmer@QLogic.com"><font
face="Courier New"><span style='font-family:"Courier New"'>Todd.Rimmer@QLogic.com</span></font></a></span></font><font
size=2 color=navy face="Courier New"><span style='font-size:10.0pt;font-family:
"Courier New";color:navy'> <a href="http://www.QLogic.com">www.QLogic.com</a></span></font><font
color=navy><span style='color:navy'><o:p></o:p></span></font></p>
<p class=MsoNormal style='margin-bottom:12.0pt'><font size=3
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