Subject: RE: [Ipoverib] More musing on address format

From: "Larsen, Roy K" <[email-masked]>
Date: Wed, 20 Mar 2002 14:13:17 -0800

> -----Original Message-----
> From: Vivek Kashyap [mailto:[email-masked]]
> Sent: Saturday, March 16, 2002 4:22 AM
> To: [email-masked]
> Cc: [email-masked]; [email-masked]
> Subject: Re: [Ipoverib] BOOTP/DHCP chaddr field

<snip>

> 
> > >Alas, a LID-based hardware address would be my first choice too.
> > 
> > Or keep GID but drop QPN and use SIDR as you've mentioned too.
> > 
> 
> I am more open to using LID + QPN rather than GID + SIDR.

Our SDP and uDAPL folks have just realized that the P_Key is not a formal
part of the IPoIB hardware address.  Both of these protocols are relying on
IPoIB for address resolution to obtain the GID and they are going to need
side/proprietary interfaces to the IPoIB driver to retrieve the P_Key
associated with an IP address.

Although I realize this is a personal problem for them, a hardware address
that consisted of P_Key + LID + QPN would be ideal from my point of view.
It is 6 bytes (how convenient), fully qualified within the scope of the IB
subnet, and would be a consistent representation of the hardware address at
the administrative level (ipconfig(8), arp(8), etc.).

The latter part of that benefit list is something that may warrant more
discussion.  That is, is there a desire to have a universal mapping of IPoIB
hardware address at the administrative interface?  For Ethernet, all
administrative tools in all OSs present the hardware address in a universal
and consistent fashion.  If we have a 20 byte IPoIB address, there are going
to be several OSs that will need to re-map that to a smaller value for
internal network stack consumption (this is how I stumbled onto the DHCP
issue).  If my re-mapping algorithm is different from others, administrators
will not see the same hardware address listed for the same node from system
to system.

I know there are some on the list that believe the data center will employ
lots of small-grain IB subnets interconnected by [relatively] expensive IB
routers.  I've never found that compelling.  Given all the ambiguity there
currently is with IBA routers, the considerations above just becomes more
food for thought on address format....

Roy

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---

From: Michael Krause <[email-masked]>
Date: Wed, 20 Mar 2002 22:58:59 -0800

>the administrative level (ipconfig(8), arp(8), etc.).

The P_Key is derived from the multicast group that one must join to get the 
GID so there is no reason to use it as part of the link address.

>will not see the same hardware address listed for the same node from system

This is why we have ARP helper modules in some implementations so that the 
format isn't as critical any longer.

>food for thought on address format....

I doubt there will be many routers used - I also doubt they will be very 
expensive.  I tend to view things as a series of partition domains that may 
span a portion of a subnet or across subnets.  These domains are centrally 
managed and the IP communication is per partition domain.

Mike