Subject: Re: [Ipoverib] BOOTP/DHCP chaddr field

From: "H.K. Jerry Chu" <[email-masked]>
Date: Sat, 16 Mar 2002 09:37:17 -0800 (PST)

Vivek,

...
<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.
>
>For example a simple issue with SIDR and DHCP:
>
>        As noted by Akihiko, and I agree, there may be multiple IPoIB
>        interfaces over the same port but these interfaces would have
>        different QPNs. Greater than one IPoIB interface per port and
>        the server or the client side CM have no way to determine the
>        QPN to send back; server doesn't have a good distinguishing
>        value to give to the client CM.

I think it's a stretch to use different QPs to build multiple
"virtual" interfaces. P_Key is the perfect mechanism for that. If one
wants multiple interfaces out of the same node to the same IP link,
one add multiple HCAs/ports. Different QPs attched to the same HCA
port has the same hardware failure domain so I don't see what value
it buys. If this is for load-balancing purpose one will probably have
to resort to SIDR like you have suggested anyway. Using GID leaves no
room for any additional flag in the hardware address. But since SIDR
must be consulted now, all the advanced functions can be moved there.

The above is just some of my own preliminary thoughts. I hate to go
down this route of debating hardware address format again unless we
decide against the broadcast flag workaround.

I'm glad this DHCP issue is brought up now, not later (thanks Roy!).
I wonder how many other issues are lurking out there. I encourage
everyone to go through the current draft proposals very carefully
(speaking as a co-chair now :-) so we don't have to go through the
pain of respin the design later.

Jerry

>Vivek

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---

From: Vivek Kashyap <[email-masked]>
Date: Sun, 17 Mar 2002 09:50:40 -0800 (PST)

Jerry,

        The solution, that I have outlined in the earlier mails based
        on the broadcast bit, should be adequate. There is no change
        required in generic DHCP servers if the broadcat bit is used.
        The DHCP clients, as far as I know, are configured per
        interface to use the broadcast bit - the same can be done for
        IPoIB interface. One will of course need to update the client
        to send the 'right' client-identifier option and handle the
        IPoIB interface.

        I too don't want to revisit the link-address discussion. The
        SIDR issue outlined in the earlier mail is an illustration of
        the kind of issues that we will have to deal with. By
        considering multiple IPoIB interfaces per port a stretch
        (which I don't think it is) we end up adding more
        restrictions. 

	The broadcast bit should be adequate.

Vivek

-- 
Vivek Kashyap
Linux Technology Center, IBM
[email-masked] 
[email-masked] 
503 578 3422 (o)