[openib-general] Unicast ARP

[Hal Rosenstock]

On Mon, 2004-11-29 at 12:10, Ido Bukspan wrote:
> 	In gen2 we have a problem if the destination path (e.g. LID)
> changes. 

Is this restricted to LID changes or apply more generally to hardware
address (GID and/or QPN) changes ? (I had seen something similar when
the QPN changed; ARP timeout/retries are needed prior to connectivity
being restored).

> Typically the kernel issues periodically unicast ARP packets to
> addresses which are in the ARP cache to ensure that the neighbors are up and
> that the ARP cache is up to date. In gen2, unicast  ARPs arrive to the ipoib
> driver (hard_xmit) with no address handle assigned. Now, SA query is
> initiated by the ipoib driver, 

Is this the PathRecord lookup for unicast GID of destination ? Is the
path record (info) cached ?

> then ARP is sent to this address, and when
> ARP response arrives back, ARP cache is not updated with the new path.

Do you mean hardware address here (GID + QPN) ?

>  In
> other words, ARP cache believes that the relevant entry is up to date and
> doesn't notice the path change.
> 
> 	I think that we should hold a link list which contains the current
> address handles with the corresponding GID. When a unicast ARP is sent
> (hard_xmit), instead of going to the SA, look up the right GID in our list,
> then send a unicast ARP with this address handle. If path has changed, then
> the ARP reply won't arrive and it will cause the ARP cache to be refreshed.
> 
> 	This solution also reduces the burden on the SA.
> 
> 	What do you think ?
> 
> 	-Ido
> 
> 
> 
> Ido Bukspan
> Mellanox Technologies Ltd.
> Phone : (972)-3-6259500 ,Ext 518.
> Fax     : (972)-3-5614943
> mailto:ido at mellanox.co.il
> http://www.mellanox.com
> 
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