[openib-general] Re: IPoIB and lid change

[Hal Rosenstock]

On Sun, 2006-02-12 at 09:09, Michael S. Tsirkin wrote:
> Quoting r. Hal Rosenstock <halr at voltaire.com>:
> > Subject: Re: IPoIB and lid change
> > 
> > On Sun, 2006-02-12 at 08:52, Michael S. Tsirkin wrote:
> > > Quoting Hal Rosenstock <halr at voltaire.com>:
> > > > > > > Hi, Roland!  One issue we have with IPoIB is that IPoIB may cache a
> > > > > > > remote node path for a long time. Remote LID may get changed e.g. if the
> > > > > > > SM is changed, and IPoIB might lose connectivity.
> > > > > > 
> > > > > > The remote LID may get changed for other reasons too without an SM
> > > > > > change (SM merge of 2 separate subnets). How can this be handled ?
> > > > > 
> > > > > Change the SM to trigger SM lid change for both subnets?
> > > > 
> > > > I think that's overly disruptive for the subnet whose SM didn't change.
> > > > There should be a gentler way...
> > > 
> > > So that another issue with IPoIB subnet spanning multiple IB subnets.
> > > The IPoIB spec already lists several of these.
> > 
> > I was referring to the subnet merge case. In the case of 2 IB subnets
> > within a single IPoIB subnet, there is another layer of this issue as
> > you point out.
> 
> But if one of the subnets being merged was not part of the IPoIB
> subnet, we dont have IPoIB chaching the IB path.
> So IB path changes dont affect IPoIB. What am I missing?

A subnet merge in the remote subnet can affect the existing LIDs of the
remote subnet to which there were paths depending on the SM policy.
That's one case related to the case in the local side. Of course, we're
talking theory here because there are no IB routers, right ?

-- Hal