[c-nsp] LAM / Mobile IP in modern times

[Lincoln Dale]

g'day,
> 
>>> The only remaining question is why for it's money have VMWare not done 
>>> the trivial task of making OSPF part of their VMotion malarkey...*sigh*
>> 
>> because its not /quite/ as simple as you suggest.
>> 
> The awkward part I see is host based (not service) L3 connectivity.  The 
> operating system would need work happily in a multihomed configuration 
> and to understand what a dead gateway means.  This probably would not be 
> easy to pull off on a Windows based guest, but it should be quite doable 
> on....well *any* other OS :)

the premise of VM mobility is that the OS and apps being virtualised are completely unaware that they have been virtualised.

what this means in reality is that you can migrate a VM from one physical host to another and there is no disruption to traffic flows.
there are no disruptions to any TCP connections to apps running on the (virtualised) server.

but in order for this trick to be pulled off, you need a common L2 domain.

if you're willing to remove that requirement and potentially have an outage or disruption at the host or app level, or you're willing to do whatever integration work is necessary to mitigate that, then i believe its technically possible to have vMotion across L3.

but note that not all apps will be supported.  nor all hosts.  and if those apps/hosts are doing any form of network-based storage access (NFS, CIFS, iSCSI et al), then bad things may well happen unless you can quiesce the virtual host on a migration.


> 
> As a mentioned before though, unfortunately I never got this beyond the 
> planning stage due to the 'quality' of the VMware consultants we hired :-/

i believe the common case is that vCenter today 'forces' all hosts in a 'cluster' to be in a common L2 domain, although i read something somewhere that said that it can be overruled.  i haven't found the nerd knob to set that if there is such a thing.
but even if there is such a nerd knob, its caveat emptor.  you might not like the result. :)


cheers,

lincoln.