<[email protected]> writes:
> Dhruv Dhody <[email protected]> writes:
>
> > (1) Sec 2.2
> > "A key requirement for live migration is that a VM retain
> > its IP address(es) and MAC address(es) in its new location
> > (to avoid tearing down existing communication)."
> > IP address must be retained but couldn't live migration be still
> > supported if the MAC address of the VM changes in the routed
> > semantics?
> In full generality, no. For example, some VMs contain software
> whose license is keyed by the VM's MAC address. If the MAC address
> changes, the software stops working.
> There are some VMs for which a MAC address change may work, but the
> MAC address change is visible to the VM's OS - the device driver for
> the virtual NIC has to reconfigure, and that's potentially
> disruptive and non-transparent depending on what that device driver
> and OS can cope with.
Goodpoints. Proposed new text (including also change from Vishwas'
comments):
A key benefit of server virtualization is virtual machine
(VM) mobility. A VM can be migrated from one server to
another, live, i.e., while continuing to run and without
needing to shut it down and restart it at the new
location. A key requirement for live migration is that a VM
retain critical network state at its new location, including
its IP and MAC address(es). Preservation of MAC addresses
is necessary when software licences are bound to MAC
addresses. More generally, any change in the VM's MAC
addresses resulting from a move would be visible to the VM
and thus potentially result in unexpected disruptions.
Retaining IP addresses after a move is necessary to prevent
existing transport (e.g., TCP) connections from breaking and
needing to be restarted.
In traditional data centers, servers are assigned IP
addresses based on their physical location, for example
based on the Top of Rack (ToR) switch for the server rack or
the VLAN configured to the server. Servers can only move to
other locations within the same IP subnet. This constraint
is not problematic for physical servers, which move
infrequently, but it restricts the placement and movement of
VMs within the data center. Any solution for a scalable
multi-tenant data center must allow a VM to be placed (or
moved to) anywhere within the data center, without being
constrained by the subnet boundary concerns of the host
servers.
Thomas
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