Libguestfs - Feb 2018 - Re: [PATCH] v2v: remove MAC address related information

On Tue, 27 Feb 2018 12:53:08 +0100
Pino Toscano <ptoscano@redhat.com> wrote:
> On Tuesday, 27 February 2018 12:35:36 CET Tomáš Golembiovský wrote:
> > Remove ties to MAC address because it is likely to change.  
> 
> v2v tries to preserve the MAC address of network interfaces; few months
> ago we did a fix regarding this:
> https://bugzilla.redhat.com/show_bug.cgi?id=1506572
> 
> The approach of this patch is IMHO not good, since it removes the MAC
> address from the network-scripts, but still the rest of v2v will try
> to preserve the MAC addresses.
> 
> What's the reason behind this patch?
Reason is that the MAC address is likely to change after the conversion
because the environment uses different MAC prefix. It depends on the
management system. For example the default pool in oVirt has prefix
00:1A:4A:... registered to Qumranet Inc. I don't know what VMware has as
as default. Big companies probably have their own prefix and thus are
OK.

Sure, you can have custom MAC addresses with different prefix on your
network. I can't say if that is good idea or bad idea.

It seems to me that this dual approach is right thing to do. Remove the
reference from guest so it is ready for new MAC, but leave the old MAC
in metadata. That way the management system can decide what is the right
way to do.


    Tomas

-- 
Tomáš Golembiovský <tgolembi@redhat.com>

On Tue, Feb 27, 2018 at 01:34:21PM +0100, Tomáš Golembiovský
wrote:
> On Tue, 27 Feb 2018 12:53:08 +0100
> Pino Toscano <ptoscano@redhat.com> wrote:
> 
> > On Tuesday, 27 February 2018 12:35:36 CET Tomáš Golembiovský wrote:
> > > Remove ties to MAC address because it is likely to change.  
> > 
> > v2v tries to preserve the MAC address of network interfaces; few
months
> > ago we did a fix regarding this:
> > https://bugzilla.redhat.com/show_bug.cgi?id=1506572
> > 
> > The approach of this patch is IMHO not good, since it removes the MAC
> > address from the network-scripts, but still the rest of v2v will try
> > to preserve the MAC addresses.
> > 
> > What's the reason behind this patch?
> 
> Reason is that the MAC address is likely to change after the conversion
> because the environment uses different MAC prefix. It depends on the
> management system. For example the default pool in oVirt has prefix
> 00:1A:4A:... registered to Qumranet Inc. I don't know what VMware has
as
> as default. Big companies probably have their own prefix and thus are
> OK.
We're passing the source MAC through into the OVF (see rasd:MACAddress
and v2v/create_ovf.ml).  Does oVirt use it?
> Sure, you can have custom MAC addresses with different prefix on your
> network. I can't say if that is good idea or bad idea.
Every (real) ethernet card comes with a different MAC address, with a
different prefix for each vendor, so at least in theory there is no
problem here.  It's not an issue for KVM either.  But it might be an
issue for a particular management system, say if oVirt is hard-coding
that prefix somewhere, or is ignoring the rasd:MACAddress field.
> It seems to me that this dual approach is right thing to do. Remove the
> reference from guest so it is ready for new MAC, but leave the old MAC
> in metadata. That way the management system can decide what is the right
> way to do.
The problem is going to be that ethernet ports get swapped around.

The other problem is that even if this is a good idea, Windows also
embeds the MAC address somewhere in the Registry and we aren't
touching that.  Plus there's likely to be multiple other places in
Linux where it is stored, NetworkManager, systemd-networkd, etc.

This suggests that perhaps we should do this conditional on the target
hypervisor, but we'd need more information about what oVirt is doing
first.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-builder quickly builds VMs from scratch
http://libguestfs.org/virt-builder.1.html

> On 27 Feb 2018, at 13:57, Richard W.M. Jones <rjones@redhat.com>
wrote:
> 
> On Tue, Feb 27, 2018 at 01:34:21PM +0100, Tomáš Golembiovský wrote:
>> On Tue, 27 Feb 2018 12:53:08 +0100
>> Pino Toscano <ptoscano@redhat.com> wrote:
>> 
>>> On Tuesday, 27 February 2018 12:35:36 CET Tomáš Golembiovský wrote:
>>>> Remove ties to MAC address because it is likely to change.  
>>> 
>>> v2v tries to preserve the MAC address of network interfaces; few
months
>>> ago we did a fix regarding this:
>>> https://bugzilla.redhat.com/show_bug.cgi?id=1506572
>>> 
>>> The approach of this patch is IMHO not good, since it removes the
MAC
>>> address from the network-scripts, but still the rest of v2v will
try
>>> to preserve the MAC addresses.
>>> 
>>> What's the reason behind this patch?
>> 
>> Reason is that the MAC address is likely to change after the conversion
>> because the environment uses different MAC prefix. It depends on the
>> management system. For example the default pool in oVirt has prefix
>> 00:1A:4A:... registered to Qumranet Inc. I don't know what VMware
has as
>> as default. Big companies probably have their own prefix and thus are
>> OK.
> 
> We're passing the source MAC through into the OVF (see rasd:MACAddress
> and v2v/create_ovf.ml).  Does oVirt use it?
no. Exactly for the reason Tomas mentioned, the MAC spaces are almost always
entirely different and we reallocate a different MAC every time
> 
>> Sure, you can have custom MAC addresses with different prefix on your
>> network. I can't say if that is good idea or bad idea.
> 
> Every (real) ethernet card comes with a different MAC address, with a
> different prefix for each vendor, so at least in theory there is no
> problem here.  It's not an issue for KVM either.  But it might be an
> issue for a particular management system, say if oVirt is hard-coding
> that prefix somewhere, or is ignoring the rasd:MACAddress field.
> 
>> It seems to me that this dual approach is right thing to do. Remove the
>> reference from guest so it is ready for new MAC, but leave the old MAC
>> in metadata. That way the management system can decide what is the
right
>> way to do.
> 
> The problem is going to be that ethernet ports get swapped around.
> 
> The other problem is that even if this is a good idea, Windows also
> embeds the MAC address somewhere in the Registry and we aren't
> touching that.  Plus there's likely to be multiple other places in
> Linux where it is stored, NetworkManager, systemd-networkd, etc.
> 
> This suggests that perhaps we should do this conditional on the target
> hypervisor, but we'd need more information about what oVirt is doing
> first.
conditional sounds good. for ovirt specifically it may be unconditionally
cleared
> 
> Rich.
> 
> -- 
> Richard Jones, Virtualization Group, Red Hat
http://people.redhat.com/~rjones
> Read my programming and virtualization blog: http://rwmj.wordpress.com
> virt-builder quickly builds VMs from scratch
> http://libguestfs.org/virt-builder.1.html