[Engine-devel] network subnet

[Livnat Peer]

On 30/08/12 23:11, Alon Bar-Lev wrote:
> 
> 
> ----- Original Message -----
>> From: "Livnat Peer" <lpeer at redhat.com>
>> To: "Alon Bar-Lev" <alonbl at redhat.com>
>> Cc: engine-devel at ovirt.org
>> Sent: Thursday, August 30, 2012 10:16:05 PM
>> Subject: Re: [Engine-devel] network subnet
>>
>> On 30/08/12 21:39, Alon Bar-Lev wrote:
>>>
>>>
>>> ----- Original Message -----
>>>> From: "Livnat Peer" <lpeer at redhat.com>
>>>> To: engine-devel at ovirt.org
>>>> Sent: Thursday, August 30, 2012 3:22:29 PM
>>>> Subject: [Engine-devel] network subnet
>>>>
>>>> Hi All,
>>>>
>>>> Today when a user wants to define a network subnet mask, he does
>>>> it
>>>> when
>>>> he attaches the network to a host NIC.
>>>>
>>>> I was wondering if there is a reason not to define the network
>>>> subnet
>>>> on
>>>> the logical network entity (Data center level).
>>>>
>>>> Thanks, Livnat
>>>
>>> Hello,
>>>
>>> I am sorry, maybe I do not understand... the IP scheme enforces the
>>> use of address mask in order to properly route packets.
>>
>> of course. My proposal is related to our user usage of the system.
>> Today
>> ovirt user, who wants to define a network subnet, has to type the
>> subnet
>> per host (per network), I think the user should only define it once
>> on
>> the logical network entity in the Data Center.
>> Propagating the value to all hosts is needed but it should be our
>> internal implementation detail.
>>
>>>
>>> Network mask is used in any case, I guess it can be dropped from
>>> configuration in favour of using the address class as mask, is
>>> that what you suggest?
>>>
>>
>> No, hope the above paragraph made it more clear.
>>
> 
> Hello,
> 
> Then you assume that a logical network, which is actually layer 2 network in our implementation, has layer 3 characteristics, right?
> 
> In our current implementation "data center logical network" is pure layer 2 segment aka layer 2 broadcast domain.
> 
> One can use the same logical network for multiple layer 3 segments, which is totally valid and consistent with standard physical layer 2 setup.
> 
> Unless I am missing something crucial, I would suggest to keep the consistent physical->virtual mapping, unless we emulate layer 3 switching. Layer 2 does not have layer 3 characteristics.
> 
> Regards,
> Alon.
> 

Generally I agree with what you wrote.

I would like to open for discussion the definition mentioned above that
a logical network is a layer 2 broadcast domain.

We have 2 types of logical networks, VM networks and 'other' (host
functionality?) networks.

When talking about VM networks, I think the definition above is
accurate, the guests using the network should get a layer 2 broadcast
domain.
It can be implemented over a single (physical) layer 2 domain or it can
be implemented over multiple (physical) layer 2 domains using
technologies like tunneling or vxlan.

When talking about other networks like storage, display, migration,
etc. we are actually discussing a network which represent a common
functionality the hosts are using but I am not sure guaranteeing a layer
2 broadcast domain is interesting for such network.

Going forward I expect we'll associate layer 3 services with logical
networks. For example DHCP, DNS, LB etc.

Any thoughts/comments on the above are welcomed.


Thanks, Livnat