openstack team mailing list archive

[gong yong sheng <gongysh@xxxxxxxxxxxxxxxxxx>]

On 11/29/2012 07:56 AM, Ahmed Al-Mehdi wrote:
> Hello,
>
> I have a few questions related to private and external network in 
> Quantum.  I am running into some odd behavior with networking related 
> to my VM instance that I am trying to resolve.
>
>
> I used the following commands to create a private network and a router 
> to which it is attached:
>
> # quantum net-create --tenant-id $put_id_of_project_one net_proj_one 
> --provider:network_type vlan --provider:physical_network physnet1 
> --provider:segmentation_id 1024
> # quantum subnet-create --tenant-id $put_id_of_project_one 
> net_proj_one 10.10.10.0/24 <http://10.10.10.0/24> (step a)
>
> # quantum router-create --tenant-id $put_id_of_project_one router_proj_one
> # quantum router-interface-add $put_router_proj_one_id_here 
> $put_subnet_id_here
>
> Q: Upon executing "step a", does Quantum reserve the first IP address 
> from the subnet's cidr range as a gateway_ip addr?  If so, why?  Does 
> that happen even if the subnet is not attached to a router?
Yes. the first IP address is reserved as default gateway ip. If  no 
quantum router needed, you can set a true physical router on it. If you 
don't want a gateway at all,
you can create a subnet without gateway ip reserved.
> I then used the following steps to create an external network:
>
> # quantum net-create --tenant-id $put_id_of_service_tenant ext_net 
> --router:external=True
> # quantum subnet-create --tenant-id $put_id_of_service_tenant 
> --allocation-pool start=192.168.50.102,end=192.168.50.126 --gateway 
> 192.168.50.1 ext_net192.168.50.100/24 
> <http://192.168.50.100/24> --enable_dhcp=False  (step b)
>
> Q: I am trying to understand the different options passed to " quantum 
> subnet-create" for an external network:
>
> -  start=192.168.50.102,end=192.168.50.126 : Is this the list of 
> floating-IPs that are accessible from outside world?  And these would 
> be mapped to a private  IP addr?
allocation pool is a range for inner IPAM. In fact you can assign an IP 
beyond this range to a Port as long as it is under the cidr of a given 
subnet.
> - 192.168.50.1 <http://192.168.50.1/>:  Is this the outside gateway IP 
> addr (provided by our IT)?
It should be.
> - 192.168.50.100/24 <http://192.168.50.100/24>:  Is 192.168.50.100 
> assigned (reserved) for any purpose?  What is this cidr represent?
It should be a wrong cidr.
I think if you are using 192.168.50.100/30, the 192.168.59.101 will be 
reserved.
> -  enable_dhcp=False : What is the effect of setting this to true?  I 
> mean how does Quantum dole out a floating IP mapping to which private 
> IP, randomly?
If the network is just for floatingips, there is no need to run dhcp 
server for the ips on this network.
only ips allocated to VMs' port needed to be in dhcp server if you want 
to use dhcp.
> Thank you,
> Ahmed.
>
>
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