Open Stack

The problem here is not VLAN but subnet. Normally you have one subnet associate with one interface (Ethernet interface), if you want multiple interfaces listen to the same DHCP server, you need to configure the multiple interfaces on the same subnet since one DHCP server can only broadcast to one subnet. But to configure multiple interfaces on the same subnet, you will run into other problems. Say you have the following configuration hypothetically on  your server,

int1: 192.168.10.100
Int2: 192.168.10.101

They both sit on the same subnet 192.168.10.0/24 or 255.255.255.0, when the traffic goes out from this server to outside, it will be confused to use which interface since both will take the same path from hop to hop, so you have a potential loop here.

Dennis Qin (aka Xiaohong Qin)

-----Original Message-----
From: Sergey Arlashin [mailto:sergeyarl.maillist at gmail.com] 
Sent: Saturday, March 19, 2016 11:58 PM
To: openstack at lists.openstack.org
Subject: [Openstack] DHCP + vlan

Hi All,

I have a simple VLAN-based setup: single controller node and multiple compute nodes. Currently neutron DHCP agent resides on controller node and uses dnsmasq as a DHCP server.

The problem is that dnsmasq is listening on tap877d3721-e2 interface which is mapped to only one particular VLAN. On this particular box (I mean controller node) VLAN tags are stripped from incoming packets (due to external network configuration which I'm not authorized to change). 
Therefore VM instances cannot get their IPs via DHCP - I see the incoming DHCP requests with tcpdump but dnsmasq is just ignoring them. I understand that it might be not a correct approach but the current situation demands that we make DHCP server be assigned to all interfaces including external bridge (br-eth0) . Not only tap877d3721-e2. 
Regardless of VLAN.
However I haven't found a way do achieve this.

Can anybody please help me to solve this situation?

Thank you!

Regards,
Sergey




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