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Re: [Qemu-discuss] qemu dhcp issue

From: Donald R Laster Jr
Subject: Re: [Qemu-discuss] qemu dhcp issue
Date: Sun, 25 Jan 2015 18:44:23 -0500
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  Could you possibly need to set the MAC address of the Ethernet interfaces for the VM 
itself?  You are referencing "vendor ID" and I making an assumption that you 
are referencing the first 3 octets of the Ethernet MAC Address.  In case you are not 
aware of what a MAC address is defined as:

        MAC, Media Access Control, address is a globally unique identifier
        assigned to network devices, and therefore it is often referred to as
        hardware or physical address. MAC addresses are 6-byte (48-bits) in
        length, and are written in MM:MM:MM:SS:SS:SS format. The first 3-bytes
        are ID number of the manufacturer, which is assigned by an Internet
        standards body. The second 3-bytes are serial number assigned by the
        manufacturer. (http://www.iplocation.net/tools/mac-address.php)

  Redhat/CentOS when booted expect specific MAC addresses when certain things 
are configured.  QEMU may not be using the expected MAC addresses with the 
current changes - it will set a default.  The files to look are in 
subdirectories of the /etc/ directory.  NetworkManager might be the tool you 
need to look at as well.

  Check if you are configuring the VM's networking with similar settings:

   -net nic,macaddr=52:54:00:10:01:2E,vlan=0,model=e1000
   -net tap,vlan=0,helper=/usr/libexec/qemu-bridge-helper
    -net nic,macaddr=52:54:00:10:01:23,vlan=0,model=e1000
   -net tap,vlan=0,helper=/usr/libexec/qemu-bridge-helper

The key is to set the macaddr= field with the appropriate vendor ID.


Vlad Yasevich wrote on 01/20/2015 06:10 PM:
On 01/20/2015 08:51 AM, czebartek wrote:
Hi All,
I have a problem with configuration of dhcp client on VM started by qemu. I 
have a server connected to some LAN network from where I get IP addresses. On 
my server I start qemu with prepared kernel image and rootfs. I set up tap 
interfaces and bridge on a host machine. The machine I'am simulating is Linux 
Centos 6.
What is the problem now:
When qemu starts up it starts some dhcp client and request the IP address from 
our external dhcp server. But, there were some security changes in dhcp server 
recently and now accepts requests only from clients with specific vendor ID.
The thing is that I don't know how qemu is starting the dhcp client and which client it 
is using. On Centos there is "dhclient". I know that it uses dhclient.conf file 
when I could set up vendor ID, but even if I set this config it doesn't work.
Do you know how to check whcih dhcp client is started when qemu starts VM ? Do 
you know how to check what configuration it is using ?
Thanks in advance for help.
Best regards,

In this case, qemu doesn't start the dhcp client on the vm.  The OS instance
running within the VM will start the dhcp client and it's whatever is installed 
for that
instance. So, look to see what is installed inside the VM and edit appropriate 



Donald R. Laster Jr.
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