[libvirt-users] How libvirt interacts with dhcpd?
Hi everybody, I'm using libvirt together with xCAT, on the same host, for testing purposes. xCAT install and manages dhcpd. How libvirt interacts with dhcpd? And if doens't how does the dhcp server of libvirt works, plus where I can find information on how to troubleshot it? Regards, -- “If you're going to try, go all the way. Otherwise, don't even start. ..." Charles Bukowski
On 06/15/2018 06:49 PM, Daniel. wrote:
Hi everybody,
I'm using libvirt together with xCAT, on the same host, for testing purposes. xCAT install and manages dhcpd. How libvirt interacts with dhcpd? And if doens't how does the dhcp server of libvirt works, plus where I can find information on how to troubleshot it?
libvirt doesn't use dhcpd. It runs a separate instance of dnsmasq for each virtual network that is defined within libvirt. Each instance listens *only* on the bridge device that was created by libvirt for that network. IIfi dhcpd has an option that tells it to listen on all interfaces (or to automatically start listening on any new interface that is created), you should disable that option so that it doesn't attempt to listen for dhcp requests on the bridges created by libvirt.
Cool, thanks!! Does it have logs? Cheers Em 18/06/2018 12:55 AM, "Laine Stump" <laine@redhat.com> escreveu: On 06/15/2018 06:49 PM, Daniel. wrote:
Hi everybody,
I'm using libvirt together with xCAT, on the same host, for testing purposes. xCAT install and manages dhcpd. How libvirt interacts with dhcpd? And if doens't how does the dhcp server of libvirt works, plus where I can find information on how to troubleshot it?
libvirt doesn't use dhcpd. It runs a separate instance of dnsmasq for each virtual network that is defined within libvirt. Each instance listens *only* on the bridge device that was created by libvirt for that network. IIfi dhcpd has an option that tells it to listen on all interfaces (or to automatically start listening on any new interface that is created), you should disable that option so that it doesn't attempt to listen for dhcp requests on the bridges created by libvirt.
On 06/18/2018 09:16 AM, Daniel. wrote:
Cool, thanks!! Does it have logs?
Whatever dnsmasq chooses to log, and wherever it chooses to log it. (I actually looked once to see if there was a way of reducing the amount of logging, and didn't find much of anything useful.) If you were planning to learn the current IP address of a particular guest's interface by looking at the logs, you can instead use the virsh domifaddr to to that.
Cheers
Em 18/06/2018 12:55 AM, "Laine Stump" <laine@redhat.com <mailto:laine@redhat.com>> escreveu:
On 06/15/2018 06:49 PM, Daniel. wrote: > Hi everybody, > > I'm using libvirt together with xCAT, on the same host, for testing > purposes. xCAT install and manages dhcpd. How libvirt interacts with > dhcpd? And if doens't how does the dhcp server of libvirt works, plus > where I can find information on how to troubleshot it?
libvirt doesn't use dhcpd. It runs a separate instance of dnsmasq for each virtual network that is defined within libvirt. Each instance listens *only* on the bridge device that was created by libvirt for that network. IIfi dhcpd has an option that tells it to listen on all interfaces (or to automatically start listening on any new interface that is created), you should disable that option so that it doesn't attempt to listen for dhcp requests on the bridges created by libvirt.
Thanks for the reply Laine. My problem is that dnsmasq is masking dhcpd, xCAT uses dhcpd for PXE stuff. If dnsmasq answer DHCP requests the PXE boot won' t work. I want to see the logs for ensuring the dnsmasq is not masking dhcpd. Regards, 2018-06-18 11:39 GMT-03:00 Laine Stump <laine@redhat.com>:
On 06/18/2018 09:16 AM, Daniel. wrote:
Cool, thanks!! Does it have logs?
Whatever dnsmasq chooses to log, and wherever it chooses to log it. (I actually looked once to see if there was a way of reducing the amount of logging, and didn't find much of anything useful.)
If you were planning to learn the current IP address of a particular guest's interface by looking at the logs, you can instead use the virsh domifaddr to to that.
Cheers
Em 18/06/2018 12:55 AM, "Laine Stump" <laine@redhat.com <mailto:laine@redhat.com>> escreveu:
On 06/15/2018 06:49 PM, Daniel. wrote: > Hi everybody, > > I'm using libvirt together with xCAT, on the same host, for testing > purposes. xCAT install and manages dhcpd. How libvirt interacts with > dhcpd? And if doens't how does the dhcp server of libvirt works, plus > where I can find information on how to troubleshot it?
libvirt doesn't use dhcpd. It runs a separate instance of dnsmasq for each virtual network that is defined within libvirt. Each instance listens *only* on the bridge device that was created by libvirt for that network. IIfi dhcpd has an option that tells it to listen on all interfaces (or to automatically start listening on any new interface that is created), you should disable that option so that it doesn't attempt to listen for dhcp requests on the bridges created by libvirt.
-- “If you're going to try, go all the way. Otherwise, don't even start. ..." Charles Bukowski
On 06/18/2018 01:00 PM, Daniel. wrote:
Thanks for the reply Laine. My problem is that dnsmasq is masking dhcpd, xCAT uses dhcpd for PXE stuff. If dnsmasq answer DHCP requests the PXE boot won' t work. I want to see the logs for ensuring the dnsmasq is not masking dhcpd.
The dnsmasq run by libvirtd only listens on bridges that libvirt itself creates for libvirt virtual networks. If the PXE boot you're talking about is happening on a different interface, then libvirt's dnsmasq will not be messing with it. If, on the other hand, you want to do PXE boot on the virtual networks created by libvirt, then you can either 1) disable libvirt's dhcp on that network by removing the <dhcp> section from the network definition and restarting it, or 2) read in the libvirt virtual network documentation on how to set it up to support PXE boot via dnsmasq (and don't configure your dhcpd to listen on that interface).
Regards,
2018-06-18 11:39 GMT-03:00 Laine Stump <laine@redhat.com>:
On 06/18/2018 09:16 AM, Daniel. wrote:
Cool, thanks!! Does it have logs?
Whatever dnsmasq chooses to log, and wherever it chooses to log it. (I actually looked once to see if there was a way of reducing the amount of logging, and didn't find much of anything useful.)
If you were planning to learn the current IP address of a particular guest's interface by looking at the logs, you can instead use the virsh domifaddr to to that.
Cheers
Em 18/06/2018 12:55 AM, "Laine Stump" <laine@redhat.com <mailto:laine@redhat.com>> escreveu:
On 06/15/2018 06:49 PM, Daniel. wrote: > Hi everybody, > > I'm using libvirt together with xCAT, on the same host, for testing > purposes. xCAT install and manages dhcpd. How libvirt interacts with > dhcpd? And if doens't how does the dhcp server of libvirt works, plus > where I can find information on how to troubleshot it?
libvirt doesn't use dhcpd. It runs a separate instance of dnsmasq for each virtual network that is defined within libvirt. Each instance listens *only* on the bridge device that was created by libvirt for that network. IIfi dhcpd has an option that tells it to listen on all interfaces (or to automatically start listening on any new interface that is created), you should disable that option so that it doesn't attempt to listen for dhcp requests on the bridges created by libvirt.
Thanks for your help Laine In my case disabling dhcpd is not an option so I took the path of disabling dhcp on virbr0. Pxe is handled by xcat which uses dhcpd for this. It seems to be working fine :) Regards Em qua, 20 de jun de 2018 10:59, Laine Stump <laine@redhat.com> escreveu:
On 06/18/2018 01:00 PM, Daniel. wrote:
Thanks for the reply Laine. My problem is that dnsmasq is masking dhcpd, xCAT uses dhcpd for PXE stuff. If dnsmasq answer DHCP requests the PXE boot won' t work. I want to see the logs for ensuring the dnsmasq is not masking dhcpd.
The dnsmasq run by libvirtd only listens on bridges that libvirt itself creates for libvirt virtual networks. If the PXE boot you're talking about is happening on a different interface, then libvirt's dnsmasq will not be messing with it.
If, on the other hand, you want to do PXE boot on the virtual networks created by libvirt, then you can either 1) disable libvirt's dhcp on that network by removing the <dhcp> section from the network definition and restarting it, or 2) read in the libvirt virtual network documentation on how to set it up to support PXE boot via dnsmasq (and don't configure your dhcpd to listen on that interface).
Regards,
2018-06-18 11:39 GMT-03:00 Laine Stump <laine@redhat.com>:
On 06/18/2018 09:16 AM, Daniel. wrote:
Cool, thanks!! Does it have logs?
Whatever dnsmasq chooses to log, and wherever it chooses to log it. (I actually looked once to see if there was a way of reducing the amount of logging, and didn't find much of anything useful.)
If you were planning to learn the current IP address of a particular guest's interface by looking at the logs, you can instead use the virsh domifaddr to to that.
Cheers
Em 18/06/2018 12:55 AM, "Laine Stump" <laine@redhat.com <mailto:laine@redhat.com>> escreveu:
On 06/15/2018 06:49 PM, Daniel. wrote: > Hi everybody, > > I'm using libvirt together with xCAT, on the same host, for
> purposes. xCAT install and manages dhcpd. How libvirt interacts
with
> dhcpd? And if doens't how does the dhcp server of libvirt works,
> where I can find information on how to troubleshot it?
libvirt doesn't use dhcpd. It runs a separate instance of dnsmasq
for
each virtual network that is defined within libvirt. Each instance listens *only* on the bridge device that was created by libvirt
for that
network. IIfi dhcpd has an option that tells it to listen on all interfaces (or to automatically start listening on any new
interface
that is created), you should disable that option so that it doesn't attempt to listen for dhcp requests on the bridges created by
testing plus libvirt.
participants (2)
-
Daniel. -
Laine Stump