[libvirt-users] Specify DNS and gateway for dnsmasq
Hi all, how I can set dhcp options as DNS, gateway, etc in libvirt's network definitions? From what I read here[1], I can use the <option> tag. However, I can not find nothing on libvirt official documentation. I am missing something? Thanks. [1] https://www.redhat.com/archives/libvir-list/2013-March/msg00166.html -- Danti Gionatan Supporto Tecnico Assyoma S.r.l. - www.assyoma.it email: g.danti@assyoma.it - info@assyoma.it GPG public key ID: FF5F32A8
On 03/12/2018 06:45 PM, Gionatan Danti wrote:
Hi all, how I can set dhcp options as DNS, gateway, etc in libvirt's network definitions?
The default GW depends on the IP address you assigned to your network: <ip address='192.168.122.1' netmask='255.255.255.0'/> This says the default GW is 192.168.122.1/24. However, you can insert other routes too: <route address="192.168.222.0" prefix="24" gateway="192.168.122.2"/> For handling DNS, you need to focus on <dns/> element. For instance, to set a different forwarder than GW: <dns> <forwarder addr="8.8.8.8"/> </dns> It's all documented here: https://libvirt.org/formatnetwork.html#elementsStaticroute and in the subsequent section.
From what I read here[1], I can use the <option> tag. However, I can not find nothing on libvirt official documentation.
No, that was just a proposal. RFC, a discussion how should we implement some special features of DHCP. Those are not patches and in fact patches implementing that were never merged. Michal
On 13/03/2018 15:30, Michal Privoznik wrote:> The default GW depends on the IP address you assigned to your network:
<ip address='192.168.122.1' netmask='255.255.255.0'/>
This says the default GW is 192.168.122.1/24. However, you can insert other routes too:
<route address="192.168.222.0" prefix="24" gateway="192.168.122.2"/>
For handling DNS, you need to focus on <dns/> element. For instance, to set a different forwarder than GW:
<dns> <forwarder addr="8.8.8.8"/> </dns>
For NATed/routed networks, sure. However, I have an isolated network like that (without the "forward" element): <network> <name>net1</name> <uuid>dcf5c09b-dcb6-4fd3-86b8-6312a7b94bf6</uuid> <bridge name='virbr1' stp='on' delay='0'/> <mac address='52:54:00:97:1b:15'/> <domain name='TEST'/> <ip address='192.168.10.1' netmask='255.255.255.0'> <dhcp> <range start='192.168.10.128' end='192.168.10.254'/> </dhcp> </ip> </network> When the client asks for an IP via DHCP, it obtain a valid IP address but *no* gateway. Is it the expected behavior for an isolated network? From my understanding, network isolation is accomplished by firewall rules in the FORWARD table, rather than by not assigning the gateway IP address to clients.
No, that was just a proposal. RFC, a discussion how should we implement some special features of DHCP. Those are not patches and in fact patches implementing that were never merged.
Michal
Ok, thank you Michal. -- Danti Gionatan Supporto Tecnico Assyoma S.r.l. - www.assyoma.it email: g.danti@assyoma.it - info@assyoma.it GPG public key ID: FF5F32A8
On 03/13/2018 11:08 AM, Gionatan Danti wrote:
On 13/03/2018 15:30, Michal Privoznik wrote:> The default GW depends on the IP address you assigned to your network:
<ip address='192.168.122.1' netmask='255.255.255.0'/>
This says the default GW is 192.168.122.1/24. However, you can insert other routes too:
<route address="192.168.222.0" prefix="24" gateway="192.168.122.2"/>
...however this wouldn't be of use to you - the routes listed in a libvirt network are routes that are added on the *host*, not on the guest. (these are used when there is a network behind a guest that the host can only access via that guest).
For handling DNS, you need to focus on <dns/> element. For instance, to set a different forwarder than GW:
<dns> <forwarder addr="8.8.8.8"/> </dns>
For NATed/routed networks, sure. However, I have an isolated network like that (without the "forward" element):
We don't want DNS requests to be forwarded by dnsmasq from an isolated network - forwarded DNS requests and responses can be used as a clandestine medium for communicating outside the guest (we actually had a bug report about this). libvirt's virtual networks are intended to be a simple way to setup the most common networking scenario. It sounds like you're beyond that, so you probably should do your own network setup on the host outside of libvirt. A libvirt virtual network is really just the combination of a bridge device, a dnsmasq instance + config, some iptables rules, and optionally some routes.
<network> <name>net1</name> <uuid>dcf5c09b-dcb6-4fd3-86b8-6312a7b94bf6</uuid> <bridge name='virbr1' stp='on' delay='0'/> <mac address='52:54:00:97:1b:15'/> <domain name='TEST'/> <ip address='192.168.10.1' netmask='255.255.255.0'> <dhcp> <range start='192.168.10.128' end='192.168.10.254'/> </dhcp> </ip> </network>
When the client asks for an IP via DHCP, it obtain a valid IP address but *no* gateway. Is it the expected behavior for an isolated network? From my understanding, network isolation is accomplished by firewall rules in the FORWARD table, rather than by not assigning the gateway IP address to clients.
It does both of those things (no gateway combined with iptables rules to prevent traffic from being forwarded from the bridge). Why set a default gateway when 1) it can't be used and 2) it may conflict with the default gateway set on a 2nd interface in the guest that *can* be used to reach outside the host? (a common use of an isolated network is to to contain inter-guest communication between guests that have 2nd interfaces used for communication with the outside).
Il 13-03-2018 20:48 Laine Stump ha scritto:
On 03/13/2018 11:08 AM, Gionatan Danti wrote:
On 13/03/2018 15:30, Michal Privoznik wrote:> The default GW depends on the IP address you assigned to your network:
<ip address='192.168.122.1' netmask='255.255.255.0'/>
This says the default GW is 192.168.122.1/24. However, you can insert other routes too:
<route address="192.168.222.0" prefix="24" gateway="192.168.122.2"/>
...however this wouldn't be of use to you - the routes listed in a libvirt network are routes that are added on the *host*, not on the guest. (these are used when there is a network behind a guest that the host can only access via that guest).
For handling DNS, you need to focus on <dns/> element. For instance, to set a different forwarder than GW:
<dns> <forwarder addr="8.8.8.8"/> </dns>
For NATed/routed networks, sure. However, I have an isolated network like that (without the "forward" element):
We don't want DNS requests to be forwarded by dnsmasq from an isolated network - forwarded DNS requests and responses can be used as a clandestine medium for communicating outside the guest (we actually had a bug report about this).
libvirt's virtual networks are intended to be a simple way to setup the most common networking scenario. It sounds like you're beyond that, so you probably should do your own network setup on the host outside of libvirt. A libvirt virtual network is really just the combination of a bridge device, a dnsmasq instance + config, some iptables rules, and optionally some routes.
<network> <name>net1</name> <uuid>dcf5c09b-dcb6-4fd3-86b8-6312a7b94bf6</uuid> <bridge name='virbr1' stp='on' delay='0'/> <mac address='52:54:00:97:1b:15'/> <domain name='TEST'/> <ip address='192.168.10.1' netmask='255.255.255.0'> <dhcp> <range start='192.168.10.128' end='192.168.10.254'/> </dhcp> </ip> </network>
When the client asks for an IP via DHCP, it obtain a valid IP address but *no* gateway. Is it the expected behavior for an isolated network? From my understanding, network isolation is accomplished by firewall rules in the FORWARD table, rather than by not assigning the gateway IP address to clients.
It does both of those things (no gateway combined with iptables rules to prevent traffic from being forwarded from the bridge). Why set a default gateway when 1) it can't be used and 2) it may conflict with the default gateway set on a 2nd interface in the guest that *can* be used to reach outside the host? (a common use of an isolated network is to to contain inter-guest communication between guests that have 2nd interfaces used for communication with the outside).
Hi Laine, thanks for the detailed answer! One more question: what about setting a custom DNS? For example, consider the scenario where a specific guest acts as a DNS server (ie: active directory server) and other clients in the same isolated network should use its IP address as DNS. If I understand it correctly, I can use the "dns forward" directive to, well, forward dnsmasq's requests to the specific IP address. But what about directly assigning the correct DNS server to the running guests? Thanks. -- Danti Gionatan Supporto Tecnico Assyoma S.r.l. - www.assyoma.it email: g.danti@assyoma.it - info@assyoma.it GPG public key ID: FF5F32A8
On 03/14/2018 03:21 AM, Gionatan Danti wrote:
One more question: what about setting a custom DNS? For example, consider the scenario where a specific guest acts as a DNS server (ie: active directory server) and other clients in the same isolated network should use its IP address as DNS.
If I understand it correctly, I can use the "dns forward" directive to, well, forward dnsmasq's requests to the specific IP address.
This *should* work. When a network is isolated, we add "no-resolv" to the dnsmasq conf file to prevent having unresolvable requests forwarded to the hosts listed in /etc/resolv.conf on the host, but since <forwarder> is handled by adding a server= option to dnsmasq.conf, that should still work (I haven't tried it though).
But what about directly assigning the correct DNS server to the running guests?
The would be nice, but there is no support for it.
Dears, This is my first post in this mailing list.I have browsed the archives, but I have not found a solution to my concern.So I decided to open a new thread.Please excuse me, if it has already been addressed here or somewhere else. And just provide me directions to the solutions. I am using Fedora 27 with kernel 4.15.8-300.fc27.x86_64 and KVM libvirt 3.7.0- 4.fc27.x86_64. My need is to be able to have the DNS server initialized by the KVM default network to answer DNS MX query for the domain.The idea is to have something similar to the below MX record lines in default network xml. <network> <name>default</name> <uuid>11111111-2222-3333-4444- 555555555555</uuid> <forward mode='nat'> <nat> <port start='1024' end='65535'/> </nat> </forward> <bridge name='virbr0' stp='on' delay='0'/> <mac address='52:54:00:00:00:01'/> <domain name='example.com' localOnly='yes'/> <dns enable='yes' forwardPlainNames='no'> <mx domain='example.com' target='mail' priority='10'/> <mx domain='example.com' target='mail_backup' priority='20'/> </dns> <ip address='192.168.122.1' netmask='255.255.255.0'> <dhcp> <range start='192.168.122.100' end='192.168.122.199'/> <host mac='52:54:00:00:00:10' name='mail.example.com' ip='192.168.122.10'/> <host mac='52:54:00:00:00:20' name='mail_backup.example.com' ip='192.168.122.20'/> </dhcp> </ip></network> So that queries such the below. dig @192.168.122.1 -t MX example.com give answers such as below. ; <<>> DiG 9.11.2-P1-RedHat-9.11.2-1.P1.fc27 <<>> -t MX example.com;; global options: +cmd;; Got answer:;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 61856;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1 ;; OPT PSEUDOSECTION:; EDNS: version: 0, flags:; udp: 8192;; QUESTION SECTION:;example.com. IN MX ;; ANSWER SECTION:example.com. 3600 IN MX 10 mail.example.com.example.com. 3600 IN MX 20 mail_backup.example.com. ;; Query time: 558 msec;; SERVER: 192.168.122.1#53(192.168.122.1);; WHEN: Fri Mar 16 16:21:00 WAT 2018;; MSG SIZE rcvd: 96 Best regards, Tshimanga
participants (4)
-
Gionatan Danti -
Laine Stump -
Michal Privoznik -
TSHIMANGA Minkoka