On Fri, May 5, 2017 at 4:29 PM, Nicolas Bock <nicolasbock@gmail.com> wrote:

Hi,

I am running a webserver on the libvirt host and would like to add a nwfilter such that a VM can access that server. The corresponding iptables rule would look like this:

iptables --append INPUT --in-interface virbr0 --destination 192.168.122.1 --protocol tcp --dport 80 --jump ACCEPT

where the network is using virbr0 and sits at 192.168.122.1. I don't want to hardcode the host IP address in the nwfilter so that I can use that filter for other networks. Is it possible to reference the host's IP address in the filter?

Thanks!

Nick

Hi Nick,

I used to have similar question before too. Not sure if this could be helpful for you,

Probably just use arp or arpscan. But to be more specific, if the domain name of the

client (assuming you want to confine HTTP service to only a selected few clients, e.g.,

192.168.122.1 in your case) is known, you probably could do

$ virsh domiflist DOMAIN

In particular, to get the IP address of a domain, it is something like the following:

$ for MAC in `virsh domiflist <DOMAIN> | grep -o -E "([0-9a-f]{2}:){5}([0-9a-f]{2})"` ; do

arp -e | grep $MAC | grep -o -P "^\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}" ;

done

Alternatively, if the NETWORK name is known, IP addr can be obtained directly with

$ virsh net-dhcp-leases NETWORK

Another way to the get IP addr, if qemu guest agent is installed on the client,

$ virsh domifaddr DOMAIN

So that you can pass IP to the XML, and somehow you can trigger the update of

NWFILTER with some magic, quite a hack.

Or, you could just use client's MAC addr to define the filter:

https://libvirt.org/formatnwfilter.html#nwfelemsRulesProtoMAC

But I don't think there is direct way to specify a client's domain name in

the NWFILTER XML definition as of now.

P.S. I am new to libvirt, so everything above could be wrong.

Dan

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