virtio vs. rtl8139

I've been doing some tests with KVM virtual machines and been launching them with virt-install. For some reason the VM wasn't activating its NIC. Changing the interface model from virtio to rtl8139 made it work again:

         virt-install --name $VM_NAME --ram 1024 --os-type=linux --os-variant=rhel7 \
-                    --disk none --network bridge=virbr0,model=virtio,mac=$VM_MAC \
+                    --disk none --network bridge=virbr0,model=rtl8139,mac=$VM_MAC \
                     --noreboot --graphics vnc \
                     --cdrom /var/tmp/tmp*/images/boot.iso --boot cdrom &

virt-install(1) says:

model
    Network device model as seen by the guest. Value can be any nic model supported by the hypervisor, e.g.: 'e1000',
    'rtl8139', 'virtio', ...

I'm not clear if this configures what drivers to be used for the NIC inside the guest or what is the driver of the host NIC. At this moment I don't know why changing the value causes networking in the guest to fail. If you do know please comment below. Thanks!

Comments !