(just to clarify - the configuration that was used above is nonsensical, and should result in an error in both cases. The <route> element's purpose is to setup routes *from the host* to networks that are otherwise *unreachable* from the host (i.e. on a network that is hidden behind a virtual machine; in the example given for this BZ, it looks like an attempt was made to provide a route for the virtual machines on network "default" to reach machines on network "default_001"; this is incorrect usage of <route> )

libvirt currently checks for route collisions only for the network's own address range, but not for its static routes. networkCheckRouteCollision() should have its calling parameters modified to take an IP and prefix/netmask rather than a network name, then it should be called from networkAddRouteToBridge()

Patches proposed upstream:

https://www.redhat.com/archives/libvir-list/2015-July/msg00418.html

Fixed upstream by v1.2.17-104-g0e3ad241f3f4:

commit 0e3ad241f3f421c23bbe2cbe11a70f8e9184dc65
Author:     Martin Kletzander <mkletzan>
AuthorDate: Thu Jul 9 15:53:25 2015 +0200

    network: Add another collision check into networkCheckRouteCollision

Verify it as follows.The result is expected.Move its status to VERIFIED.

# rpm -q libvirt
libvirt-1.2.17-6.el7.x86_64

# virsh net-list --all
 Name                 State      Autostart     Persistent
----------------------------------------------------------
 default              inactive   yes           yes
 test                 inactive   no            yes

# virsh net-dumpxml default
<network>
  <name>default</name>
  <uuid>06242766-3cab-4475-a794-1d655e228f14</uuid>
  <forward mode='nat'/>
  <bridge name='virbr0' stp='on' delay='0'/>
  <mac address='52:54:00:c0:18:da'/>
  <bandwidth>
    <inbound average='10000' peak='50000' burst='10240'/>
    <outbound average='1280' peak='2560' burst='2560'/>
  </bandwidth>
  <ip address='192.168.122.1' netmask='255.255.255.0'>
    <dhcp>
      <range start='192.168.122.2' end='192.168.122.254'/>
    </dhcp>
  </ip>
  <route address='192.168.222.0' prefix='24' gateway='192.168.122.1'/>
</network>

# virsh net-dumpxml test
<network>
  <name>test</name>
  <uuid>246e457b-42e5-497e-bd98-5a178a2a4a6f</uuid>
  <forward mode='nat'>
    <nat>
      <port start='1024' end='65535'/>
    </nat>
  </forward>
  <bridge name='virbr5' stp='on' delay='0'/>
  <mac address='52:54:00:25:cf:91'/>
  <ip address='192.168.222.1' netmask='255.255.255.0'>
    <dhcp>
      <range start='192.168.222.2' end='192.168.222.254'/>
    </dhcp>
  </ip>
</network>

# virsh net-start test
Network test started

# virsh net-start default
error: Failed to start network default
error: internal error: Route address '192.168.222.0' conflicts with IP address for 'virbr5'

# virsh net-destroy test
Network test destroyed

# virsh net-start default
Network default started

# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         10.66.7.254     0.0.0.0         UG    0      0        0 eno1
10.66.4.0       0.0.0.0         255.255.252.0   U     0      0        0 eno1
10.72.17.5      10.66.7.254     255.255.255.255 UGH   100    0        0 eno1
192.168.122.0   0.0.0.0         255.255.255.0   U     0      0        0 virbr0
192.168.222.0   192.168.122.1   255.255.255.0   UG    1      0        0 virbr0

# virsh net-start test
error: Failed to start network test
error: internal error: Network is already in use by interface virbr0

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://rhn.redhat.com/errata/RHBA-2015-2202.html