I've been trying to do "Neutron with existing external network" install by using the latest centos 7 + RDO. When booting a Fedora 23 instance, I'm stuck with this (cirros has similar symptoms as well):

ci-info: +--------+------+-----------+-----------+-------+-------------------+
ci-info: | Device |  Up  |  Address  |    Mask   | Scope |     Hw-Address    |
ci-info: +--------+------+-----------+-----------+-------+-------------------+
ci-info: |  lo:   | True | 127.0.0.1 | 255.0.0.0 |   .   |         .         |
ci-info: |  lo:   | True |     .     |     .     |   d   |         .         |
ci-info: | eth0:  | True |     .     |     .     |   .   | fa:16:3e:34:71:a3 |
ci-info: | eth0:  | True |     .     |     .     |   d   | fa:16:3e:34:71:a3 |
ci-info: +--------+------+-----------+-----------+-------+-------------------+
[WARNING]: Calling 'http://169.254.169.254/2009-04-04/meta-data/instance-id' failed [0/120s]: request error [('Connection aborted.', OSError(101, 'Network is unreachable'))]

What I did was:

1. Follow instructions in https://www.rdoproject.org/networking/neutron-with-existing-external-network/ (https://www.rdoproject.org/networking...) (except added "--os-horizon-ssl=y --ntp-servers=..." to packstack and modified /etc/neutron/plugins/ml2/openvswitch_agent.ini and /etc/neutron/plugins/ml2/ml2_conf.ini as instructed in https://ask.openstack.org/en/question/86601/neutron-with-existing-external-network/ (https://ask.openstack.org/en/question...) (except replaced physnet1 by extnet)).

2. Fixed the quota problem: https://ask.openstack.org/en/question/87002/cinder-volume-quotas-broken-for-rdo-install-in-centos/ (https://ask.openstack.org/en/question...)

3. Tried to create a Fedora/Cirros instance: https://www.rdoproject.org/networking/running-an-instance-with-neutron/ (https://www.rdoproject.org/networking...)

I can ping the first address of the floating IP range, but not the assigned one.

# ifconfig
br-ex: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.122.50  netmask 255.255.255.0  broadcast 192.168.122.255
        inet6 2001:db8::7a2b:cbff:fe47:f037  prefixlen 64  scopeid 0x0<global>
        inet6 fe80::7a2b:cbff:fe47:f037  prefixlen 64  scopeid 0x20<link>
        ether 78:2b:cb:47:f0:37  txqueuelen 0  (Ethernet)
        RX packets 17433  bytes 2293095 (2.1 MiB)
        RX errors 0  dropped 15  overruns 0  frame 0
        TX packets 2751  bytes 2667610 (2.5 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

em1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet6 fe80::7a2b:cbff:fe47:f037  prefixlen 64  scopeid 0x20<link>
        ether 78:2b:cb:47:f0:37  txqueuelen 1000  (Ethernet)
        RX packets 18641  bytes 2452312 (2.3 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 3904  bytes 2760240 (2.6 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 0  (Local Loopback)
        RX packets 286112  bytes 44247917 (42.1 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 286112  bytes 44247917 (42.1 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

qbrd0bd198a-f7: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet6 fe80::643b:4ff:fe60:bbfe  prefixlen 64  scopeid 0x20<link>
        ether 6a:cc:4a:ac:f1:f7  txqueuelen 0  (Ethernet)
        RX packets 28  bytes 5260 (5.1 KiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 8  bytes 648 (648.0 B)
        TX errors 0 ...