Open Stack

So I'm having a problem getting my head around the network setup for a
nova-compute server. When install the base OS on the physical server I
have only one network interface available, eth2. That is a limitation
I can work with.  I am using a bridged NIC.

br100 172.16.16.16 static  (in reality not an rfc1918 IP but just for
this example)
br101 10.9.128.16 static
eth2 10.8.53.163 dhcp

This stays the same until I spin up a VM.

br100 changed to 172.16.124.2
br101 changed to 10.9.132.3
eth2 stayed the same.

Can anyone explain to me why the IP changes on the br100 and br101?
When I look at my iptable nat table I see

-A nova-compute-snat -j nova-compute-float-snat
-A nova-network-POSTROUTING -s 10.9.132.0/22 -d  172.16.16.16/32 -j ACCEPT
-A nova-network-POSTROUTING -s 10.9.132.0/22 -d 169.254.169.254/32 -j ACCEPT
-A nova-network-POSTROUTING -s 10.9.132.0/22 -d 10.9.132.0/22 -m
conntrack ! --ctstate DNAT -j ACCEPT
-A nova-network-PREROUTING -d 169.254.169.254/32 -p tcp -m tcp --dport
80 -j DNAT --to-destination 172.16.16.16:8775
-A nova-network-snat -j nova-network-float-snat
-A nova-network-snat -s 10.9.132.0/22 -j SNAT --to-source 172.16.16.16
-A nova-postrouting-bottom -j nova-compute-snat
-A nova-postrouting-bottom -j nova-network-snat

But since the IP has changed on br100 there isn't a 172.16.16.16 IP
address any more.  It never changes to the current IP of the server
which is now 172.16.124.2.

My /etc/nova/nova.conf

[DEFAULT]

# LOGS/STATE
verbose=true
auth_strategy=keystone
dhcpbridge_flagfile=/etc/nova/nova.conf
dhcpbridge=/usr/bin/nova-dhcpbridge
logdir=/var/log/nova
use_syslog=true
syslog_log_facility=LOG_LOCAL1
state_path=/var/lib/nova
lock_path=/var/lock/nova
iscsi_helper=tgtadm

# RABBITMQ
rabbit_password=guest
rabbit_port=5672
rabbit_host=172.16.16.13

# SCHEDULER
# scheduler_manager=nova.scheduler.manager.SchedulerManager
scheduler_driver=nova.scheduler.simple.SimpleScheduler
node_availability_zone=nova
default_schedule_zone=nova

# NETWORK
network_manager=nova.network.manager.FlatDHCPManager
#--flat_interface=eth1
#--flat_network_dhcp_start=10.20.1.2
#--public_interface=eth0
fixed_range=10.9.132.0/22
dmz_cidr=169.254.169.254/32
force_dhcp_release=true
send_arp_for_ha=True
libvirt_use_virtio_for_bridges=true

# GLANCE
image_service=nova.image.glance.GlanceImageService
glance_api_servers=172.16.16.14:9292

# COMPUTE
compute_manager=nova.compute.manager.ComputeManager
sql_connection=mysql://nova:<REMOVED>@10.9.128.11/nova
connection_type=libvirt
libvirt_type=kvm
root_helper=sudo nova-rootwrap
vncserver_listen=0.0.0.0
vncserver_proxyclient_address=172.16.16.15

# VNCPROXY
novncproxy_base_url=http://172.16.16.15:6080/vnc_auto.html
xvpvncproxy_base_url=http://172.16.16.15:6081/console
# This is only required on the server running xvpvncproxy
xvpvncproxy_host=172.16.16.15
xvpvncproxy_port=6081

# MISC
use_deprecated_auth=false
allow_admin_api=true
enable_zone_routing=true


# KEYSTONE
keystone_ec2_url=http://172.16.16.11:5000/v2.0/ec2tokens

# Volumes
iscsi_helper=tgtadm