I've a virtual machine (Ubuntu 14.04) on VMware player 7.0. I setup openstack by using devstack script in one node, used nova network, and create 3 instances. In my previous question ( https://ask.openstack.org/en/question/59325/i-cant-pingssh-instance-from-vm/?comment=59329#comment-59329 (https://ask.openstack.org/en/question...) ), i can ping some instances but i cant ping others. when i looked their logs, i saw that in pingable instance

Starting network...
udhcpc (v1.20.1) started
Sending discover...
Sending select for 10.0.0.2...
Lease of 10.0.0.2 obtained, lease time 120
deleting routers
adding dns 10.0.0.1
check-version already run per instance
Starting dropbear sshd: OK
userdata already run per instance

and this is my not pingable instance's log

Starting network...
udhcpc (v1.20.1) started
Sending discover...
Sending select for 10.0.0.3...
Received DHCP NAK
Sending discover...
Sending select for 192.168.177.140...
Lease of 192.168.177.141 obtained, lease time 1800
deleting routers
adding dns 192.168.177.2
check-version already run per instance
Starting dropbear sshd: OK
userdata already run per instance

also when i restart my pingable instance, i couldnt ping it. it's log was like that.

Starting network...
udhcpc (v1.20.1) started
Sending discover...
Sending select for 10.0.0.2...
Received DHCP NAK
Sending discover...
Sending select for 192.168.177.140...
Lease of 192.168.177.140 obtained, lease time 1800
deleting routers
adding dns 192.168.177.2
check-version already run per instance
Starting dropbear sshd: OK
userdata already run per instance

How can i solve this ? Why do i get a nak issue ? Can anyone help me? Thanks.