OpenVPN Server gives clients the same ip, how to fix it?

Question

openvpn

Raised on Ubuntu OpenVPN server. Every time clients connect to it, they all get the same ip 10.15.0.2. How to fix it?
server.conf

port 1194
proto udp
dev tun
user openvpn
group openvpn
cd /etc/openvpn
persist-key
persist-tun
tls-server
tls-timeout 120
dh /etc/openvpn/dh2048.pem
ca /etc/openvpn/ca.crt
cert /etc/ openvpn/server.crt
key /etc/openvpn/server.key
tls-auth /etc/openvpn/ta.key 0
server 10.15.0.0 255.255.255.0
client-config-dir /etc/openvpn/ccd
client-to-client
topology subnet
max-clients 10
push "dhcp-option DNS 10.15.0.1"
route 10.15.0.1 255.255.255.0
comp-lzo
keepalive 10 120
status /var/log/openvpn/openvpn-status.log 1
status-version 3
log-append /var/log/openvpn/openvpn-server.log
verb 3
mute 20

client.conf

dev tun
proto udp
remote 10.0.0.54 1194
client
resolv-retry infinite
ca ca.crt
cert vpn.windows.crt
key vpn.windows.key
tls-auth ta.key 1
remote-cert-tls server
persist-key
persist-tun
comp -lzo
verb 3
status openvpn-status.log 1
status-version 3
log-append openvpn-client.log

Answer 1

Probably because all clients have the same certificates.
And yes, what do you have in /etc/openvpn/ccd?