Thanks for the answer.
NAT is enabled on the server. It's a gateway for the internal network stations.
# ip addr list
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
2: eth0: <BROADCAST,MULTICAST,PROMISC,UP,LOWER_UP> mtu 1500 qdisc mq state UP qlen 1000
link/ether 00:15:c5:5f:e1:1a brd ff:ff:ff:ff:ff:ff
3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP qlen 1000
link/ether 00:15:c5:5f:e1:1b brd ff:ff:ff:ff:ff:ff
4: dummy0: <BROADCAST,NOARP> mtu 1500 qdisc noop state DOWN
link/ether 10:00:01:02:03:04 brd ff:ff:ff:ff:ff:ff
5: ppp0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1492 qdisc pfifo_fast state UNKNOWN qlen 3
link/ppp
inet xx.xxx.xxx.xxx peer 178.132.16.219/32 scope global ppp0
6: br0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN
link/ether 00:15:c5:5f:e1:1a brd ff:ff:ff:ff:ff:ff
inet 192.168.1.1/24 brd 192.168.1.255 scope global br0
7: tap0: <BROADCAST,MULTICAST,PROMISC,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN qlen 100
link/ether fa:27:a7:ae:66:8d brd ff:ff:ff:ff:ff:ff
# ip route list
178.132.16.219 dev ppp0 proto kernel scope link src xx.xxx.xxx.xxx
192.168.1.0/24 dev br0 proto kernel scope link src 192.168.1.1
default dev ppp0 scope link
The server is connected by a ppp router. The client is behind a internet box. The internal network, behind the server is in the network 192.168.1.0/24.