Packet Data Setup

Transport Modes

FOU is recommended — offloads IP routing and NAT to a separate machine.

PDSN Configuration

FOU (Recommended)

{ "packet": { "transport": "fou", "fou_remote": "192.168.1.100:17010", "fou_local_port": 17011 } }

TUN

{ "packet": { "transport": "tun" } }

Creates a kernel TUN device per session with automatic IP config and NAT rules. Requires root.

FOU Remote Setup

On the Linux box handling IP routing (replace <pdsn_ip> with the PDSN/runtime host IP):

sudo modprobe fou
sudo ip fou add port 17010 ipproto 4
sudo ip link add fou0 type ipip \
    remote <pdsn_ip> local <linux_ip> \
    encap fou encap-dport 17011 encap-sport 17010
sudo ip addr add 10.55.0.1/24 dev fou0
sudo ip link set fou0 up
sudo sysctl -w net.ipv4.ip_forward=1
sudo iptables -t nat -A POSTROUTING -s 10.55.0.0/24 -o eth0 -j MASQUERADE

Verify

sudo ip fou show
ip addr show fou0
sudo tcpdump -i fou0 -n
sudo iptables -t nat -L -n -v | grep 10.55.0

Teardown

sudo ip link del fou0
sudo ip fou del port 17010
sudo iptables -t nat -D POSTROUTING -s 10.55.0.0/24 -o eth0 -j MASQUERADE

IP Pool

Lowest available address assigned per session, released on close.

Data Path

Uplink: Mobile → PPP/HDLC → RLP → MuxPDU → BTS → Abis bearer → BSC → A8 → PCF → A10 → PDSN PPP/IPCP → FOU/TUN/FOU-TCP → NAT/internet

Downlink: Internet/NAT → FOU/TUN/FOU-TCP → PDSN → A10 → PCF → A8 → BSC → Abis bearer → BTS → RLP/MuxPDU → mobile

Throughput

Troubleshooting