📡 Add PPP over Hysteria2 (experimental)

[luunarrr]

Summary

Add PPP over Hysteria2, making Hysteria2 a true VPN server.

Motivation

Hysteria2 is an application proxy, even under TUN mode. It proxies IPv4 and IPv6 with simple authentication, and that's it.
We want a full VPN solution that utilises existing ISP and telecom ecosystems, all over the existing Hysteria2 protocol.

What's New

• PPP session support in the Hysteria2 - clients can now initiate a PPP session with pppd over Hysteria2, opening up true VPN-style connectivity with dual-stack and non-IP payload support.
• Data transport modes:
  • Datagram mode: data transported as QUIC datagrams
  • Multi-stream mode: N parallel QUIC streams with per-flow hashing
• Termination modes:
  • Local mode: Hysteria2 terminates PPP session with pppd
  • BRAS/BNG/LAC mode: Hysteria2 terminates the the Hysteria2 connection and forwards PPP to LNS (standard LAC-LNS topology) with realm-based routing and load balancing
  • stdio mode: for luci-proto-hysteria
• SSTP bridge

Tested With

• Client: Windows 11 built-in SSTP client (IPv4 and IPv6) with datagram mode. Server: local termination
• Client: Windows 11 built-in SSTP client (IPv4 and IPv6) with multi-stream mode. Server: local termination
• Client: Windows 11 built-in SSTP client (IPv4 and IPv6) with datagram mode x2 (MLPPP). Server: local termination
• Client: Windows 11 built-in SSTP client (IPv4 and IPv6) with datagram mode. Server: LAC
• Client: OpenWRT 25.12 with datagram mode. Server: LAC (IPv6 only LNS)

Example 1

Client (Windows)

server: myserver.example.com:443-10000-50000

auth: myuser:mypass

ppp:
  sstp:  // Windows only have native SSTP client. Omit if you do not need SSTP bridge.
    certDir: "D:\\.hysteria-ppp"
    endpoint: main    //no MLPPP: omit
    user: <ppp user name>
    password: <ppp password>
  dataStreams: 128  // datagram mode: 0 or omit

Open Manage Computer Certificate, import the generated ca.crt as Trusted Root, then create a new SSTP connection points to 127.0.0.1:8443.
Hysteria2 client needs to run with admin privilege for auto server route pining.

Server (Linux)

listen: :443

acme:
  domains:
    - myserver.example.com
  email: me@myserver.example.com

auth:
  type: userpass
  userpass:
    myuser: mypass

// <whatever standard configs you want>
// ACL, outbounds are not supported

ppp:
  enabled: true
  sudo: true
  ipv4Pool: "10.99.0.0/24"
  dns:
    - 8.8.8.8
    - 1.1.1.1

/etc/ppp/pap-secrets

* * hysteria *

If you want IPv6: /etc/ppp/ipv6-up.d/radvd

#!/bin/sh
IFACE="$1"
NUM="${IFACE#ppp}"
PREFIX="fd00:abcd:1234:${NUM}"

ip -6 addr add ${PREFIX}::1/64 dev "$IFACE"
ip -6 route add ${PREFIX}::/64 dev "$IFACE"

cat > /tmp/radvd-${IFACE}.conf <<EOF
interface ${IFACE}
{
    AdvSendAdvert on;
    prefix ${PREFIX}::/64
    {
        AdvOnLink on;
        AdvAutonomous on;
    };
    RDNSS 2001:4860:4860::8888 2001:4860:4860::8844
    {
        AdvRDNSSLifetime 300;
    };

};
EOF
radvd -C /tmp/radvd-${IFACE}.conf -p /tmp/radvd-${IFACE}.pid -n &

If you want the client to access the Internet, you need something like:

sysctl -w net.ipv4.ip_forward=1

iptables -t nat -A PREROUTING -i eth1 -p udp --dport 10000:50000 -j REDIRECT --to-ports 443
ip6tables -t nat -A PREROUTING -i eth1 -p udp --dport 10000:50000 -j REDIRECT --to-ports 443

ip6tables -A FORWARD -i ppp+ -o eth0 -j ACCEPT
ip6tables -A FORWARD -i eth0 -o ppp+ -m state --state RELATED,ESTABLISHED -j ACCEPT
ip6tables -t nat -A POSTROUTING -s fd00:abcd:1234::/48 -o eth0 -j MASQUERADE

ip route replace <ip eth1>/24 dev eth1 scope link table rt_eth1
ip route replace default via <ip eth1> dev eth1 src <gw eth1> table rt_eth1
ip -6 route replace <ip6 eth1>/64 dev eth1 table rt_eth1
ip -6 route replace default via <ip6 eth1> dev eth1 table rt_eth1
ip rule add pref 100 from <ip eth1>/32 lookup rt_eth1
ip -6 rule add pref 100 from <ip6 eth1>/128 lookup rt_eth1

iptables -A FORWARD -i ppp+ -o eth0 -j ACCEPT
iptables -A FORWARD -i eth0 -o ppp+ -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

Example config for LAC:

listen: :443

acme:
  domains:
    - <my domain>
  email: <my email>

auth
  type: userpass
  userpass:
    <user>: <password>

ppp:
  enabled: true
  mode: l2tp
  l2tp:
    hostname: "hysteria-lac"
    helloInterval: 60
    groups:
      default:
        lns:
          - address: "<my LNS>:1701"
            secret: "<L2TP tunnel password>"
            weight: 1
    routes:
      - id: "<user>"
        group: default