easypi/pptpd repository overview

~/fig/pptpd/
├── docker-compose.yml
└── data/
    ├── pptpd.conf
    ├── pptpd-options
    └── chap-secrets

flowchart LR
    subgraph Client["Windows Client"]
        C["PPTP Client<br/>192.168.127.100"]
    end

    subgraph Server["Raspberry Pi (host)"]
        P["ppp0<br/>192.168.127.1"]
        E["eth0<br/>192.168.100.x"]
        P -- "FORWARD<br/>src=192.168.127.100" --> E
    end

    subgraph Upstream["Upstream Network"]
        R1["192.168.100.1<br/>gateway"]
        R2["internet"]
        R1 --> R2
    end

    C -->|"PPTP tunnel<br/>TCP 1723 + GRE"| P
    E -- "POSTROUTING MASQUERADE<br/>src→192.168.100.x" --> R1

    classDef client fill:#fff4e5,stroke:#d97706,color:#000
    classDef server fill:#e8f4ff,stroke:#1f6feb,color:#000
    classDef upstream fill:#f0fdf4,stroke:#16a34a,color:#000
    class C client
    class P,E server
    class R1,R2 upstream

$ modprobe nf_conntrack_pptp nf_nat_pptp
$ lsmod | grep pptp
$ ls /dev/ppp

$ cd ~/fig/pptpd/
$ docker compose up -d
$ docker compose logs -f

$ sudo sysctl -w net.ipv4.ip_forward=1
$ iptables --version
iptables v1.8.9 (nf_tables)
$ sudo iptables -L FORWARD -n
$ sudo iptables -A FORWARD -i ppp+ -o eth0 -j ACCEPT
$ sudo iptables -A FORWARD -i eth0 -o ppp+ -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
$ sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

C:\> ipconfig /all
PPP adapter pptp:

   Connection-specific DNS Suffix  . :
   Description . . . . . . . . . . . : pptp
   Physical Address. . . . . . . . . :
   DHCP Enabled. . . . . . . . . . . : No
   Autoconfiguration Enabled . . . . : Yes
   IPv4 Address. . . . . . . . . . . : 192.168.127.100(Preferred)
   Subnet Mask . . . . . . . . . . . : 255.255.255.255
   Default Gateway . . . . . . . . . : 0.0.0.0
   DNS Servers . . . . . . . . . . . : 8.8.8.8
                                       8.8.4.4
   NetBIOS over Tcpip. . . . . . . . : Disabled

C:\> netsh interface ipv4 show interfaces

Idx     Met         MTU          State                Name
---  ----------  ----------  ------------  ---------------------------
 62          25        1400  connected     pptp
  1        4300  4294967295  connected     Loopback Pseudo-Interface 1
 17        4250        1500  connected     Ethernet

C:\> route print -4
C:\> route print -6

C:\> netsh interface ipv4 show interfaces
C:\> netsh interface ipv6 show interfaces

C:\> netsh interface ipv4 show dnsservers
C:\> netsh interface ipv6 show dnsservers

PS C:\> nslookup google.com
Server:  OpenWrt.lan
Address:  192.168.100.1

PS C:\> Get-DnsClientServerAddress -AddressFamily IPv4
PS C:\> Get-DnsClientServerAddress -AddressFamily IPv6

PS C:\> Get-NetIPInterface | Sort-Object InterfaceMetric
ifIndex InterfaceAlias                  AddressFamily NlMtu(Bytes) InterfaceMetric Dhcp     ConnectionState PolicyStore
------- --------------                  ------------- ------------ --------------- ----     --------------- -----------
62      pptp                            IPv4                  1300              25 Disabled Connected       ActiveStore
17      Ethernet                        IPv6                  1500              25 Enabled  Connected       ActiveStore
17      Ethernet                        IPv4                  1500            4250 Enabled  Connected       ActiveStore
1       Loopback Pseudo-Interface 1     IPv4            4294967295            4300 Disabled Connected       ActiveStore

PS C:\> Set-NetIPInterface -InterfaceAlias "pptp" -AddressFamily IPv4 -InterfaceMetric 1

PS C:\> nslookup google.com
Server:  dns.google
Address:  8.8.8.8