packages/net/pppossh

This package will add the so-called pppossh protocol support to OpenWrt. The idea is mainly from pvpn project (poor man’s VPN over SSH).

PPPoSSH is generally not considered a network setup for production use mainly due to the TCP-over-TCP styles of traffic transport, but it can be quite handy for personal use. And with what’s already in OpenWrt, it is really easy and takes little extra space to configure it up running.

Prerequisites and dependency.

pppossh depends on either dropbear or openssh-client; dropbear is normally enabled in OpenWrt by default.

The following requirements need to be fulfilled for it to work.

• A SSH account on the remote machine with CAP_NET_ADMIN capability is required.

• Public key authentication must be enabled and setup properly.

  Public key of the one generated automatially by dropbear can be induced by the following command. But you can always use your own (dropbear can work with OpenSSH public key).

  dropbearkey -y -f /etc/dropbear/dropbear_rsa_host_key
  

• SSH server’s fingerprint has to be present in ~/.ssh/known_hosts for the authentication to proceed in an unattended way.

  Manually logging in at least once to the remote server from OpenWrt should do this for you.

How to use it.

The protocol name to use in /etc/config/network is pppossh. Options are as described below.

• server, SSH server name
• port, SSH server port (defaults to 22).
• sshuser, SSH login username
• identity, list of client private key files. ~/.ssh/id_{rsa,dsa} will be used if no identity file was specified and at least one of them must be valid for the public key authentication to proceed.
• ipaddr, local ip address to be assigned.
• peeraddr, peer ip address to be assigned.
• ssh_options, extra options for the ssh client.
• use_hostdep, set it to 0 to disable the use of proto_add_host_dependency. This is mainly for the case that the appropriate route to server is not registered to netifd and thus causing a incorrect route being setup.

Tips

An uci batch command template for your reference. Modify it to suite your situation.

uci batch <<EOF
delete network.fs
set network.fs=interface
set network.fs.proto=pppossh
set network.fs.sshuser=root
set network.fs.server=ssh.example.cn
set network.fs.port=30244
add_list network.fs.identity=/etc/dropbear/dropbear_rsa_host_key
set network.fs.ipaddr=192.168.177.2
set network.fs.peeraddr=192.168.177.1
commit
EOF

Allow forward and NAT on the remote side (ppp0 is the peer interface on the remote side. eth0 is the interface for Internet access).

sysctl -w net.ipv4.ip_forward=1
iptables -t filter -A FORWARD -i ppp0 -j ACCEPT
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

It’s possible that pppd may output protocol negotiation incompatibilities issues to syslog, such as something like the following which did not hurt the connectivity and was annoying only because we thought it can do better.

Sun Oct 25 09:45:14 2015 daemon.err pppd[22188]: Received bad configure-rej:  12 06 00 00 00 00

To debug such problems, we can try adding option pppd_optinos debug to the interface config. In the above case, it’s a LCP CCP configure rej (the CCP options struct is exactly 6 octets in size as indicated in source code pppd/ccp.h) and since the internet fee is not charged on the bytes transfered, I will just use noccp to disable the negotiation altogether.

Also to optimize bulk transfer performance, you can try tweaking the ciphers. OpenSSH client does not support none cipher by default and you have to patch and install it for by yourself. Another option is to try ciphers like arcfour and blowfish-cbc. In my case, arcfour has the best throughput.

option ssh_options '-o "Ciphers arcfour"'