Ian Dunn » Networking

Connecting to a PPTP VPN from an OpenVZ CentOS VPS

Ian — Wed, 18 Apr 2012 17:25:08 +0000

When setting up the PPTP and PPP packages on an OpenVZ VPS in order to connect to a VPN, there are a few extra steps you need to take that you don’t have to do with a non-virtualized box.

First, you have to load the following kernel modules on the hardware node and/or set them to automatically start during the boot up process:


modprobe ppp_mppe
modprobe ppp_deflate
modprobe zlib_deflate
modprobe ppp_async
modprobe ppp_generic
modprobe slhc
modprobe crc_ccitt

After doing that you should see something similiar to this when running lsmod


[root@me ~]# lsmod | grep ppp
ppp_mppe 39816 0
ppp_deflate 39168 0
zlib_deflate 52760 1 ppp_deflate
ppp_async 45056 0
ppp_generic 63632 4 ppp_mppe,ppp_deflate,ppp_async
slhc 39680 1 ppp_generic
crc_ccitt 35200 1 ppp_async

Second, you have to tweak the VPS’s conf file:


vzctl stop [VEnumber]
vzctl set [VEnumber] --features ppp:on --save
vzctl start [VEnumber]
vzctl set [VEnumber] --devices c:108:0:rw --save
vzctl exec [VEnumber] mknod /dev/ppp c 108 0
vzctl exec [VEnumber] chmod 600 /dev/ppp

Once that’s done, you can follow the normal instructions.

After that, you might need to uncomment the require-mppe-128 or mppe required,stateless line in /etc/ppp/options.pptp (depending on the VPN server). You may also need to manually create a static route to the network, with route add -net 10.1.1.0 netmask 255.255.255.0 ppp0.

You can check /var/log/messages for details about negotiation errors.

Deflating the Hype Behind Cloud Computing

Ian — Sat, 12 Nov 2011 06:18:16 +0000

In a lot of ways I’m leery of the recent trends towards converting traditional products that you buy once and own into services that you have to lease every month, and hosting data with centralized corporate networks instead of locally, so I appreciate Mark Maunder’s post on his experiences collocating his company’s hardware instead of using the cloud. I think there are valid cases for the cloud, but there are also a lot of drawbacks that get dismissed in all the hype surrounding it.

The Correct Way to Roll Cables

Ian — Sat, 26 Mar 2011 21:01:57 +0000

This video explains the right way to roll cables, alternating over- and under-hand loops to maintain the natural curve of the cable. Using this method helps avoid knots, makes it quicker to unravel, reduces wear on the cable and makes it easier to get a clean, symmetrical coil. The video is geared towards audio cables, but applies equally to networking and other types of cabling.

At the end he demonstrates a way to secure the ends without velcro straps, which is useful because straps and ties are less common in the IT world. I don’t think his method works well for stiffer cables, like CAT5, though, so I prefer to run the last 2-3′ through the entire loop, alternating inside and outside, and then slipping the end between two parallel sections to hold it in place.

Memorable IP Address

Ian — Mon, 01 Mar 2010 21:16:29 +0000

If you’re troubleshooting a network’s uplink to the Internet and want a memorable external IP address to ping, then you can use 4.2.2.2, which is one of Verizon’s DNS servers.