diff options
2 files changed, 80 insertions, 3 deletions
diff --git a/README.md b/README.md
index cca2b7f..23224c3 100644
--- a/README.md
+++ b/README.md
@@ -37,7 +37,7 @@ I wrote this program because I run some applications under a VPN (e.g.,
clients for peer-to-peer protocols) and leave others untouched (like a
game client).
-For more details, see [openvpn-example.md][5].
+For more details, see `openvpn-example.md` ([cgit][5], [github][6]).
@@ -47,7 +47,8 @@ license
[2]: https://en.wikipedia.org/wiki/Setuid
[3]: https://github.com/ausbin/nsdo/blob/master/LICENSE
[4]: https://aur.archlinux.org/packages/nsdo-git/
-[5]: https://github.com/ausbin/nsdo/blob/master/openvpn-example.md
+[5]: https://code.austinjadams.com/nsdo/plain/openvpn-example.md
+[6]: https://github.com/ausbin/nsdo/blob/master/openvpn-example.md
diff --git a/openvpn-example.md b/openvpn-example.md
index 968cf57..7ab121d 100644
--- a/openvpn-example.md
+++ b/openvpn-example.md
@@ -32,7 +32,7 @@ or daemon restarts (e.g., after a suspend), I put the following in
-And then create a `netns@.service` in `/etc/systemd/system`:
+And then created a `netns@.service` in `/etc/systemd/system`:
Description=network namespace %I
@@ -118,7 +118,83 @@ Alternatively, if you don't want to bother with nsdo:
$ sudo ip netns foo sudo -u $USER firefox
+addendum: configuring veth
+*Note: if you're curious about veth, [Scott Lowe's handy blog post][5],
+where I found the commands below, serves as a good introduction.*
+Suppose that I want to use nsdo+openvpn as described above to tunnel an
+application that also provides a server (for RPC, for instance). That
+is, I run an application that binds to a port *in* a namespace, but I
+want to connect to it outside of that namespace.
+With the setup I've described up to this point, I simply cannot do this.
+Certainly, network namespaces separate running programs from one another
+-- an application can't cross the line willy-nilly. For instance, I
+could not use netcat to listen on a port in one namespace and then
+connect to it from another:
+ $ nsdo foo nc -l -p 5050 <<<"hi!" &
+ $ nc -v localhost 5050 <<<"hello"
+ localhost [] 5050 (mmcc): Connection refused
+ $ nsdo foo !!
+ hi!
+ hello
+So (as far as I know) I have no other choice but to use veth, a kernel
+feature [designed][6] to allow network namespaces to communicate. veth
+interfaces act just like any interface but come in pairs -- one for each
+You can set them up with a systemd service like the following (I've
+named it `foo-veth.service`):
+ [Unit]
+ Description=veth for foo netns
+ After=netns@foo.service
+ [Service]
+ Type=oneshot
+ RemainAfterExit=yes
+ # configure our end
+ ExecStart=/usr/bin/ip link add ns-foo up type veth peer name ns-def netns foo
+ ExecStart=/usr/bin/ip addr add dev ns-foo
+ # configure vpn end
+ ExecStart=/usr/bin/ip -netns foo link set dev ns-def up
+ ExecStart=/usr/bin/ip -netns foo addr add dev ns-def
+ # tear down everything
+ ExecStop=/usr/bin/ip link del ns-foo
+ [Install]
+ WantedBy=netns@foo.service
+(Note: I've chosen not to make this example systemd service generic --
+like `netns-veth@.service` -- because I currently use veth with only one
+vpn/namespace and I'm not sure how I'd assign unique IP addresses
+Now, make `netns@foo` start the new service automatically and then (this
+time) start it manually:
+ # systemctl enable foo-veth
+ # systemctl start foo-veth
+For convenience, make the name of the namespace resolve to the IP
+address assigned to its corresponding veth interface:
+ # printf 'foo\t10.0.255.2\n' >>/etc/hosts
+Done! You can now reach servers running in namespaces by simply
+connecting to the namespace by name. If a hypothetical application
+listens on port 5050 in namespace `foo`, for instance, you can access it
+by pointing your client to `foo:5050`:
+ $ curl foo:5050
+ Hello, world!
[1]: http://naju.se/articles/openvpn-netns
[2]: https://projects.archlinux.org/svntogit/packages.git/tree/trunk/openvpn@.service?h=packages/openvpn
[3]: http://www.freedesktop.org/software/systemd/man/systemd.service.html
[4]: https://community.openvpn.net/openvpn/wiki/Openvpn23ManPage
+[5]: http://blog.scottlowe.org/2013/09/04/introducing-linux-network-namespaces/
+[6]: https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=e314dbdc1c0dc6a548ecf0afce28ecfd538ff568