vde_slirp.md

VDE Slirp

Slirp is a network stack emulator. It emulates a router providing NAT/masquerading. Every connection from a machine within the virtual network to the slirp address is translated, masqueraded and re-generated by slirp and redirected to the host machine stack. It provides functionalities like dhcp service, port forwarding and dns requests re-mapping.

A virtual network connected to the Internet

In this example a VDE switch provides a routing service to the Internet through the slirp plugin.

Note: Slirp does not need any privilege or capability to run.

start the VDE switch

Open a terminal and run:

$ vde_plug switch:///tmp/mysw slirp://

start the clients

For example start a qemu/kvm VM:

$ qemu-system-x86_64 -cdrom alpine-virt-3.12.0_rc5-x86_64.iso -monitor stdio \
        -device e1000,netdev=vde0,mac=$(randmac -q) -netdev vde,id=vde0,sock=vde:///tmp/mysw

Log-in the VM as root. The configuration of eth0 can be done by dhcp:

# ip link set eth0 up
# udhcpc

Ping cannot be used to test the connectivity as slirp does not forward ICMP packets. nc can be used instead.

# nc -vz 80.80.80.80 53
80.80.80.80 (80.80.80.80:53) open
# nc -zv www.google.com 80
www.google.com (216.58.208.164:80) open

This is just a connectivity test. As a test on a real network service let us try ssh.

# apk add openssh-client
# ssh user@your.favourite.host
....

Slirp + vdens

This experiment shows how to create a namespace providing user-mode networking.

Just run the following list of commands:

vdens -R 10.0.2.3 slirp://
$# /sbin/udhcpc -i vde0

Note: 10.0.2.3 is the default address for the DNS forwarder provided by slirp. Any reachable open/available domain name server can be used instead, e.g. 80.80.80.80,

As above we can use netcat to test the connectivity.

$# nc -zv google.com 80
Connection to google.com (216.58.206.46) 80 port [tcp/http] succeeded!
$# nc -vz 80.80.80.80 53
Connection to 80.80.80.80 53 port [tcp/domain] succeeded!

A foreign namespace

This tutorial shows how to set up a vdens whose networking connections are routed through a remote host.

Note: ssh access as a ordinary user is all what it is needed on the remote host. (VDEplug4 and the slirp plugin can be installed inside the user's home directory).

Create a ssh key and set up the key-based authorization on the remote host

$ ssh-keygen
...
Your public key has been saved in /home/user/.ssh/id_rsa.pub
...
$ cat /home/user/.ssh/id_rsa.pub | ssh user@my.remote.host cat >> .ssh/authorized_keys

Now if everything works as expected you should be able to login using the key authorization:

$ ssh user@my.remote.host
remote.host.prompt$ logout
$

start vdens

This tutorial uses the cmd plugin. cmd://'command args' runs command, all the VDE packets are exchanged using a VDE stream on stdin/stdout.

So the commands to start and configure the architecture depicted in the figure above are:

$ vdens -R 10.0.2.3 cmd://"ssh user@my.remote.host vde_plug slirp://"
$# /sbin/udhcpc -i vde0

The namespace lives in a virtual network. All the network traffic is routed through the remote host.

As above we can use netcat to test the connectivity.

$# nc -zv google.com 80
Connection to google.com (216.58.206.46) 80 port [tcp/http] succeeded!
$# nc -vz 80.80.80.80 53
Connection to 80.80.80.80 53 port [tcp/domain] succeeded!

All the connections will be seen as if they were originated by the remote host. The following command will show the IP address of the remote host.

$# wget -qO - icanhazip.com

A remotely routed local area cloud

A nice combination of VDE tools permit to implement a local area cloud whose traffic is routed through a remote node. All the VDE clients (virtual machines, vdens, etc.) connected to the local area cloud will use the remote slirp.

The command to set up this infrastucutre is:

vde_plug vxvde://234.0.0.1 cmd://'ssh user@my.remote.host vde_plug slirp://'

Now (on any host of the local area network) run a VDE client, for example a vdens:

$ vdens -R 80.80.80.80 vxvde://234.0.0.1
$# /sbin/udhcpc -i vde0
$# wget -qO - icanhazip.com

it returns the IP address of the remote host.