The Design and Implementation of the Anykernel and Rump Kernels

B–15
B.3 Networking
This section explains how to run any dynamically linked networking program against
a rump TCP/IP stack without requiring any modifications to the application, including
no recompilation. The application we use in this example is the Firefox
browser. It is an interesting application for multiple reasons. Segregating the web
browser to its own TCP/IP stack is an easy way to increase monitoring and control
over what kind of connections the web browser makes. It is also an easy way to get
some increased privacy protection (assuming the additional TCP/IP stack can have
its own external IP). Finally, a web browser is largely ”connectionless”, meaning
that once a page has been loaded a TCP/IP connection can be discarded. We use
this property to demonstrate killing and restarting the TCP/IP stack from under
the application without disrupting the application itself.
A rump server with TCP/IP capability is required. If the plan is to access the
Internet, the virt interface must be present in the rump kernel and the host kernel
must have support for tap and bridge. You also must have the appropriate privileges
for configuring the setup — while rump kernels do not themselves require privileges,
they cannot magically access host resources without the appropriate privileges. If
you do not want to access the Internet, using the shmif interface is enough and no
privileges are required. However, for purposes of this tutorial we will assume you
want to access the Internet and all examples are written for the virt+tap+bridge
combination.
Finally, if there is a desire to configure the rump TCP/IP stack with DHCP, the
rump kernel must support bpf. Since bpf is accessed via a file system device node,
vfs support is required in this case (without bpf there is no need for file system
support). Putting everything together, the rump kernel command line looks like
this: