--- wikisrc/ports/xen/howto.mdwn	2014/12/26 16:17:25	1.45
+++ wikisrc/ports/xen/howto.mdwn	2014/12/26 16:43:51	1.46
@@ -465,19 +465,29 @@ similarly to vnds.
 Virtual Networking
 ------------------
 
-TODO: explain xvif concept, and that it's general.
-
-There are two normal styles: bridging and NAT.
+Xen provides virtual ethernets, each of which connects the dom0 and a
+domU.  For each virtual network, there is an interface "xvifN.M" in
+the dom0, and in domU index N, a matching interface xennetM (NetBSD
+name).  The interfaces behave as if there is an Ethernet with two
+adaptors connected.  From this primitive, one can construct various
+configurations.  We focus on two common and useful cases for which
+there are existing scripts: bridging and NAT.
 
 With bridging, the domU perceives itself to be on the same network as
-the dom0.  For server virtualization, this is usually best.
+the dom0.  For server virtualization, this is usually best.  Bridging
+is accomplished by creating a bridge(4) device and adding the dom0's
+physical interface and the various xvifN.0 interfaces to the bridge.
+One specifies "bridge=bridge0" in the domU config file.  The bridge
+must be set up already in the dom0; an example /etc/ifconfig.bridge0
+is:
+
+        create
+        up
+        !brconfig bridge0 add wm0
 
 With NAT, the domU perceives itself to be behind a NAT running on the
 dom0.  This is often appropriate when running Xen on a workstation.
 
-One can construct arbitrary other configurations, but there is no
-script support.
-
 Sizing domains
 --------------
 
@@ -509,9 +519,41 @@ obtain domU kernels.
 Config files
 ------------
 
-TODO: give example config files.   Use both lvm and vnd.
+The following is an example domain configuration file, lightly
+sanitized from a known working on Xen 4.1 (NetBSD 5 amd64 dom0 and
+NetBSD 6 i386 domU):
+
+        # -*- mode: python; -*-
+
+        kernel = "/netbsd-XEN3PAE_DOMU-i386-foo.gz"
+
+        memory = 1024
+
+        name = "foo"
+
+        #cpu = -1
+
+        vif = [ 'mac=aa:00:00:d1:00:09,bridge=bridge0' ]
+
+        disk = [ 'file:/n0/xen/foo-wd0,0x1,w',
+                 'file:/n0/xen/foo-wd1,0x2,w' ]
+
+        root = "xbd0"
+
+        autorestart = True
+
+The kernel has the host/domU name in it, so that on the dom0 one can
+update the various domUs independently.  The vif line causes an
+interface to be provided, with a specific mac address (do not reuse
+MAC addresses!), in bridge mode.  Two disks are provided, and they are
+writable.
+
+TODO: explain if the root line is really necessary.
+TODO: explain or remove autorestart.
+
+TODO: Add an example with lvm
 
-TODO: explain the mess with 3 arguments for disks and how to cope (0x1).
+TODO: explain, someplace the mess with 3 arguments for disks and how to cope (0x1).
 
 Starting domains
 ----------------
@@ -655,7 +697,7 @@ working vif-bridge is also provided with
 
     #!/bin/sh
     #============================================================================
-    # $NetBSD: howto.mdwn,v 1.44 2014/12/26 14:20:27 gdt Exp $
+    # $NetBSD: howto.mdwn,v 1.45 2014/12/26 16:17:25 gdt Exp $
     #
     # /usr/pkg/etc/xen/vif-bridge
     #