Add a proxy ARP example.

diff --git a/examples/bridging.mdwn b/examples/bridging.mdwn
index 8d43427..c7c0d8f 100644 (file)
--- a/examples/bridging.mdwn
+++ b/examples/bridging.mdwn
@@ -15,6 +15,11 @@ In switch and hub mode, broadcast packets are broadcast to other daemons and
 in order to route packets. With these mode tinc can be used to act as a bridge
 between two or more Ethernet segments.
 
+Bridging allows all nodes in the VPN to share the same subnet.  However, if
+this is the only reason for bridging, and you do not need to tunnel broadcast
+or non-IP packets, you can alternatively use [[proxy ARP|examples/proxy-arp]]
+instead of bridging.
+
 ### Overview
 
 The network setup is as follows:

diff --git a/examples/proxy-arp.mdwn b/examples/proxy-arp.mdwn
new file mode 100644 (file)
index 0000000..5d25f21
--- /dev/null
+++ b/examples/proxy-arp.mdwn
@@ -0,0 +1,78 @@
+[[!meta title="proxy ARP as an alternative to bridging"]]
+
+## Example: proxy ARP as an alternative to bridging
+
+If one wants to have a remote node appear to be on a local LAN (i.e., having an
+IP address inside the local LAN's subnet), one can set up a bridge at the local
+node, as described in the [[bridging example|examples/bridging]].  However,
+setting up a bridge is rather complex, and if one only needs unicast IP traffic
+to work, and broadcast or non-IP traffic is not a requirement, one can use the
+[proxy ARP](http://en.wikipedia.org/wiki/Proxy_ARP) features of the operating
+instead.
+
+Since we only use unicast IP traffic, proxy ARP works with both router and
+switch mode.
+
+### Overview
+
+The network setup is as follows:
+
+* Office LAN, the LAN on interface eth0 uses the range 192.168.1.0/24. The office node uses the address 192.168.1.2.
+* Road warrior, using the address 192.168.1.123. 
+
+### Configuration of tinc at the office
+
+>     host# cat /etc/tinc/vpn/tinc.conf
+>     Name = office
+>     #Optional:
+>     #Mode = switch
+>     
+>     host# cat /etc/tinc/vpn/tinc-up
+>     #!/bin/sh
+>     
+>     ifconfig $INTERFACE 192.168.1.2 netmask 255.255.255.255
+>     route add 192.168.1.123 dev $INTERFACE
+>     echo 1 >/proc/sys/net/ipv4/conf/eth0/proxy_arp
+>     echo 1 >/proc/sys/net/ipv4/conf/$INTERFACE/proxy_arp
+>     
+>     host# ls /etc/tinc/vpn/hosts
+>     office  roadwarrior  ...
+>     
+>     host# cat /etc/tinc/vpn/hosts/office
+>     Address = 123.234.123.42
+>     Subnet = 192.168.1.0/24
+>     -----BEGIN RSA PUBLIC KEY-----
+>     ...
+>     -----END RSA PUBLIC KEY-----
+>     
+>     host# cat /etc/tinc/vpn/hosts/roadwarrior
+>     Subnet = 192.168.1.123
+>     -----BEGIN RSA PUBLIC KEY-----
+>     ...
+>     -----END RSA PUBLIC KEY-----
+
+### Configuration of tinc at the road warrior
+
+>     host# cat /etc/tinc/vpn/tinc.conf
+>     Name = roadwarrior
+>     #Optional:
+>     #Mode = switch
+>     
+>     host# cat /etc/tinc/vpn/tinc-up
+>     #!/bin/sh
+>     
+>     ifconfig $INTERFACE 192.168.1.123 netmask 255.255.255.0
+
+The host config files are, of course, identical to those on the office node.
+
+### Automatically adding routes
+
+In the above configuration, the `tinc-up` script of the office node has a route
+to the roadwarrior's address hardcoded.  To have tinc automatically add the
+necessary routes, remove the `route add` command from the `tinc-up` script, and
+instead add this `subnet-up` script:
+
+>     host# cat /etc/tinc/vpn/subnet-up
+>     #!/bin/sh
+>     [ "$NAME" = "$NODE" ] && exit 0
+>     ip route replace $SUBNET dev $INTERFACE