Add docs for 8routers topology

Author: cscarpitta

nets-unmantained/8routers/README.md

@@ -10,6 +10,9 @@ In folder nodeconf/
 	- host folders contain start.sh for each host
 		- sets IPv6 address for hosts
 		- adds IPv6 routing to gateway
+	- datacenter folders contain start.sh for each datacenter
+		- sets IPv6 address for datecenters
+		- adds IPv6 routing to gateway
 	- router folders contain 
 		- zebra.conf
 			- sets for each interface the IPv6 address
@@ -42,6 +45,12 @@ host - router links:
 	h82 - r8: fd00:0:82::2/64	r8 - h82: fd00:0:82::1/64
 	h83 - r8: fd00:0:83::2/64	r8 - h83: fd00:0:83::1/64
 
+datacenter - router links:
+
+	hdc1 - r2: fcff:2:1::2/48	r2 - hdc1: fcff:2:1::1/48
+	hdc2 - r8: fcff:8:1::2/48	r8 - hdc2: fcff:8:1::1/48
+	hdc3 - r5: fcff:5:1::2/48	r5 - hdc3: fcff:5:1::1/48
+
 router - router links:
 
 	r1 -r2: fcf0:0:1:2::1/64	r2 - r1: fcf0:0:1:2::2/64
@@ -53,4 +62,24 @@ router - router links:
 	r5 -r6: fcf0:0:5:6::1/64	r6 - r5: fcf0:0:5:6::2/64
 	r6 -r7: fcf0:0:6:7::1/64	r7 - r6: fcf0:0:6:7::2/64
 	r6 -r8: fcf0:0:6:8::1/64	r8 - r6: fcf0:0:6:8::2/64
-	r7 -r8: fcf0:0:7:8::1/64	r8 - r7: fcf0:0:7:8::2/64
+	r7 -r8: fcf0:0:7:8::1/64	r8 - r7: fcf0:0:7:8::2/64
+
+
+Note that datacenters are special hosts, which have a public address.
+
+
+The file etc-hosts in the topology folder maps each IP address to its hostname.
+
+For example,
+fcff:1::1       r1
+fd00:0:11::2    h11
+fcff:2:1::2     hdc1
+...
+
+When you start the topology, the entries defined in this file are loaded and added to the system /etc/hosts file.
+
+This allows you to ping the nodes using their hostnames instead of the IP addresses:
+h11# ping6 h83
+h83# ping6 h11
+
+The entries are automatically removed from the /etc/hosts file when the emulation is stopped.