The script I use to setup uml_net for the uml kernel, modify as required.

yard/replacements/root/umlnet

@@ -0,0 +1,8 @@
+#!/bin/bash
+
+# This is what I use to set-up the network from within uml using tap. Edit it to 
+# your own requirments
+
+ifconfig eth0 192.168.1.2 up
+route add -net 192.168.1.0 gw 192.168.1.5 netmask 255.255.255.0
+route add default gw 192.168.1.5