upstream (eth0)
	eth0: 192.168.7.1,255.255.255.0
	ip route 192.168.100.0 255.255.255.0 192.168.7.2
router 1 (se0,eth0)
	eth0: 192.168.7.2,255.255.255.0
	se0 : 10.10.17.1,255.255.255.252
	ip route 192.168.100.0 255.255.255.0 se0
router 2 (se0,se1)
	se0: 10.10.17.2,255.255.255.252
	se1: 10.10.17.5,255.255.255.252
	ip route 192.168.100.0 255.255.255.0 se1
router 3 (se0,eth0)
	se0: 10.10.17.6,255.255.255.252
	eth0: 192.168.100.1,255.255.255.0
	ip route 192.168.100.0 255.255.255.0 eth0
	ip route 0.0.0.0 0.0.0.0 10.10.17.6