Allied Telesis L2TP Tunnel manual Network Operation, Routing Information

An example scenario for RIP over L2TP

Network Operation

There is a single static route configured to bring up the L2TP tunnel and a secure point-to- point connection (PPP0) is established over the L2TP tunnel between the 'Central' and 'Remote' office routers. This allows secure communication between the offices across the Internet.

Each local office site is using OSPF as their routing protocol, as it offers some advanced routing features and is scalable and flexible. The 'local' VLAN networks in our example at each office site use OSPF.

RIP is used across the secure Internet connection between offices to provide a more robust network, as discussed previously. So RIP is used on the point-to-point interface (PPP0) over the L2TP tunnel. OSPF is configured to import and export routing information with RIP.

This allows RIP to propagate the dynamically learnt OSPF 'local' VLAN network information to the other office router.

Routing Information

The routing table in each router shows locally learnt routes and the routes learnt from the remote router via RIP across the L2TP tunnel. The example output below is from the show ip route command on the 'Central office' router.

You can see that the 'local' VLAN networks (222.222.1.0 and 222.222.2.0) have been learnt via OSPF. The 'Remote office' OSPF VLAN networks (200.200.1.0 and 200.200.2.0) have been learnt via RIP. These were exported from OSPF on the 'Remote' router and propagated by RIP over the secure point-to-point connection (PPPO) using the L2TP tunnel.

IP Routes

-----------------------------------------------------------------------------

Destination	Mask	NextHop	Interface	Age
	Type	Policy Protocol	Metrics	Preference

-----------------------------------------------------------------------------

10.10.10.0	255.255.255.0		0.0.0.0	eth0	644
	direct	0	interface	1	0
10.10.10.0	255.255.255.0		10.10.10.2	eth0	644
	direct	0	static	1	60
10.10.10.0	255.255.255.0		192.168.1.2	ppp0	627
	remote	0	rip	2	100
192.168.1.0	255.255.255.0		0.0.0.0	ppp0	644
	direct	0	interface	1	0
200.200.1.0	255.255.255.0		192.168.1.2	ppp0	627
	remote	0	rip	2	100
200.200.2.0	255.255.255.0		192.168.1.2	ppp0	627
	remote	0	rip	2	100
222.222.1.0	255.255.255.0		0.0.0.0	vlan1	644
	direct	0	interface	1	0
222.222.1.0	255.255.255.0		0.0.0.0	vlan1	641
	remote	0	ospf-Intra	1	10
222.222.2.0	255.255.255.0		0.0.0.0	vlan2	644
	direct	0	interface	1	0
222.222.2.0	255.255.255.0		0.0.0.0	vlan2	636
	remote	0	ospf-Intra	1	10

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Page 3 AlliedWare™ OS How To Note: Dynamic Routing over L2TP