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
-----------------------------------------------------------------------------
10.10.10.0
10.10.10.0
10.10.10.0
192.168.1.0
200.200.1.0
200.200.2.0
222.222.1.0
222.222.1.0
222.222.2.0
222.222.2.0
-----------------------------------------------------------------------------
Page 3 | AlliedWare™ OS How To Note: Dynamic Routing over L2TP
Mask
NextHop
Type
Policy
Protocol
255.255.255.0
0.0.0.0
direct
0
interface
255.255.255.0
10.10.10.2
direct
0
static
255.255.255.0
192.168.1.2
remote
0
rip
255.255.255.0
0.0.0.0
direct
0
interface
255.255.255.0
192.168.1.2
remote
0
rip
255.255.255.0
192.168.1.2
remote
0
rip
255.255.255.0
0.0.0.0
direct
0
interface
255.255.255.0
0.0.0.0
remote
0
ospf-Intra
255.255.255.0
0.0.0.0
direct
0
interface
255.255.255.0
0.0.0.0
remote
0
ospf-Intra
An example scenario for RIP over L2TP
Interface
Metrics
Preference
eth0
1
eth0
1
ppp0
2
ppp0
1
ppp0
2
ppp0
2
vlan1
1
vlan1
1
vlan2
1
vlan2
1
Age
644
0
644
60
627
100
644
0
627
100
627
100
644
0
641
10
644
0
636
10
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