Allied Telesis AR400 Series Manuale utente

C613-16037-00 REV C www.alliedtelesis.com

AlliedWare™ OS

How To |

Introduction

This How To Note shows an example of using a dynamic routing protocol over an L2TP

tunnel.

Running dynamic routing protocols over a secure Internet connection can be a complex

issue, with the possibility of intermittent connections causing routing problems.

OSPF (or BGP) are more connection-oriented than RIP and therefore are more susceptible

to problems caused by intermittent loss of connection between 'neighbours'. A neighbour

that may bounce up and down can cause havoc to the correct propagation of OSPF routing

information for a network.

The following example scenario is for setting up RIP over an L2TP tunnel. RIP is simpler and

has less overhead and control, so it provides a more robust setup as a dynamic routing

protocol over an L2TP tunnel.

Which products does it apply to?

This Note applies to the following Allied Telesis routers, running software version 2.6.1 or

later:

zAR400 series

zAR700 series

Configure Dynamic Routing Over An L2TP Tunnel

Page 2 | AlliedWare™ OS How To Note: Dynamic Routing over L2TP

An example scenario for RIP over L2TP

Related How To Notes

You may also find the following How To Notes useful:

zHow To Configure Remote L2TP Tunnels

zHow To Configure Allied Telesis and Cisco Routers To Interoperate Over L2TP

How To Notes are available from www.alliedtelesis.com/resources/literature/howto.aspx.

An example scenario for RIP over L2TP

Our example uses two office sites that are connected via a WAN connection over the

Internet using an L2TP tunnel for security.

The setup (shown below) shows the 'Central office' and 'Remote office' routers connected,

in this case, back to back via their Ethernet interfaces (this would likely be the remote WAN

connection across the Internet, with perhaps static IP assignment from the ISPs).

WAN

X PC

HUB

POWER ETH0

X PC

HUB

POWER

ETH0

Central office router

Remote office router

VLAN 2 IP=222.222.2.1

VLAN 1 IP=222.222.1.1

VLAN 2 IP=200.200.2.1

VLAN 1 IP=200.200.1.1

192.168.1.1

192.168.2.1

Eth0 IP=10.10.10.1

Eth0 IP=10.10.10.2

PPP0 over

L2TP tunnel

RIP propogates

VLAN OSPF

routes over

L2TP tunnel

to remote router

OSPF used on

local VLAN

networks

OSPF used on

local VLAN

networks

rip-l2tp.eps

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

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

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

Page 4 | AlliedWare™ OS How To Note: Dynamic Routing over L2TP

An example scenario for RIP over L2TP

Routing Considerations

A routing issue to consider in this set up is the fact that RIP is relatively slow to react to

route changes as it only updates, by default, every 30 seconds.

To improve the responsiveness of RIP you can alter the default timers for updating, flushing

and so on. You do need to keep in mind that if you lose some packets (quite possible across

a lossy Internet connection) some of your routes may flap too much. So the RIP timers need

to be adjusted to provide an optimal compromise between responsiveness and robustness.

In this particular example, the various RIP timers are set at half default value.

set ip riptimer update=15 invalid=90 holddown=60 flush=150

Consideration would need to be given to each specific set up to get an optimal balance when

adjusting these timers.

Page 5 | AlliedWare™ OS How To Note: Dynamic Routing over L2TP

Configurations

Central Office Router

set system name=Central_Office

enable l2tp

enable l2tp server=both

add l2tp call="tunnel" rem="tunnel" ip=10.10.10.2 ty=virtual prec=in

create vlan="vlan2" vid=2

add vlan="2" port=3,4

create ppp=0 over=tnl-tunnel

set ppp=0 bap=off username="chap" password="chap"

enable ip

add ip int=eth0 ip=10.10.10.1 mask=255.255.255.0

add ip int=ppp0 ip=192.168.1.1

add ip int=vlan1 ip=222.222.1.1

add ip int=vlan2 ip=222.222.2.1

add ip rou=10.10.10.0 mask=255.255.255.0 int=eth0 next=10.10.10.2

add ip rip int=ppp0 send=rip2 receive=rip2

set ip riptimer update=15 invalid=90 holddown=60 flush=150

set ospf routerid=222.222.1.1 rip=both

add ospf area=backbone stubarea=off summary=send

add ospf range=222.222.1.0 area=backbone mask=255.255.255.0

add ospf range=222.222.2.0 area=backbone mask=255.255.255.0

add ospf interface=vlan1 area=backbone

add ospf interface=vlan2 area=backbone

enable ospf

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C613-16037-00 REV C

Remote Office Router

set system name=Remote_Office

enable l2tp

enable l2tp server=both

add l2tp call="tunnel" rem="tunnel" ip=10.10.10.1 ty=virtual prec=out

create vlan="vlan2" vid=2

add vlan="2" port=3,4

create ppp=0 over=tnl-tunnel

set ppp=0 bap=off username="chap" password="chap"

enable ip

add ip int=ppp0 ip=192.168.1.2

add ip int=eth0 ip=10.10.10.2 mask=255.255.255.0

add ip int=vlan1 ip=200.200.1.1

add ip int=vlan2 ip=200.200.2.1

add ip rou=10.10.10.0 mask=255.255.255.0 int=eth0 next=10.10.10.1

add ip rip int=ppp0 send=rip2 receive=rip2

set ip riptimer update=15 invalid=90 holddown=60 flush=150

set ospf routerid=200.200.1.1 rip=both

add ospf area=backbone stubarea=off summary=send

add ospf range=200.200.1.0 area=backbone mask=255.255.255.0

add ospf range=200.200.2.0 area=backbone mask=255.255.255.0

add ospf interface=vlan1 area=backbone

add ospf interface=vlan2 area=backbone

enable ospf

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