Configure VPNs in a Corporate Network, with
Optional Prioritisation of VoIP
Introduction
In this How To Note’s example, a headquarters office has VPNs to two branch offices and a
number of roaming VPN clients. The example illustrates the following possible components
that you could use in a corporate network:
zVPNs between a headquarters office and roaming VPN clients, such as travellers’ laptops
zVPNs between a branch office and roaming VPN clients, such as travellers’ laptops
za VPN between a headquarters office and a branch office with a fixed IP address, when the
branch office has an ADSL PPPoA connection to the internet
za VPN between a headquarters office and a branch office with a dynamically assigned IP
address, when the branch office has an ADSL PPPoEoA connection to the internet
zusing software QoS to prioritise voice (VoIP) traffic over the VPNs
Select the solution components that are relevant for your network requirements and
internet connection type.
Contents
Which products and software versions does this information apply to? ................................... 2
Related How To Notes .......................................................................................................................... 2
About IPsec modes: tunnel and transport ......................................................................................... 3
Background: NAT-T and policies .......................................................................................................... 4
How to configure VPNs in typical corporate networks ................................................................. 6
Before you start ............................................................................................................................... 7
How to configure the headquarters VPN access concentrator ........................................... 8
1
How to configure the AR440S router at branch office
How to configure the AR440S router at branch office 2 ..................................................... 24
AR440S configuration—the PPPoA site with VPN client access
router ......................... 33
Which products and software versions does this
information apply to?
The information provided in this document applies to the following products:
zAR400 Series routers
zAR750S and AR770S routers
zRapier and Rapier i Series switches
zAT-8800 Series switches
running software version 2.6.6 and above. However, prioritising the voice traffic requires
1
Software Quality of Service, which is available with version 2.7.
On the roaming VPN clients, we tested this solution with Microsoft® Windows Virtual
Private Network.
This How To Note shows how to prioritise VoIP traffic at the offices, but does not show how
to set up the VoIP facility itself on your VPN client PCs. You need to find suitable PC
software to provide that.
and above.
Related How To Notes
Allied Telesis offers How To Notes with a wide range of VPN solutions, from quick and
simple solutions for connecting home and remote offices, to advanced multi-feature setups.
Notes also describe how to create a VPN between an Allied Telesis router and equipment
from a number of other vendors.
For a complete list of VPN How To Notes, see the Overview of VPN Solutions in How To Notes
in the How To Library at www.alliedtelesis.com/resources/literature/howto.aspx.
Page 2 | AlliedWare™ OS How To Note: VPNs for Corporate Networks
About IPsec modes: tunnel and transport
vpn-protocol-stack.eps
This solution uses two types of VPN:
zIPsec tunnel mode, for the headquarters office to branch office VPNs. These are site-to-
site (router-to-router) VPNs.
zIPsec transport mode with L2TP, for the roaming Windows VPN clients.
The following figure shows the protocol stacks for the tunnel mode VPN and the transport
mode VPN for the connection type PPPoA.
IP
IP
IPsec payload (dynamic
PPP using template)
using L2TP server
definition
transport mode:
policy “roaming”
statically-defined
interface ppp0
IPsec payload
IP
IP
tunnel mode:
policy “hq”
statically-defined
interface ppp0
encrypted
by IPsec
IPsec
PPP
ATM
ADSL
Tunnel mode - for site-to-site VPNsTransport mode - for roaming clients
In this How To Note, branch office
PPP
L2TP
IPsec
PPP
ATM
ADSL
1
uses PPPoA. The other offices in this How To Note use
different connection types and therefore have different stacks below IP. Branch office 2 uses
PPP over virtual Ethernet over ATM, and headquarters simply uses IP over an actual Ethernet
WAN connect i on.
Page 3 | AlliedWare™ OS How To Note: VPNs for Corporate Networks
Background: NAT-T and policies
vpn-nat-t.eps
NAT-TNAT Traversal (NAT-T) can be enabled on any of our IPsec VPN links. It automatically allows
IPsec VPNs to traverse any NAT gateways that may be in the VPN path. This is likely to occur
with the VPNs from the roaming VPN clients—they are likely to use a LAN at a remote site
that is behind a NAT gateway.
NAT-T may also be applicable for a site-to-site VPN, if one of the routers is behind a NAT
gateway, such as some ADSL devices. Note that AR44xS series routers provide an ADSL
interface, which removes the need for a separate ADSL device. Therefore, the examples in
this How To Note do not include NAT-T for the site-to-site VPNs.
The following figure shows how the addresses in the IPsec headers change as a packet from a
roaming client traverses NAT gateways in the VPN pathway. The figure illustrates IPsec
transport mode with L2TP.
roaming VPN
client
NAT gateway
hotel
headquarters
192.168.200.1
192.168.200.254
211.211.211.1
Internet
Encrypted
Encrypted
IP
PPP
L2TP
IPsec
IP
ETH
IP
PPP
L2TP
IPsec
IP
ETH
Source Addr
192.168.143.1
N/A
N/A
N/A
192.168.200.1
N/AN/A
Source Addr
192.168.143.1
N/A
N/A
N/A
211.211.211.1
N/AN/A
hotel
Dest Addr
192.168.140.27
N/A
N/A
N/A
200.200.200.1
Dest Addr
192.168.140.27
N/A
N/A
N/A
200.200.200.1
200.200.200.1
VPN access
concentrator
192.168.140.254
192.168.140.27
Page 4 | AlliedWare™ OS How To Note: VPNs for Corporate Networks
IP
ETH
headquarters
Source Addr
192.168.143.1
N/A
Dest Addr
192.168.140.27
N/A
Policies and
interfaces
It is useful to keep in mind that you apply firewall rules and IPsec policies to interfaces in the
following different ways:
zFirewall rules can be applied on either private or public interfaces. The rules are matched
against traffic that comes into the interface to which they were applied. Rules applied to
private interfaces are typically quite different to rules applied to public interfaces.
zIPsec policies are applied only on the public interface. The policy definitions, and any active
Security Associations (SAs), are considered for both incoming and outgoing traffic on that
interface.
Page 5 | AlliedWare™ OS How To Note: VPNs for Corporate Networks
How to configure VPNs in typical corporate
vpn-corporate.eps
networks
This section describes a typical corporate network using secure VPN. The network consists
of a headquarters (HQ) router and two branch office routers. The headquarters router is
acting as a VPN Access Concentrator, and allows for VPN access from either of the branch
office sites or from roaming laptop VPN clients. The network is illustrated in the following
figure.
uses the PPPoA ADSL link type, and branch office 2 uses the PPPoEoA ADSL
ISP’s
router
200.200.200.1
211.211.211.1
hotel’s NAT gateway
192.168.200.254
roaming VPN client
physical address: 192.168.200.1
VPN tunnel address from pool: 192.168.143.1
headquarters
VPN access
concentrator
Pool of addresses available
for roaming clients:
192.168.143.1-50
corporate
link type. We have done this to illustrate these two commonly used ADSL link types. For
information about the ADSL link type you need, see your ADSL provider.
This How To Note gives you the commands for configuring each of the following:
LAN
1. The headquarters VPN access concentrator router, which includes:
zan ethernet connection to the Internet
za fixed Internet address. This means that the branch offices and the roaming VPN
clients have a known target for the headquarters end of the VPN
zVPN access to and from branch office
1
. This can be initiated from the headquarters
or branch office end. This is a site-to-site VPN and uses IPsec tunnel mode (see
"Background: NAT-T and policies" on page 4).
zVPN access from branch office 2. This can only be initiated from the branch office end,
because the branch office has a dynamically-assigned IP address. This also uses IPsec
tunnel mode.
zVPN client access from roaming users on Windows 2000 and Windows XP. This is
provided by using IPsec transport mode with L2TP (see "About IPsec modes: tunnel
and transport" on page 3)
zoptionally, prioritisation of voice (VoIP) traffic for these VPN clients by using Software
Quality of Service (SQoS). If the VPN clients use VoIP to establish voice calls via the
headquarters network, this helps maintain voice quality.
Page 6 | AlliedWare™ OS How To Note: VPNs for Corporate Networks
2. The branch office 1 router, which provides:
headquarters
branch office
1
branch office 2
zan ADSL PPPoA Internet connection. Note that the PPPoA connection requires an
ATM DS LA M
zVPN access to headquarters using IPsec tunnel mode
zincoming VPN client access from roaming users
za fixed Internet address so that roaming VPN clients have a known target for the
branch office end of the VPN
3. The branch office 2 router, which provides:
zan ADSL PPPoEoA Internet connection
zVPN access to headquarters using IPsec tunnel mode
za dynamically assigned Internet address, as used by many ISPs.
Color codingFor your convenience, the configurations are color-coded:
Before you start
Don’t forget to check you have the following when planning your secure VPN network:
1.ISAKMP shared key
2. Fixed public IP addresses to use where appropriate
3. The IP subnets to use on private LANs at the branch and headquarters sites
4. The range of IP addresses to use in the IP pools for allocating to the remote users
5. Usernames and passwords for the remote users
6. IP addresses from which SSH connections can be made to the routers (if applicable)
7. Connection parameters for the ADSL connections at the branch offices
8. VPN client PCs set up, as described in the How To Notes in "Related How To Notes" on
page 2.
Page 7 | AlliedWare™ OS How To Note: VPNs for Corporate Networks
Headquarters
How to configure the headquarters VPN access
concentrator
Before you begin to configure your router, ensure that it is running the appropriate software
release, patch and GUI files and has no configuration.
set inst=pref rel=<rel-file> pat=<patch-file> gui=<gui-file>
set conf=none
disable system security
restart reboot
Note: A software QoS extension to this configuration, to prioritise VoIP traffic over the
VPNs, is available in "How to prioritise outgoing VoIP traffic from the headquarters router" on
Enable security mode so that VPN keys are stored securely, and other security features are
enabled.
enable system security
Once security mode is enabled, you need to log in as a security officer to enter most
configuration-altering commands.
login secoff
password: <your-secoff-password>
It is important to keep this security officer username and password secure, and to consider
proper handover of it in the event of IT staff changes.
Also, we recommend you leave a “manager” privilege user defined because this may provide
backup access if the security officer password is lost. Do not leave the manager password at
the factory default—change it to a password in keeping with your company's security policy.
set user=manager password=<your-company-policy-password>
When security mode is enabled, router configuration access times out after inactivity to
prevent unauthorised access. The default timeout is 60 seconds, but you may temporarily
raise it to 600 seconds if desired.
set user securedelay=600
Page 8 | AlliedWare™ OS How To Note: VPNs for Corporate Networks
Headquarters
2.Configure IP for internet access
Give a fixed public address to the interface eth0, which is the Internet connection interface.
You can replace eth0 with ppp0 if you use a leased line.
enable ip
add ip int=eth0 ip=200.200.200.1
Give a fixed private address to the interface vlan1, which connects the router to the
headquarters LAN.
add ip int=vlan1 ip=192.168.140.254
Set the default route. The next hop is the gateway address provided by the ISP.
add ip rou=0.0.0.0 mask=0.0.0.0 int=eth0 next=200.200.200.254
If desired, set up the router as a DHCP server for the headquarters LAN.
Enable the user who connects via SSH to log in as secoff, by adding the secoff user as an SSH
user. Also, you may choose to restrict access so that it is only permitted from particular
addresses.
Secure Shell is a more secure, encrypted method of remote management access than telnet.
If you need to use telnet, even though it is insecure, you should restrict access by defining
Page 9 | AlliedWare™ OS How To Note: VPNs for Corporate Networks
If desired, you can configure SNMP to inform you or your service provider of network
events, such as the LAN interface of the router going down. We recommend SNMPv3 for
security reasons. For details, see How To Configure SNMPv3 On Allied Telesis Routers and Managed Layer 3 Switches. This How To Note is available from www.alliedtelesis.com/
resources/literature/howto.aspx.
5.Configure dynamic PPP over L2TP connections
You need to configure dynamic PPP over L2TP to accept incoming Windows VPN client
connections.
Create an IP pool to allocate unique internal payload addresses to incoming VPN clients.
create ip pool=roaming ip=192.168.143.1-192.168.143.50
Define a PPP template. This defines authentication and uses the IP pool of addresses.
create ppp template=1
set ppp template=1 bap=off ippool=roaming authentication=chap echo=10
lqr=off
Configure L2TP. When the router successfully negotiates an L2TP tunnel connection from
any remote peer, it then creates a PPP interface over that tunnel, using the PPP parameters
defined by the PPP template. If you intend to prioritise voice traffic (see page 30), also turn
on TOS (type of service) reflection, so that DSCP marked VoIP packets can be classified for
prioritisation at the PPP level.
Create a group of SA specifications for the roaming VPN clients. These SA specifications use
IPsec transport mode for Windows VPN interoperability. Multiple specifications allow IPsec
to negotiate different levels of encryption to match what your version of the VPN client
provides.
Create an IPsec policy for the VPN traffic between headquarters and branch office 1. Identify
the traffic by its local and remote addresses—in this example the subnet used on the LAN at
branch office
1
(remote) is 192.168.141.0/24. Note that the local address selector is wider
than the headquarter’s LAN; in fact, we cover all site subnets with this supernet.
Create another IPsec policy for the VPN traffic between headquarters and branch office 2.
1
The subnet used on the LAN at branch office 2 is
92.168.142.0/24. This policy uses
peeraddress=dynamic. The dynamic option is designed for only one dynamic peer to
connect at a time under that policy, which makes sense when the policy is intended for one
branch office.
Create another IPsec policy for direct Internet traffic from the headquarters LAN to the
Internet, such as web browsing.
create ipsec pol=internet int=eth0 ac=permit
Note: The order of the IPsec policies is important. The Internet permit policy must be last.
Create your ISAKMP pre-shared key. This key is used when initiating your VPN during phase
one ISAKMP exchanges with your VPN peers. Share the value of this pre-shared key with all
VPN peers that use it—in this example, the roaming VPN clients and the branch office
routers. The router only uses this key during phase one ISAKMP exchanges.
This example uses separate ISAKMP policies for each peer. Note the following points about
the policies:
zdifferent ISAKMP policies meet the different needs of the different types of peer—Allied
Telesis routers versus Windows VPN clients. For example, Allied Telesis peers support
heartbeats; Windows VPN clients do not.
Page 12 | AlliedWare™ OS How To Note: VPNs for Corporate Networks
Headquarters
zthe branch office policies use a different encryption transform—3des2key—than the
roaming policy. When a new incoming ISAKMP message starts, this lets the router identify
whether to match it to the roaming policy or one of the branch office policies.
zthe policies include local IDs. These allow the remote peers to identify incoming ISAKMP
packets from the headquarters router through any NAT gateways in the path.
Create an ISAKMP policy for the VPN to branch
1
, with a fixed address. Use ISAKMP
heartbeats, which allow ISAKMP to clear SAs if either end of the link resets.
Create an ISAKMP policy for VPNs to roaming VPN clients, with peer=any because the
peers have dynamic addresses. Note that you cannot use heartbeats with Windows peers.
We recommend that you enable NAT-T, because the roaming VPN clients will sometimes
need to connect through a NAT-T gateway.
The roaming policy uses the same key as the branch office policies. If you want to, you can
instead generate a unique pre-shared key to use with the roaming clients, and attach it to the
roaming policy.
8.Configure the firewall’s basic settings
Enable the firewall and create a firewall policy.
enable firewall
create firewall policy=hq
enable firewall policy=hq icmp_f=all
Specify the LAN-facing interface of the router as a private (trusted) interface on the firewall.
add firewall policy=hq int=vlan1 type=private
Specify the Internet-facing interface of the router as a public (not trusted) interface on the
firewall.
add firewall policy=hq int=eth0 type=public
Define a firewall dynamic definition to enable dynamically created interfaces to participate in
the firewall. In this case, the definition provides for the dynamic PPP over L2TP interfaces
that incoming Windows VPN connections use. In other words, when the router dynamically
creates PPP interfaces over the L2TP connections from the roaming PC clients, the router
automatically adds these dynamic interfaces as private interfaces on the firewall. The router
Page 13 | AlliedWare™ OS How To Note: VPNs for Corporate Networks
Headquarters
can trust traffic arriving on the dynamic interfaces because—in this example configuration—it
can only come from an authenticated and encrypted VPN connection.
Note: Windows VPN client default behaviour does not support “split tunnelling”. This
means that when the Windows VPN tunnel is up, all traffic passes through it, whether the
traffic is destined for the headquarters office LAN or for Internet surfing destinations.
Therefore, we suggest you define the second NAT above, to allow clients to access the
Internet via the headquarters router when their VPN connection is up.
9.Configure the firewall’s access rules
Create a rule to allow incoming ISAKMP negotiation messages to pass through the firewall.
Create a rule to support NAT-T. If a NAT gateway is detected in the VPN path, NAT-T “port
floats” IKE to port 4500, and also encapsulates IPsec inside UDP headers to the same port.
Therefore, UDP traffic to port 4500 must be allowed to pass through the firewall.
Create a rule for the roaming VPN clients. Windows VPN client uses L2TP (UDP to port
1701
) encapsulated inside IPsec. This rule allows L2TP traffic through the firewall if it
originally arrived at the router encapsulated in IPsec (and was decapsulated by the IPsec
process before it passed to the firewall).
Create a pair of rules to allow office-to-office payload traffic to pass through the firewall
without applying NAT. This traffic must bypass NAT so that the traffic matches subsequent
IPsec policy address selectors. You need two rules—one for the public interface and one for
the private interface—so that office-to-office payload traffic bypasses NAT regardless of
which side initiated the session.
The rule for the public interface uses encapsulation=ipsec to identify incoming VPN
traffic—decrypted payload data that came from the IPsec module.
It is important to save your configuration when you finish, to preserve the configuration over
any power cuts.
create conf=<your-file.cfg>
This is particularly important in security configurations because it preserves the security
officer definition. Without this, regaining configuration access would destroy encryption
information such as keys.
Once you have saved the configuration to a file, specify that file as the configuration script to
use when the router boots up.
set config=<your-file.cfg>
Note: If you forget your secoff user password, log in as manager. The manager user cannot
edit a router in system security mode, so enter the command disable system security. This
destroys your encryption keys. Edit your configuration file to redefine your secoff user
password, then reboot, then log in as secoff, then enable system security again, then recreate
the keys.
Page 15 | AlliedWare™ OS How To Note: VPNs for Corporate Networks
branch office
1
How to configure the AR440S router at branch office
1
Before you begin to configure your router, ensure that it is running the appropriate software
release, patch and GUI files and has no configuration.
set inst=pref rel=<rel-file> pat=<patch-file> gui=<gui-file>
set conf=none
disable system security
restart reboot
Note: A software QoS extension to this configuration, to prioritise VoIP traffic over the
1
VPNs, is available in "How to prioritise outgoing VoIP traffic from the branch office
Enable security mode so that VPN keys are stored securely, and other security features are
enabled.
enable system security
Once security mode is enabled, you need to log in as a security officer to enter most
configuration-altering commands.
login secoff
password: <your-secoff-password>
It is important to keep this security officer username and password secure, and to consider
proper handover of it in the event of IT staff changes.
Also, we recommend you leave a “manager” privilege user defined because this may provide
backup access if the security officer password is lost. Do not leave the manager password at
the factory default—change it to a password in keeping with your company's security policy.
set user=manager password=<your-company-policy-password>
When security mode is enabled, router configuration access times out after inactivity to
prevent unauthorised access. The default timeout is 60 seconds, but you may temporarily
raise it to 600 seconds if desired.
set user securedelay=600
Page 16 | AlliedWare™ OS How To Note: VPNs for Corporate Networks
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