Contents

Use a Branch Office VPN for Failover From a Private Network Link

Example configuration files created with — WSM v11.10.1

Revised — 7/22/2015


Use Case

In this configuration example, an organization has networks at two sites and uses a private network link to send traffic between the two networks. To make their network configuration more fault-tolerant, they want to set up a secondary route between the networks to use as a backup if the private network link fails, but they do not want to spend money on a second private network connection. To solve this problem, they can use a branch office VPN with dynamic routing.

This configuration example provides a model of how you could set up your network to automatically fail over to a branch office VPN if a primary private network connection between two sites becomes unavailable. To use the branch office VPN connection for automatic failover, you must enable dynamic routing on the Firebox at each site. You can use any supported dynamic routing protocol (RIP v1, RIP v2, OSPF, or BGP v4).

This configuration example is provided as a guide. Additional configuration settings might be necessary, or more appropriate, for your network environment.

Solution Overview

A routing protocol is the method routers use to communicate with each other and share information about the status of network routing tables. On the Firebox, static routes are persistent and do not change, even if the link to the next hop goes down. When you enable dynamic routing, the Firebox automatically updates the routing table based on the status of the connection. When you configure dynamic routing for traffic sent through the private network connection, if the private network connection fails, the Firebox automatically removes that route from the routing table.

After you configure dynamic routing between the two sites, you then configure a branch office VPN tunnel between the two sites on another Firebox interface. As part of the VPN configuration, you enable the global VPN setting Enable the use of non-default (static or dynamic) routes to determine if IPSec is used.

How It Works

When the global VPN setting is enabled, the Firebox uses the status of the routing table to decide whether to send traffic through the branch office VPN tunnel.

With this configuration:

  • When the private network connection is established between the two sites, the Firebox at each site adds the dynamic route to the routing table. Because the route is present in the routing table, each Firebox sends traffic to the other site over the private connection.
  • If the private network connection fails, the Firebox at each site removes that route from the routing table. Because the route is not present in the routing table, each Firebox sends traffic to the other site through the encrypted IPSec branch office VPN tunnel.
  • When the private network connection is restored, the dynamic route is added to the routing table at each site, and the two devices automatically begin to send traffic over the private network connection again.

Requirements

For VPN failover to operate correctly, the configuration must meet these requirements:

  • The Firebox at each site must use Fireware v11.3.1 or higher.
  • The two sites must have a primary connection over a private network link, such as a leased line or MPLS network.
  • The primary network connection between the two sites must terminate at the Firebox at each site.
  • The trusted and optional networks at each site must use the Firebox as the default gateway.
  • Dynamic routing (OSPF, BGP, or RIP) must be enabled on the Fireboxes for the primary private network link between sites. Fireware with a Pro upgrade is required to use OSPF or BGP v4.
  • A branch office VPN must be configured between the Fireboxes at each site.
  • The Enable the use of non-default (static or dynamic) routes to determine if IPSec is used global VPN setting must be enabled on the Fireboxes at both sites.

Network Topology

To configure automatic network failover, the private network link between the two sites must terminate at the Fireboxes at each site. At a high level, this generic network diagram shows the relationship between the networks at the two sites.

Network topology diagram of Site A and Site B connected over a private network cloud and the Internet

In this diagram, the Private Network Cloud could represent any one of several possible methods to connect the two sites over a private network. All of these connection types are supported for dynamic failover to a VPN connection.

Point-to-Point Link

In this type of connection, the Fireboxes at the two sites connect directly to each other. Typical examples of this type of connection are fiber optic connection, fiber-to-Ethernet converters, layer 2 VLAN connections, or a leased line with serial-to-Ethernet converters at each end.

Multi-Hop Link

In this type of connection, the Firebox at each site is connected to a router and the routers are connected by point-to-point links. The routers could be managed by the network administrators at each site, or by the service provider. A typical example of this type of connection is a leased line terminated on routers at each site.

MPLS Link

In this type of connection, the Firebox at each site connects to a router on an MPLS network. In this case, the routers are usually owned and managed by the service provider. A typical example of this type of connection is an MPLS or L2TP private network connection.

These connection types are explained more fully in the next section.

Example Network Topologies

For automatic failover to a VPN to operate correctly, the private network link between the two sites must terminate on a trusted or optional network interface on the Firebox at each site. This interface must be separate from the trusted network.

In this configuration example, we present two specific network topologies to illustrate the supported network connection types: private network connection over point-to-point link and private network connection over multi-hop link or MPLS. The example configuration files that accompany this document show configuration settings for each private network connection type. For similar topologies that are not supported, see the section Appendix — Unsupported Network Topologies.

Private Network Connection Over Point-to-Point Link

In a point-to-point link, the private network connection between the two sites is a leased line, with a serial-to-Ethernet converter at each end. This point-to-point link connects directly to an interface on each Firebox.

In this network diagram, the Fireboxes at the two sites have these IP addresses:

  Site A Site B
External interface IP address 192.0.2.20/24 198.51.100.30/24
Default Gateway IP address 192.0.2.1 198.51.100.1
IP address of the Firebox interface connected to the trusted network 10.0.20.1/24 10.0.30.1/24

Trusted network IP address

10.0.20.0/24 10.0.30.0/24
IP address of the Firebox interface connected to the private leased line 192.168.100.1/30 192.168.100.2/30

With this type of connection, there are no routers to configure. Only these addresses are required to enable dynamic routing over the private leased line between the two sites. The recommended dynamic routing protocol for this type of private network topology is OSPF.

Private Network Connection Over Multi-Hop Link or MPLS

If the private network link is a multi-hop link or MPLS network, the Firebox at each site connects to a router configured at the edge of a leased line or MPLS network. In this topology, you must add a static route on each Firebox to define the IP address of the local router on the private network as the next hop to the other Firebox.

Network diagram for Multi-Hop Link or MPLS Network private network connection

In this network diagram, the Fireboxes at the two sites use these IP addresses:

  Site A Site B
External interface IP address 192.0.2.20/24 198.51.100.30/24
Default gateway IP address 192.0.2.1 198.51.100.1
IP address of the Firebox interface connected to the trusted network 10.0.20.1/24 10.0.30.1/24

Trusted network IP address

10.0.20.0/24 10.0.30.0/24
IP address of the Firebox interface connected to the router 192.168.100.1/30 192.168.200.1/30
LAN IP address of the router connected to the private network link 192.168.100.2/30 192.168.200.2/30
WAN IP address of the router connected to the private network link 10.0.3.1/30 10.0.3.2/30

At each end of the leased line or MPLS network between the two Fireboxes, are routers that can either be managed by the network administrator at each site, or managed by the network service provider. In this configuration, you must set up static routes on each Firebox and on each router to correctly direct the traffic between the two networks.

For the Firebox at Site A to be able to reach the interface of the Firebox at Site B (192.168.200.1/30), you must add static routes to the Firebox and to the router at Site A. For the Firebox at Site B to be able to reach the interface of the Firebox at Site A (192.168.100.1/30), you must add static routes to the Firebox and to the router at Site B. You must also configure static routes on the routers at each site to allow the traffic between the trusted networks at each site.

If you configure dynamic routing between each Firebox and the local MPLS router, you do not have to add static routes to the MPLS routers. For this configuration example, we assume you use static routing between the Firebox and the local router.

The static routes for the Firebox and the router at each site are:

Static Routes at Site A

  Firebox at Site A Site A Router
Route to Site B Firebox

Network: 192.168.200.0/30
Next Hop: 192.168.100.2

Network: 192.168.200.0/30
Next Hop: 10.0.3.2

Route to Site A trusted network

 

Network: 10.0.20.0/24
Next Hop: 192.168.100.1

Route to Site B trusted network  

Network: 10.0.30.0/24
Next Hop: 10.0.3.2

Static Routes at Site B

  Firebox at Site B Site B Router
Route to Site A Firebox

Network: 192.168.100.0/30

Next Hop: 192.168.200.2

Network: 192.168.100.0/30
Next Hop: 10.0.3.1

Route to Site A trusted network  

Network: 10.0.20.0/24
Next Hop: 10.0.3.1

Route to Site B trusted network  

Network: 10.0.30.0/24
Next Hop: 192.168.200.1

After you configure the static routes and verify that the devices can contact each other, you can configure dynamic routing across the private network link. The recommended dynamic routing protocol for this configuration is BGP.

In this example configuration, dynamic routing occurs only between the Fireboxes. The routers connected to the private network link do not use dynamic routing.

Example Configuration Files

For your reference, we have included six example configuration files with this document. These configuration files are included in the vpn_failover_configs.zip file.

To examine the details of the example configuration files, you can open them with Policy Manager. Make sure to use Policy Manager v11.3.1 or higher, because the VPN failover option is not supported in earlier versions of Policy Manager.

The example configuration files show the configurations for Site A and Site B for each of the three dynamic routing configuration protocols. Only the BGP configuration files include the static routes required for a multi-hop link or an MPLS private network connection.

Description Configuration Filename
BGP configuration

BGP-Site-A-multi-hop-with-VPN.xml
BGP-Site-B-multi-hop-with-VPN.xml

OSPF configuration

OSPF-Site-A-with-VPN.xml
OSPF-Site-B-with-VPN.xml

RIP configuration

RIP-Site-A-with-VPN.xml
RIP-Site B-with-VPN.xml

The settings configured in the example configuration files are described in the next sections.

Dynamic Routing Configuration

After you have established the primary connection between the two networks over the private network, you must enable dynamic routing between the Fireboxes at each site. You can use any supported dynamic routing protocol (RIP v1, RIP v2, OSPF, or BGP v4), but we recommend you use these dynamic routing protocols:

  • For point-to-point link — OSPF
  • For multi-hop link or MPLS connection — BGP

Each example configuration file contains a dynamic routing configuration that uses the IP addresses from the topology diagrams in this document. The dynamic routing configuration between the two Fireboxes is the same, regardless of the type of primary private network connection. To see the dynamic routing configuration for the two sites in this example, use Policy Manager to open the example files for the relevant dynamic routing protocols.

Dynamic Routing Settings

To see the settings for dynamic routing:

  1. From Policy Manager, select Network > Dynamic Routing.
  2. Select the RIP, OSPF or BGP tab.
    For example, the dynamic routing settings in the Site A OSPF example configuration file look like this:

In the example configuration file, eth13 is the interface that connects to the private network connection.

Dynamic Routing Policy

When you enable a dynamic routing protocol, a policy is required to allow the traffic. Policy Manager automatically creates the required policy.

To see the dynamic routing policy:

  1. From Policy Manager, open one of the example configuration files.
  2. Double-click the DR-RIP-Allow, DR-OSPF-Allow, or DR-BGP-Allow policy to edit it.
    For example, the DR-OSPF-Allow policy in the Site A OSPF example configuration looks like this:

Static Routes

Because BGP is the recommended dynamic routing protocol to use with a multi-hop link or MPLS private network connection, the BGP example configuration files include the required static routes for the multi-hop link or MPLS topology.

To see the static route configuration:

  1. From Policy Manager, open one of the BGP example configuration files.
  2. Select Network > Routes.
    For example, the static route in the BGP example configuration file for Site A looks like this:

VPN Configuration

Each of the example configuration files contains a branch office gateway and a branch office tunnel that are configured to match any of the network diagrams presented in this use case. The gateway and tunnel settings for each site are the same, regardless of the dynamic routing protocol, or the type of private network connection between the two sites. You can open any of the Site A or Site B example configuration files to see these settings.

VPN Settings at Site A

The VPN Gateway settings at Site A are available in any of the example configuration files for Site A.

To see the gateway settings:

  1. Select VPN > Branch Office Gateways.
  2. Select the gateway name, SiteA-SiteB-GWY. Click Edit.

To see the tunnel settings:

  1. Select VPN > Branch Office Tunnels.
  2. Select the tunnel name, SiteA-SiteB-Tunnel. Click Edit.

For example, the tunnel in the example configuration file for Site A looks like this:

To see the VPN failover setting:

  1. Select VPN > VPN Settings.
  2. The Enable the use of non-default (static or dynamic) routes to determine if IPSec is used check box is selected.

This check box enables the automatic failover to the VPN based on dynamic changes to the routing table.

VPN Settings at Site B

The VPN Gateway settings at Site B are available in any of the example configuration files for Site B. To see the gateway, tunnel, and VPN failover settings for Site B, repeat the same steps you completed for Site A.

Conclusion

This configuration example demonstrates one method you can use to configure dynamic routing over a private link between two sites, and how to configure the Fireboxes at each site for automatic failover from the private network link to a branch office VPN. When you use this type of configuration, if the private network link route fails, a packet between the two networks can automatically use the VPN tunnel to get to its destination.

For more information about dynamic routing and branch office VPNs, see Fireware Help.

Appendix — Unsupported Network Topologies

This section illustrates two network topologies that are not supported for this example.

Topology 1

The router that connects to the private network cloud is also the default gateway for the trusted network.

Network diagram that shows the private network cloud and connected to a router that is the default gateway for the trusted network at each site

In this topology, the default gateway for the trusted network at each site is the router that connects each site. Because of this, the Firebox cannot control routing between the two networks. You can, however, configure the routers that connect the two sites for dynamic routing and to fail over to a route through the VPN tunnel on the Firebox. This network topology method is out of the scope of this configuration example because to do this you must configure that type of failover on the router.

There is also a possible security concern with this topology: because there is no firewall on the private network link between the two sites, any security compromise at one site can affect both sites.

Topology 2

The router that connects to the private network cloud connects directly to the trusted network, but is not the default gateway for the trusted network.

Network diagram that shows Site A and Site B connection over the private network terminating on a network router on the trusted network

In this topology, the Firebox cannot control network failover between the two sites because there is not a single ingress and egress point at each site. We always recommend that you configure the Firebox as the single ingress and egress point on each network.

The larger problem with this topology is that it can create asymmetric routes between the two sites. Connections between the two sites can fail regardless of whether TCP SYN checking is enabled, because the firewall at each site might see only one side of the TCP handshake.

Asymmetric routing can occur because:

  1. Packets sent from a computer at Site A to a computer at Site B are routed through the default gateway at Site A (the Site A Firebox). The packets are then routed over the peer link to the computer at Site B. These packets do not go through the Site B Firebox.
  2. The returned packets from the computer at Site B are routed through the default gateway at Site B (the Site B Firebox). The packets are then routed over the peer link to the computer at Site A. These packets do not go through the Site A Firebox.

Even without dynamic routing or failover to a VPN, this network configuration can cause routing problems and is not recommended.

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