how to forward gre traffic over ipsec vpn tunnel

8/10/2019 How to Forward GRE Traffic Over IPSec VPN Tunnel

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How ToForward GRE Traffic over IPSec VPN Tunnel

Applicable Version: 10.00 onwards

OverviewGeneric Routing Encapsulation (GRE) is a simple IP packet encapsulation protocol, GRE tunnels are

mainly used as a means to carry other routed protocols across a predominantly IP network. They

remove the need of all protocols, except IP, for data transfer, thus reducing much overhead on the

network administrators part.Non-IP protocols such as IPX and AppleTalk are tunnelled through the

IP core via GRE.

Generally, GRE tunnels are used in the following scenarios:

- To carry Multicast traffic just like real network interface traffic.

- To carry non-routable protocol traffic like NetBIOS or non-IP traffic over IP network.

- To link two similar networks which are connected with different IP addressing

Scenario

Create an IPSec tunnel between a Head Office network and a Branch Office network. The clients at

the Branch Office are to connect to the Head Office Media Server. So we have created GRE tunnel

over the IPSec connection to allow transfer of multicast traffic between the Head Office and Branch

Office. The network scenario is described in the diagram below.

How To Forward GRE Traffic over IPSec VPN

Tunnel


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Network Schema

Branch Office Head Office

Cyberoam WAN IP Address202.134.168.208 Cyberoam WAN IP Address202.134.168.202

LAN IP172.50.50.2 LAN IP172.16.16.10

LAN Subnet172.50.50.0/24 LAN Subnet172.16.16.0/24

GRE Tunnel Virtual IP5.5.5.1 GRE Tunnel Virtual IP5.5.5.2

Media Server :

Source IP172.16.16.2

Multicast IP225.0.0.1

Configuration

To forward GRE traffic over IPSec VPN connection, follow the steps given below. The configuration is

to be done from the Web Admin Console using Administrator profile.

Step 1: Create IPSec VPN Tunnel

Create an IPSec VPN tunnel between the Head Office and Branch Office. To know how to create an

IPSec VPN connection, refer to the article How To - Establish Site-to-Site IPSec Connection using

Preshared Key.

Note:

In the IPSec configuration:

- Make sure that WAN IP of Head Office Cyberoam is included in the Trusted Local Subnet at the

Head Office side and Trusted Remote Subnet at the Branch Office side.

- Similarly, Make sure that WAN IP of Branch Office Cyberoam is included in the Trusted Local

Subnet at the Branch Office side and Trusted Remote Subnet at the Head Office side.

Step 2: Create GRE Tunnel

Create a GRE Tunnel between the Head Office and the Branch Office. To know how to create a GRE

tunnel, refer to the articleHow ToConfigure a GRE Tunnel on Cyberoam.

Step 3: Enable Multicast Forwarding in Cyberoam

Enable Multicast Forwarding on Cyberoam by going to NetworkStatic RouteMulticastand

checking Enable Multicast Forwardingas shown below.
http://kb.cyberoam.com/default.asp?id=1633&Lang=1&SID=http://kb.cyberoam.com/default.asp?id=1633&Lang=1&SID=http://kb.cyberoam.com/default.asp?id=1633&Lang=1&SID=http://kb.cyberoam.com/default.asp?id=2192&Lang=1&SID=http://kb.cyberoam.com/default.asp?id=2192&Lang=1&SID=http://kb.cyberoam.com/default.asp?id=2192&Lang=1&SID=http://kb.cyberoam.com/default.asp?id=2192&Lang=1&SID=http://kb.cyberoam.com/default.asp?id=2192&Lang=1&SID=http://kb.cyberoam.com/default.asp?id=2192&Lang=1&SID=http://kb.cyberoam.com/default.asp?id=1633&Lang=1&SID=http://kb.cyberoam.com/default.asp?id=1633&Lang=1&SID=


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Step 4: Add Static Multicast Routes

Add static multicast routes both at the Head Office and Branch Office.

Head Office

Go to NetworkStatic RouteMulticastand click Add to add a new multicast route using the

parameters given below.

Parameter Description

Parameter Value Description

Source IP Address 172.16.16.2 Specify Source IP Address.

Source Interface PortA 172.16.16.10 Select Source Interface from the list.

Multicast Address 225.0.0.1Specify range of Multicast IP

Address

Destination Interface gre_tunnel_ho 5.5.5.2

Select Destination Interface from the

list. You can select more than one

destination interface.


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Branch Office

Go to NetworkStatic RouteMulticastand click Add to add a new multicast route using the

parameters given below.


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Parameter Description

Parameter Value Description

Source IP Address 172.16.16.2 Specify Source IP Address.

Source Interface gre_tunnel_bo 5.5.5.1 Select Source Interface from the list.

Multicast Address 225.0.0.1Specify range of Multicast IP

Address

Destination Interface PortA-172.50.50.2

Select Destination Interface from the

list. You can select more than one

destination interface.

Note:

Make sure that Firewall Rules allowing traffic from LAN to VPN and vice versa are present. If they are

not present, create them manually. They are necessary for the VPN connections to function properly.

The above configuration forwards all GRE traffic to the IPSec VPN connection between Head Officeand Branch office.

Document Version: 2.0 07/05/2013

how to forward gre traffic over ipsec vpn tunnel

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