Network setup - How to - Routers - Cisco - Linux

One of the most common mechanisms for testing IPv6 network interconnection, are 6over4 tunnels, which are used to encapsulate IPv6 packets in IPv4 native network, creating a peer to peer network between two machines that are communicating by this protocol .

Normally an IPv6/IPv4 node, or dual stack, in order to communicate with another computer through an IPv4 network, you need a tunnel interface, in which IPv6 addresses are configured as shown in the graph.

6over4 Tunnels Configuration

Configure the tunnel 6over4 is in principle a relatively simple task, the configuration is similar to that performed in a GRE tunnel

For configuration, you must define the start and destination addresses on both computers, in some cisco equipment does not allow defining the start address, so they can define the start of the tunnel through the interface with local public IPv4 address. To 6over4 tunnel configuration is not necessary to define an IPv4 address.

Router1#configure terminal 
Router1(config)#interface Tunnel10
Router1(config)# ipv6 address 2800:100:101::1/64
Router1(config-if)#tunnel source 154.54.6.5
Router1(config-if)#tunnel destination 206.167.13.198
Router1(config-if)#tunnel mode ipv6ip
Router1(config-if)#end
Router1#

On Router 2, you must create another tunnel interface, as Router 1, and associate the source and destination addresses.

Router2#configure terminal 
Router2(config)#interface Tunnel20
Router1(config)# ipv6 address 2800:100:101::2/64
Router2(config-if)#tunnel source 206.167.13.198
Router2(config-if)#tunnel destination 154.54.6.5
Router1(config-if)#tunnel mode ipv6ip
Router2(config-if)#end
Router2#

As discussed above in some cases the equipment can not define the starting IP address, so you will need to specify the start of the tunnel with the physical interface name, for our example, will the interface f0/0, the command will be the following: "Router2 (config-if) # tunnel source int f0/0".

At the end of these configurations, the resulting topology will be as shown in the graph below, with an interface Tunnel10 in router1, connected with a direct cable to Tunnel20 interface on Router 2 and allow the simulation of having a link dedicated to communicate via IPv6, this is a simple way to interconnect their networks for IPv6 testing.

Routing traffic through the tunnel 6over4

The next step now will allow routing from network 2800:20:20 :: 0/64 with the network 2800:10:10 :: 0/64. This is very simple, just simply turn on IPv6 routing and then add a route to reach the other network, the commands needed are:

Router1(config)#ipv6 route 2800:10:10::/64 2800:100:10::2
Router1(config)#ipv6 unicas-routing
Router2(config)#ipv6 route 2800:10:10::/64 2800:100:10::1
Router2(config)#ipv6 unicas-routing

GRE (Generic Router Encapsulation) is a protocol that can encapsulate a wide variety of different protocol types inside IP tunnels, creating a peer to peer network between two machines that are communicating by this protocol. Its main use is to create VPN tunnels. GRE is defined by RFC 1701, 1702 and 2784.

It is important to understand the need to make when configuring GRE tunnels, it could be difficult to manage if the number of them grows too. These tunneles turn out to be useful when you need to work with a protocol that is not routable as NetBIOS, or IP routable protocols other than through an IP network. Currently the use of GRE has become a major transition mechanisms for IPv6 network deployment. This means you can connect two IPv6 islands over IPv4 tunnel.

Configuring GRE Tunnels

Configure the GRE tunnel is in principle a relatively simple task, just define the start and destination addresses on both devices and create the tunnel interface. To run the example will use Cisco 2800 series routers, although it is possible to make a tunnel with a variety of equipment.

Router1#configure terminal 
Router1(config)#interface Tunnel10
Router1(config-if)#ip address 192.168.2.6 255.255.255.252
Router1(config-if)#tunnel source 154.54.6.5
Router1(config-if)#tunnel destination 206.167.13.198
Router1(config-if)#end
Router1#

On Router 2, you must create another tunnel interface, as Router 1, and associate the source and destination addresses.

Router2#configure terminal 
Enter configuration commands, one per line.  End with CNTL/Z.
Router2(config)#interface Tunnel30
Router2(config-if)#ip address 192.168.2.5  255.255.255.252
Router2(config-if)#tunnel source 206.167.13.198
Router2(config-if)#tunnel destination 154.54.6.5
Router2(config-if)#end
Router2#

At the end of these configurations, the resulting topology will be as shown in the graph below, with an interface Tunnel10 in router1, connected with a direct cable to Tunnel30 interface on Router 2.


The next step now will allow routing from 172.16.2.0/24 to 172.16.3.0/24. In practice this is simple and does not hit the network performance, thus creating tunneles, can solve many problems of connectivity between remote sites without much complexity. The only thing that should be taken into account when creating the tunneles is no mistakes with the start addresses and destination.

Commands to configure static routing:

Router1(config)#ip route 172.16.3.0 255.255.255.0 tunnel 10 192.168.2.5
Router1(config-if)#end
Router2(config)#ip route 172.16.2.0 255.255.255.0 tunnel 30 192.168.2.6
Router2(config-if)#end

Selecting the type of tunnel to use

When you create a tunnel, usually do not specify the protocol to use, so that devices default, select the GRE protocol. However it is possible to define the protocol, by a single command, as shown below:

Router1(config)#interface Tunnel1
Router1(config-if)#tunnel mode ipip 

Ipip mode is the type of tunnel that allows IP packets encapsulated within another IP packet, very useful to allow communication between IPv6 networks through IPv4 networks. The process for selecting the protocol is simple and need to be configured on both sides of the tunnel, as defined ipip protocol can also select any of the following: AURP, Cayman, dvmrp, eon, gre ip, ip gre multipoint, ipip, iptalk.