IPv6 tunneling over IPv4 Configuration

Since IPv4 and IPv6 are not compatible with each other, we need some migration strategies. One technique that we can use is tunneling. Basically, it means that we encapsulate IPv6 packets into IPv4 packets (or the other way around) so they can be routed. In this lesson, I’ll show you how to configure IPv6 static tunneling over an IPv4 network. There are two methods:

• Manual tunnels
• GRE (Generic Routing Encapsulation) tunnels

Both tunnel types are very similar, with just minor differences. Both support IPv6 IGPs through the tunnel interface and forwarding of multicast traffic. The manual tunnels refer to RFC 4213, which defines how to encapsulate IPv6 packets in IPv4. GRE is a generic encapsulation type that rides on top of IPv4 and isn’t only for IPv6. It can carry many different protocols and if you ever configured an IPSEC VPN with IGPs running through it you had to use GRE.

Configuration

Let’s continue by looking at some examples and how to configure the static point-to-point IPv6 tunnels.

This is the topology we’ll be using. Three routers are running IPv4. R1 and R3 also run IPv6, and we want connectivity between them without adding IPv6 support on R2. Let’s configure all IPv4 and IPv6 addresses:

R1(config)#interface loopback 0
R1(config-if)#ipv6 address 2001::1/128
R1(config-if)#exit
R1(config)#interface fastEthernet 0/0
R1(config-if)#ip address 192.168.12.1 255.255.255.0

R2(config)#interface fastEthernet 0/0
R2(config-if)#ip address 192.168.12.2 255.255.255.0
R2(config-if)#exit  
R2(config)#interface fastEthernet 1/0
R2(config-if)#ip address 192.168.23.2 255.255.255.0

R3(config)#interface fastEthernet 0/0
R3(config-if)#ip address 192.168.23.3 255.255.255.0
R3(config-if)#exit
R3(config)#interface loopback 0
R3(config-if)#ipv6 address 2001::3/128

Our next step is to create a tunnel interface between R1 and R3. They need to be able to reach each other through IPv4. I’ll create a new loopback interface on R1 and R3, advertise them in EIGRP, and use these addresses for the tunnel:

R1(config)#interface loopback 1
R1(config-if)#ip address 1.1.1.1 255.255.255.0
R1(config-if)#exit
R1(config)#router eigrp 123
R1(config-router)#no auto-summary 
R1(config-router)#network 192.168.12.0
R1(config-router)#network 1.1.1.0

R2(config)#router eigrp 123
R2(config-router)#no auto-summary 
R2(config-router)#network 192.168.12.0
R2(config-router)#network 192.168.23.0

R3(config)#interface loopback 1
R3(config-if)#ip address 3.3.3.3 255.255.255.0
R3(config-if)#exit
R3(config)#router eigrp 123
R3(config-router)#no auto-summary 
R3(config-router)#network 192.168.23.0
R3(config-router)#network 3.3.3.0

I could also use physical interfaces, but they can go down. Whenever a physical interface goes down, our IGP (EIGRP in this example) could find another path to the loopback interfaces (if there is one).

R1(config)#interface tunnel 0
R1(config-if)#tunnel source loopback 1
R1(config-if)#tunnel destination 3.3.3.3
R1(config-if)#tunnel mode ipv6ip

R3(config)#interface tunnel 0
R3(config-if)#tunnel source loopback 1
R3(config-if)#tunnel destination 1.1.1.1
R3(config-if)#tunnel mode ipv6ip

This is how we configure a tunnel interface. By default, a tunnel interface is always GRE, so with the tunnel mode ipv6ip command, I changed it to a “manual” tunnel. Let’s check the tunnel: