IPv6 Tunneling - ISATAP

R2, R5 and R6 connected via an IPv4 frame-relay network.
There is no PVC in use between R5 and R6.
Each device has a loopback 192.168.x.x where x is router number.
The goal here is to allow the remote IPv6 networks to communicate over the IPv4 cloud.


Below are the configs.

Loopback 100 = tunnel endpoint
Loopback 101 = "remote" network

R6:

interface Loopback100
ip address 192.168.6.6 255.255.255.255

interface Loopback101
no ip address
ipv6 address 2001:600::6/64

interface Tunnel1
ipv6 address 2001:200::/64 eui-64
tunnel source Loopback100
tunnel mode ipv6ip isatap

R5:

interface Loopback100
ip address 192.168.5.5 255.255.255.255

interface Loopback101
no ip address
ipv6 address 2001:500::5/64

interface Tunnel1
ipv6 address 2001:200::/64 eui-64
tunnel source Loopback100
tunnel mode ipv6ip isatap

Static routes on R5 and R6:

R5(config)#ipv6 route 2001:600::/64 tunnel 1 fe80::5efe:c0a8:0606

R6(config)#ipv6 route 2001:500::/64 tunnel 1 fe80::5efe:c0a8:0505

Where did I get these next hops? Well when you create an ISATAP tunnel they are created in a modified eui-64 format. Take a look

at R5:

R5#show ipv6 interface brief tun 1
Tunnel1 [up/up]
FE80::5EFE:C0A8:505
2001:200::5EFE:C0A8:505

When the router decides to route a packet out of that tunnel interface, it calculates the Ipv4 next hop address from the last 32 bits of the modified eui-64 address. In this case C0A8:505 converts to 192.168.5.5. R6 sends all packets destined for 2001:500::/64 to 192.168.5.5.

Key things to remember:

-The tunnel source address must be reachable by remote routers
-There is no manually specified tunnel destination
-You must specify the tunnel interface and link layer address in static routes