ISATAP (Intra Site Automatic Tunnel Addressing Protocol) is an IPv6 tunneling technique that allows you to connect IPv6 over an IPv4 network, similar to the automatic 6to4 tunnel.
On your IPv4 network, you can configure one of your routers as an IPv6 “headend” ISATAP router that your IPv6 hosts can connect to. The IPv4 source address of the ISATAP clients and router is embedded in the IPv6 address so that each device knows how to get to the other side of the IPv4 network.
Here’s what the IPv6 address looks like:
The first 64 bits are for the prefix, and you can pick anything you like. Global unicast, link-local addresses, both are possible. The next 64 bits are divided into two parts:
- 0000:5EFe: this is a reserved UOI value which indicates that this is an ISATAP address.
- the remaining 32 bits embed the IPv4 address, in hexadecimal.
ISATAP was designed for intra site, in other words…within your site, not between sites. However, nothing is stopping you from running this between sites.
It is easy to configure, and many clients support ISATAP, including any recent Windows or Linux OS. You can configure the tunnel destination address manually or add it to a DNS server so that it’s easy to find.
Cisco IOS supports both the ISATAP client and headend router. In this lesson, I use the following topology:
R1 is the ISATAP client, R3 is the headend router. We will use 2001:DB8:13:13::/64 as the prefix on the tunnel interface. I use OSPFv2 so that R1 and R3 are able to reach each other through IPv4. R3 also has a loopback interface with an IPv6 address, something we can try to ping from R1.
Want to take a look for yourself? Here you will find the startup configuration of each device.
hostname R1 ! ip cef ! interface FastEthernet0/0 ip address 192.168.12.1 255.255.255.0 ! router ospf 1 router-id 220.127.116.11 log-adjacency-changes network 192.168.12.0 0.0.0.255 area 0 ! end
hostname R2 ! ip cef ! interface FastEthernet0/0 ip address 192.168.12.2 255.255.255.0 ! interface FastEthernet1/0 ip address 192.168.23.2 255.255.255.0 ! router ospf 1 router-id 18.104.22.168 network 192.168.12.0 0.0.0.255 area 0 network 192.168.23.0 0.0.0.255 area 0 ! end
hostname R3 ! ip cef ! interface Loopback0 ipv6 address 2001:DB8:3:3::3/128 ! interface FastEthernet0/0 ip address 192.168.23.3 255.255.255.0 ! router ospf 1 router-id 22.214.171.124 log-adjacency-changes network 192.168.23.0 0.0.0.255 area 0 ! end
Let’s start with the headend router. First, we need to enable IPv6 unicast routing:
Now we can focus on the tunnel interface:
R3(config)#interface Tunnel 0 R3(config-if)#ipv6 address 2001:db8:13:13::/64 eui-64 R3(config-if)#no ipv6 nd suppress-ra R3(config-if)#tunnel source FastEthernet0/0 R3(config-if)#tunnel mode ipv6ip isatap
I configure the 2001:DB8:13:13::/64 prefix and let the router configure the last 64 bits using EUI-64. You’ll see in a bit what address we end up with. By default, the router will not send router advertisements on the tunnel interface which is why we need to add the no ipv6 and suppress-ra command,
Let’s configure our client:
R1(config)#interface Tunnel 0 R1(config-if)#ipv6 address autoconfig R1(config-if)#tunnel source FastEthernet 0/0 R1(config-if)#tunnel destination 192.168.23.3 R1(config-if)#tunnel mode ipv6ip
The tunnel interface is configured to configure its IPv6 address automatically. The tunnel source is our FastEthernet 0/0 interface and the destination is the IPv4 address of R3.
Let’s see if our configuration works. I’ll start with the headend router…
Let’s take a look at our tunnel interface:
R3#show ipv6 interface Tunnel 0 Tunnel0 is up, line protocol is up IPv6 is enabled, link-local address is FE80::5EFE:C0A8:1703 Global unicast address(es): 2001:DB8:13:13:0:5EFE:C0A8:1703, subnet is 2001:DB8:13:13::/64 [EUI] Joined group address(es): FF02::1 FF02::2 FF02::1:FFA8:1703 MTU is 1480 bytes ICMP error messages limited to one every 100 milliseconds ICMP redirects are enabled ND DAD is not supported ND reachable time is 30000 milliseconds ND advertised reachable time is 0 milliseconds ND advertised retransmit interval is 0 milliseconds ND router advertisements live for 1800 seconds Hosts use stateless autoconfig for addresses.
Above, we see a couple of interesting things:
- Both the link-local and global unicast prefix have the 0000:5EFE: bits that indicate that this is an ISATAP address.
- Our IPv6 addresses end with C0A8:1703.
- We can verify that this router is sending router advertisements.
Below you can see the decimal IPv4 address that is embedded in the IPv6 address:
Let’s take a look at our client:
R1#show ipv6 interface Tunnel 0 Tunnel0 is up, line protocol is up IPv6 is enabled, link-local address is FE80::C0A8:C01 Global unicast address(es): 2001:DB8:13:13::C0A8:C01, subnet is 2001:DB8:13:13::/64 [PRE] valid lifetime 2591842 preferred lifetime 604642 Joined group address(es): FF02::1 FF02::2 FF02::1:FFA8:C01 MTU is 1480 bytes ICMP error messages limited to one every 100 milliseconds ICMP redirects are enabled ND DAD is enabled, number of DAD attempts: 1 ND reachable time is 30000 milliseconds Default router is FE80::5EFE:C0A8:1703 on Tunnel0
Above, we see two interesting items: