IPv6 ISATAP (Intra Site Automatic Tunnel Addressing Protocol)

This topic is to discuss the following lesson:

HI Rene’

I not understand very well why the eui-64 i s needed, and also why on R1 the command
tunnel mode ipv6ip isatap
is not needed.
Also I’m testing this configuration on gns3 and router r1 not install a static route.

Hello Giovanni

According to Cisco documentation, when configuring ISATAP:

The IPv6 tunnel interface must be configured with a modified EUI-64 address
because the last 32 bits in the interface identifier are constructed using the IPv4 tunnel source address.

If you were to specify the address fully, the ISATAP operation would not function.

Also, when you configure tunnel mode ipv6ip isatap on the headend, there is no need to specify the mode in which the tunnel will be functioning on the client. On the client, you also set ipv6 address autoconfig, which means that it will obtain the IPv6 address (and the mode of the tunnel) from the headend.

I hope this has been helpful!


Hi Rene and Laz,

Would you say that the ISATAP operation is very similar to the DMVPN Phase 1 where all of the tunnel traffic has to traverse the “Headend” router just like with DMVPN phase 1 and its “HUB”?

Hello Nitay

It is similar only so far as the traffic actually traverses the router itself (either the head end or the HUB in each case) to get to its destination. However, beyond that, the purpose and the mechanisms of the two features you mention are completely different.

I hope this has been helpful!


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In the ISATAP lesson, client config section, the tunnel mode command says: tunnel mode ipv6ip and there is no isatap in the end. Was that left out on purpose -because it’s a client- or is that a typo?

Hello @haniyeh.maghsoudi,

That’s right, the client only needs tunnel mode ipv6ip . No need to add the isatap keyword there.


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