CCIE Study Notes

Here's the meat of the 1.6 section - IPv6 Tunnel types. If I was going to create a question on the 1.6 section, it would probably be on IPv6 tunnel types. There are 5 of them covered in the exam:

Manual
GRE

IPv4-compatible

6to4
ISATAP

Note that you will see other types mentioned in some resources. You may see something about 6RD - which is IPv6 Rapid Deployment. This is the same as a 6to4 tunnel, but you can use addresses from any range. Also note that although each type is covered separately, you should really group them. Manual and GRE are Point-to-Point IPv6 tunnels. 6to4 and ISATAP are point-to-multipoint tunnels. If there are a group of items, any test is going to ask you about the similarities and differences. That's the land from which test questions come.

So now for the differences. The point-to-point group: Manual supports only IPv6 traffic. GRE supports multiple protocols, including IPv6. The point-to-multipoint group: 6to4 requires sites to use the IPv6 addresses in the 2002::/16 range. (6RD - can use any range) ISATAP is designed to be used between devices in the same site and uses a specific converted address. Both of these use a converted address. It's important to know the difference and how that affects the addressing and routing as explained in my previous post. I see this as an important functional difference and would create a question on it.

Cisco has a downloadable guide specifically for Manually Configured IPv6 over IPv4 Tunnels. Know the design decisions for each tunnel type. Table 1 in this doc gives you this information. The example configuration for this:

interface ethernet 0
ip address 192.168.99.1 255.255.255.0
interface tunnel 0
ipv6 address 3ffe:b00:c18:1::3/127
tunnel source ethernet 0
tunnel destination 192.168.30.1
tunnel mode ipv6ip

Notice that the tunnel has an IPv6 address. The source and destination are IPv4 addresses. The mode is ipv6ip.

There is a separate Cisco doc for IPv6 over IPv4 GRE Tunnels. It has the same Table 1 with the design use cases. The example they use is not as clear as the first document, but it is something you could see on an exam. They give you two examples. The first example has an IPv4 address as the source and an IPv6 address as the destination. The second example has an IPv4 address for both source and destination.

And so the pattern continues that Cisco has a document for IPv6 Automatic IPv4-Compatible Tunnels. It's a bit shorter than the others. Note that in this type you configure the source but no destination. The tunnel mode is "ipv6ip auto-tunnel." The configuration example shows the integration of this with BGP.

The next type of tunnel is Automatic 6to4. There is a note you should read : "The configuration of only one IPv4-compatible tunnel and one 6to4 IPv6 tunnel is supported on a router." The little note box explains this further. To give you a teaser, it relates to these tunnels both being NBMA "point-to-multipoint" access links. Probably something more likely to be on the R/S track, but interesting.

And the last one is ISATAP (IntraSite Automatic Tunnel Addressing Protocol). This is the one that is an IETF Standard that is covered in RFC 5214. RFC 5214 is the new one - which makes RFC 4214 (the previous ISATAP standard) obsolete. Note: an updated standard may be something that might be fair game on a test. The configuration example:

ipv6 unicast-routing
interface tunnel 1
tunnel source ethernet 0
tunnel mode ipv6ip isatap
ipv6 address 2001:DB8::/64 eui-64
no ipv6 nd ra suppress

Items of note - the eui-64 and the removal of Neighbor Discovery Router Advertisement suppression.

Along with similarities and differences - note Table 2, which is the same on each of these documents. Only the GRE command is different [gre ip]. All the rest use ipv6ip. This may help you to spot a correct / incorrect answer quickly.

tunnel mode ipv6ip [auto-tunnel | 6to4 | rd | isatap]

This completes section 1.6. One last item that you might see mentioned in your study materials - Teredo Tunneling. This is between hosts over the Internet. IPv6 datagrams are encapsulated in IPv4 UDP packets. It may pop up as a distractor. Note that the types of tunnels discussed above are ones that you configure site-to-site on routers. Teredo is between hosts.