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====== IPv6 Lab - 6rd ======

===== Exploring IPv6 “Rapid Deploy" =====

6rd is a technology which allows network operators to deploy IPv6 to end users without having to upgrade the entire infrastructure between them and their customer to support IPv6. This is typically the case where the ISP has old DSLAMs which don’t support IPv6 framing, or are leasing a third party’s access network which perhaps also is not quite IPv6 ready.

In this lab we will configure a 6rd tunnel between our Customer router and our Border router. To do this we will disable IPv6 on our core network, leaving IPv6 operational only on our Border router.

===== Preparation =====

Before we start this lab, remove any previous extra lab configuration on the Access and Customer routers and revert both routers to the configuration as it was at the end of the [[training:apricot2019:d-static|Static Lab]]. Check connectivity is working from the Customer router to the rest of the lab network as expected.

We also need to remove any IPv6 configured on the network as we will be replacing it with 6rd technology. The following subsections describe what needs to be done.

==== Disabling IPv6 on the Core and Access routers ====

The first step is to disable IPv6 on the Access and Core routers. Be sure to keep a copy of the configuration of the Access and Core routers first! (We won’t worry about the Peering Router as it isn’t needed for this part of the lab work.)

The simplest way to do this is simply to turn off IPv6 Unicast Routing, like this:

  no ipv6 unicast-routing

This will remove all the IPv6 routing protocol configuration on those two routers, including OSPF/IS-IS and BGP. The IPv4 configuration will still remain, and the IPv4 routing will still function. You will notice that IPv6 addressing will remain on the router interfaces, and configuration like IPv6 packet filters etc. 

Confirm that IPv4 routing still works.

And confirm that IPv6 routing no longer works - you should no longer have any IPv6 connectivity between the Border, Peering and Access routers.

==== Originating IPv6 Aggregate on the Border router ====

Because we have removed IPv6 routing from the Core router, we have also stopped announcing our IPv6 aggregate to the Transit network. To test that our 6rd deployment is working, we need to temporarily originate our IPv6 aggregate from the Border router. Here is an example:

  router bgp X0
   address-family ipv6
    network 2001:DB8:X::/48
  !
  ipv6 route 2001:DB8:X::/48 Null0



==== Removing IPv6 configuration on Customer Router ====

We also need to remove any remaining IPv6 configuration on the Customer Router:

  interface FastEthernet0/1
   description P2P Link to ASX0
   no ipv6 address 2001:DB8:X:20::1/127
   no ipv6 nd ra suppress all
  !
  no ipv6 route 2001:DB8:X:4000::/52 Null0
  no ipv6 route ::/0 2001:DB8:X:20::
  !

And finally we need to remove the loopback interface from the Customer Router. Remember we created it as an anchor point for testing. Simply do:

  no interface loopback 0

and it will be removed completely.

We leave `ipv6 unicast-routing` turned on though, as we still will need IPv6 on the router in the next part of the lab.

===== Configuring the Access Router =====

==== Originating Customer IPv4 Point-to-Point link in iBGP ==== 

The point-to-point link address from the network operator to the customer is normally not carried in the IGP or even in the BGP. However, 6rd uses the point-to-point link address as the basis for the IPv6 prefix generated for 6rd. So the network operator needs to carry the point-to-point link address at least as far as the 6BR router so that the IPv6 tunnel can see its end point on the customer router.

The simple and scalable way to do this is to put the point-to-point link address into iBGP on the Access Router. Like this:

  router bgp X0
   address-family ipv4
    network 100.68.X.32 mask 255.255.255.252
  !

Once you have done this, connect to the Core and Border routers to make sure that you now see this point to point link address in the BGP. And check that connectivity works from the Border router by trying to ping the end point on the Customer router:

  BX# ping 100.68.X.34

If there is no answer, check the BGP table, and that there is a default route on the Customer router point back to the Access router.

==== Removing IPv6 on the Access Router link to the Customer ====

We also need to remove any remaining IPv6 configuration on the link between the Access Router and the Customer Router. Here is an example for the Access Router:

  interface FastEthernet0/1
   description P2P Link to CustX
   no ipv6 address 2001:DB8:X:20::0/127
   no ipv6 nd ra suppress all
  !
  no ipv6 route 2001:DB8:X:4000::/52 2001:DB8:X:20::1
  !

===== Setting up 6rd =====

==== Background ====

The lab instructors will have explained how 6rd works during the presentations. But suffice to say, the router configuration on this CPE is the same across all CPE that would be deployed by the network operator – there is no per end user configuration which makes 6rd a very simple to deploy technology, as all their CPE devices can have the same configuration prior to shipping to the end-user.

What we will set up is something similar to the diagram below.

{{:training:apricot2019:6rd-diagram.png?600|}}

The Customer Router in the diagram is our Customer Router in our network. And the ISP 6rd BR capability will be configured on our autonomous system’s Border Router.

==== Addressing ====

We will be using the address block 2001:DB8:X:C000::/52 for 6rd. All end users will be automatically assigned a /60 out of this /52 – the final 8 bits of the address will come from the last quad of the IPv4 address of the point-to-point link connecting the Customer Router to the Access Router.

This is how it works: the point-to-point link address on the Customer Router is 100.68.X.**34**, so we will configure 6rd to use the final **8** bits of this IPv4 address to generate the unique /60 for this end-site. **34** in decimal is **22** in hexadecimal. Which makes the /60 for the end-site is 2001:DB8:X:C**22**0::/60.

**Note:** Real world examples are not likely to be as constrained as our lab network. If end-users were to get /56s by 6rd, we could set aside a /40 pool, and determine the IPv6 address for 6rd from that pool. For example, if 2001:0DB8:0D00::/40 is used as the pool, then we could create the /56 the end user gets from the final 16 bits of the IPv4 point to point link address. If this was 10.0.10.18, then 10 in decimal becomes **0A**, and 18 in decimal becomes **12** in hexadecimal, making the unique IPv6 address block for the end-site 2001:DB8:0D**0A**:**12**00::/56.

===== Configuring the 6BR =====


Now we need to set up the 6BR functionality on the Border router. We need to create the tunnel end point:

  interface Tunnel0
   ipv6 enable
   tunnel source Loopback0
   tunnel mode ipv6ip 6rd
   tunnel 6rd ipv4 prefix-len 24
   tunnel 6rd prefix 2001:DB8:X:C000::/52
  !
  ipv6 route 2001:DB8:X:C000::/52 Tunnel0

The Loopback0 interface already exists - we created that for the iBGP session anchor point earlier on in the workshop.

Explaining the configuration:

  * `ipv6 enable` - enables IPv6 on the tunnel interface, but only uses link-local addressing. Global unicast addressing is not needed.
  * `tunnel source Loopback0` - the 6rd tunnel uses the loopback address of the Border router as the source.
  * `tunnel mode ipv6ip 6rd` - specifies that this is a 6rd tunnel.
  * `tunnel 6rd ipv4 prefix-len 24` - drop the first 24 bits, using only the final 8 bits for the 6rd address.
  * `tunnel 6rd prefix 2001:DB8:X:C000::/52` - the address block the ISP uses for 6rd – the final 8 bits of the IPv4 address will make this up to the /60.


===== Configuring the Customer Router =====

Now create the tunnel on the Customer Router. The configuration will look like this:

  interface Tunnel0
   ipv6 enable
   tunnel source FastEthernet0/1
   tunnel mode ipv6ip 6rd
   tunnel 6rd ipv4 prefix-len 24
   tunnel 6rd prefix 2001:DB8:X:C000::/52
   tunnel 6rd br 100.68.X.1
  !

To explain this configuration:

  * `ipv6 enable` - enables IPv6 on the tunnel interface, but only uses link-local addressing. Global unicast addressing is not needed.
  * `tunnel source FastEthernet0/1` - the 6rd tunnel uses the point-to-point link address to the Access Router as the source – when creating the 6rd address block, it uses part of this IPv4 address.
  * `tunnel mode ipv6ip 6rd` - specifies that this is a 6rd tunnel.
  * `tunnel 6rd ipv4 prefix-len 24` - drop the first 24 bits, using only the final 8 bits for the 6rd address.
  * `tunnel 6rd prefix 2001:DB8:X:C000::/52` - the address block the ISP uses for 6rd – the final 8 bits of the IPv4 address will make this up to the /60.
  * `tunnel 6rd br 100.68.X.1` - specifies the address of the 6rd Border Router (we are using the Loopback address of the Border Router).

==== Setting up the IPv6 Routes ====

To complete the configuration, we now add static routes so that IPv6 traffic goes over the 6rd tunnel to all destinations. The Customer router needs the following:

  ipv6 route 2001:DB8:X:C000::/52 Tunnel0
  ipv6 route ::/0 2001:DB8:X:C010::


The first static route points the entire /52 address block to the 6rd tunnel.

The second static route defaults all IPv6 traffic to the IPv6 6rd address of the 6rd BR router (using the same mechanism, namely last 8 bits of the IPv4 address (1) converted to hexadecimal (01)). It has to be routed towards the 6rd BR, not just the Tunnel interface.

==== Configuring Local Interfaces ====

We will use a feature in Cisco IOS called “general-prefix”. This allows us to refer to learned addresses (by 6rd, DHCPv6PD etc) without configuring specific addresses on each prefix. The IOS command is very simple:

  ipv6 general-prefix 6RDLAB 6rd Tunnel0

which says: what ever prefix we learn by 6rd from Tunnel0 (ie the /60 which 6rd creates), we will assign the name “6RDLAB” – and when we need to assign addresses to other interfaces on the router, we can refer to them using this name.

Now we have the general prefix configured, we can use it to apply address to local interfaces. For example, FastEthernet0/1 on the edge/customer routers is a local LAN, and would get this configuration:

  interface FastEthernet0/0
   description Local LAN
   ipv6 address 6RDLAB ::1:0:0:0:1/64
  !

For good measure, let’s recreate our Loopback interface too; this will restore our anchor point we can test against:

  interface Loopback0
   description Customer Router Loopback
   ipv6 address 6RDLAB ::2:0:0:0:1/64
   no shutdown
  !

And the resulting IPv6 addresses for the Customer router would look like this:

  Cust6# show ipv6 interface brief  
  FastEthernet0/0        [up/up]  
      FE80::C81D:5FF:FEAF:8  
      2001:DB8:6:C221::1  
  FastEthernet0/1        [up/up]  
      unassigned  
  Tunnel0                [up/up]  
      FE80::6444:3C22
  Loopback0              [up/up]  
    FE80::C81D:5FF:FEAF:8  
    2001:DB8:60:C222::1

Refer to the earlier discussion about the “general-prefix”. We have `2001:DB8:6:C220::/60` as the IPv6 subnet created by 6rd. Taking this and appending `::1:0:0:0:0` results in the first subnet to be allocated to the network - the `FastEthernet0/0` interface there is automatically assigned `2001:DB8:6:C221::/64`, with the IPv6 address on the interface being `2001:DB8:6:C221::1/64`.


===== Testing =====

With the 6BR and the Customer router now set up to support 6rd, try some IPv4 and IPv6 traceroutes from the Customer router to the backbone Transit providers and out to the Internet, for example, to 8.8.8.8 (IPv4) and 2001:4860:4860::8888 (IPv6).

(Note that if the lab doesn’t have IPv6 connectivity, try IPv6 traceroutes into the Transit backbone and to other groups.)

What do you see?


 
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