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  1. Hey Rene,

    Great write up! Why does Cisco recommend using Automatic 6 to 4 tunneling over ISATAP for inter area routing? I mean, I see the name intra-site, but trying to get more clarity on why ISATAP would not/or could not be used for inter area.

    Thank you


  2. Hello,

    I have a question regarding the 6to4 implementation:
    Should it work if i use another prefix than 2002:?

    I read couple of articles and in every place it’s written that 2002 is reserved for 6to4 implementation (like router knows how to extract 32 bit IPv4 address encoded in Hex format that goes after that prefix).

    But in my lab i just used another prefix (just for testing): 1002: and the 6to4 stuff worked properly as well.

    Can you please explain this behavior? Is it a correct and expected behavior or not?


  3. Hi @hussien.samer

    Remove the following two static routes:

    R1(config)#ipv6 route 2001::3/128 2002:C0A8:1703::3  
    R3(config)#ipv6 route 2001::1/128 2002:C0A8:C01::1  

    And then add a BGP configuration like this. R1:

    R1(config)#router bgp 13
    R1(config-router)#bgp log-neighbor-changes
    R1(config-router)#neighbor 2002:C0A8:1703::3 remote-as 13
    R1(config-router)#address-family ipv6
    R1(config-router-af)# neighbor 2002:C0A8:1703::3 activate


    R3(config)#router bgp 13
    R3(config-router)#bgp log-neighbor-changes
    R3(config-router)#neighbor 2002:C0A8:C01::1 remote-as 13
    R3(config-router)#address-family ipv6
    R3(config-router-af)#neighbor 2002:C0A8:C01::1 activate

    This will establish a BGP IPv6 neighbor adjacency:

    R1#show ip bgp ipv6 unicast neighbors
    BGP neighbor is 2002:C0A8:1703::3,  remote AS 13, internal link
      BGP version 4, remote router ID
      BGP state = Established, up for 00:05:06
      Last read 00:00:01, last write 00:00:31, hold time is 180, keepalive interval is 60 seconds
      Neighbor sessions:
        1 active, is not multisession capable (disabled)
  4. Hello Inon

    If we have an IPv4 address of as in the lesson, then the automatic 6to4 tunnelling will use 2002:C0A8:1703 as the beginning of the IPv6 address. Now from this, we can use any subnet prefix of /48 to /64 to represent the IPv6 addresses behind each end of the tunnel. So in a sense, 2002:C0A8:1703::/48 represents the tunnel interface on R1. All IPv6 addresses behind R1 will be mapped to the appropriate address. For example:

    We ping from 2001::3/128 to 2001::1/128. When the ping reaches R3, it will be converted to 2002:C0A8:1703::1, sent over the tunnel to R1 where it will be converted back to 2001::1.

    When you are referring to specific hosts, you would use the host mask of /128, but when referring to the tunnelling prefix, you will always use the /48 prefix.

    Now the general-prefix command automatically configures the prefix as /48 but you are able to use a /64 or anything in between if you like.

    I hope this has been helpful!


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