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Forum Replies

  1. Hi Rene,

    Do Windows, Linux and Mac hosts calculate it some way ?

     

  2. Hi Diego,

    EUI-64 is described in the RFC, most hosts will use this for automatically assigning an address. Linux and MAC both use this.

    Windows however seems to use something else. It seems Vista, 7/8/10 and Server 2008 create random interface IDs instead of EUI-64. I believe you can change this though.

    Rene

  3. Hi Jose,

    Let's look at an example:

    R1#show interfaces GigabitEthernet 1 | include bia
      Hardware is CSR vNIC, address is fa16.3e60.0217 (bia fa16.3e60.0217)

    The 7th bit is in the first two hexadecimal characters:

    fa = 1111 1010

    As you can see, the 7th bit is set to 1 here. Now let's check the IPv6 address:

    R1#show ipv6 interface GigabitEthernet 1 | include link-local
      IPv6 is enabled, link-local address is FE80::F816:3EFF:FE60:217

    Let's write down the complete uncompressed address:

    FE80:0000:0000:0000:F816:3EFF:FE60:0217

    Let's look only at the EUI-64 part:

    F816:3EFF:FE60:0217

    We only care about the first two hexadecimal characters:

    F8 = 1111 1000

    As you can see, the 7th bit has been inverted from 1 to 0.

    Let's see what happens when we change the 7th bit in the MAC address, right now it starts with fa:

    fa = 1111 1010

    Let's make it:

    f8 = 1111 1000

    R1(config)#interface gigabitEthernet 1
    R1(config-if)#mac-address f816.3e60.0217

    Our IPv6 address has become:

    R1#show ipv6 interface GigabitEthernet 1 | include link-local
      IPv6 is enabled, link-local address is FE80::FA16:3EFF:FE60:217

    The complete uncompressed address is:

    FE80:0000:0000:0000:0000:FA16:3EFF:FE60:0217

    Here's the EUI-64 part:

    FA16:3EFF:FE60:0217

    First two hexadecimal characters:

    FA = 1111 1000

    As you can see, it got inverted. No matter if the 7th bit of the MAC address is a 0 or 1, it always gets inverted.

    Hope this helps!

    Rene

  4. Hi Itai,

    Oops...the FFFF is a typo indeed, that should be 1111. Just fixed it.

    When you use EUI-64 to automatically use the MAC address as input for the "host" part then the 7th bit will be inverted, this is all done automatically though.

    If you make up some IPv6 addresses of your own then you can pick whatever addresses you like...

    Rene

  5. Hi Diana,

    Here's an example:

    R1#show ipv6 interface GigabitEthernet 0/1
    GigabitEthernet0/1 is up, line protocol is up
      IPv6 is enabled, link-local address is FE80::F816:3EFF:FEE6:7777

    That's the IPv6 link-local address that uses EUI-64. You can configure it manually if you want:

    R1(config)#int gi0/1                                                      
    R1(config-if)#ipv6 address FE80:1111:1111:1111:ABCD:ABCD:ABCD:ABCD link-local

    R1#show ipv6 interface GigabitEthernet 0/1 | include FE80
      IPv6 is enabled, link-local address is FE80:1111:1111:1111:ABCD:ABCD:ABCD:ABCD

    Here's a global unicast address with EUI-64:

    R1(config-if)#ipv6 address 2001:1111:1111:1111::/64 eui-64

    R1#show ipv6 interface GigabitEthernet 0/1 | include 2001:
        2001:1111:1111:1111:F816:3EFF:FEE6:7777, subnet is 2001:1111:1111:1111::/64

    If you don't want to use EUI-64 then you can configure global unicast addresses yourself:

    R1(config-if)#ipv6 address 2001:1111:1111:1111:ABCD:ABCD:ABCD:ABCD/64

    R1#show ipv6 interface GigabitEthernet 0/1 | include ABCD 
        2001:1111:1111:1111:ABCD:ABCD:ABCD:ABCD, subnet is 2001:1111:1111:1111::/64 
        FF02::1:FFCD:ABCD

    That's it. Hope this helps.

    Rene

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