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Forum Replies

  1. 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:

    F

    ... Continue reading in our forum

  2. 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:AB
    ... Continue reading in our forum

  3. Hi Joel,

    First of all, I wouldn’t worry too much about this too much. The bit flipping is just one minor sub-topic of all IPv6 related stuff you can expect in the exam. It’s possible that you don’t get any questions about it so don’t stress about it too much. You can expect a lot of regular subnetting questions so that’s why I highly recommend a “cheat sheet” for that.

    It seems this list would work. It might be a quick method if you’d get 10 bit flipping questions but if you only would get 1 question, it might be just as fast to quickly calculate it?

    hex > bina

    ... Continue reading in our forum

  4. Hello Nadav,

    That is no problem, the prefix is different so you will have a unique 128-bit IPv6 address. Here’s an example:

    R1(config)#interface GigabitEthernet 0/1
    R1(config-if)#ipv6 address 2001:DB8:1:1::/64 eui-64 
    R1(config-if)#ipv6 address 2001:DB8:2:2::/64 eui-64 
    R1(config-if)#ipv6 address 2001:DB8:3:3::/64 eui-64
    

    Gets you:

    R1#show ipv6 interface brief | include 2001
        2001:DB8:1:1:F816:3EFF:FE42:B409
        2001:DB8:2:2:F816:3EFF:FE42:B409
        2001:DB8:3:3:F816:3EFF:FE42:B409
    

    Rene

  5. Hello Nadav

    This is an excellent question. According to RFC 5375 in section B.2.4 EUI-64 ‘u’ and ‘g’ Bits, it states the following:

    When using subnet prefix lengths other than /64, the interface
    identifier cannot be in Modified EUI-64 format as required by
    [RFC4291]. However, nodes not aware that a prefix length other than
    /64 is used might still think it’s an EUI-64; therefore, it’s prudent
    to take into account the following points when setting the bits.

    The document continues to state several considerations that should be checked carefully. In general, d

    ... Continue reading in our forum

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