Valid IPv6 address

Answered Question
Apr 9th, 2010

Hi all,

I was studying for cisco exam and there is question if this address is valid IPv6 or not

2002:7654:a1ad:61:81af:ccc1

any answers

thanks

mahesh

I have this problem too.
0 votes
Correct Answer by Giuseppe Larosa about 5 years 4 months ago

Hello Mahesh,

an IPv6 address is made of 128 bits and it is represented using exadecimal digits.

Each hex digits represents 4 binary digits  = 1 hex = 4 bits

So an IPv6 address is made of 128/4 = 32 hexadecimal digits

the usual hex dotted representation groups 4 hex and separate these groups using a ':'

So an IPv6 address is made of 8 4hex groups divided by :

the notation allows to represent one of more 4 hex consecutive groups made of all zeroes with a ::

This can appear only once in the number.

In your case the proposed hexadecimal sequence is:

2002:7654:a1ad:61:81af:ccc1

2002:7654:a1ad:0061:81af:ccc1

Here we see only 6 4-hex groups, no :: appears in the middle to represent all zero groups so it is too short.

an IPv6 prefix is represented with a final ::/prefix length

this is not a valid IPv6 address because it is too short, it could be an IPv6 prefix if written as:

2002:7654:a1ad:61:81af:ccc1::/96

see

http://www.cisco.com/en/US/docs/ios/ipv6/configuration/guide/ip6-addrg_bsc_con.html#wp1027186

Hope to help

Giuseppe

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Correct Answer
Giuseppe Larosa Fri, 04/09/2010 - 11:36

Hello Mahesh,

an IPv6 address is made of 128 bits and it is represented using exadecimal digits.

Each hex digits represents 4 binary digits  = 1 hex = 4 bits

So an IPv6 address is made of 128/4 = 32 hexadecimal digits

the usual hex dotted representation groups 4 hex and separate these groups using a ':'

So an IPv6 address is made of 8 4hex groups divided by :

the notation allows to represent one of more 4 hex consecutive groups made of all zeroes with a ::

This can appear only once in the number.

In your case the proposed hexadecimal sequence is:

2002:7654:a1ad:61:81af:ccc1

2002:7654:a1ad:0061:81af:ccc1

Here we see only 6 4-hex groups, no :: appears in the middle to represent all zero groups so it is too short.

an IPv6 prefix is represented with a final ::/prefix length

this is not a valid IPv6 address because it is too short, it could be an IPv6 prefix if written as:

2002:7654:a1ad:61:81af:ccc1::/96

see

http://www.cisco.com/en/US/docs/ios/ipv6/configuration/guide/ip6-addrg_bsc_con.html#wp1027186

Hope to help

Giuseppe

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