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mahesh18
Frequent Contributor

Valid IPv6 address

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

1 ACCEPTED SOLUTION

Accepted Solutions
Giuseppe Larosa
Hall of Fame Master

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

View solution in original post

2 REPLIES 2
Giuseppe Larosa
Hall of Fame Master

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

Hi giuslar,

many thanks for correct reply

regards

mahesh