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Kuldeep singh

IPv6 addressing confusion

Hi Experts (Only Experienceholders),

What is exact address format of IPv6 to assign to any

Router or computer / Laptop ? I have seen many posts

and online articles where information about IPv6 is not

clear. I am giving here some examples like as

IPv6 address =   2001:0DB8:1111:2222::1/64

(in this example, there are only 5 octet and sign :: comes in last) 


IPv6 address =   fe80::2e0:b6ff:fe01:3b7a

(in this example, there are only 5 octet and sign :: comes in starting)


IPv6 address =  2001:410:1:2:212:43FF:FEE3:C600

(in this example, there are 8 octet and no :: sign)


Nagendra Kumar Nainar
Cisco Employee

Hi Kuldeep,

IPv6 address is of 128 bit length (or 8 octect  length). Inorder to have it user friendly (to some extent), the text  representation is defied in a way that concecutive zeros can be denoted  with :: symbol.

For example, 2001:0DB8:1111:2222::1/64 is actually 2001:0DB8:1111:2222:0000:0000:0000:0001/64

Similarly, fe80::2e0:b6ff:fe01:3b7a is actually FE80:0000:0000:0000:02e0:b6ff:fe01:3b7a.

Below RFC will give you a better understanding on the text representation,



Hi Nagendra,

You mean to say, i can put any one of them in address field

of Pc/Laptop or Router interface whether it is 5 octet or 8 octet.

am i right ? plz give me confirmed final answer.........


Scenario 1: Apply IPv6 Global address to router interface, V6 Link-local is auto generated.

Scenario 2: Apply IPv6 Global address and link-local to router interface.

For more info on V6 addressing, refer

Hope this clarifies your doubt.

Please rate the content, if you find the content helpfil.



Regards, Sunil Khanna

why Global Address and Link-local ip address different ?

can i configure router interface ip without link-local ?

The link-local IP address is used for point to point communication between adjacent interfaces. When you enable v6, the router will generate a link local address for each v6 enabled interface automatically. IPv6 requires a link local ip on each active interface; it's used for neighbor discovery at the very least.

The equivalent in IPv4 is the subnet that gets assigned when you boot up a machine without any network connectivity. However, in v6 it is not optional and does not go away when a global address gets assigned.

Beyond the resources others have provided above, you might have a look at the general description of IPv6 at


Hi Kuldeep,

Good question. Link local address has a scope defined, which is to the link only. Any packet forwarded to the link local address will not be forwarded ahead by the receiving device. I really appreciate the concept of link local address in IPv6 as it removes lot of confusion and is pretty straight forward. The concept of knowing link local address is pretty important as some routing protocols use link local address as next hop to reach a destination.

If you really want to clear your concepts on IPv6 in a way that it helps you to implement the protocol, I would recommend you studying the CCNP Route official study guide written by Wendell Odom. It's really good and I really like it.



ipv6 is not like ipv4 I try to explan you first task in ipv6 is that

it is 128 bit

in ipv6 0000:0000:0000:0000:0000:0000:0000:0000

in ipv4

number starts with 2001 or 2002 is just like starting number 192 in ipv4

eg 2001:0000:1111:2222:3333:4444:5555:6666

u can write 2001:0:1111:2222:3333:4444:5555:6666

2nd eg: 2001:0000:0000:1111:1111:2222:3333:4444

u can write 2001::1111:1111:2222:3333:4444 (here u find only 6 places)

:: you can use only one time

Kuldeep singh


Why we use 4 in IPv4 and 6 in IPv6. what is logic behind this ?

4 and 6 are ip version. Better you get CCNA level knowledge

Internet protocol version 1-3 were lab-only; version 4 is the experiment that build the modern internet; 5 was a real-time streaming idea which never got any traction, and 6-9 were candidates to replace 4, with the winner being 6, "simple internet procotol plus".  The simple part is the v6 is still packet-switched, next-hop routed, best-effort delivery like v4, only with 128 bit addresses. The plus part is more complicated (neighbor discovery, new multicast design, mobility enhancements, IPsec, ...).

Anyway, the successor to IPv4 is IPv6, and any future successor to 6 would be IPv10 or larger.

-- Jim Leinweber, WI State Lab of Hygiene

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