Learning IPv6

Recently I was fortunate enough to enable IPv6 on the router and all connected devices are now with IPv6 addresses. You will ask why would one want to switch to use IPv6?

Let's start simple, look at the graph at https://www.google.com/intl/en/ipv6/statistics.html , there is a trend growing in IPv6 adoption since mid yeer 2010. If that's not convincing enough to enable IPv6 in the router, then read on. I will explain based on the article found here.

First, what is IPv6?

Internet Protocol version 6 (IPv6) is the latest version of the Internet Protocol (IP), the communications protocol that provides an identification and location system for computers on networks and routes traffic across the Internet. IPv6 was developed by the Internet Engineering Task Force (IETF) to deal with the long-anticipated problem of IPv4 address exhaustion.

Because IPv4 address is exhausted with the current addresses usage trends, more devices released soon will not get be able to get a unique public address from IPv4 pool.

Below is a summary in points form of the facts of IPv6.

•  As of June 2014, the percentage of users reaching Google services with IPv6 surpassed 4% for the first time.


• IPv6 uses a 128-bit address, allowing 2¹²⁸, or approximately 3.4 × 10³⁸ addresses. whilst IPv4 used 32-bit address and provide only 4.3 billion addresses.


• IPv4 and IPv6 are not interoperable and thus adoption has been slow. To expedite the adoption, there are transition mechanisms have been devised to permit communication between IPv4 and IPv6 hosts.


• IPv6 was first formally described in Internet standard document RFC 2460, published in December 1998.


• IPv6 simplifies aspects of address assignment (stateless address autoconfiguration), network renumbering and router announcements when changing network connectivity providers.


• IPv6 simplifies processing of packets by routers by placing the need for packet fragmentation into the end points.


• The standard size of a subnet in IPv6 is 2⁶⁴ addresses, the square of the size of the entire IPv4 address space.


• IPv6 does not implement traditional IP broadcast, i.e. the transmission of a packet to all hosts on the attached link using a special broadcast address, and therefore does not define broadcast addresses. In IPv6, the same result can be achieved by sending a packet to the link-local all nodes multicast group at address ff02::1, which is analogous to IPv4 multicast to address 224.0.0.1.


• The IPv6 packet header has a fixed size (40 octets).


• IPv4 limits packets to 65535 (216−1) octets of payload. An IPv6 node can optionally handle packets over this limit, referred to as jumbograms, which can be as large as 4294967295 (232−1) octets.


• In the Domain Name System, hostnames are mapped to IPv6 addresses by AAAA resource records, so-called quad-A records.

IPv6 addresses are represented as 8 groups of four hexadecimal digits separated by colons, for example 2001:0db8:85a3:0042:1000:8a2e:0370:7334, but methods of abbreviation of this full notation exist.  Each group is written as 4 hexadecimal digits and the groups are separated by colons (:). IPv6 unicast addresses other than those that start with binary 000 are logically divided into two parts: a 64-bit (sub-)network prefix, and a 64-bit interface identifier.



For convenience, an IPv6 address may be abbreviated to shorter notations by application of the following rules, where possible.

• One or more leading zeroes from any groups of hexadecimal digits are removed; this is usually done to either all or none of the leading zeroes. For example, the group 0042 is converted to 42.


• Consecutive sections of zeroes are replaced with a double colon (::). The double colon may only be used once in an address, as multiple use would render the address indeterminate.

An example of application of these rules:

• Initial address: 2001:0db8:0000:0000:0000:ff00:0042:8329


• After removing all leading zeroes: 2001:db8:0:0:0:ff00:42:8329


• After omitting consecutive sections of zeroes: 2001:db8::ff00:42:8329

The loopback address, 0000:0000:0000:0000:0000:0000:0000:0001, may be abbreviated to ::1 by using both rules.

Stateless Autoconfiguration

IPv6 lets any host generate its own IP address and check if it's unique in the scope where it will be used. IPv6 addresses consist of two parts. The leftmost 64 bits are the subnet prefix to which the host is connected, and the rightmost 64 bits are the identifier of the host's interface on the subnet. This means that the identifier need only be unique on the subnet to which the host is connected, which makes it much easier for the host to check for uniqueness on its own.

|Subnet Prefix 64 bits | Interface identifier 64 bits |

The mac address is used to derive the address for interface link local. I have written blog on how to do just that. please read here.

With the link-local derived, without the prefix fe80, and then use the remaining by concat with the network lan IPv6 prefix.

So an example of mac address 4c:33:22:11:aa:ee

Derived link local fe80::4e33:22ff:fe11:aaee

Public ip 2001:e68:5424:d2dd:4e33:22ff:fe11:aaee where 2001:e68:5424:d2dd is the network lan IPv6 prefix assigned by the router and 4e33:22ff:fe11:aaee is the local-link address without prefix fe80.

Dual IP stack implementation

Dual-stack (or native dual-stack) refers to side-by-side implementation of IPv4 and IPv6. That is, both protocols run on the same network infrastructure, and there's no need to encapsulate IPv6 inside IPv4 (using tunneling) or vice-versa. Dual-stack is defined in RFC 4213.

The dual-stack should only be considered as a transitional technique to facilitate the adoption and deployment of IPv6, as it has some major drawbacks and consequences: it will not only more than double the security threats from both IPv4 and IPv6 for the existing network infrastructure, but also ultimately overburden the global networking infrastructure with both dramatically increased Internet traffic. The ultimate objective is to deploy the single stack of IPv6 globally.

There are others which can be found in the wikipedia, http://en.wikipedia.org/wiki/IPv6 but the above should get you started. It works for me the first time I enable IPv6 and it works wonder after that.

Derive IPv6 link-local address for network interface

When you show the interface configuration using command ip, you will noticed there is a inet6 address start with fe80. Today, we will learn what is this and how this address is derive. Example below

user@localhost:~$ ip addr show wlan0
3: wlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP qlen 1000
    link/ether 4c:33:22:11:aa:ee brd ff:ff:ff:ff:ff:ff
    inet 192.168.133.50/24 brd 192.168.133.255 scope global wlan0
       valid_lft forever preferred_lft forever
    inet6 2001:e68:5424:d2dd:4e33:22ff:fe11:aaee/64 scope global dynamic 
       valid_lft 86399sec preferred_lft 14399sec
    inet6 fe80::4e33:22ff:fe11:aaee/64 scope link 
       valid_lft forever preferred_lft forever

So first, what is Link-local address?

In a computer network, a link-local address is a network address that is valid only for communications within the network segment (link) or the broadcast domain that the host is connected to.

Link-local addresses are usually not guaranteed to be unique beyond a single network segment. Routers therefore do not forward packets with link-local addresses.

For protocols that have only link-local addresses, such as Ethernet, hardware addresses that the manufacturer delivers in network circuits are unique, consisting of a vendor identification and a serial identifier.

Link-local addresses for IPv4 are defined in the address block 169.254.0.0/16, in CIDR notation. In IPv6, they are assigned with the fe80::/10 prefix.

So it is a wire address that is locally within a segment of a network and it is not routable beyond a router.

With this said, let's calculate link-local address.

1. take the mac address from ip command.
from above example 4c:33:22:11:aa:ee

2. add ff:fe in the middle of the current mac address.
4c:33:22:ff:fe:11:aa:ee

3. reformat to IPv6 notation by concatenate two hex groups into one.
4c33:22ff:fe11:aaee

4. convert the first octet from hexadecimal to binary
4c -> 01001100

5. invert the bit at position 6, starting from left with first bit as 0.
01001100 -> 01001110

6. convert the octet back in step 5 back to hexadecimal
01001110 -> 4e

7. replace first octet with newly calculated from step 6.
4e33:22ff:fe11:aaee

8. prepend the link-local prefix
fe80::4e33:22ff:fe11:aaee

That's it.

How to check if Debian Jessie, Ubuntu Trusty, Nokia N900 if it IPv6 ready?

With recent rise of IPv6 usage, it is imperative that we understand if our devices are ready for IPv6. Linux kernel supported IPv6 as early as year 1996! Chances are, all these distributions should be IPv6 ready. But for the sake to be sure and learning the basic, we will check these distribution to be sure.

To check, launch a terminal and execute this command as a user.

$ cat /proc/net/if_inet6
fe80000000000000022401fffed782ea 03 40 20 80 eth2
00000000000000000000000000000001 01 80 10 80 lo

You should see the above output and if you are not , maybe the kernel is not compile with ipv6 module. If so, you can enable it and check if it loaded.

# modprobe ipv6
# lsmod | grep ipv6
ipv6 237436 14

You can run the above commands for all the devices, they are all IPv6 ready.



There are many articles out there to disable IPv6 but with the depletion of IPv4 addresses, I think this practice should not continue but be ready and prepared for it. Of cause unless you got good reason not to use IPv6.