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Learning IPv6 - Important Points

Learning IPv6 - Important Points

This is an important blog on Learning IPv6 - Important Points, its Importance and advantages of IPv6. IPv6 is the replacement Internet protocol for IPv4. It corrects some of the deficiencies of IPv4 and simplifies the way that addresses are configured and how they are handled by Internet hosts.

IPv4 has proven to be robust, easily implemented, and interoperable, and has stood the test of scaling an inter-network to a global utility the size of the Internet. However, the initial design did not anticipate the following conditions:

  • Recent exponential growth of the Internet and the impending exhaustion of the IPv4 address space.
  • The ability of Internet backbone routers to maintain large routing tables.
  • Need for simpler auto-configuration and renumbering.
  • Requirement for security at the IP level (IPSec)
  • Need for better support for real-time delivery of data, known as quality of service (QoS)


Why is IPv6 required?

With its 32-bit address format, IPv4 can handle a maximum 4.3 billion unique IP addresses. While this number may seem very large, it is not enough to sustain and scale the rapidly rising growth of the Internet. Although improvements to IPv4, including the use of NAT, have allowed the extended use of the protocol, address exhaustion is inevitable and could happen as soon as 2012.

With its 128-bit address format, IPv6 can support 3.4 x 1038 exchange   unique IP addresses. This number of addresses is large enough to configure a unique address on every node in the Internet and still have plenty of addresses left over. It is also large enough to eliminate the need for NAT, which has its own inherent problems.

A few countries, governmental agencies, and multinational corporations have either already deployed or mandated deployment of IPv6 in their networks and software products. Some emerging nations have no choice but to deploy IPv6 because of the unavailability of new IPv4 addresses.


Advantages of IPv6

Besides providing an almost limitless number of unique IP addresses for global end-to-end reachability and scalability, IPv6 has the following additional advantages:

  • Simplified header format for efficient packet handling
  • Larger payload for increased throughput and transport efficiency
  • Hierarchical network architecture for routing efficiency
  • Support for widely deployed routing protocols (OSPF, BGP, etc.)
  • Autoconfiguration and plug-and-play support
  • Elimination of need for network address translation (NAT) and application layered gateway (ALG)
  • Increased number of multicast addresses .

Methods of Transitioning from IPv4 to IPv6

The transition from IPv4 to IPv6 will not happen quickly because of the scope of the change. The two protocols will likely need to coexist for many years before IPv6 replaces IPv4 completely. Many countries and corporations are currently using one or more of the methods described below to transition their networks to IPv6.

  • Dual Stack - A dual stack means that IPv4 and IPv6 addresses coexist on the same platform and support hosts of both types. This method is a way to transition from IPv4 to IPv6 with coexistence as a first step. The ACE supports a dual stack arrangement for IPv6.
  • VPN Tunneling.
  • NAT -  For IPv6, the ACE supports the NATing of client or VIP IPv4 addresses to server IPv6 and the reverse for HTTP and HTTPS load balancing.

IPv6 - Characteristics

  • Its a 128bit addresses, divided into 8 groups of 4 Hexadecimal characters each.
Learning IPv6 - Important Points, IPv6 Address
  •  128 bits IPv6 address is divided in to 64 bit Network and 64 bit Host portion.  The 64 bit Network portion is further divided into Global Routing Prefix (48bits) and Subnet (16 bits) fields. The Enterprises or Providers are assigned /48 addresses and have 16 bits of subnetting available.
Learning IPv6 - Important Points, IPv6 Address format
  • The Global Routing Prefix (48 bits) have following elements:
           The first three bits (/3) of a unicast address are always 001.
           The next 13 bits (/16) identify the Top-Level Aggregator (TLA); the upstream ISP.
           The next 24 bits (/40) identify the next-level aggregator, or regional ISP.       
  • Rules to define an IPv6 address:
         1. Eliminate groups of consecutive zeros once per address.


         2. Drop leading zeros.

  • There are two Types of IPv6 Address.   Link Local Address and  Global Address. Each interface will be assigned one Link Local and a Global address.
  • A Link-Local address starts with FE80.  Below are details to define a Link Local address.
  • FE80 + Followed by 54 zeros + 48 bit mac-address of interface (with some difference)  inserted with FFFE in the middle.
                   R1# sh int f0/0 | i bia
                   Hardware is DEC21140, address is ca01.2f2c.0000 (bia ca01.2f2c.0000)
                   R1#sh ipv6 int f0/0
                   FastEthernet0/0 is up, line protocol is up
                   IPv6 is enabled, link-local address is FE80::C801:2FFF:FE2C:0
                   No Virtual link-local address(es):
                   Global unicast address(es):
                   2001:1111:A::1, subnet is 2001:1111:A::/64
  • A Link-Local address enables a node to communicate with other nodes on the link.
  • A Link-Local addresses are not routable in the network.
  • Global addresses have high level 3 bits to 001 (2000::/3).
  • IPv6 only support Unicast and Multicast type of traffic and no Broadcast exists in IPv6. Protocols like ARP/Gratuitous ARP are not used in IPv6. IPv6 uses Neighbor Discovery mechanism to identify duplicate addresses assigned on link. Alternate command for "show ip arp" in IPv6 is "show ipv6 neighbors"
            R1#sho ipv6 neighbors
            IPv6 Address                               Age   Link-layer Addr   State        Interface
            2001:1111:A::2                              9      ca02.073c.0000   STALE       Fa0/0
            FE80::C802:7FF:FE3C:0              9      ca02.073c.0000   STALE       Fa0/0
  • No NAT or PAT is required for IPv6 addressing.
  • There are tunneling techniques  that we can use to transport ipv6 over ipv4 network to support Backward compatibility.
  • Running IPv4 and IPv6 simultaneously is called “Dual Stack”.
  • IPv6 unicast-routing and ipv6 cef are not enabled by default and must be configured separately.  "ipv6 unicast-routing" command is necessary if you want to run any IPv6 IGP routing protocol. For example RIPng, OSPFv3 etc.
          R1(config)#ipv6 unicast-routing
          R1(config)#ipv6 cef  
  • IPv6 uses "Stateless Autoconfiguration" method to automatically assign IPv6 addresses to hosts or interfaces on the node similar to DHCP.
  • DNS service is also available for IPv6.  Like A- Resource Record is used for hostname to IP resolution, AAAA Resource Record is used for hostname to IPv6 address resolution. See my blog "How DNS Works?"
  • You can manually assign/configure more than one IPv6 address on an interface of node.
            R1#show run int f0/0
             interface FastEthernet0/0
             no ip address
             duplex full
             ipv6 address 2001:1111:A::1/64
             ipv6 address 2001:2222:B::1/64

  • Multicast address in IPv6 start from FF0x. For example Multicast addresses  for "All-Hosts" and "All-Routers" are  is FF02::1 and FF02::2 respectively.
  • For IPv6 running and Network Layer, Ethernet -Type field value for an Ethernet Frame is 0x86DD
  • As we have range reserved as Loopback address range in IPv4, Loopback IP reserved for IPv6 is 0000:0000:0000:0000:0000:0000:0000:0001/128 or ::1/128
  • Default route in IPv6 is defined as (::/0)

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