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Aug 2, 2013

IPv6, I am no longer intimidated by you.


IPv6 is one of those CCNA topics I was not confident explaining to someone. I was intimidated by its new features and whenever I see those series of 32 hexadecimal numbers, I get really uneasy. So I decided to put an end to it by getting in the bottom of things with IPv6. Now I am no longer intimidated and I am glad to finally get this off of my chest. ;)

So here, I want to share my study notes on IPv6.


Some facts about IPv6

- 128 bit address; 32 hexadecimal numbers; 8 quartets of 4 hex digits
- IPsec is required on IPv6 hosts
- improvement of IPv6 header: no more recalculation of checksum for every packet sent & includes flow label for easy identifaction of packets sent over the same TCP/UDP connection
- strategic IPv6 address assignment has been adapted from IPv4 and this process is being handled by Internet Corporation for Assigned Network Numbers (ICANN)
- no more broadcast (uses multicast, unicast and anycast)



Subnetting

A company was assigned by ISP with address 2340:1111:AAAA::/48

Engineer tries to break it to smaller subnets of /64 prefix

Subnet 0 - 2340:1111:AAAA::/64
Subnet 1 - 2340:1111:AAAA:1::/64
Subnet 2 - 2340:1111:AAAA:2::/64
...
Subnet 65535 - 2340:1111:AAAA:FFFF::/64
(Yep, that's a lot of subnets!)

IPv6 Host Address Assignment

1. Static IPv6 autoconfiguration
    a. Entire address (128 bit)
        int fa0/0
        ipv6 address 2001:1234:5678:8002::1/64
    b. Eui-64 (64 bit prefix)
        int fa0/0
        ipv6 address 2001:1234:5678:8002::/64 eui-64

2. Stateless Autoconfiguration
-host automatically learns the /64 prefix used on the subnet and uses eui-64 for the Interface ID
-uses Neighbor Discovery Protocol messages (NDP)
-host sends Router Solicitation (RS) to multicast FF02::2 (all routers on the link)
-routers replies with Router Advertisement (RA) using multicast FF02::1 (all hosts on the link) contatining the IPv6 prefix and its own address as well as addresses of other routers on the same subnet

3. Stateful DHCPv6
- same as DHCPv4 except that host uses multicast FF02:1::2 to send the requests and this is received by DHCP relay agents
- server supplies IPv6 address and prefix, default router, DNS address


Learning the IP address of DNS Servers
1. Stateful DHCP
2. Stateless DHCP
-used in conjuction with stateless autoconfiguration
-server does not need to track any state information about each client


EUI-64
I knew you were thinking, what the heck is this EUI-64? Easy, here's what it is about.

- IPv6 separates MAC address into two 2-byte halves and inserts hex FFFE in between, inverting the seventh bit (universal/local bit) in the first byte

Example
Interface MAC address = 0034:5678:9ABC
Interface ID = 0234:56FF:FE78:9ABC

0 = 0000
2 = 0010

3 Types of Unicast IPv6 Address

a. Global Unicast Address
- public & globally unique IPv6 address allowing host to communicate without the need for NAT, closely matching the purpose of public IPv4 addresses
- 2000::/3 (any address that starts with hex 2 or 3)

b. Unique Local Unicast Address
- have the same function as IPv4 RFC 1918 private addresses
- FD (8 bits) | Global ID (40 bits) | Subnet (16 bits) | Interface ID (64 bits)

c. Link local Unicast Address
- host can calculate its own link local address to be used as source address for overhead messages (e.g. sending NDP RS)
- FE80 (10 bits) | All 0s (54 bits) | Interface ID (64 bits)
- Likes hosts, routers automatically calculate their link local address and interestingly, uses it as the next-hop IP address in IPv6 routes



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aspiring computer and network engineer, programmer, with fascination in webdesign and development

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