IPv6 Technical Overview: Address Architecture, DHCPv6 and DNS

IPv6 Technical Overview: Address
Architecture, DHCPv6 and DNS
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IPv6 Address Architecture
128-bit address space
2128
possible addresses
3.4 x 1038
(340 undecillion)
340,282,366,920,939,463,374,607,431,768,211,456 addresses
128 bits allow for multi-level, hierarchical routing infrastructure
64-bit subnet prefix
64-bit interface identifier
www.netuf.net | 404-635-6667 | info@netuf.net

Benefits of 128 bit address
• Easier address management and delegation
• Easier address auto-configuration
• Deploy end-to-end IPsec
– (NATs removed as unnecessary)

Hexadecimal Review
● Grouping binary bits into groups of 4.
● Each group (nibble) is assigned a hex digit value.
● Digits are the same as for decimal up to 9
● Letters A through F are used for 10 through 15.
0000 = 0 1000 = 8
0001 = 1 1001 = 9
0010 = 2 1010 = A
0011 = 3 1011 = B
0100 = 4 1100 = C
0101 = 5 1101 = D
0110 = 6 1110 = E
0111 = 7 1111 = F
Thus the 16-bit binary number:
1011 0100 1010 0111
converted to hex is:
B4A7

IPv6 Address Syntax
● Binary
0010000000000001000011011011100000000000000000000010111100111011
0000001010101010000000001111111111111110001010001001110001011010
● Divided on 16-bit boundaries
0010000000000001 0000110110111000 0000000000000000 0010111100111011
0000001010101010 0000000011111111 1111111000101000 1001110001011010
● 16-bit blocks converted to hexadecimal, delimited with colons
2001:0DB8:0000:2F3B:02AA:00FF:FE28:9C5A
● Suppressing leading zeroes in each block
2001:DB8:0:2F3B:2AA:FF:FE28:9C5A

IPv6 Format and Header
IPv6
Header
Upper layer
Protocol Data Unit
Payload
IPv6 Packet
Extension
Headers

IPv4 and IPv6 Header Comparison
40 bytes
20 bytes
IPv4
IPv6
0 15 16 31
vers hlen TOS total length
identification flags flag-offset
TTL protocol header checksum
source address
destination address
options and padding
vers traffic class flow-label
payload length next header hop limit
source address
destination address
Removed (6)
ID, flags, flag offset TOS,
hlen ,header checksum
Changed (3)
Added (2)
Expanded
- total length => payload
- protocol => next header
- TTL => hop limit
- traffic class
- flow label
address 32 to
128 bits

IPv6 Prefixes
● Always uses address/prefix-length notation
Similar to CIDR
Subnet prefix: 2001:DB8:0:2F3B::/64
Route prefix: 2001:DB8:3F::/48

Address Types
• Unicast
– Address of single interface, delivery to single interface
• Anycast
– Address of set of interfaces, delivery to single interface within set
• Multicast
– Address of set of interfaces, delivery to all interfaces in set
• No more broadcast
• IPv6 nodes will have more than one IP address

Identification
Address Type Identification
IPv4 IPv6
Internet address classes N/A
Multicast address 224.0.0.0/4 IPv6 multicast address FF00::/8
Broadcast addresses N/A
Unspecified address 0.0.0.0 Unspecified address ::
Loopback address 127.0.0.1 Loopback address ::1
Public IP address Global Unicast Address
Private IP address Unique-local address FD00::/8
APIPA address Link-local address FE80::/64
Dotted decimal format Colon hexadecimal format
Subnet mask or prefix length Prefix length notation only

Questions

Router Advertisements
● Router Advertisements (RA) replace dependence on DHCPv4
○ Default router address
○ Prefix
○ Bits to tell devices how to get configuration information
Provides stateful address configuration or stateless configuration settings for
IPv6 hosts
Managed Address Configuration (M) flag
When set to 1, this flag instructs the host to use a configuration protocol to
obtain stateful addresses
Other Stateful Configuration (O) flag
When set to 1, this flag instructs the host to use a configuration protocol to
obtain other configuration settings

Neighbor Discovery
● Neighbor Discovery (ND) replaces ARP
○ Uses a much more efficient multicast process to discover link level
information about other LAN devices
● ONLY ND IS REQUIRED FOR BASIC IPV6 TO WORK LOCALLY ON A
LAN

DHCPv6 Components
● IPv6 hosts do not automatically configure a directly
attached subnet route for a DHCPv6-assigned IPv6 address
■ On-Link flag in the Prefix Information option
● There is no Router option in DHCPv6 to assign a default
router
■ Default route is configured from the RA

Additional DHCPv6 Components
• Components of a DHCPv6 infrastructure
– DHCPv6 clients
– DHCPv6 servers
– DHCPv6 relay agents

DHCPv6 Messages
● User Datagram Protocol (UDP) messages
DHCPv6 clients listen on UDP port 546
DHCPv6 servers and relay agents listen on UDP port 547
● Multicast addresses
DHCPv6 servers and relay agents listen on ff02::1:2
DHCPv6 client sends messages to ff02::1:2
Relay agent forwards multicasts as unicasts to configured DHCPv6 servers

DHCPv6 Message Types
● Solicit
● Advertise
● Request
● Confirm
● Renew
● Rebind
● Reply
● Release
● Decline
● Reconfigure
● Information-Request
● Relay-Forward
● Relay-Reply

DHCPv6 Relay Agent
• Node that acts as an intermediary to deliver DHCP
messages between clients and servers
– On the same link as the client
– Listening on multicast addresses
• All_DHCP_Relay_Agents_and_Servers (FF02::1:2)

IPv6 Router Renumbering
● New address prefixes can be introduced, old ones
withdrawn
● Hosts learn prefix lifetimes and preference order from
router advertisements
● Old TCP connections can survive until end of overlap
● New TCP connections use longest preferred lifetime
● Router renumbering protocol
- allow domain-interior routers to learn of prefix introduction /
withdrawal

Autoconfiguration: Plug-and-Play
• Hosts generally construct addresses from RA:
– subnet prefix(es) learned from periodic multicast advertisements from
neighboring router(s)
– interface IDs generated locally
– MAC addresses : pseudo-random temporary
• Other IP-layer parameters also learned from router adverts (e.g., router addresses,
recommended hop limit, etc…)
• Higher-layer info (e.g., DNS server and NTP server addresses) discovered by
multicast / anycast-based service-location protocol, or DHCPv6
• DHCP is available

Stateful Message Exchange
1. A Solicit message sent by the client to locate the servers
2. An Advertise message sent by a server to indicate that it can
provide addresses and configuration settings
3. A Request message sent by the client to request addresses and
configuration settings from a specific server
4. A Reply message sent by the requested server that contains
addresses and configuration settings

Why is DNS Important?
• Hides intricacies of underlying network structure
– Translation between symbolic names and IP addresses
• Provides applications (domain name servers, mail exchangers)
reverse lookups, mapping IP numbers to a name
• YOU DON’T HAVE TO REMEMBER 2620:144:2D00::138

Changes to DNS for IPv6
• DNS Enhancements
– DNS extensions to support IP version 6
• RFC 3596
– Name to address records
• AAAA record type
– Address to name records
• New reverse domain: IP6.ARPA

DNS Structure
• Resource Record (RRs): Data records stored by name servers
• Types of RRs:
– Start of Authority (SOA): Marks the beginning of a DNS zone
– Name Servers (NS): Domain name of a server in a DNS zone
– Canonical Names (CNAMEs): Aliases for FQDN
– Pointer (PTR): IP number to name mapping

DNS Extensions
In Use Experimental/Deprecated
AAAA record A6 and DNAME records
Textual representation in PTR record Binary Labels type
IP6.arpa IP6.int domain
New DNS Queries
•AAAA
• Forward lookup (Name → IPv6 Address)
A 192.134.0.49
AAAA 2001:660:3006:1::1:1
•PTR
• Reverse lookup (IPv6 Address → Name)
Main tree: ip6.arpa

Reverse Lookup
• Reverse DNS lookups for IPv6 addresses use similarly the ip6.
arpa domain
– Top-Level Domain (TLD).
• IPv6 address represented as a name in the ip6.arpa domain by
a sequence of nibbles in reverse order
• Represented as hexadecimal digits, separated by dots with
the suffix .ip6.arpa
IPv6: 4321:0:1:2:3:4:567:89AB.ip6.arpa
B.A.9.8.7.6.5.0.4.0.0.0.3.0.0.0.2.0.0.0.1.0.0.0.0.0.0.0.1.2.3.4.IP6.ARPA

Brandon Ross
CEO and Chief Network Architect
bross@netuf.net
404-635-6667
Thank You

IPv6 Technical Overview: Address Architecture, DHCPv6 and DNS

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