Introduction to IPv6 Addressing

Need for IPv6

• IPv4 is running out of addresses a key motivator for IPv6.
• IPv6 development by IETF aimed to fix IPv4 limitations and include enhancements.
• ICMPv6 includes address resolution and autoconfiguration, unlike ICMPv4.
• NAT slows IPv4 depletion but is problematic for applications, creates latency, and limits peer-to-peer communication.
• The IETF migration techniques into IPv6 are dual stack, tunneling, and NAT64.
• Dual stack allows IPv4 and IPv6 coexistence with devices running both protocol stacks.
• Tunneling transports IPv6 packets over IPv4 networks by encapsulating IPv6 packets inside IPv4 packets.
• NAT64 translates IPv6 packets to IPv4 and vice versa, enabling communication between IPv6 and IPv4 devices.

IPv6 Addressing Formats

• IPv6 addresses are 128 bits long and written in hexadecimal values.
• Every four bits is represented by a hexadecimal digit, totaling 32 hexadecimal values.

Preferred Format

• IPv6 addresses are written as x:x:x:x:x:x:x:x, where each "x" is four hexadecimal values.
• A hextet in IPv6 is the unofficial term for a 16-bit segment, or four hexadecimal values.
• Preferred format uses all 32 hexadecimal digits to represent an IPv6 address.

Rule 1 - Omit Leading Zeros

• Leading zeros in any hextet can be omitted to simplify IPv6 address notation.
• 01ab can be represented as 1ab, 09f0 as 9f0, 0a00 as a00, and 00ab as ab.

Rule 2 - Double Colon

• A double colon (::) replaces one contiguous string of one or more all-zero 16-bit hextets.
• 2001:db8:cafe:1:0:0:0:1 can be shortened to 2001:db8:cafe:1::1 using the double colon.
• Double colon can only be used once per address to avoid ambiguity.
• 2001:db8::abcd::1234 is an incorrect use of the double colon.
• Possible expansions of 2001:db8::abcd::1234 include: 2001:db8::abcd:0000:0000:1234, 2001:db8::abcd:0000:0000:0000:1234, 2001:db8:0000:abcd::1234, and 2001:db8:0000:0000:abcd::1234.
• Best practice dictates using the double colon on the longest string of all-zero hextets.
• If strings are of equal length, the first string should use the double colon.

Address Types

• IPv6 addresses include unicast, multicast, and anycast types.
• An IPv6 unicast address uniquely identifies an interface on an IPv6-enabled device.
• An IPv6 multicast address sends a single IPv6 packet to multiple destinations.
• An IPv6 anycast address is assigned to multiple devices; packets are routed to the nearest device with that address.

IPv6 Prefix Length

• The prefix length indicates the network portion of an IPv6 address.

• It uses slash notation, similar to IPv4 but without dotted-decimal subnet masks.

• The prefix length ranges from 0 to 128, with /64 recommended for LANs.

• An IPv6 unicast address identifies an interface on an IPv6-enabled device, ensuring packets reach the intended recipient.

• Source IPv6 addresses must be unicast, while destination addresses can be unicast or multicast.

• IPv6 addresses typically have a Global Unicast Address (GUA) and a Link-Local Address (LLA).

• GUAs are globally unique and internet-routable, similar to public IPv4 addresses, whether configured statically or dynamically.

• LLAs are required for every IPv6-enabled device and communicate with devices on the same local link.

• Link refers to a subnet in IPv6, and LLAs are confined to a single link and not routable beyond it.

• IPv6 unique local addresses have some similarities to RFC 1918 private IPv4 addresses but with differences.

• Unique local addresses are used for local addressing within a limited number of sites.

• They are not globally routed or translated to a global IPv6 address.

• Public IPv4 addresses are equivalent to IPv6 global unicast addresses (GUAs).

• ICANN allocates IPv6 address blocks to five RIRs; GUAs with the first three bits of 001 (2000::/3) are being assigned.

• The first hextet for available GUAs begins with 2 or 3, representing 1/8th of the IPv6 address space.

IPv6 GUA Structure

• A GUA consists of a Global Routing Prefix, Subnet ID, and Interface ID.

• The global routing prefix is the network portion assigned by a provider like an ISP.

• ISPs may assign a /48 global routing prefix to customers, varying based on ISP policies.

• With a /48 prefix, 2001:db8:acad::/48 shows the first 48 bits are for the network, and ::/48 indicates the rest are 0s.

• The Subnet ID is between the Global Routing Prefix and the Interface ID; IPv6 designs subnetting unlike IPv4.

• The Subnet ID identifies subnets within the organization, with larger subnet IDs allowing more subnets.

• A /32 global routing prefix combined with the recommended /64 prefix leaves a 32-bit Subnet ID and 4.3 billion subnets.

• With a /48 Global Routing Prefix in IPv6, the first four hextets are for the network, the fourth indicating the Subnet ID.

• The remaining four hextets are for the Interface ID.

• IPv6's Interface ID mirrors the host portion of IPv4 addresses; a single host has single/multiple interfaces for IPv6 addresses.

• The structure of an IPv6 GUA recommends /64 subnets creating a 64-bit interface ID for 18 quintillion hosts per subnet.

• The /64 subnet or prefix (Global Routing Prefix + Subnet ID) uses 64 bits for the interface ID, allowing SLAAC-enabled devices.

• Unlike IPv4, IPv6 can assign all-0s and all-1s host addresses because IPv6 traffic does not use broadcast addresses. The all-0s address is reserved for Subnet-Router anycast.

• Link-local Address (LLA) enables devices to communicate on the same link (subnet).

• GUA is not required when using LLA; still, every IPv6 network interface requires an LLA to function.

• An LLA automatically creates an IPv6 LLA without contacting a DHCP server, even without a global unicast IPv6 address.

• The IPv6 LLA devices will communicate on the same subnet, including with the default gateway (router).

• IPv6 LLAs range from fe80::/10 (1111 1110 10xx xxxx), giving the first hextet range of from fe80 to febf.

• It is typically the LLA of the router, instead of the GUA, that other devices on the link use as the default gateway.

• Two ways exist for a device to obtain an LLA: statically (manually configured) or dynamically (creates its own interface ID using methods such as random generation).

GUA and LLA Static Configuration

• IPv6 GUAs are public IPv4 addresses, globally routable on the IPv6 internet.
• IPv6 LLAs: 2 IPv6-enabled devices communicate on the same link (subnet).
• The command to configure an IPv6 GUA on a Cisco interface is ipv6 address ipv6-address/prefix-length.

IPv6 GUA Automatic Configuration

• Two ways exist for a device to get an IPv6 GUA automatically and dynamically: Stateless Address Autoconfiguration (SLAAC) and Stateful DHCPv6.

LLA Static Configuration

• Manual LLA configuration creates rememberable addresses.

• It is necessary to create recognizable LLAs on routers because gateway and routing advertisement messages use router LLAs.

• LLAs configured manually via ipv6 address ipv6-link-local-address link-local, the link-local parameter must follow if address starts with the fe80 to febf hextet.

• Statically configured LLAs allow easier router R1 identification.

• For instance, router R1 interfaces have LLAs starting with fe80::n:1.

Dynamic Addressing for IPv6 GUAs

• Devices obtain their GUA using Internet Control Message Protocol version 6 (ICMPv6) messages.
• IPv6 routers send ICMPv6 RA messages every 200 seconds to all IPv6-enabled network devices.
• An RA message is initiated upon receiving a host’s ICMPv6 RS message.
• The ICMPv6 RA message needs IPv6 routing to be enabled on the router.
• To enable the router as such, use the command ipv6 unicast-routing.
• ICMPv6 RA message dictates devices on how to obtain an IPv6 GUA; decision reliant the device operating system.
• The ICMPv6 RA message includes: network prefix, prefix length, default gateway, DNS addresses, and domain name.

RA message methods

• SLAAC provides needed components like prefix, prefix length, and default gateway address.
• SLAAC with a stateless DHCPv6 server specifies needing other components, such as DNS addresses, from the stateless server.
• Stateful DHCPv6 gives a default gateway address, requiring a stateful DHCPv6 server.
• SLAAC grants devices to create GUAs without DHCPv6, by using ICMPv6 RA messages from local routers.
• RA gives devices information via creating their own IPv6 GUAs and information.
• SLAAC is stateless, as there is no central DHCPv6 server.
• SLAAC uses RAs to create the GUA (prefix) and its Interface ID (EUI-64 or 64-bit number), depending on device O/S.

SLAAC and Stateless DHCPv6

• Enables router interfaces to send RAs by using SLAAC and stateless DHCPv6.
• Method requires the following: SLAAC, router LLA, IPv6 address, and other addresses from a stateless IPv6 DHCP server.

Stateful DHCPv6

• A router interface is configured by sending an RA by only using stateful DHCPv6.
• Stateful DHCPv6 is similar to IPv4; the device can automatically receive its addressing information.
• Method requires the router LLA and a stateful DHCPv6 server.
• A stateful DHCPv6 server allocates lists devices.
• DHCP for IPv4 is also stateful, and only obtained using RA message with default gateways.
• The stateless/stateful DHCPv6 server, however, does not provide default gateways.

EUI-64

• EUI-64 relies on the RA’s SLAAC message, and clients generate an interface ID (prefix from RA message).
• Interface ID gets created from the EUI-64 process by using the random 64-bit number.

EUI-64 Process

• The Institute of Electrical and Electronics Engineers (IEEE) provides the process for EUI. This process uses a client's 48-bit Ethernet MAC address by inserting an additional 16 bits.

• Ethernet MAC addresses comprise Organizationally Unique Identifier (OUI) and Device Identifier.

• EUI-64 is made of a 24-bit OUI, 16-bit value "fffe" and the other "Device Identifier", U/L also reversed.

• The easy ID of 1-64 is that "fffe" is located in the middle interface.

• EUI tracks IPv6 with MAC, so administrators can track.

• Privacy concerns caused users' worries that packets could expose them to real computers.

• With random GUAs, devices use random interfaces rather than MAC addresses and OSs like Windows.

Dynamic Addressing for IPv6 LLAs

• All IPv6 requires LLAs like GUAs, and the LLAs' configurations must verify.
• Windows dynamically creates LLAs with the interface ID on the EUI-64 process, or by the 64-bit number.

Dynamic LLAs on Cisco Routers

• Cisco routers automatically create an IPv6 LLA by assigning a GUA to the interface.
• By default, routers use EUI for the IPv6, with serial interface.
• A drawback is ID, which challenges address identification that needs configuration which enables EUI.

Verification

• The command show ipv6 interface brief displays the IPv6 and interface with the correct generated interface ID.

• Additionally, abbreviated output for each of the interfaces that indicates the 1/2 state, similar to IPv4.

• Interfaces come with two IPv6: GUA and LLA, created with GUA assigned, with the LLAs being Serial 0,1/0.

• The command show ipv6 route can confirm specific IPv6 traffic and IPv6 interface addresses in the IPv6 table.

• A "C" next to the route indicates that this is directly accessible, and when a local GU and "up/up" is, the IPvD gets put onto IPv6 as accessible.

• The "L" is the LLA, excluded with IPv6 because IPv6s, using 128 for efficiency with routers.

Pinging

• The ping command for IPv6s is similar to that for IPv4, where exit provides the ping for which one to use.
• Configuring uses verified the R1 through routers.

IPv6 Multicast Addresses

• ICMPv6 traffic uses a solo number and destination.
• IPv6s also use "ff00::/8" as the prefix to exclude addresses, but multicast destinations can be sent to the address instead.
• "Well known multipoint" is commonly used to refer also to "solicited".
• Well-known devices give you 1 for all nodes and 2 for all numbers; for example, running common processes.

Subnets

• A solo traffic is also used to connect.
• Benefit is for those that do, and no conversions require the hex.
• For example, using the prefix /48 generates the bit, and those are the organizations.
• With 64 available, the task becomes the administrator.
• Numbers range with a serial 2 traffic.
• This is unlike the prefixes for LANs.