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Notes

reference notes

IPv4 Issues

Need for IPv6

IPv6 is designed to be the successor to IPv4. IPv6 has a larger 128-bit address space, providing 340 undecillion (i.e., 340 followed by 36 zeroes) possible addresses. However, IPv6 is more than just larger addresses.

world become more connected to the internet, there are not enough IPv4 addresses to accommodate this growth.

Private addresses in combination with Network Address Translation (NAT) have been instrumental in slowing the depletion of IPv4 address space. However, NAT is problematic for many applications, creates latency, and has limitations that severely impede peer-to-peer communications.

With an increasing internet population, a limited IPv4 address space, issues with NAT and the IoT, the time has come to begin the transition to IPv6.

IPv4 and IPv6 Coexistence

There is no specific date to move to IPv6. Both IPv4 and IPv6 will coexist in the near future and the transition will take several years. The IETF has created various protocols and tools to help network administrators migrate their networks to IPv6.

The migration techniques can be divided into three categories:

  1. Dual stack allows IPv4 and IPv6 to coexist on the same network segment. Dual stack devices run both IPv4 and IPv6 protocol stacks simultaneously.
  2. Tunneling is a method of transporting an IPv6 packet over an IPv4 network. The IPv6 packet is encapsulated inside an IPv4 packet, similar to other types of data.
  3. Network Address Translation 64 (NAT64) allows IPv6-enabled devices to communicate with IPv4-enabled devices using a translation technique similar to NAT for IPv4. An IPv6 packet is translated to an IPv4 packet and an IPv4 packet is translated to an IPv6 packet.

Note: Tunneling and translation are for transitioning to native IPv6 and should only be used where needed. The goal should be native IPv6 communications from source to destination.

IPv6 Address Representation

IPv6 Addressing Formats

IPv6 addresses are 128 bits in length and written as a string of hexadecimal values.

Every four bits is represented by a single hexadecimal digit; for a total of 32 hexadecimal values, as shown in the figure.

IPv6 addresses are not case-sensitive and can be written in either lowercase or uppercase.

ip

Preferred Format: The previous figure also shows that the preferred format for writing an IPv6 address is x:x:x:x:x:x:x:x, with each “x” consisting of four hexadecimal values. The term octet refers to the eight bits of an IPv4 address. In IPv6, a hextet is the unofficial term used to refer to a segment of 16 bits, or four hexadecimal values. Each “x” is a single hextet which is 16 bits or four hexadecimal digits.

Preferred format means that you write IPv6 address using all 32 hexadecimal digits. It does not necessarily mean that it is the ideal method for representing the IPv6 address. In this module, you will see two rules that help to reduce the number of digits needed to represent an IPv6 address.

These are examples of IPv6 addresses in the preferred format.

2001 : 0db8 : 0000 : 1111 : 0000 : 0000 : 0000: 0200 
2001 : 0db8 : 0000 : 00a3 : abcd : 0000 : 0000: 1234 
2001 : 0db8 : 000a : 0001 : c012 : 9aff : fe9a: 19ac 
2001 : 0db8 : aaaa : 0001 : 0000 : 0000 : 0000: 0000 
fe80 : 0000 : 0000 : 0000 : 0123 : 4567 : 89ab: cdef 
fe80 : 0000 : 0000 : 0000 : 0000 : 0000 : 0000: 0001 
fe80 : 0000 : 0000 : 0000 : c012 : 9aff : fe9a: 19ac 
fe80 : 0000 : 0000 : 0000 : 0123 : 4567 : 89ab: cdef 
0000 : 0000 : 0000 : 0000 : 0000 : 0000 : 0000: 0001 
0000 : 0000 : 0000 : 0000 : 0000 : 0000 : 0000: 0000

Rule 1 – Omit Leading Zeros

The first rule to help reduce the notation of IPv6 addresses is to omit any leading 0s (zeros) in any hextet. Here are four examples of ways to omit leading zeros:

This rule only applies to leading 0s, NOT to trailing 0s, otherwise the address would be ambiguous. For example, the hextet “abc” could be either “0abc” or “abc0”, but these do not represent the same value.

Rule 2- Double Colon

The second rule to help reduce the notation of IPv6 addresses is that a double colon (::) can replace any single, contiguous string of one or more 16-bit hextets consisting of all zeros. For example, 2001:db8:cafe:1:0:0:0:1 (leading 0s omitted) could be represented as 2001:db8:cafe:1::1. The double colon (::) is used in place of the three all-0 hextets (0:0:0).

The double colon (::) can only be used once within an address, otherwise there would be more than one possible resulting address. When used with the omitting leading 0s technique, the notation of IPv6 address can often be greatly reduced. This is commonly known as the compressed format.

Here is an example of the incorrect use of the double colon: 2001:db8::abcd::1234.

The double colon is used twice in the example above. Here are the possible expansions of this incorrect compressed format address:

If an address has more than one contiguous string of all-0 hextets, best practice is to use the double colon (::) on the longest string. If the strings are equal, the first string should use the double colon (::).

IPv6 Address Types

Unicast, Multicast, Anycast

As with IPv4, there are different types of IPv6 addresses. In fact, there are three broad categories of IPv6 addresses:

Unlike IPv4, IPv6 does not have a broadcast address. However, there is an IPv6 all-nodes multicast address that essentially gives the same result.

IPv6 Prefix Length

The prefix, or network portion, of an IPv4 address can be identified by a dotted-decimal subnet mask or prefix length (slash notation). For example, an IPv4 address of 192.168.1.10 with dotted-decimal subnet mask 255.255.255.0 is equivalent to 192.168.1.10/24.

In IPv6 it is only called the prefix length. IPv6 does not use the dotted-decimal subnet mask notation. Like IPv4, the prefix length is represented in slash notation and is used to indicate the network portion of an IPv6 address.

The prefix length can range from 0 to 128. The recommended IPv6 prefix length for LANs and most other types of networks is /64, as shown in the figure.

The graphic shows an IPv6 address divided into a 64-bit prefix and a 64-bit interface ID. The 64-bit prefix is 2001:0db8:000a:0000. The 64-bit interface ID is 0000:0000:0000:0000.

IPv6 Prefix Length:

PrefixInterface ID0000:0000:0000:00002001:0db8:000a:000064 bits64 bitsExample: 2001:db8:a::/64 The prefix or network portion of the address is 64 bits in length, leaving another 64 bits for the interface ID (host portion) of the address.

It is strongly recommended to use a 64-bit Interface ID for most networks. This is because stateless address autoconfiguration (SLAAC) uses 64 bits for the Interface ID. It also makes subnetting easier to create and manage.

Types of IPv6 Unicast Addresses

An IPv6 unicast address uniquely identifies an interface on an IPv6-enabled device.

A packet sent to a unicast address is received by the interface which is assigned that address.

Similar to IPv4, a source IPv6 address must be a unicast address. The destination IPv6 address can be either a unicast or a multicast address.

the types of Ipv6 addresses are:

Unlike IPv4 devices that have only a single address, IPv6 addresses typically have two unicast addresses:

A Note About the Unique Local Address

Unique local addresses (range fc00::/7 to fdff::/7) are not yet commonly implemented. Therefore, this module only covers GUA and LLA configuration. However, unique local addresses may eventually be used to address devices that should not be accessible from the outside, such as internal servers and printers.

The IPv6 unique local addresses have some similarity to RFC 1918 private addresses for IPv4, but there are significant differences:

Note: Many sites also use the private nature of RFC 1918 addresses to attempt to secure or hide their network from potential security risks. However, this was never the intended use of these technologies, and the IETF has always recommended that sites take the proper security precautions on their internet-facing router.

IPv6 GUA

IPv6 global unicast addresses (GUAs) are globally unique and routable on the IPv6 internet. These addresses are equivalent to public IPv4 addresses

The figure shows the range of values for the first hextet where the first hexadecimal digit for currently available GUAs begins with a 2 or a 3. This is only 1/8th of the total available IPv6 address space, excluding only a very small portion for other types of unicast and multicast addresses.

ip

IPv6 Address with a /48 Global Routing Prefix and /64 Prefix:

ip

IPv6 GUA Structure

Global Routing Prefix

The global routing prefix is the prefix, or network, portion of the address that is assigned by the provider, such as an ISP, to a customer or site.

The previous figure shows a GUA using a /48 global routing prefix. /48 prefixes are a common global routing prefix that is assigned and will be used in most of the examples throughout this course.

For example, the IPv6 address 2001:db8:acad::/48 has a global routing prefix that indicates that the first 48 bits (3 hextets) (2001:db8:acad) is how the ISP knows of this prefix (network). The double colon (::) following the /48 prefix length means the rest of the address contains all 0s. The size of the global routing prefix determines the size of the subnet ID.

Subnet ID

The Subnet ID field is the area between the Global Routing Prefix and the Interface ID.

Unlike IPv4 where you must borrow bits from the host portion to create subnets, IPv6 was designed with subnetting in mind. The Subnet ID is used by an organization to identify subnets within its site. The larger the subnet ID, the more subnets available.

Note: Many organizations are receiving a /32 global routing prefix. Using the recommended /64 prefix in order to create a 64-bit Interface ID, leaves a 32 bit Subnet ID. This means an organization with a /32 global routing prefix and a 32-bit Subnet ID will have 4.3 billion subnets, each with 18 quintillion devices per subnet. That is as many subnets as there are public IPv4 addresses!

The IPv6 address in the previous figure has a /48 Global Routing Prefix, which is common among many enterprise networks. This makes it especially easy to examine the different parts of the address. Using a typical /64 prefix length, the first 3 hextets are for the network portion of the address, with the fourth hextet indicating the Subnet ID. The remaining four hextets are for the Interface ID.

Interface ID

The IPv6 interface ID is equivalent to the host portion of an IPv4 address. The term Interface ID is used because a single host may have multiple interfaces, each having one or more IPv6 addresses. The figure shows an example of the structure of an IPv6 GUA. It is strongly recommended that in most cases /64 subnets should be used, which creates a 64-bit interface ID. A 64-bit interface ID allows for 18 quintillion devices or hosts per subnet.

A /64 subnet or prefix (Global Routing Prefix + Subnet ID) leaves 64 bits for the interface ID. This is recommended to allow SLAAC-enabled devices to create their own 64-bit interface ID. It also makes developing an IPv6 addressing plan simple and effective.

Note: Unlike IPv4, in IPv6, the all-0s and all-1s host addresses can be assigned to a device. The all-1s address can be used because broadcast addresses are not used within IPv6. The all-0s address can also be used, but is reserved as a Subnet-Router anycast address, and should be assigned only to routers.

IPv6 LLA

An IPv6 link-local address (LLA) enables a device to communicate with other IPv6-enabled devices on the same link and only on that link (subnet). Packets with a source or destination LLA cannot be routed beyond the link from which the packet originated.

The GUA is not a requirement. However, every IPv6-enabled network interface must have an LLA.

If an LLA is not configured manually on an interface, the device will automatically create its own without communicating with a DHCP server. IPv6-enabled hosts create an IPv6 LLA even if the device has not been assigned a global unicast IPv6 address. This allows IPv6-enabled devices to communicate with other IPv6-enabled devices on the same subnet. This includes communication with the default gateway (router).

IPv6 LLAs are in the fe80::/10 range. The /10 indicates that the first 10 bits are 1111 1110 10xx xxxx. The first hextet has a range of 1111 1110 1000 0000 (fe80) to 1111 1110 1011 1111 (febf).

The figure shows an example of communication using IPv6 LLAs. The PC is able to communicate directly with the printer using the LLAs.

There are two ways that a device can obtain an LLA:

GUA and LLA Static Configuration

Static GUA Configuration on a Router

the command to configure an IPv6 GUA on an interface is ipv6 address ipv6-address/prefix-length

The example configuration uses the topology shown in the figure and these IPv6 subnets:

2001:db8:acad:1::/64 2001:db8:acad:2::/64 2001:db8:acad:3::/64

The graphic shows two PCs, PC1 and PC2. PC1 is connected to a switch and has the IPv6 address 2001:db8:acad:1::10/64. PC2 is connected to a switch and has the IPv6 address 2001:db8:acad:2::10/64. The two switches are connected to a router, R1. PC1 is connected through the switch to R1s G0/0/0 interface which has IPv6 address 2001:db8:acad:1::1/64. PC2 is connected through the switch to R1s G0/0/1 interface which has IPv6 address 2001:db8:acad:2::1/64. R1 connects to the cloud through its S0/1/0 interface which has IPv6 address 2001:db8:acad:3::1/64.

Example Topology

Example Topology

IPv6 GUA Configuration on Router R1

R1(config)# interface gigabitethernet 0/0/0
R1(config-if)# ipv6 address 2001:db8:acad:1::1/64
R1(config-if)# no shutdown
R1(config-if)# exit
R1(config)# interface gigabitethernet 0/0/1
R1(config-if)# ipv6 address 2001:db8:acad:2::1/64
R1(config-if)# no shutdown
R1(config-if)# exit
R1(config)# interface serial 0/1/0
R1(config-if)# ipv6 address 2001:db8:acad:3::1/64
R1(config-if)# no shutdown

Static GUA Configuration on a Windows Host

Manually configuring the IPv6 address on a host is similar to configuring an IPv4 address.

Just as with IPv4, configuring static addresses on clients does not scale to larger environments. For this reason, most network administrators in an IPv6 network will enable dynamic assignment of IPv6 addresses.

There are two ways in which a device can obtain an IPv6 GUA automatically:

Note: When DHCPv6 or SLAAC is used, the LLA of the router will automatically be specified as the default gateway address.

LLAs can be configured manually using the ipv6 address ipv6-link-local-address link-local command. When an address begins with this hextet within the range of fe80 to febf, the link-local parameter must follow the address.

The figure shows an example topology with LLAs on each interface.

The graphic shows two PCs, PC1 and PC2. PC1 is connected to a switch and has the IPv6 address 2001:db8:acad:1::10/64. PC2 is connected to a switch and has the IPv6 address 2001:db8:acad:2::10/64. The two switches are connected to a router, R1. PC1 is connected through the switch to R1s G0/0/0 interface which has IPv6 address 2001:db8:acad:1::1/64 and the LLA address of fe80::1:1. PC2 is connected through the switch to R1s G0/0/1 interface which has IPv6 address 2001:db8:acad:2::1/64 and the LLA address of fe80::2:1. R1 connects to the cloud through its S0/1/0 interface which has IPv6 address 2001:db8:acad:3::1/64 and the LLA address of fe80::3:1.

Example Topology with LLAs

Example Topology with LLAs

IPv6 LLA Configuration on Router R1

R1(config)# interface gigabitethernet 0/0/0
R1(config-if)# ipv6 address fe80::1:1 link-local
R1(config-if)# exit
R1(config)# interface gigabitethernet 0/0/1
R1(config-if)# ipv6 address fe80::2:1 link-local
R1(config-if)# exit
R1(config)# interface serial 0/1/0
R1(config-if)# ipv6 address fe80::3:1 link-local
R1(config-if)# exit

Statically configured LLAs are used to make them more easily recognizable as belonging to router R1. In this example, all the interfaces of router R1 have been configured with an LLA that begins with fe80::n:1.

Note: The exact same LLA could be configured on each link as long as it is unique on that link. This is because LLAs only have to be unique on that link. However, common practice is to create a different LLA on each interface of the router to make it easy to identify the router and the specific interface.

Dynamic Addressing for IPv6 GUAs

RS and RA Messages

For the GUA, a device obtains the address dynamically through Internet Control Message Protocol version 6 (ICMPv6) messages.

IPv6 routers periodically send out ICMPv6 RA messages, every 200 seconds, to all IPv6-enabled devices on the network. An RA message will also be sent in response to a host sending an ICMPv6 RS message, which is a request for an RA message.

RA messages are on IPv6 router Ethernet interfaces. The router must be enabled for IPv6 routing, which is not enabled by default. To enable a router as an IPv6 router, the ipv6 unicast-routing global configuration command must be used.

The ICMPv6 RA message is a suggestion to a device on how to obtain an IPv6 GUA. The ultimate decision is up to the device operating system. The ICMPv6 RA message includes the following:

There are three methods for RA messages:

Method 1: SLAAC(Stateless Address Autoconfiguration)

SLAAC is a method that allows a device to create its own GUA without the services of DHCPv6.

Using SLAAC, devices rely on the ICMPv6 RA messages of the local router to obtain the necessary information.

By default, the RA message suggests that the receiving device use the information in the RA message to create its own IPv6 GUA and all other necessary information. The services of a DHCPv6 server are not required.

SLAAC is stateless, which means there is no central server (for example, a stateful DHCPv6 server) allocating GUAs and keeping a list of devices and their addresses. With SLAAC, the client device uses the information in the RA message to create its own GUA. As shown in the figure, the two parts of the address are created as follows:

SLAAC

Method 2: SLAAC and Stateless DHCPv6

A router interface can be configured to send a router advertisement using SLAAC and stateless DHCPv6.

As shown in the figure, with this method, the RA message suggests devices use the following:

Note: A stateless DHCPv6 server distributes DNS server addresses and domain names. It does not allocate GUAs.

SLAAC and Stateless DHCPv6

Method 3: Stateful DHCPv6

A router interface can be configured to send an RA using stateful DHCPv6 only.

Stateful DHCPv6 is similar to DHCP for IPv4. A device can automatically receive its addressing information including a GUA, prefix length, and the addresses of DNS servers from a stateful DHCPv6 server.

As shown in the figure, with this method, the RA message suggests devices use the following:

Stateful DHCPv6

A stateful DHCPv6 server allocates and maintains a list of which device receives which IPv6 address. DHCP for IPv4 is stateful.

Note: The default gateway address can only be obtained dynamically from the RA message. The stateless or stateful DHCPv6 server does not provide the default gateway address.

EUI-64 Process vs. Randomly Generated

EUI-64 Process

The IEEE defined the Extended Unique Identifier (EUI) or modified EUI-64 process which performs the following:​

A 16 bit value of fffe (in hexadecimal) is inserted into the middle of the 48-bit Ethernet MAC address of the client.​

The 7th bit of the client MAC address is reversed from binary 0 to 1.​

Example:

+-----------------+-----------------+
| 48-bit MAC Address | fc:99:47:75:ce:e0 |
+-----------------+-----------------+
| EUI-64 Interface ID | fe:99:47:ff:fe:75:ce:e0 |
+-----------------+-----------------+

Randomly Generated

Depending upon the operating system, a device may use a randomly generated interface ID instead of using the MAC address and the EUI-64 process.​

Beginning with Windows Vista, Windows uses a randomly generated interface ID instead of one created with EUI-64.

C:\> ipconfig
Windows IP Configuration
Ethernet adapter Local Area Connection:
   Connection-specific DNS Suffix  . :
   IPv6 Address. . . . . . . . . . . : 2001:db8:acad:1:50a5:8a35:a5bb:66e1
   Link-local IPv6 Address . . . . . : fe80::50a5:8a35:a5bb:66e1
   Default Gateway . . . . . . . . . : fe80::1
C:\>

Note: To ensure the uniqueness of any IPv6 unicast address, the client may use a process known as Duplicate Address Detection (DAD). This is similar to an ARP request for its own address. If there is no reply, then the address is unique.

Dynamic Addressing for IPv6 LLAs

Dynamic LLAs

All IPv6 interfaces must have an IPv6 LLA.​

Like IPv6 GUAs, LLAs can be configured dynamically.​

The figure shows the LLA is dynamically created using the fe80::/10 prefix and the interface ID using the EUI-64 process, or a randomly generated 64-bit number.

Dynamic LLAs

Dynamic LLAs on Windows

Operating systems, such as Windows, will typically use the same method for both a SLAAC-created GUA and a dynamically assigned LLA.​

Cisco routers automatically create an IPv6 LLA whenever a GUA is assigned to the interface. By default, Cisco IOS routers use EUI-64 to generate the interface ID for all LLAs on IPv6 interfaces.​

Here is an example of a LLA dynamically configured on the G0/0/0 interface of R1:​

R1# show interface gigabitEthernet 0/0/0
GigabitEthernet0/0/0 is up, line protocol is up
  Hardware is ISR4221-2x1GE, address is 7079.b392.3640 (bia 7079.b392.3640)
(Output omitted)
R1# show ipv6 interface brief
GigabitEthernet0/0/0   [up/up]
    FE80::7279:B3FF:FE92:3640
    2001:DB8:ACAD:1::1
GigabitEthernet0/0/1   [up/up]
    FE80::7279:B3FF:FE92:3641
    2001:DB8:ACAD:2::1
Serial0/1/0            [up/up]
    FE80::7279:B3FF:FE92:3640
    2001:DB8:ACAD:3::1
Serial0/1/1            [down/down]
    unassigned
R1#

Verify IPv6 Address Configuration

C 2001:DB8:ACAD:1::/64 [0/0] via GigabitEthernet0/0/0, directly connected L 2001:DB8:ACAD:1::1/128 [0/0] via GigabitEthernet0/0/0, receive C 2001:DB8:ACAD:2::/64 [0/0] via GigabitEthernet0/0/1, directly connected L 2001:DB8:ACAD:2::1/128 [0/0] via GigabitEthernet0/0/1, receive C 2001:DB8:ACAD:3::/64 [0/0] via Serial0/1/0, directly connected L 2001:DB8:ACAD:3::1/128 [0/0] via Serial0/1/0, receive L FF00::/8 [0/0] via Null0, receive R1#


- The ping Command on R1

R1# ping 2001:db8:acad:1::10 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 2001:DB8:ACAD:1::10, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/1 ms R1#


# IPv6 Multicast Addresses

### Assigned IPv6 Multicast Addresses

IPv6 multicast addresses have the prefix ff00::/8.
Note: Multicast addresses can only be destination addresses and not source addresses.

There are two types of IPv6 multicast addresses:
- Well-known multicast addresses
- Solicited node multicast addresses

### Well-Known IPv6 Multicast Addresses

Well-known IPv6 multicast addresses are assigned. Assigned multicast addresses are reserved multicast addresses for predefined groups of devices.

An assigned multicast address is a single address used to reach a group of devices running a common protocol or service.

There are two common IPv6 Assigned multicast groups:​
- ff02::1 All-nodes multicast group - This is a multicast group that all IPv6-enabled devices join. A packet sent to this group is received and processed by all IPv6 interfaces on the link or network. ​
- ff02::2 All-routers multicast group - This is a multicast group that all IPv6 routers join. A router becomes a member of this group when it is enabled as an IPv6 router with the `ipv6 unicast-routing` global configuration command.

### Solicited-Node IPv6 Multicast Addresses

The advantage of a solicited-node multicast address is that it is mapped to a special Ethernet multicast address.

This allows the Ethernet NIC to filter the frame by examining the destination MAC address without sending it to the IPv6 process to see if the device is the intended target of the IPv6 packet.

# Subnet an IPv6 Network

### Subnet Using the Subnet ID

IPv6 was designed with subnetting in mind. ​
- A separate subnet ID field in the IPv6 GUA is used to create subnets. ​
- The subnet ID field is the area between the Global Routing Prefix and the interface ID.

### IPv6 Subnetting Example

Given the 2001:db8:acad::/48 global routing prefix with a 16 bit subnet ID.​
- Allows 65,536 /64 subnets​
- The global routing prefix is the same for all subnets.​
- Only the subnet ID hextet is incremented in hexadecimal for each subnet.

![IPv6 Subnetting Example](/imgs/ipv610.png)

### IPv6 Subnet Allocation

As shown in the figure, the example topology requires five subnets, one for each LAN as well as for the serial link between R1 and R2. Unlike the example for IPv4, with IPv6 the serial link subnet will have the same prefix length as the LANs. Although this may seem to “waste” addresses, address conservation is not a concern when using IPv6.

![IPv6 Subnet Allocation](/imgs/ipv611.png)

As shown in the next figure, the five IPv6 subnets were allocated, with the subnet ID field 0001 through 0005 used for this example. Each /64 subnet will provide more addresses than will ever be needed.

![IPv6 Subnet Allocation](/imgs/ipv612.png)

### Router Configured with IPv6 Subnets

R1(config)# interface gigabitethernet 0/0/0 R1(config-if)# ipv6 address 2001:db8:acad:1::1/64 R1(config-if)# no shutdown R1(config-if)# exit R1(config)# interface gigabitethernet 0/0/1 R1(config-if)# ipv6 address 2001:db8:acad:2::1/64 R1(config-if)# no shutdown R1(config-if)# exit R1(config)# interface serial 0/1/0 R1(config-if)# ipv6 address 2001:db8:acad:3::1/64 R1(config-if)# no shutdown ```