Dynamic Addressing for IPv6 LLAs
Dynamic Addressing for IPv6 LLAs

Dynamic Addressing for IPv6 LLAs

Dynamic Addressing for IPv6 LLAs

Summary

This topic configure link-local addresses dynamically. Start learning CCNA 200-301 for free right now!!

Note: Welcome: This topic is part of Chapter 12 of the Cisco CCNA 1 course, for a better follow up of the course you can go to the CCNA 1 section to guide you through an order.

Dynamic LLAs

All IPv6 devices must have an IPv6 LLA. Like IPv6 GUAs, you can also create LLAs dynamically. Regardless of how you create your LLAs (and your GUAs), it is important that you verify all IPv6 address configuration. This topic explains dynamically generated LLAs and IPv6 configuration verification.

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

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. See the highlighted areas in the following examples that were shown previously.

EUI-64 Generated Interface ID

C:\> ipconfig
Windows IP Configuration
Ethernet adapter Local Area Connection:
Connection-specific DNS Suffix . :
IPv6 Address. . . . . . . . . . . : 2001:db8:acad:1:fc99:47ff:fe75:cee0
Link-local IPv6 Address . . . . . : fe80::fc99:47ff:fe75:cee0
Default Gateway . . . . . . . . . : fe80::1
C:\>

Random 64-bit Generated Interface ID

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:\>

Dynamic LLAs on Cisco Routers

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. For serial interfaces, the router will use the MAC address of an Ethernet interface. Recall that an LLA must be unique only on that link or network. However, a drawback to using the dynamically assigned LLA is its long interface ID, which makes it challenging to identify and remember assigned addresses. The example displays the MAC address on the GigabitEthernet 0/0/0 interface of router R1. This address is used to dynamically create the LLA on the same interface, and also for the Serial 0/1/0 interface.

To make it easier to recognize and remember these addresses on routers, it is common to statically configure IPv6 LLAs on routers.

IPv6 LLA Using EUI-64 on Router 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

The figure shows the example topology.

Verify IPv6 Address Configuration
Verify IPv6 Address Configuration

Click each button for the output and a description of the command.

The show ipv6 interface brief command displays the MAC address of the Ethernet interfaces. EUI-64 uses this MAC address to generate the interface ID for the LLA. Additionally, the show ipv6 interface brief command displays abbreviated output for each of the interfaces. The [up/up] output on the same line as the interface indicates the Layer 1/Layer 2 interface state. This is the same as the Status and Protocol columns in the equivalent IPv4 command.

Notice that each interface has two IPv6 addresses. The second address for each interface is the GUA that was configured. The first address, the one that begins with fe80, is the link-local unicast address for the interface. Recall that the LLA is automatically added to the interface when a GUA is assigned.

Also, notice that the R1 Serial 0/1/0 LLA is the same as its GigabitEthernet 0/0/0 interface. Serial interfaces do not have Ethernet MAC addresses, so Cisco IOS uses the MAC address of the first available Ethernet interface. This is possible because link-local interfaces only have to be unique on that link.

The show ipv6 interface brief Command on R1

R1# show ipv6 interface brief
GigabitEthernet0/0/0 [up/up]
FE80::1:1
2001:DB8:ACAD:1::1
GigabitEthernet0/0/1 [up/up]
FE80::1:2
2001:DB8:ACAD:2::1
Serial0/1/0 [up/up]
FE80::1:3
2001:DB8:ACAD:3::1
Serial0/1/1 [down/down]
unassigned
R1#

As shown in the example, the show ipv6 route command can be used to verify that IPv6 networks and specific IPv6 interface addresses have been installed in the IPv6 routing table. The show ipv6 route command will only display IPv6 networks, not IPv4 networks.

Within the route table, a C next to a route indicates that this is a directly connected network. When the router interface is configured with a GUA and is in the “up/up” state, the IPv6 prefix and prefix length is added to the IPv6 routing table as a connected route.

Note: The L indicates a Local route, the specific IPv6 address assigned to the interface. This is not an LLA. LLAs are not included in the routing table of the router because they are not routable addresses.

The IPv6 GUA configured on the interface is also installed in the routing table as a local route. The local route has a /128 prefix. Local routes are used by the routing table to efficiently process packets with a destination address of the router interface address.

The show ipv6 route Command on R1

R1# show ipv6 route
IPv6 Routing Table - default - 7 entries
Codes: C - Connected, L - Local, S - Static, U - Per-user Static route

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 for IPv6 is identical to the command used with IPv4, except that an IPv6 address is used. As shown in the example, the command is used to verify Layer 3 connectivity between R1 and PC1. When pinging an LLA from a router, Cisco IOS will prompt the user for the exit interface. Because the destination LLA can be on one or more of its links or networks, the router needs to know which interface to send the ping to.

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#

Packet Tracer – Configure IPv6 Addressing

In this activity, you will practice configuring IPv6 addresses on a router, servers, and clients. You will also practice verifying your IPv6 addressing implementation.

Glossary: If you have doubts about any special term, you can consult this computer network dictionary.

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