IntroductionThis document describes how the IPv6 Link-Local address works within a network. Show
PrerequisitesRequirementsCisco recommends that you have knowledge of these topics:
Components UsedThe information in this document is based on the Cisco 3700 series router with Cisco IOS® Software Release 12.4 (15)T1. The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, ensure that you understand the potential impact of any command. ConventionsRefer to Cisco Technical Tips Conventions for more information on document conventions. Background InformationA link-local address is an IPv6 unicast address that can be automatically configured on any interface that uses the link-local prefix FE80::/10 (1111 1110 10) and the interface identifier in the modified EUI-64 format. Link-local addresses are not necessarily bound to the MAC address (configured in a EUI-64 format). Link-local addresses can also be manually configured in the FE80::/10 format with the ipv6 address link-local command. These addresses refer only to a particular physical link and are used for addresses on a single link for purposes such as automatic address configuration and neighbor discovery protocol. Link-local addresses can be used to reach the neighboring nodes attached to the same link. The nodes do not need a globally unique address to communicate. Routers do not forward datagram with link-local addresses. IPv6 routers must not forward packets that have link-local source or destination addresses to other links. All IPv6 enabled interfaces have a link-local unicast address. ConfigurationFor this example, the routers R1, R2 and R3 are connected via serial interface and have the IPv6 addresses configured as mentioned in the network diagram. Loopback addresses are configured on the routers R1 and R3, and the routers use OSPFv3 to communicate with each other. This example uses the ping command to demonstrate the connectivity between the routers with link-local addresses. The routers R1 and R3 can ping each other with the IPv6 local unicast address, but not with their link-local address. However, router R2 is directly connected to R1 and R3 hence it can communicate with both the routers with their link-local address, because link-local addresses are used only within that local network specific to the physical interface. Network DiagramThis document uses this network setup: Configurations UsedThis document uses these configurations:
This video demonstrates the key difference between the IPv6 Link-Local Address and global unicast address in Cisco IOS routers:
VerificationVerify OSPF ConfigurationTo verify the OSPF has been configured properly, use the
Verify Link-Local Address ReachabilityThe routers can ping each other with the global unicast address. If the routers use the link-local address only, the directly connected networks can communicate. For example, R1 can ping R3 with global unicast address but the two routers cannot communicate with link-local addresses. This is shown with the ping and debug ipv6 icmp commands in router R1 and R3. Ping Link-Local Address From Remote NetworkWhen the router R1 tries to communicate with router R3 with the link local address, the router R1 returns with an ICMP time-out message that indicates the link-local address is locally specific and cannot communicate to link-local addresses that are outside the directly connected network.
Ping Link-Local Address From Directly Connected NetworkFor router R2, the routers R1 and R3 are directly connected and can ping the link-local address of both router R1 and R2 when they communicate the related interface that is connected to the router. The output is shown here:
The link-local address is specific only to that local network. The routers can have the same link-local address and still the directly connected network can communicate with each other without any conflict. This is not the same in case of global unicast address. The global unicast address that are routable must be unique in a network. The show ipv6 interface brief command shows the information about link-local address on the interface.
In this example, R1 and R3 are assigned with the same link-local address and R2 can still reach both the routers when they specify the related output interface.
Note: The R2 can ping the link-local address of R1 and R3 only because they are directly connected. R2 cannot ping the link-local address of the loopback interfaces in routers R1 and R3 as they are not directly connected. Ping works on link-local addresses only in case of directly connected networks. Note: Traceroutes do not work in case of link-local addresses and return with the % No valid source address for destination error message. This is because IPv6 routers must not forward packets that have link-local source or destination addresses to other links. Related Information
Which type of address is required for a device to be IPv6 enabled?To be an IPv6-enabled device, a device must have an IPv6 link-local address. The device doesn't have to have an IPv6 global unicast address, but it must have a link-local address. Link-local addresses are not routable off the link (IPv6 subnet). Routers do not forward packets with a link-local address.
What does IPv6 uses to find devices in same LAN?IPv6 has two different methods for automatically configuring devices: stateful autoconfiguration using DHCPv6, and. stateless autoconfiguration, known as Neighbor Discovery Protocol (NDP).
What are the 3 options for a host to configure an IPv6 address?And, when it comes to IPv6, there are THREE ways to configure one IPv6 global address: Static configuration. Use of Dynamic Host Configuration Protocol (DHCP) in the stateful version which can lease IPv6 addresses to IPv6 nodes.
Which protocols are used in IPv6?IP v6 was developed by Internet Engineering Task Force (IETF) to deal with the problem of IP v4 exhaustion. IP v6 is a 128-bits address having an address space of 2^128, which is way bigger than IPv4. In IPv6 we use Colon-Hexa representation.
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