Access to most tools on the Cisco Support and Documentation website requires a Cisco. The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train.
Unless noted otherwise, subsequent releases of that software release train also support that feature. The following commands were introduced or modified: ipv6 address , ipv6 address anycast , ipv6 address eui , ipv6 address link-local , ipv6 enable , ipv6 unicast-routing. To view a list of Cisco trademarks, go to this URL: www. Third-party trademarks mentioned are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company.
Any Internet Protocol IP addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers.
Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental. Skip to content Skip to footer.
Book Contents Book Contents. Find Matches in This Book. PDF - Complete Book 1. Updated: July 19, Chapter: IPv6 Unicast Routing. A value of 0 indicates a locally administered identifier; a value of 1 indicates a globally unique IPv6 interface identifier. For other interface types for example, ATM, Frame Relay, loopback, serial, and tunnel interface types except tunnel interfaces used with IPv6 overlay tunnels , the interface ID is constructed in the same way as the interface ID for IEEE interface types; however, the first MAC address from the pool of MAC addresses in the device is used to construct the identifier because the interface does not have a MAC address.
For tunnel interface types that are used with IPv6 overlay tunnels, the interface ID is the IPv4 address assigned to the tunnel interface with all zeros in the high-order 32 bits of the identifier. Note For interfaces using point-to-point protocol PPP , given that the interfaces at both ends of the connection might have the same MAC address, the interface identifiers used at both ends of the connection are negotiated picked randomly and, if necessary, reconstructed until both identifiers are unique.
If no MAC addresses are available in the device, the serial number of the device is used to form the link-local addresses. If the serial number of the device cannot be used to form the link-local addresses, the device uses a message digest algorithm 5 MD5 hash to determine the MAC address of the device from the hostname of the device. A unique local address has the following characteristics: It has a globally unique prefix that is, it has a high probability of uniqueness. It has a well-known prefix to allow for easy filtering at site boundaries.
It allows sites to be combined or privately interconnected without creating any address conflicts or requiring renumbering of interfaces that use these prefixes. It is ISP-independent and can be used for communications inside of a site without having any permanent or intermittent Internet connectivity. If it is accidentally leaked outside of a site via routing or DNS, there is no conflict with any other addresses.
Applications may treat unique local addresses like global scoped addresses. The figure below shows the structure of a unique local address. Enter your password if prompted. Specifying the ipv6 address eui command configures global IPv6 addresses with an interface identifier ID in the low-order 64 bits of the IPv6 address. Only the bit network prefix for the address needs to be specified; the last 64 bits are automatically computed from the interface ID.
Specifying the ipv6 address link-local command configures a link-local address on the interface that is used instead of the link-local address that is automatically configured when IPv6 is enabled on the interface. Specifying the ipv6 address anycast command adds an IPv6 anycast address. All rights reserved. Was this Document Helpful?
Yes No Feedback. Related Cisco Community Discussions. For interfaces using point-to-point protocol PPP , given that the interfaces at both ends of the connection might have the same MAC address, the interface identifiers used at both ends of the connection are negotiated picked randomly and, if necessary, reconstructed until both identifiers are unique.
Enables privileged EXEC mode. Specifies an interface type and number, and places the device in interface configuration mode. Exits interface configuration mode, and returns the device to global configuration mode. IPv6 addressing and connectivity. IPv6 Configuration Guide.
IPv4 addressing. You may proceed to assign an EUI address to the interface and verify if the interface ID calculated by the router matches the one you calculated. We will show you shortly how to assign EUI addresses to router interfaces.
The example shows EUI address being assigned to a serial interface as well. Now, we know that serial interfaces do not have MAC addresses but the serial interface not only accepted the EUI configuration but also got an EUI address assigned. IPv6 addresses configured statically are the more natural choice for router interfaces. However, routers can also be configured to use dynamically learned IPv6 addresses. Cisco routers can dynamically learn IPv6 addresses using:.
Both of these methods use the usual ipv6 address command with the appropriate keyword, though none of these two methods configures the actual IPv6 address. IPv6 link-local addresses are a special kind of unicast addresses. These addresses are not used for regular user traffic flows. These addresses are rather used by other protocols as well as for routing. Each IPv6 host including routers uses an additional unicast address called a link-local address. The most important fact to remember about link-local addresses is that routers do not forward packets that have a link-local address as its destination address.
Many IPv6 protocols function between directly connected routers and need to send messages on a single subnet only. IPv6 routers also use link-local addresses as the next-hop address in IPv6 routes. IPv6 hosts have the concept of a default gateway router similar to IPv4, but hosts refer to the link-local address of the gateway instead of the router address in the same subnet.
The show ipv6 route command lists the link-local address of the next hop router and not the global unicast or unique local unicast address. IPv6 hosts and routers can autonomously calculate their own link-local addresses, for each interface.
There are two parts of a link-local address: a prefix and the interface ID. As a result, a link-local address should always start with FE that covers the first 64 bits of the address. The second half of a link-local address, can be formed with different rules depending on the platform. Host operating systems have their own way of generating interface IDs.
For example, Microsoft Windows variants use a random process to choose the interface ID and change it over time as well. The Cisco IOS Software automatically configures a link-local address for any interface that has at least one unicast address configured using the ipv6 address command. So, there is no configuration separately needed for link-local addresses. The usual show ipv6 interface and show ipv6 interface brief can be used to display link-local addresses as well.
Please note that the two mentioned interfaces are already configured with global unicast addresses. The router uses the EUI rules for automatic calculation of link-local addresses even if the interface unicast address does not use EUI You can also use the ipv6 address address link-local command in interface configuration mode to configure link-local addresses.
IPv6 has the concept of multicast addresses that are used for a variety of purposes. Overhead protocols often use multicast addresses to simultaneously send multicast packets to multiple IPv6 hosts. Application programs also use multicast addresses to send IPv6 packets to multiple hosts at a time saving bandwidth on intermediate network links.
IPv6 multicast addresses can have either a link-local scope or an organizational-local scope. The addresses with link-local scope imply that a packet sent to that address should be confined to the local link. The addresses with organization-local scope can be routed to other subnets inside the organization. The following table lists some of the most commonly used IPv6 multicast addresses with link-local scope.
The output of show ipv6 interface command lists the multicast addresses used by the router on the interface. We will briefly discuss solicited-node multicast addresses to round off the coverage of IPv6 addressing in this chapter. These addresses provide a destination address so that one packet can be sent in an IPv6 subnet with link-local scope to all hosts whose unicast addresses have the same value in the last six hexadecimal digits.
In other words, the solicited-node multicast address for a particular host is a multicast address with link-local scope based on only the last six hex digits of the unicast IPv6 address of the same host.
All host having the same value in the last six hex digits of their IPv6 unicast addresses, will have the same solicited-node multicast address. Each host must listen for IPv6 packets sent to its solicited-node multicast address. The last two multicast addresses highlighted below are solicited-node multicast addresses! All routers in a network must learn routes to all subnets in the network to make sure a host in one part of the network can reach hosts in all other parts of the network.