![]() This use is common in most IEEE 802 networking technologies, including Ethernet, Wi-Fi, and Bluetooth. Label of a UMTS router with MAC addresses for LAN and WLAN modulesĪ MAC address (short for medium access control address) is a unique identifier assigned to a network interface controller (NIC) for use as a network address in communications within a network segment. In short, a Link Local Address can only be used for local network communication, while a Global Unicast address can be used anywhere on the IPv6 Internet (to include the local network).Not to be confused with Mac Address (YouTube channel). To do that, it must use another type of address: Global Unicast address. Your router (using its Link Local Address) can speak to other machines on the same network (using their LLA), but it can't use its LLA address to speak across/beyond another router. Hence, when you enabled IPv6 on fe0/0 (by configuring an IPv6 address), your router automatically generated the (required) Link Local Address.Ī Link Local Address is only valid on a particular link. IANA has reserved FE80::/10 for this very purposes - this network exists on EACH IPv6 link, all over the world, but is not allowed to be routed. Per IPv6 protocol, each interface MUST have a locally scoped IPv6 address (called a Link Local Address, or LLA). This command sets the address of the interface to 2001:db8::/64, the parameter "eui-64" at the end of this command tells the router to generate the last 64 bits using EUI-64.Īs to your other questions. Router(config-if)# do show ipv6 interface f0/0 ![]() Hardware is Gt96k FE, address is 0012.7feb.6b40 (bia 0012.7feb.6b40)Īfter assigning an EUI-64-designated IPv6 address to the interface, we can verify that the interface ID has been drawn from the MAC address in the process described for both the assigned and the link local address: First, take note of the interface's MAC address (this is typically the same as its burned-in address, or BIA).įastEthernet0/0 is up, line protocol is down We can see this conversion in action when we assign an IPv6 address to a router interface. Rather, the meaning of the bit is inverted for convenience, so the value of the bit must be inverted as well. The important part to remember here is that the scope of the address never changes: global addresses are still global and local addresses are still local. The alternative would have been for these to be of the form 0200:0:0:1, 0200:0:0:2, etc., instead of the much simpler ::1, ::2, etc. This is expected to be case for serial links, tunnel end-points, etc. The motivation for inverting the "u" bit when forming the interface identifier is to make it easy for system administrators to hand configure local scope identifiers when hardware tokens are not available. The answer lies buried in section 2.5.1 of RFC 2373: The U/L bit is inverted when using an EUI-64 address as an IPv6 interface ID.Īgain, you're probably wondering why this is done. ![]() Likewise, locally created addresses, such as those used for virtual interfaces or a MAC address manually configured by an administrator, will have this bit set to one. Globally unique addresses assigned by the IEEE originally have this bit set to zero, indicating global uniqueness. The second step is to invert the universal/local (U/L) flag (bit 7) in the OUI portion of the address. In other words, any EUI-64 address having 0xFFFE immediately following its OUI portion can be recognized as having been generated from an EUI-48 (or MAC) address. Why 0xFFFE? As explained in the IEEE's Guidelines for EUI-64 Registration Authority, this is a reserved value which equipment manufacturers cannot include in "real" EUI-64 address assignments. The 16-bit hex value 0xFFFE is then inserted between these two halves to form a 64-bit address. To do this, we break the MAC address into its two 24-bit halves: the Organizationally Unique Identifier (OUI) and the NIC specific part. The first step is to convert the 48-bit MAC address to a 64-bit value. RFC 2373 dictates the conversion process, which can be described as having two steps. This is accomplished on Ethernet interfaces by referencing the already unique 48-bit MAC address, and reformatting that value to match the EUI-64 specification. By implementing the IEEE's 64-bit Extended Unique Identifier (EUI-64) format, a host can automatically assign itself a unique 64-bit IPv6 interface identifier without the need for manual configuration or DHCP. One of IPv6's key benefits over IPv4 is its capability for automatic interface addressing. ![]()
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