- A global unicast address can also be set by selecting a preconfigured general
prefix for the network portion of the address from the Based on General Prefix
scroll-down list and marking the check bo x next to this field to enable your
choice (see “Configuring an IPv6 General Network Prefix” on page 4-15), and
then specifying the address (in the IPv6 Address field) a nd the full net work
prefix length (e.g., /64 append ed to the end of the speci fied addr ess) whi ch
includes the general prefix and any contiguous bi ts startin g at the lef t of the
address that are appended to the network prefix.
Note About Prefix Length – To specify the prefix length, enter a forward slash
followed by a decimal value indicating how many contiguous bits (s tarting at the
left) of the address comprise the prefix (i.e., the network portion of th e address ).
When used with a general network prefix to c onf igure a globa l un icast add ress ,
this length includes both that specified by the general prefix and a ny c on tiguo us
prefix bits (starting at the left of the specifi ed add re ss ) th at ex cee d th e len gth of
the general prefix. If the prefix length specified by this parameter is shorter than
the general prefix, then the length of the general prefix takes precedence.
•
Based on General Prefix
– Defines a general prefix for the network segment of
the address (see “Configuring an IPv6 General Network Prefix” on page 4-15).
When configuring a global unicast address based on a general ne twork prefix,
the prefix length includes both that specified by the gene ral pref ix and any
number of subsequent prefix bits that exceed the length of the general prefix.
Therefore, depending on the specified prefix length, some of the address bits
entered in the IPv6 Address field may be appended to the gener al prefix.
However, if the prefix length is shorter than the general prefix, then the le ngth of
the general prefix takes precedence, and some of the address bits entered in the
IPv6 Address field will be ignored.
• Address Type – Defines the address type configured for this interf ace.
• Link Local – Configures an IPv6 link-local address.
- The address p refix mus t be FE80.
- You can configure only one link-local address per interface.
- The specified address repla ces a li nk-l oc al add re ss that was automatically
generated for the interface.
• EUI-64 (Extended Universal Identifi er) – Co nfi gures an I Pv6 addres s for an
interface using an EUI-64 interface ID in the low order 64 bits.
- When using EUI-64 format for the low-order 64 bits in the host portion of the
address, the value entered in the IPv6 Address field includ es the net work
portion of the address, and the prefix length indicates how many contiguous
bits (starting at the left) of the address comprise the prefix (i.e., the network
portion of the address). Note that the value specified in the IPv6 Addre ss
field may include some of the high-order h ost bits if th e specif ied prefix
length is less than 64 bits. If the specified prefix length exceeds 64 bits, then
the bits used in the network portion of the address will take precedence over
the interface identifier.
- IPv6 addresses are 16 bytes long, of which the bottom 8 bytes typically form
a unique host identifier based on the device’s MAC addr ess. The EUI- 64
4-12
Basic Management Tasks
4