Mac Address Allocator - Cisco 7000 Series Hardware Installation And Maintenance Manual

Fddi2/0 is administratively down, line protocol is down
You can also use variables such as the interface type (Ethernet, Token Ring, FDDI, serial, or HSSI)
and the port address (slot/port) to display information about a specific interface only. The following
example shows the display for the top Ethernet port on an EIP in slot 1:
7010# show int ether 4/0
Ethernet1/0 is up, line protocol is up
For complete command descriptions and instructions, refer to the related software documentation,
which is available on UniverCD.

MAC Address Allocator

All network interface connections (ports) require a unique Media Access Control (MAC)-layer
address, which is also known as a physical or hardware address. Typically, the MAC address of an
interface is stored on a component that resides directly on the interface circuitry, as it does on our
earlier router platforms (for example, on individual appliques). Every interface on the earlier
platforms contains a programmable read-only memory (PROM) component with a unique MAC
address for that interface. The router system code reads the PROM for each interface in the system,
learns the MAC addresses, and then initializes appropriate hardware and data structures.
However, the OIR feature makes it necessary to use a different method of handling the MAC
addresses in Cisco 7000 series routers. OIR allows you to remove an interface processor and replace
it with another identically-configured one. If the new interfaces match the current configuration (that
of the interfaces you removed), the system immediately brings them on line. In order to allow OIR,
an address allocator with 40 unique MAC addresses is stored in an EEPROM on the RP. (Because
the RP is used on both the 7-slot and 5-slot platforms, the address bank must contain addresses for
the maximum possible configuration: 40 possible interfaces [5 interface processor slots x 8 ports] in
the 7-slot model. The 5-slot model uses only the first 24 addresses [3 interface processor slots x 8
ports] in the MAC allocator.) Each address is reserved for a specific slot/port in the router regardless
of whether an interface resides in that port.
The MAC addresses are assigned to the ports in sequence; the first address is assigned to port 0/0,
the ninth to port 1/0, and the last (40th) to port 4/8. This address scheme allows you to remove
interface processors and insert them into other routers without causing the MAC addresses to move
around the network or be assigned to multiple devices.
Note that if the MAC addresses were stored on each interface processor, OIR would not function
because you could never replace one interface with an identically configured one; the MAC
addresses would always be different. Also, each time an interface was replaced, other devices on the
network would have to update their data structures with the new address and, if they did not do so
quickly enough, could cause the same MAC address to appear in more than one device at the same
time. Storing the MAC addresses on the RP avoids these problems. When an interface is replaced
with another interface with the same configuration, there is no need for other devices in the network
to update their data structures and routing tables.
(display text omitted)
Hardware is cxBus Fddi, address is 0000.0c02.adc2 (bia 0000.0c02.adc2)
Internet address is 131.108.31.4, subnet mask is 255.255.255.0
(display text omitted)
Hardware is cxBus Ethernet, address is 0000.0c02.d0ce (bia 0000.0c02.d0ce)
Internet address is 131.108.31.7, subnet mask is 255.255.255.0
MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec, rely 255/255, load 1/255
Encapsulation ARPA, loopback not set, keepalive set (10 sec)
(display text omitted)
Functional Overview
Product Overview 1-37