Cisco 7200 VXR User Manual page 62

Chapter 1 Cisco 7200 VXR Product Overview
Functional Overview
For complete descriptions and instructions of the commands used to configure
your Cisco 7200 VXR router, refer to the Configuration Fundamentals
Configuration Guide and Configuration Fundamentals Command Reference
publications, which are available on the Documentation CD-ROM or in print.
MAC-Layer Address
All LAN interfaces (ports) require unique MAC-layer addresses, also known as
hardware addresses. Typically, the MAC address of an interface is stored on a
memory component that resides directly on the interface circuitry; however, the
OIR feature requires a different method. (For a description of OIR, see the
"Online Insertion and Removal" section on page 1-63.)
Using OIR you can remove a port adapter and replace it with another identically
configured one. If the new port adapter matches the port adapter you removed, the
system immediately brings it online. In order to enable OIR, an address allocator
with unique MAC addresses is stored in an EEPROM on the router midplane.
Each address is reserved for a specific port and slot in the router regardless of
whether a port adapter resides in that slot. The MAC addresses are assigned to the
slots in sequence. The first address is assigned to slot 0, and the last address is
assigned to slot 4 in the Cisco 7204VXR or to slot 6 in the Cisco 7206VXR. Using
this address scheme, you can remove port adapters 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 port adapter, OIR would not
function because you could never replace one port adapter with an identical one;
the MAC addresses would always be different. Also, each time a port adapter was
replaced, other devices on the network would have to update their data structures
with the new address. If the other devices did not update quickly enough, the same
MAC address could appear in more than one device at the same time.
Note Storing the MAC addresses for every slot in one central location
means the addresses stay with the memory device on which they are
stored.
Cisco 7200 VXR Installation and Configuration Guide
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