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Cisco 7401ASR Installation and Configuration Guide
OL-5419-01 B0
Chapter3 Starting and Configuring Functional Overview
For complete descriptions and instructions of the commands used to configure your Cisco 7401ASR
router, refer to the Cisco IOS Configuration Fundamentals Configuration Guide and Cisco IOS
Configuration Fundamentals Command Reference publications, which are available onl ine , o n the
Documentation CD-ROM, and in print.
MAC Address
All LAN interfaces (ports) require unique MAC 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 O IR, see the
“Online Insertion and Removal” section on page3-3.)
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. I n order
to enable OIR, an address allocator with unique MAC addresses is stored in an EEPROM on the system
board. Each address is reserved for a specific port and slot in th e ro ut er r egardle ss o f wh et her a po rt
adapter resides in that slot. The MAC address for the port adapter slo t in th e Ci sco 7 401 A SR is slo t 0.
You can remove a port adapter and insert it into another router 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 beca use 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 upd ate 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.
Online Insertion and Removal
All port adapters and service adapters in the Cisco 7401ASR router s suppor t on lin e i nserti on and
removal (OIR). This function allows you to install and replace port adapters and service adapters while
the router is operating; you do not need to notify the sof tware or shu t down the sy stem power. This
provides a method that is seamless to end users on the network, maintains all routing information, and
preserves sessions.
The following is a functional description of OIR for background information only; for specific
procedures for installing and replacing a port adapter or service adap ter in a Cisco 7401ASR router, refer
to the configuration note that ships with each port adapter or service adapter.
Each port or service adapter has a bus connector that connects it to the router. The connector has a set
of tiered pins in three lengths that send specific signals to the system as they make contact with the port
adapter or service adapter. The system assesses the signals it receives and the order in which it receives
them to determine if a port adapter or service adapter is being removed or inserted into the system. From
these signals, the system determines whether to reinitialize a new interface or shut down a removed
interface.
For example, when you insert a port adapter or service adapter, the longest pins make contact with the
port adapter or service adapter first, and the shortest pins make contact last. The system recognizes the
signals and the sequence in which it receives them.