What do SNMP MIB table indexes stands for ?

Dear All,
I just came across a problem where I need to access MIB tables. For accessing any table in SNMP at least one index is there. So what is this index?
Here meaning of index is same as book index you find at the end of the books.
So every table leafs has a OID(Object Identifier which gives the location of managed object data in the MIB tree data structure) and all index must be appended in sequential order to the get the actual row data in the table. For example take interface table with entry OID(.1.3.6.1.2.1.2.2.1) in standard MIB-II. To access a row in the interface table you need to append interface number to the leaf OID. Like you want to access interface description of second interface then you need query OID (.1.3.6.1.2.1.2.2.1.2.2) using GET SNMP commands. Other way to fetch entire MIB table is to use GetTable command. Although GetTable command is not a standard command but many SNMP implementation like(NetSNMP, SNMP4J etc) support it.

Importance of Loopback address in network management using SNMP protocol

One of my colleague asked why do we require Loopback IP address for managing a network device(Router,Switch Modem etc) using SNMP protocol. There are several reasons for that:-
1. Since loopback is software based address, it will be always up. Therefore as long as device is up and reachable through any of its interface, we will get SNMP response by polling the Loopback address.
2. If you choose any other interface IP other than Loopback and if that interface goes down, the SNMP query will fail. In this scenario, even though your device/machine is up, you will get wrong information that machine is down.
3. In case of Desktop, you do not require a separate Loopback because usually desktop has only one cable connecting it network.
4. Loopback address provides unique identity to the network device which can be used as primary key in management database.
5. So if a device has multiple connectivity it is always better to use Loopback address as management address for all management purpose including TELNET and SSH.