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The CNA link-monitor process obtains link usage data from SNMP MIB tables maintained on the edge device.
If you are not able to use either the polling interface-ip-address or polling interface-index command, the link-monitor process will have to “walk” the edge router’s interface table to locate the interface’s index.
And, before you can use either the index or description command, you must first obtain the value of the ifIndex or ifDescr variable.
The ifDescr variable which you enter into the link monitor configuration must match exactly the value of the variable in the router’s MIB.
The following MIB example shows the ifIndex and ifDescr blocks in a MIB table taken from an Avaya lab router:
[user1@hostname]% ./snmpwalk router_1 public interface | more interfaces.ifNumber.0 = 9 interfaces.ifTable.ifEntry.ifIndex.1 = 1 interfaces.ifTable.ifEntry.ifIndex.2 = 2 interfaces.ifTable.ifEntry.ifIndex.3 = 3 interfaces.ifTable.ifEntry.ifIndex.4 = 4 interfaces.ifTable.ifEntry.ifIndex.5 = 5 interfaces.ifTable.ifEntry.ifIndex.7 = 7 interfaces.ifTable.ifEntry.ifIndex.8 = 8 interfaces.ifTable.ifEntry.ifIndex.9 = 9 interfaces.ifTable.ifEntry.ifIndex.10 = 10 interfaces.ifTable.ifEntry.ifDescr.1 = GigabitEthernet0/0/0 interfaces.ifTable.ifEntry.ifDescr.2 = FastEthernet1/0/0 interfaces.ifTable.ifEntry.ifDescr.3 = FastEthernet1/1/0 interfaces.ifTable.ifEntry.ifDescr.4 = Serial8/0/0 interfaces.ifTable.ifEntry.ifDescr.5 = Serial8/0/1 interfaces.ifTable.ifEntry.ifDescr.7 = Null0 interfaces.ifTable.ifEntry.ifDescr.8 = Loopback0 interfaces.ifTable.ifEntry.ifDescr.9 = Tunnel1 interfaces.ifTable.ifEntry.ifDescr.10 = Tunnel2
If the link of interest is reached through the GigabitEthernet0/0/0 interface, you would need to locate the ifDescr block in the MIB using your own SNMP management utility and copy either the exact value of interfaces.ifTable.ifEntry.ifDescr.1 entry in the table, or the number following the final period in the entry name, in this case 1.
The string following the equals sign (=) is the ifDescr variable’s value. The number is the ifIndex value for this interface.
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