A conceptual row in the addressMapTable.
The protocolDirLocalIndex in the index identifies the network
layer protocol of the addressMapNetworkAddress.
An example of the indexing of this entry is
addressMapSource.783495.18.4.128.2.6.6.11.1.3.6.1.2.1.2.2.1.1.1.
Note that some combinations of index values may result in an
index that exceeds 128 sub-identifiers in length, which exceeds
the maximum for the SNMP protocol. Implementations should take
care to avoid such combinations.