Each entry contains one IP summary address.
Dynamically created rows MUST survive an agent reboot.
Implementers need to be aware that if the total number
of elements (octets or sub-identifiers) in
isisSummAddress and isisSummAddrPrefixLen is too great,
then OIDs of column instances in this table will have
more than 128 subidentifiers and cannot be accessed
using SNMPv1, SNMPv2c, or SNMPv3.