The value of tmnxTwampSrvPrefixLen specifies the number of bits to
match when comparing a TWAMP client address in an incoming message to
tmnxTwampSrvPrefixAddr. This is the third index for
tmnxTwampSrvPrefixTable.
Best-fit is used when matching a TWAMP client's IP address against the
set of configured prefixes. For example, suppose the first row of this
table has the prefix 138.120.0.0/16, and the second row has the prefix
138.120.214.0/24. The TWAMP client address 138.120.214.52 matches the
second row.