The IP-address (or one of them) of the VTP Server which
last updated the Configuration Revision Number, as indicated
in the most recently received VTP advertisement for this
management domain, when managementDomainVersionInUse is
version1(1) or version2(2).
If managementDomainVersionInUse is version3(4), this object
has the value of 0.0.0.0.
Before an advertisement has been received, this value is
0.0.0.0.