It is possible to filter the search requests sent
to a zone so that it is only queried for aliases
that match certain criteria.
For example, assume all endpoints in your
regional sales office are registered to their local
VCS with a suffix of @sales.example.com.
In this situation, it makes sense for your Head
Office VCS to query the Sales Office VCS only
when it receives a search request for an alias
with a suffix of @sales.example.com. Sending
any other search requests to this particular VCS
would take up resources unnecessarily.

To achieve this, on your Head Office VCS create
a zone to represent the Sales Office VCS, and
set up an associated search rule with a Mode
of Alias Pattern Match mode and a Pattern
type of Suffix.
It would also be wasteful of resources to send
search requests for aliases that match this
pattern to any other zone (there may be other
lower priority search rules defined that would
also apply to these aliases). In which case
setting On successful match to Stop means
that the VCS will not apply any further (lower
priority) search rules.

Allowing calls to IP addresses only if
they come from known zones

In addition to aliases, calls can be made to
specified IP addresses. To pass on such calls to
the appropriate target zones you must set up
search rules with a mode of Any IP Address.
To provide extra security you can set the rule's
Source option to All Zones. This means that
the query is only sent to the target zone if it
originated from any configured zone or the Local
Zone.