Juniper POLICY MANAGEMENT - CONFIGURATION GUIDE V11.1.X Configuration Manual page 133

Baseline enable/disable Enable or disable baselining for the attachment.
Merge or Replace Allow an attachment to become merge-capable and merge
with any other attachments that are merge-capable. If the merge keyword is not
specified, then it replaces any existing attachments with the new attachment.
Merging always preserves statistics.
Preserve Preserve statistics from earlier attachment when replacing an
attachment. This keyword is mutually exclusive with merge keyword.
Various possibilities result from a policy attachment at an interface due to the presence
or absence of these keywords. The same rules apply while attaching policies based
on interface profiles provided by Service Manager except as noted.
Attachments made through Interface Configuration mode follow these rules:
If an attachment is issued with the merge keyword specified:
Any existing attachment of the same type at the interface without the merge
keyword is replaced by the new attachment, which then becomes
merge-capable.
An attachment is merged with any existing attachments of the same type
that have the merge keyword set. If a merged policy already exists for the
set of component policies, then this merged policy is used or a new merged
policy is created dynamically and attached. The statistics for common
classifier groups are preserved when replacing the existing merged
attachment.
If an attachment is issued when no merge or preserve keyword is set, then it
replaces all other attachments with the same type at the interface. This
attachment is not merge-capable for future use and statistics from previous
attachments are not preserved.
If an attachment is issued when the merge keyword is not set, but the preserve
keyword is set, it replaces all other attachments with the same type at the
interface. This attachment is not merge-capable for future use. Statistics from
existing attachments are preserved for all the common classifier-groups.
You cannot have multiple attachments of the same policy on a single attachment
point. Only Service Manager executes multiple attachments of the same policy
at the same attachment point.
A detachment based on the policy name removes all attachments for that policy
at the specified attachment point in a single command regardless of creation
source. A detachment based on attachment type detaches all attachments at
that attachment point regardless of creation source. Service Manager can delete
only one attachment at a time through service deactivation.
The statistics and baseline keywords for the merged policy attachment are
computed as a logical OR for all attachments at the specified attachment point.
If you delete an attachment:
The merged policy is recomputed with the remaining attachments of the
same type that have the merge keyword set. The statistics for common
classifier groups are preserved when replacing the existing merged
attachment.
Chapter 6: Merging Policies
Policy Attachment Rules for Merged Policies
107