The Bidirectional Neighbor Filter pane shows the
PIM bidirectional neighbor filters, if any, that are configured on the ASA. A
PIM bidirectional neighbor filter is an ACL that defines the neighbor devices
that can participate in the DF election. If a PIM bidirectional neighbor filter
is not configured for an interface, then there are no restrictions. If a PIM
bidirectional neighbor filter is configured, only those neighbors permitted by
the ACL can participate in the DF election process.
When a PIM bidirectional neighbor filter
configuration is applied to the ASA, an ACL appears in the running
configuration with the name
interface-name_multicast, in which the
interface-name is the name of the
interface to which the multicast boundary filter is applied. If an ACL with
that name already exists, a number is appended to the name (for example,
inside_multicast_1). This ACL defines which devices can become PIM neighbors of
Bidirectional PIM allows multicast routers to
keep reduced state information. All of the multicast routers in a segment must
be bidirectionally enabled for bidir to elect a DF.
The PIM bidirectional neighbor filters enable
the transition from a sparse-mode-only network to a bidir network by letting
you specify the routers that should participate in the DF election, while still
allowing all routers to participate in the sparse-mode domain. The
bidir-enabled routers can elect a DF from among themselves, even when there are
non-bidir routers on the segment. Multicast boundaries on the non-bidir routers
prevent PIM messages and data from the bidir groups from leaking in or out of
the bidir subset cloud.
When a PIM bidirectional neighbor filter is
enabled, the routers that are permitted by the ACL are considered to be
bidirectionally capable. Therefore, the following is true:
If a permitted neighbor does not support
bidir, then the DF election does not occur.
If a denied neighbor supports bidir, then
the DF election does not occur.
If a denied neighbor does not support bidir,
the DF election can occur.