A.PIM join messages are sent every 60 seconds to refresh the upstream router’s mroute state for the multicast tree.
B.Routers send a PIM join acknowledgement in response to each PIM join message received from a downstream router.
C.PIM join messages are only sent when the multicast distribution tree is first being established.
D.PIM join messages are sent every three minutes to refresh the upstream router’s mroute state for the multicast tree.

A.The source must send a PIM Register message to the rendezvous point （RP）
B.The source must first join the multicast group using IGMP before sending
C.The source must perform a Request to Send （RTS） and Clear to Send （CTS） handshake with the PIM designated router （DR）
D.No control plane signaling needs to be performed；the source can simply begin sending on the local subnet

A.Attempt to TELNET from the router connected to the inside of the firewall to the router connected to the outside of the firewall. If telnet works， BGP will work， since telnet and BGP both use TCP to transport data.
B.Ping from the router connected to the inside interface of the firewall to the router connected to the outside interface of the firewall. If you can ping between them， BGP should work， since BGP uses IP to transport packets.
C.There is no way to make BGP work across a firewall without special configuration， so there is no simple test that will show you if BGP will work or not， other than trying to start the peering session.
D.There is no way to make BGP work across a firewall.

A.Port 3/12 was already up and forwarding before the loop was created.
B.Port priority is based on lowest priority and lowest port number.
C.You connected the wire on port 3/18 last.
D.None of the above， it is purely random.