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.Change your Internet provider.
B.Change your public IP address.
C.Allow the email server to send traffic only to TCP port 25.
D.Put your email server in a DMZ.
E.Use a separate public IP address for your email server only.

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.

A.Increase memory allocation for ACLs.
B.Remove all entries from the ACL and use a single permit ip any any statement.
C.Remove the log keyword from each ACL entry.
D.Reboot the device after the ACL has been applied.

A. Only use fiber in pairs.
B. Configure root guard on your switches.
C. Do not use fiber but use copper.
D. Configure UDLD to prevent one-way link conditions.