Witch access list entry checks for an ACK within a packet header?
A. Access-list 49 permit ip any any eq 21 tcp-ack
B. Access-list 49 permit tcp any any eq 21 tcp-ack
C. Access-list 149 permit tcp any any eq 21 established
D. Access-list 49 permit tcp any any eq 21 established
Answer:C
The “established” keyword is used to indicate an established connection for TCP protocol. An established connection can be considered as the TCP protocol traffic originating inside your network, not from an external network.
Good answer C
The keyword estabilished has the role to check if the ACK (aknowledgment) RST (Reset) is set or not,
It is a bit on the header.
If set it is okay,
if not set it blocks the packet.
D is not a good answer because Access-lis has to be an extended one, and 49 is standard, so the command is fault.