An ACL is applied inbound on router interface. The ACL consists of a single entry:
access-list 210 permit tcp 172.18.20.0 0.0.0.47 any eq ftp
If a packet with a source address of 172.18.20.40, a destination address of 10.33.19.2, and a protocol of 21 is received on the interface, is the packet permitted or denied?
- permitted
- denied
Explanation: The packet is permitted because it satisfies all the criteria defined in the Access Control Entry (ACE):
- Protocol and Port: The ACE specifies TCP and the port ftp (which corresponds to port 21). The packet uses protocol 21, creating a match.
- Source Address: The ACE uses the network 172.18.20.0 with a wildcard mask of 0.0.0.47. In binary, the mask 47 is 00101111, meaning the router must match the bits in the 128, 64, and 16 positions (where the wildcard is 0). The packet source .40 in binary is 00101000. Since the bits in the 128, 64, and 16 positions are all 0 in both the ACE and the packet, the source address is a match.
- Destination: The ACE specifies any, which matches the packet's destination address of 10.33.19.2.
Since a match is found on this permit statement, the router carries out the instruction and allows the packet to pass.
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