With dynamic access, there is the possibility that an unauthorized host, spoofing your authenticated address, can gain access behind the firewall. The problem is only identified here as a concern to the user. This causes the SSE switching path to slow down momentarily. These entries must be handled in the protocol fast-switching path. Pay close attention to the border router configurations.
Remote users create access list entries on the border router.
The access list will grow and shrink dynamically. Large access lists degrade packet switching performance. When you want a subset of hosts on a network to access a host on a remote network protected by a firewall. The Cisco IOS software receives the Telnet packet and performs a user authentication process. The user must pass authentication before access is allowed.