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A packet filtering router may act as part of a firewall. A Cisco router can filter packets in several ways:
- The first filtering point to consider is the IP address in the IP layer. A packet filtering router can accept or reject packets based on the source or destination IP address.
- The host to host layer. It may filter access to or from certain services, allowing or denying tftp, telnet access, and ftp access.
- Established connection. It can allow connections that have originated from within the protected network but block all those originating outside.
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