Cisco routers provide packet filtering to control what traffic is allowed to come in and go out of your network. You can apply rules to either permit or deny certain types of traffic from passing through the router's interfaces.
The following table describes the number ranges Cisco has reserved for specific protocols.
| Protocol | Range |
| IP | 001-099 |
| Extended IP | 100-199 |
| Ethernet Type Code | 200-299 |
| DECNet | 300-399 |
| XNS | 400-499 |
| Extended XNS | 500-599 |
| AppleTalk | 600-699 |
| Ethernet Address | 700-799 |
| IPX | 800-899 |
| Extended IPX | 900-999 |
| IPX SAP | 1000-1099 |