| ACL (access control list) | A sequential collection of permit or deny statements that apply to addresses or upper-layer protocols |
| Bit bucket | Where the discarded bits go |
| DDR (Dial-on-demand routing) | Technique whereby a Cisco router can automatically initiate and close a circuit-switched session as transmitting stations demand. The router spoofs keepalives so that end stations treat the session as active.DDR permits routing over ISDN or telephone lines using an external ISDN terminal adaptor or modem. |
| Deny | A statement on an access control list that will deny traffic. |
| DNS (Domain Name System) | System used in the Internet for translating names of network nodes into addresses |
| Extended access lists | Extended ACLs check for both source and destination packet addresses. They also can check for specific protocols, port numbers, and other parameters. This gives you more flexibility to describe what checking the ACL will do. |
| Firewall | Router or access server, or several routers or access servers, designated as a buffer between any connected public networks and a private network. A firewall router uses access lists and other methods to ensure the security of the private network. |
| IP | Network layer protocol in the TCP/IP stack offering a connectionless internetwork service. IP provides features for addressing, type-of-service specification, fragmentation and reassembly, and security. |
| Packet | Logical grouping of information that includes a header containing control information and (usually) user data. |
| Permit | Statement on an ACL that permits traffic. |
| Queue | 1.) Generally, an ordered list of elements waiting to be processed.
2.) In routing, a backlog of packets waiting to be forwarded over a router interface. |
| Standard access lists | Standard ACLs check the source address of packets that could be routed. The result permits or denies output for an entire protocol suite, based on the network, subnet, and host addresses. |
| TCP - Transmission Control Protocol. | Connection-oriented transport layer protocol that provides reliable full-duplex data transmission. TCP is part of the TCP/IP protocol stack. |
| TCP/IP - Transmission Control Protocol/Internet Protocol | Common name for the suite of protocols developed by the U.S. DoD in the 1970s to support the construction of worldwide internetworks. |
| UDP - User Datagram Protocol. | Connectionless transport layer protocol in the TCP/IP protocol stack. UDP is a simple protocol that exchanges datagrams without acknowledgments or guaranteed delivery, requiring that error processing and retransmission be handled by other protocols. |
| Wildcard Bits | The 1's and 0's used in the wildcard mask for checking. |
| Wildcard masking | 32-bit quantity used in conjunction with an IP address to determine which bits in an IP address should be ignored when comparing that address with another IP address. A wildcard mask is specified when setting up access lists. |