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CIT237 Ch 4 GuideTCP
CIT237 Chapter 4 Data Link and Network Layer Protocols
| Term | Definition |
|---|---|
| Address Resolution Protocol (ARP) | This Network layer protocol translates numeric IP addresses into the equivalent MAC layer addresses necessary to transfer frames from one machine to another on the same cable segment or subnet. |
| adjacencies database | A database of the local network segment and its attached routers. Designated routers share the adjacencies database view across link-state networks. |
| agent | In general, an agent is a piece of software that performs services on behalf of another process or user. In the case of Mobile IP, the agent in question is |
| area border router (ABR) | A router used to connect separate areas. |
| areas | Groups of contiguous networks. Areas are used in link-state routing to provide route table summarization on larger networks. |
| ARP cache | - A temporary table in memory that consists of recent ARP entries. Entries in the ARP cache are discarded after two minutes on Windows 2000 and Windows XP systems. |
| autonomous system (AS) | A group of routers that is under a single administrative authority. |
| autonomous system border router (ASBR) | A router that connects an independent routing area, or AS, to another AS or the Internet. |
| backbone area | A required area to which all other routers should be attached directly or through a tunnel. |
| backup designated router (BDR) | The router with the second-highest priority on a broadcast segment of a link-state network. The BDR allows service to be restored quickly in the event of an outage affecting the DR. See also designated router. |
| bit-level integrity check | A special mathematical calculation performed on the payload of a packet (a datagram at the Data Link layer) before the datagram is transmitted, whose value may be stored in a datagram’s trailer. |
| black hole | A point on the network where packets are silently discarded. |
| Border Gateway Protocol (BGP) | An inter-domain routing protocol that replaces Exterior Gateway Protocol (EGP) and is defined in RFC 1163.BGP exchanges reachability information with other BGP routers. |
| circuit switching | A method of communications wherein a temporary or permanent connection between a sender and a receiver, called a circuit, is created within a communications carrier’s switching systems. |
| converge | The process of ensuring all routers on a network have up-to-date information about available networks and their costs. |
| counting to infinity | A network routing problem caused by a routing loop. Packets circulate continuously until they expire. |
| Cyclical Redundancy Check (CRC) | A special 16- or 32-bit equation performed on the contents of a packet. The result of the CRC equation is placed in the Frame Check Sequence field at the end of a frame. A CRC is performed by NICs on all outgoing and incoming packets. |
| data encapsulation | The technique whereby higher-level protocol data is enclosed within the payload of a lower-layer protocol unit and labeled with a header (and possibly, a trailer), so the protocol data unit may be safely transmitted from a sender to a receiver. |
| data link address | The address of the local machine based on the hardware address. The data link address also is referred to as the MAC address. |
| default gateway | The name given to the router IP address through which a machine attached to a local network must pass outbound traffic to reach beyond the local network, thereby making that address the “gateway” to the world of IP addresses outside the local subnet. |
| delimitation | The use of special marker bit strings or characters, called delimiters, that distinguish the payload of a PDU from its header and trailer, and that also may mark the beginning (and possibly the end) of a PDU itself, as transmitted. |
| delimiter | A special bit string or character that marks some boundary in a PDU, be it at the beginning or end of a PDU, or at the boundary between the header and the payload, or the payload and the trailer. |
| designated router (DR) | The router with the highest priority on a segment of a link-state network. A DR advertises LSAs to all other routers on the segment. |
| diameter | The number of hops that a network routing protocol can span. RIP has a network diameter of 15; most other routing protocols (such as OSPF and BGP) have an unlimited network diameter. |
| Differentiated Services (Diffserv) | A method for providing different levels of service to network traffic based on a marker placed in the IP header. |
| Dijkstra algorithm | An algorithm used to compute the best route on a link-state network. |
| distance vector | The source point or location for determining distance to another network. |
| distance vector routing protocol | A routing protocol that uses information about the distances between networks, rather than the amount of time it takes for traffic to make its way from the source network to the destination network. RIP is a distance vector routing protocol. |
| E1 | A standard European digital communications service used to carry thirty 64-Kbps digital voice or data channels, along with two 64-Kbps control channels, for a total bandwidth of 2.048 Mbps of service. |
| E3 | A standard European digital communications service used to carry 16 E1 channels for a total bandwidth of 34.368 Mbps of service. E3 is widely used outside North America as a replacement for T3 service. |
| error-detection mechanism | A method for detecting corrupted packets. The CRC process is an error-detection mechanism. The IP header checksum is another method of error detection. |
| Ethernet II frame type | The de facto standard frame type for TCP/IP communications. |
| Explicit Congestion Notification (ECN) | A method for notifying next-hop devices that a link is experiencing congestion and packet loss is imminent at the current transmission rates. |
| exterior gateway protocols (EGPs) | Routing protocols used to exchange routing information between separate autonomous systems. |
| external route entry | A route entry received from a different area. |
| forwarding table | The actual table referenced to make forwarding decisions on a link-state network. |
| Fragment Offset field | The field that defines where a fragment should be placed when the entire data set is reassembled. |
| fragment | In the context of IP networking, a fragment is a piece of a larger set of data that must be divided to cross a network that supports a smaller MTU than the original packet size. |
| Frame Check Sequence (FCS) | The type of bit-level integrity check used in the trailer of PPP datagrams; the specific algorithm for the FCS is documented in RFC 1661. The FCS field contains a CRC value. All Ethernet and token ring frames have an FCS field. |
| hardware address | The address of the NIC. This address is typically used as the data link address. |
| Hello process | A process link-state routers use to discover neighbor routers. |
| High-level Data Link Control (HDLC) | A synchronous communication protocol. |
| host route | A routing table entry with a 32-bit subnet mask designed to reach a specific network host. |
| host route entry | A route table entry that matches all four bytes of the desired destination. Network route table entries only match the network bits of the desired address. |
| IEEE 802.3 | The IEEE-defined standard for a carrier sense, multiple access method with collision detection. |
| informational/supervisory format | A connection-oriented format that can be used by LLC packets. |
| inter-autonomous system routing | A term used in BGP, this refers to the ability to provide routing between autonomous systems. |
| interdomain routing protocols | Routing protocols used to exchange information between separate autonomous systems. |
| interior gateway protocols (IGPs) | Routing protocols used within an autonomous system. |
| internal route entry | A route entry learned from within the same area as the computing device. |
| Internet Protocol Control Protocol (IPCP) | A special TCP/IP Network Control Protocol used to establish and manage IP links at the Network layer. |
| intra-autonomous system routing | A term used in BGP that refers to the ability to provide routing within an autonomous system. |
| intradomain routing protocols | Routing protocols used to exchange routing information within an autonomous system. |
| Ipconfig | A command-line utility used to identify the local host’s data link address and IP address. |
| lifetime value | The time that a packet can remain on the network. Routers discard packets when their lifetimes expire. |
| link-state | A type of routing protocol that uses and shares information only about adjacent neighbors, and that uses transit time to assess link costs, rather than hop counts or routing distances. |
| link-state advertisement (LSA) | A packet that includes information about a router, its neighbors, and the attached network. |
| link-state routing protocol | A routing protocol based on a common link-state picture of the network topology. Link-state routers can identify the best path based on bandwidth, delay, or other path characteristics |
| Logical Link Control (LLC) | The data link specification for protocol identification as defined by the IEEE 802.2 specification. The LLC layer resides directly above the Media Access Control layer. |
| master router | In link-state routing, a router that distributes its view of the link-state database to slave routers. |
| name resolution process | The process of obtaining an IP address based on a symbolic name. DNS is a name resolution process. |
| neighbor routers | On a link-state network, neighbor routers are connected to the same network segment. |
| Network Control Protocols (NCPs) | A family of TCP/IP Network layer protocols used to establish and manage protocol links made at the Network layer (TCP/IP’s Internet layer). |
| Network Layer Reachability Information (NLRI) | The information about available networks and the routes whereby they may be reached, which routing protocols collect, manage, and distribute to the routers or other devices that use such routing protocols. |
| network route entry | A route table entry that provides a next-hop router for a specific network. |
| next-hop router | The local router that is used to route a packet to the next network along its path. |
| On-Demand Routing (ODR) | A low-overhead feature that provides IP routing for sites on a hub-and-spoke network. Each router maintains and updates entries in its routing table only for hosts whose data passes through the router, thus reducing storage requirements and bandwidth. |
| Open Shortest Path First (OSPF) | A sophisticated Layer 3 or TCP/IP Internet layer routing protocol that uses link-state information to construct routing topologies for local internetworks and provides load-balancing capabilities. |
| packet priority | A TOS priority that defines the order in which packets should be processed through a router queue. |
| pad | Bytes placed at the end of the Ethernet Data field to meet the minimum field length requirement of 46 bytes. These bytes have no meaning and are discarded by the incoming data link driver when the packet is processed. |
| pass-through autonomous system routing | A term used in BGP routing, this routing technique is used to share BGP routing information across a non-BGP network. |
| plain text password | A password that is transferred across the cable in plain ASCII text. |
| point-to-point | A type of Data Link layer connection, in which a link is established between exactly two communications partners so the link extends from one partner (the sender) to the other (the receiver). |
| Point-to-Point Protocol over Ethernet (PPPoE) | A protocol used by many Internet service providers to authenticate and manage broadband subscribers. PPPoE is a kind of PPP designed for serial communications adapted specifically for Ethernet networks |
| poison reverse | A process used to make a router undesirable for a specific routing path. This process is one of the methods used to eliminate routing loops. |
| preamble | The initial sequence of values that precedes all Ethernet packets. Placed on the front of the frame by the outgoing NIC and removed by the incoming NIC, the preamble is used as a timing mechanism |
| protocol identification (PID) | A datagram service necessitated when any single protocol carries multiple protocols across a single connection (as PPP can do at the Data Link layer); PIDs permit individual datagram payloads to be identified by the type of protocol they contain. |
| protocol identification field | A field that is included in most headers to identify the upcoming protocol. The PID of Ethernet headers is the Type field. The PID of IP headers is the Protocol field. |
| proxy ARP | The process of replying to ARP requests for IP hosts on another network. A proxy ARP network configuration effectively hides subnetting from the individual IP hosts. |
| Registry setting | A configuration that controls the way in which Windows devices operate. There are numerous settings that define how Windows 2000 and Windows XP operate in a TCP/IP environment. |
| Reverse Address Resolution Protocol (RARP) | Layer 2 or TCP/IP Network Access protocol that translates numeric IP addresses into MAC layer addresses (usually to verify that the identity claimed by a sender matches its real identity). This protocol was superseded by DHCP. |
| route priority | A TOS priority that defines the network to route packets. The router must support and track multiple network types to make the appropriate forwarding decision based on the TOS defined in the IP header. |
| route resolution process | The process that a host undergoes to determine whether a desired destination is local or remote and, if remote, which next-hop router to use. |
| Routing Information Protocol (RIP) | A simple, vector-based TCP/IP networking protocol used to determine a single pathway between a sender and a receiver on a local internetwork. |
| routing loops | A network configuration that enables packets to circle the network. Split horizon and poison reverse are used to resolve routing loops on distance vector networks. OSPF networks automatically resolve loops by defining best paths through an internetwork. |
| routing protocol | A Layer 3 protocol designed to permit routers to exchange information about networks that are reachable, the routes by which they may be reached, and the costs associated with such routes. |
| routing tables | Local host tables maintained in memory. The routing tables are referenced before forwarding packets to remote destinations in order to find the most appropriate next-hop router for the packet. |
| Service Access Point (SAP) | A protocol identification field that is defined in the 802.2 LLC header that follows the MAC header. |
| slave router | On an OSPF network, this type of router receives and acknowledges link-state database summary packets from a master router. |
| split horizon | A rule used to eliminate the counting-to-infinity problem. The split horizon rule states that information cannot be sent back the same direction from which it was received. |
| Synchronous Data Link Control (SDLC) | A synchronous communication protocol. |
| Synchronous Optical Network (SONET) | A family of fiber-optic digital transmission services that offers data rates from 51.84 Mbps (OC-1) to 38.88 Gbps (OC-768). SONET provides the infrastructure for high-rate ATM services |
| T1 | A digital signaling link, whose name stands for trunk level 1, used as a standard for digital signaling in North America. T1 links offer aggregate bandwidth of 1.544 Mbpschannels of 64 Kbps each, or may be split between voice and data. |
| T3 | A digital signaling link, whose name stands for trunk level 3, used as a standard for digital signaling in North America. T3 links offer aggregate bandwidth of 28T1s, or 44.736 Mbps. |
| T-carrier | The generic telephony term for trunk carrier connections that offer digital services to communications customers directly from the communications carrier itself |
| unnumbered format | A format of 802.2 LLC packet that is connectionless. |
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