Backup designated router. An elected router in a multi-access OSPF network that acts as the backup if the designated router fails. All neighbors form adjacencies with the backup designated router (BDR) as well as the designated router.
Border Gateway Protocol. BGP is an interdomain or exterior gateway protocol.
A remote BGP speaker that is an established neighbor of the local BGP speaker.
Measure of the operating cost to route over a link.
The point at which all routers in a network have identical routing information.
The time within which an OSPF router must receive a Hello packet from an OSPF neighbor. The dead interval is usually a multiple of the hello interval. If no Hello packet is received, the neighbor adjacency is removed.
A router to which all unroutable packets are sent. Also called the router of last resort.
The length of time required to move a packet from the source to the destination through the internetwork.
Defines routes by distance (for example, the number of hops to the destination) and direction (for example, the next-hop router) and then broadcasts to the directly connected neighbor routers.
Domain Name System client. Communicates with DNS server to translate a host name to an IP address.
Designated router. An elected router in a multi-access OSPF network that sends LSAs on behalf of all its adjacent neighbors. All neighbors establish adjacency with only the designated router and the backup designated router.
Diffusing Update Algorithm. EIGRP algorithm used to select optimal routes to a destination.
External Border Gateway Protocol (BGP). Operates between external systems.
Enhanced Interior Gateway Protocol. A Cisco routing protocol that uses the Diffusing Update Algorithm to provide fast convergence and minimized bandwidth utilization.
The lowest calculated distance to a network destination in EIGRP. The feasibility distance is the sum of the advertised distance from a neighbor plus the cost of the link to that neighbor.
Neighbors in EIGRP that advertise a shorter distance to the destination than the current feasibility distance.
Fowarding Information Base. The forwarding table on each module that is used to make the Layer 3 forwarding decisions per packet.
A switch or router that forwards Layer 3 traffic from a LAN to the rest of the network.
The configurable time between each hello packet sent by an OSPF or EIGRP router.
A special message used by OSPF or IS-IS to discover neighbors. Also acts as a keepalive messages between established neighbors.
In BGP, the maximum time limit allowed in BGP between UPDATE or KEEPALIVE messages. If this time is exceeded, the TCP connection between the BGP peers is closed.
In EIGRP, the maximum time allowed between EIGRP hello messages. If this time is exceeded, the neighbor is declared unreachable.
The number of routers that can be traversed in a route. Used by RIP.
Internal Border Gateway Protocol (BGP). Operates within an autonomous system.
Internet Engineering Task Force Request for Comments.
Interior Gateway Protocol. Used between routers within the same autonomous system.
An independent, configurable entity, typically a protocol.
Internet Protocol version 4.
A special message sent between routing peers to verify and maintain communications between the pair.
An arbitrary number configured on an OSPF interface which is in shortest path first calculations.
Shares information about a link, link cost to neighboring routers.
Link-state advertisement. An OSPF message to share information on the operational state of a link, link cost, and other OSPF neighbor information.
OSPF database of all LSAs received. OSPF uses this database to calculate the best path to each destination in the network.
The time that OSPF floods the network with LSAs to ensure all OSPF routers have the same information.
The degree to which a network resource, such as a router, is busy.
The distribution of network traffic across multiple paths to a given destination.
A one-way hash applied to a message using a shared password and appended to the message to authenticate the message and ensure the message has not been altered in transit.
A standard of measurement, such as the path bandwidth, that is used by routing algorithms to determine the optimal path to a destination.
MD5 authentication digest
A cryptographic construction that is calculated based on an authentication key and the original message and sent along with the message to the destination. Allows the destination to determine the authenticity of the sender and guarantees that the message has not been tampered with during transmission.
Maximum transmission unit. The largest packet size that a network link will transmit without fragmentation.
network layer reachability information
BGP network layer reachability information (NRLI). Contains the a list of network IP addresses and network masks for networks that are reachable from the advertising BGP peer.
The next router that a packet is sent to on its way to the destination address.
Not-So-Stubby-Area. Limits AS external LSAs in an OSPF area.
Open Shortest Path First. An IETF link-state protocol. OSPFv2 supports IPv4.
Sum of all link costs or the hop count that a packet experiences when routed from the source to the destination.
One routing protocol accepts route information from another routing protocol and advertises it in the local autonomous system.
Reliable Transport Protocol
Responsible for guaranteed, ordered delivery of EIGRP packets to all neighbors.
The dependability (usually described in terms of the bit-error rate) of each network link.
Routing Information Base. Maintains the routing table with directly connected routes, static routes, and routes learned from dynamic unicast routing protocols.