Network Glossary H

half duplex Ethernet feature in which a NIC or Ethernet port can only transmit or receive at the same instant in time, but not both. Half duplex is required when a possibility of collisions exists.

hardware queue A small FIFO queue associated with each router’s physical interface, for the purpose of making packets available to the interface hardware, removing the need for a CPU interrupt to start sending the next packet out the interface.

HDB3 See High Density Binary 3.

Hello (EIGRP) An EIGRP message that identifies neighbors, exchanges parameters, and is sent periodically as a keepalive function. Hellos do not require an Ack.

Hello (OSPF) A type of OSPF packet used to discover neighbors, check for parameter agreement, and monitor the health of another router.

hello interval With some routing protocols, the time period between successive Hello messages.

Hello timer An STP timer that dictates the interval at which the Root switch generates and sends Hello BPDUs.

High Density Binary 3 A serial-line encoding standard like B8ZS, but with each set of four consecutive 0s being changed to include a Bipolar Violation to maintain synchronization.

Hold timer With EIGRP, the timer used to determine when a neighboring router has failed, based on a router not receiving any EIGRP messages, including Hellos, in this timer period.

Hot Standby Router Protocol A Cisco-proprietary feature by which multiple routers can provide interface IP address redundancy so that hosts using the shared, virtual IP address as their default gateway can still reach the rest of a network even if one or more routers fail.

Holddown timer With RIP, a per-route timer (default 180 seconds) that begins when a route’s metric changes to a larger value.

HSRP See Hot Standby Router Protocol.