H

hash

A one-way function that takes a message of any length and produces a fixed-length digest. In security, a message digest is used to validate that the contents of a message have not been altered in transit. The Secure Hash Algorithm (SHA-1) and Message Digest 5 (MD5) are commonly used hashes.

Hashed Message Authentication Code (HMAC)

A mechanism for message authentication that uses cryptographic hash functions. HMAC can be used with any iterative cryptographic hash function—for example, MD5 or SHA-1—in combination with a secret shared key. The cryptographic strength of HMAC depends on the properties of the underlying hash function.

hello interval

The amount of time an OSPF router sends a hello packet to each adjacent neighbor. The JUNOS software uses a default value of 10 seconds for this timer.

hello mechanism

Process used by an RSVP router to enhance the detection of network out- ages in an MPLS network.

High-Level Data Link Control (HDLC)

An International Telecommunication Union (ITU) standard for a bit-oriented data link layer protocol on which most other bit-oriented protocols are based.

High-Speed Circuit-Switched Data (HSCSC)

Circuit-switched wireless data transmission for mobile users, at data rates up to 38.4Kbps.

hold down

A timer used by distance-vector protocols to prevent the propagation of incorrect routing knowledge to other routers in the network.

hold time

Maximum number of seconds allowed to elapse between the time a BGP system receives successive keepalive or update messages from a peer.

Home Location Register (HLR)

Database containing information about a subscriber and the current location of a subscriber’s mobile station.

Host Membership Query

IGMP packet sent by a router to determine whether interested receivers exist on a broadcast network for multicast traffic.

Host Membership Report

IGMP packet sent by an interested receiver for a particular multicast group address. Hosts send Report messages when they first join a group or in response to a Query packet from the local router.

host module

On an M160 router, provides routing and system management functions of the router. Consists of the Routing Engine and Miscellaneous Control Subsystem (MCS).

host subsystem

On a T640 routing node, provides routing and system-management functions of the router. Consists of a Routing Engine and an adjacent Control Board (CB).




JNCIP. Juniper Networks Certified Internet Professional Study Guide Exam CERT-JNCIP-M
JNCIP: Juniper Networks Certified Internet Professional Study Guide
ISBN: 0782140734
EAN: 2147483647
Year: 2003
Pages: 132

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