Network Glossary G

Garbage timer See Flush timer.

Gateway Load Balancing Protocol A Cisco-proprietary feature by which multiple routers can provide interface IP address redundancy, as well as cause a set of clients to load-balance their traffic across multiple routers inside the GLBP group.

gateway of last resort The notation in a Cisco IOS IP routing table that identifies the route used by that router as the default route.

generic routing encapsulation A tunneling protocol that can be used to encapsulate many different protocol types, including IPv4, IPv6, IPsec, and others, to transport them across a network.

Get In the context of SNMP, the Get command is sent by an SNMP manager, to an agent, requesting the value of a single MIB variable identified in the request. The Get request identifies the exact variable whose value the manager wants to retrieve. Introduced in SNMPv1.

GetBulk In the context of SNMP, the GetBulk command is sent by an SNMP manager, to an agent, requesting the values of multiple variables. The GetBulk command allows retrieval of complex structures, like a routing table, with a single command, as well as easier MIB walking.

GetNext In the context of SNMP, the GetNext command is sent by an SNMP manager, to an agent, requesting the value of a single MIB variable. The GetNext request identifies a variable for which the manager wants the variable name and value of the next MIB leaf variable in sequence.

GLBP See Gateway Load Balancing Protocol.

global routing prefix The first 48 bits of an IPv6 global address, used for efficient route aggregation.

GLOP addressing The range 233.0.0.0 through 233.255.255.255 that IANA has reserved (RFC 2770) on an experimental basis. It can be used by anyone who owns a registered autonomous system number to create 256 global multicast addresses.

going active EIGRP jargon meaning that EIGRP has placed a route into active status.

Goodbye (EIGRP) An EIGRP message that is used by a router to notify its neighbors when the router is gracefully shutting down.

graceful restart (OSPF) As defined in RFC 3623, graceful restart allows for uninterrupted forwarding in the event that an OSPF router’s OSPF routing process must restart. The router does this by first notifying the neighbor routers that the restart is about to occur; the neighbors must be RFC 3623–compliant, and the restart must occur within the defined grace period.

Graft Ack message Message sent by a PIM-DM router to a downstream router when it receives a Graft message from the downstream router; sent using the unicast address of the downstream router.

Graft message Message sent by a PIM-DM router to its upstream router asking to quickly restart forwarding the group traffic; sent using the unicast address of the upstream router.

granted window See receiver’s advertised window.

GRE See generic routing encapsulation.