study journal

cisco proprietary, distance vector
user configurable metrics: bandwidth, delay, reliability, load, MTU
metrics: uses ticks as primary metric, but falls back to hops in case of a tie
default max diameter - 100 hops, configurable up to 255
three types of routes: interior, system, exterior
interior routes - routes between subnets attached to router int. if network not subnetted, igrp does not advertise interior routes
system routes - routes to network with AS. derived from directly connected network int’s & system route info provided by other igrp routers. do not include subnet info
exterior routes - routes to network outside AS; considered when identifying gateway of last resort
update broadcast sent every 90 seconds
route marked “possibly down” if no update received within 3 update periods (270s)
after 7 update periods (630s), route removed
if route “possibly down”, traffic still passes even though it might not be successful
flash update - sending of update sooner than standard periodic update to notify routers of metric change
poison reverse - sent to remove a route and place in holddown, which keeps new routing info from being used for some time
to propagate ‘gateway of last resort’ the route specified by ip default-network command must already be known as a network - it must be igrp-derived, or a static route redistributed from another protocol

ccie in security