- 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
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- RIP 2 versions, distance-vector v1 - classful, fixed length subnet...
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