Cisco has two proprietary routing protocols

see:  An Introduction to IGRP,  Charles L. Hedrick 
Find it at www.cisco.com, search on 
		hedrick,igrp 

	IGRP - Internet Gateway Routing Protocol
	EIGRP (replacement) 
		E for enhanced

	both fundamentally V/D in style

IGRP
	response to limitations of RIP
	marketed before OSPF done
	proprietary
		cure some of RIP's limitations
	broadcast every 90 seconds

	pros:
		multiple defaults
		multipath routing
		multiple metric heuristic that includes
			delay/bandwidth/reliability/load
	cons:
		no CIDR (late 80's design)
		count to infinity may be harder but still possible

metric:
	function of (Delay, Bandwidth, Reliability, Load)

	delay/bandwidth static characteristics of link.
	Reliability and Load calculated from link itself.
		

 	M = ((K1 * B + K2 * B)/(256-L) + K3 * D) * K5/(R + K4)

	default:
	K1 = K3 = 1, K2 = K4 = K5 = 0 

	can tune it or go with defaults

default routes
	0.0.0.0 RIP/OSPF convention for default route
	
	0.0.0.0 is wildcard, placeholder for 45k routes ...  
		obviousally all computers can't tolerate that

	view as fake entry:
		to outside, send to next hop Y

	might however desire to replace said wildcard with A.S.
		route address and associated cost to reach it ...

	thus IGRP notion of default route can be list:

	(to outside world, really X, cost Y)
	(to outside world, really XXX, cost YYY)

	IGRP periodically rechooses from list for default route ...

	IGRP can deal with case where you have two gateways
		to outside world and they have different link speeds.
		Can handle metric dynamically here without hardwiring it

loop detection

	uses split horizon/triggered updates
	does not use poison reverse, rather route poisoning

	path holddown (not used anymore):impose quarantine after
		link failure (don't accept info from other routers)

	
multipath routing
	IGRP implementation keeps knowledge of mult. paths in memory.
	load-splitting can be done with "variance" (cisco keyword)
		limited to equal-length multipaths
 
EIGRP - enhanced IGRP

	handles CIDR
	multi-protocol
		e.g., will do IPX too
	uses "DUAL" algorithm, so does not suffer from
		count to infinity